Biology Form Five

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Student’s Book Form Five GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Tanzania Institute of Education 10/10/2019 14:05 BIOLOGY FORM 5 KIWANDANI.indd 1

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools © Tanzania Institute of Education, 2019 Published 2019 ISBN 978-9987-09-031-0 Tanzania Institute of Education GOFVOERRNONMLEINNTE PURSOEPOENRLTYY P.O.Box 35094 Dar es Salaam Tel: +255 22 2773005/+255 22 2771358 Fax: +255 22 2774420 Email: [email protected] Website: www.tie.go.tz All rights reserved. This book may not be reproduced, stored in any retrieval system or transmitted in any form or by any means: electronic, mechanical, photocopying, recording or otherwise, without prior written permission of the Tanzania Institute of Education. ii Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 2 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Preface This book Biology for Advanced Level Secondary Schools, is written specifically for Form Five Biology Students in the United Republic of Tanzania. The book is prepared according to the 2009 Biology Syllabus for Advanced Level Secondary Education Form V-VI, issued by the Ministry of Education and Vocational Training. The Book consists of seven chapters, which are: Cytology, Principles of classification, Comparative studies of natural groups of organisms, Coordination, Nutrition, Gaseous exchange and respiration, and Regulation. In addition to the content, each chapter contains activities, illustrations, exercises and revision questions. Learners are encouraged to do all activities and answer all questions so as to enhance their understanding, and promote acquisition of the intended skills, knowledge, and attitudes. Tanzania Institute of Education GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Student’s Book Form Five iii BIOLOGY FORM 5 KIWANDANI.indd 3 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Acknowledgments The Tanzania Institute of Education (TIE) would like to acknowledge the contributions of all organisations, and individuals who participated in the design and development of this textbook. Writers: Dr Charles M. Lyimo, Dr Emmanuel K. Laisser, Dr Ernest S. Kira, Ms Mwanahamisi A. Jokolo, Ms Jamila M. Mweta, Ms Theonestina A. Lema & Mr WilliamTungalaja Editors: Dr Hashim Mangosongo, Dr Bruno Nyundo & Dr Heriel Moshi (Chairman of the panel) Designer: Mr Anton Asukile Illustrators: Mr Fikiri A. Msimbe & Alama Art and Media Production Co. Ltd. Coordinator: Ms Mwanahamisi A. Jokolo TIE also extends its sincere gratitude to secondary school teachers who participated in the trial phase of the manuscript. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Likewise, the Institute would like to thank the Ministry of Education, Science and Technology for facilitating the writing of this textbook. Dr Aneth A. Komba Student’s Book Form Five Director General Tanzania Institute of Education 10/10/2019 14:05 iv BIOLOGY FORM 5 KIWANDANI.indd 4

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Table of contents Preface .................................................................................................... iii Acknowledgements ................................................................................ iv Chapter One: Cytology........................................................................................... 1GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 1.1 Concept of cytology ........................................................................................... 1 1.2 The cell theory ................................................................................................... 2 1.3 Types of cells ....................................................................................................... 3 1.4 The organic constituents of cells (Biochemistry) ............................................. 33 1.5 Water as a constituent of the cell ....................................................................... 74 Revision questions ................................................................................................... 76 Chapter Two: Principles of classification........................................................... 77 2.1 The concept of classification ..................................................................................77 2.2 Classiﬁcation systems........................................................................................79 2.3 Taxonomic ranks ............................................................................................... 83 2.4 Nomenclature .....................................................................................................84 2.5 Taxonomic keys..................................................................................................86 Revision questions .................................................................................................. 90 Chapter Three: Comparative studies of natural groups of organisms.............92 3.1 General overview of classification ..................................................................92 3.2 Viruses ................................................................................................................ 93 3.3 Kingdom Monera .............................................................................................. 100 3.4 Kingdom Protoctista .........................................................................................112 3.5 Kingdom Fungi ...............................................................................................127 3.6 Kingdom Plantae .............................................................................................1. 37 3.7 Kingdom Animalia .......................................................................................... 1. 66 Revision questions ................................................................................................ . 210 Chapter Four: Coordination and irritability....................................................212 4.1 Nervous coordination in mammals ..................................................................212 4.2 Receptor ............................................................................................................230 4.3 Hormonal coordination in mammals ...............................................................244 4.4 Coordination in plants .....................................................................................248 4.5 Plant hormones (Phytohormones) ...................................................................252 Revision questions .................................................................................................256 Student’s Book Form Five v BIOLOGY FORM 5 KIWANDANI.indd 5 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Chapter Five: Nutrition ......................................................................................257 5.1 Concept of nutrition .........................................................................................257 5.2 Autotrophic nutrition .......................................................................................257 5.3 Heterotrophic nutrition ....................................................................................275 Revision questions .................................................................................................290 Chapter Six: Gaseous exchange and respiration ..............................................291 6.1 Gaseous exchange in mammals.......................................................................291 6.2 Gaseous exchange in plants..............................................................................303 6.3 Respiration .......................................................................................................305 Revision questions .................................................................................................323 Chapter Seven: Regulation (Homeostasis) ...................................................... 325 7.1 The concept of regulation .................................................................................325 7.2 Temperature regulation ...................................................................................330 7.3 Excretion ...........................................................................................................335 7.4 Osmoregulation ................................................................................................347 Revision questions ..................................................................................................351 GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Glossary .................................................................................................................................352 Bibliography ........................................................................................................................358 Index .....................................................................................................................................359 vi Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 6 10/10/2019 14:05

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OneChapter FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Introduction All living organisms are made up of units called cells. A cell is the basic structural, fundamental and functional unit of life. Understanding and learning about cells supports the learning of other biological processes. In this chapter, you will learn about the concept of cytology, cell theory, types of cells, and cell structure and function. You will also learn about cell differentiation, organic constituents of cells, and water as a constituent of the cell. 1.1 Concept of cytology GOFVOERRNONMLEINNTE PURSOEPOENRLTYYsmall chambers surrounded by walls; he Cytology is the branch of biology that gave the spaces the name “cell” meaning deals with the study of the structure “little room” or “cavity”. He thought the and function of the cells. The cell is the objects he had discovered looked like the basic structural and functional unit of individual rooms in a monastery, which all organisms. All living organisms may were known as cells. The cells observed be composed of a single or many cells. by Hooke gave no indication of the The unicellular organisms consist of a nucleus and other organelles found in most single cell while multicellular organisms living cells. However, in his invention, consist of multiple cells. For multicellular Hooke did not discover the true biological organisms, the cells are differentiated and function of cells. organised into groups to form different structures that perform various functions. Robert Hooke, who is also known as the Chambers of father of cytology, was the ﬁrst scientist to the cork cell study the cell structure using a primitive microscope. In 1665, he examined a Figure 1.1 First view of the cork cells by Robert cross-section of the back of a cork tree Hooke and observed its structure (Figure 1.1). He found that the cork was made up of Source: http://ucmp.berkeley.edu 1 BIOLOGY FORM 5 KIWANDANI.indd 1 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools He was later followed by Anton von in the biochemical evolution theory Leeuwenhoek, who in 1674 discovered free of origin of life on the earth, various living cells in pond water. Leeuwenhoek chemical compounds were combined made a microscope consisting of a single and mobilized into prokaryotes, which high-quality lens which could magnify an gave rise to eukaryotes in the course of object 270 times. This instrument was at that evolution. time referred to as a compound microscope. g) Helps to understand the basis of With this microscope, Leeuwenhoek was genetics; the location, structure, able to make a number of important chemistry, and role of nucleic acid scientific discoveries, including single- (DNA and RNA). celled animals, plants, bacteria, and h) Cytopathology, a study of cellular spermatozoa. abnormalities, helps to diagnose diseases by using cellular changes. The importance of studying cytology GOFVOERRNONMLEINNTE PURSOEPOENRLTYY1.2 The Cell Theory The study of cytology helps us to The origin of the concept of “cell theory” understand the role of cells as the can be traced to as 1830’s when two building blocks of all living organisms, scientists, Matthias Schleiden a Belgian including their anatomy and physiology. botanist (1838) and Theodor Schwann, Additionally, the signiﬁcance of studying a German zoologist (1839) provided the cytology includes the following: ﬁrst deﬁnition of the cell. It was stated a) Helps to realise the role of cells that, all living organisms, both simple and complex, are made up of one or more in metabolic processes such as cells. It was described that, the cell is the respiration, protein synthesis, excretion, structural and functional unit of life. This and growth. led to the formation of the concept of cell b) Aids in understanding the detailed theory. The theory states that “All living structure and functions of different organisms are made up of cells”. In 1855, cells. Rudolf Virchow, a German physiologist, c) Enhance an understanding on the was among the first scientists to accept structural (anatomical and chemical) and extend the work of Robert Hooke. composition of cells. He showed that, the origins of cells was d) Gives knowledge about the process and the division of pre-existing cells, and signiﬁcance of cellular differentiation, concluded that “new cells arise from pre- that is, a process in which cells are existing cells”. specialised for their functions, such as reproductive cells, red blood cells, 1.2.1 The main ideas of the cell theory absorptive cells, and nerve cells. The principal ideas of the cell theory are e) Enables us to understand how similar as follows: cells are organised into tissues. a) All living organisms are composed of f) Helps to show how organisms are evolutionarily related. For example, one or more cells and cell products. 2 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 2 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology b) Cells are the basic or fundamental GOFVOERRNONMLEINNTE PURSOEPOENRLTYYin every cell, but mature human red blood units of life, as all life processes are cells and sieve tube cells of angiosperm controlled by cells. are some of the cells that lack genetic material. Furthermore, the cell theory c) All new cells arise from pre-existing revealed that new cells arise from the pre- cells. existing cells by cell division. However, it does not show the origin of the ﬁrst cell. However, in the modern version of the cell theory, the following were added: Exercise 1.1 a) Cells contain genetic material which 1. Explain the importance of studying carry hereditary information (DNA) cytology. that is passed from one generation to another. 2. Analyse the main ideas of the cell b) Energy flow occurs within cells in theory and its shortcomings. which all metabolic processes of life occur. 3. Explain why the cell is regarded as c) All cells have the same basic chemical the basic unit of life. composition, and the structure and functions of cells complement each 1.3 Types of cells other. The living organism’s activities Based on the level of cell organisation, depend upon the combined actions of cells can be divided into two main types, individual cells. namely prokaryotic cells and eurykaryotic d) All new cells arise from pre-existing cells. Prokaryotic cells have simple cell cells through cell division. organisation, while eukaryotic cells have high level of cell organisation. 1.2.2 Shortcomings of the cell theory Due to increased understanding on cell 1.3.1 The prokaryotic cells biology, the concept of “cell theory” has The word prokaryotes comes from two been challenged based on the modern Greek words pro meaning ‘primitive’ knowledge of virology, blood cells or ‘before’ and karyo (karyon) meaning and origin of life. The study of viruses ‘nucleus.’ From this basic implication, indicated that these living infectious prokaryotic cells refer to those cells which particles are non-cellular. Schleiden and lack true or well organised nuclei such that Schwann could not explain the structure the nuclear materials are freely suspended and functioning of a virus. They said in the cytoplasm. The common examples that the body function is coordinated by of prokaryotic cells are bacteria and blue- the cell, which is not the case in a virus green algae. Prokaryotic cells have the because it only starts its functioning when following general characteristics: hosted by bacterial, plant or animal cell. a) They are microscopic with an average Thus, as per the cell theory, they are non- living creatures (akaryotes). However, diameter of 0.5-10 nm. when they are in host cells, they exhibit living characteristics. Regarding the cell theory, there should be genetic material 3 BIOLOGY FORM 5 KIWANDANI.indd 3 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools b) They lack well organised nuclei. GOFVOERRNONMLEINNTE PURSOEPOENRLTYYpeptidoglycan in the cell wall and lacks the That is, their nucleus has no nuclear outer membrane, while the Gram-negative membrane, therefore, the nuclear bacterium contains a thin cell wall made materials are freely suspended in the up of a few layers of peptidoglycan and cytoplasm. possesses the outer membrane. c) They have small, circular and naked The glycocalyx or capsule is a layer DNA. That is, the DNA is not surrounding the cell wall of some bacteria. associated with histone protein coat to This layer protects the bacteria from drying form chromosomes. out, especially in hypertonic conditions. The ﬁmbriae are structures that help bacteria to d) They have few and small ribosomes of adhere to target cells. They thus play a major 70s sedimentation coefﬁcient. role in bacterial virulence. The ﬂagella are long whip-like extensions that help bacteria e) They lack membrane bound organelles to move about in the environment. The axial such as mitochondria, Golgi bodies, ﬁlaments or endoﬂagella are long structures and plastids. which move in waves enabling the bacteria to spin. f) The cell wall is chemically composed of a carbohydrate-protein complex Beneath the cell wall, there is a plasma called peptidoglycan or murein. membrane, which is a double layer of phospholipids associated with proteins g) Cilia and ﬂagella, if present do not and other molecules. It protects the arise from basal bodies, and they lack intracellular materials and regulates the microtubules of a “9+2” arrangement movement of materials into and out of the pattern. cell. In some bacteria, there is infolding of the cell membrane that forms mesosome Structure of prokaryotic cells (which appeared to be associated with The prokaryotic cell does not have a deﬁned DNA during cell division, and also used nucleus, as it lacks a nuclear membrane. in respiration), photosynthetic membrane Almost all prokaryotes have a protective (which contain photosynthetic pigment cell wall that prevents them from bursting example bacteriochlorophyll used for in hypotonic conditions. Such cell walls photosynthesis) and or nitrogen fixing have different components depending on membrane (for nitrogen fixing bacteria). the type of organism. Beneath the cell membrane, there is cytoplasm, a gel-like ﬂuid ﬁlling the cell. However, most of the prokaryotic cells It is a place where cellular organelles such have cell walls containing major organic as ribosomes are suspended. Ribosomes molecules of proteins, carbohydrates and (70s) are small structures in the cytoplasm lipids. Bacterial cell walls have a unique that play crucial role in protein synthesis molecule known as peptidoglycan. This within the bacterial cell (Figure 1.2). component of the cell walls allows scientists to classify bacteria as either Gram-positive or Gram-negative. The Gram–positive bacterium contains many layers of 4 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 4 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Additional structures sometimes Structures always present present Cell wall Flagellum Cell surface membrane Cytoplasm Capsule Circular DNA Infolding of cell surface membrane Ribosomes Mesosomes Plasmid Pili Figure 1.2 The structure of a typical prokaryotic cell The prokaryotic cell consists of the exchanged between bacteria through pili nucleoid, a region of the prokaryotic during conjugation process. cytoplasm containing the genome, which is the main genetic material (Figure 1.3). Most bacteria have a slender tubule- It possesses a single, circular DNA with like structure on the cell wall called pili. a double-stranded DNA molecule. Some There are two types of pili. The ﬁrst type bacteria have additional genes located is used by related bacteria to exchange in small circular molecules of DNA genetic material through the process of called plasmids. These genes play roles conjugation while the second type of in maintaining virulence to bacteria, pili enables bacteria to stick to their host for instance, by developing resistance or substrate which increases chances of to drugs. The resistant genes can be infection. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Cell wall Capsule membrane Plasma Cytroplasm Pili Plasmid Bacterial flagellum Ribosomes Nucleoid (circular DNA) Figure 1.3 Structure of the rod shaped bacterium 5 BIOLOGY FORM 5 KIWANDANI.indd 5 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Functions of parts of prokaryotic cells GOFVOERRNONMLEINNTE PURSOEPOENRLTYYcells are those cells whose nuclei are a) The cell wall of prokaryotic cells bounded by nuclear membranes. Cells are typically composed of plasma membrane, provides structural and protective cytoplasm, nucleus, and organelles such functions. In some prokaryotes, the as mitochondria, endoplasmic reticulum, cell wall is surrounded by a thin sheath, ribosomes, and Golgi apparatus. The while in others, it is surrounded by a examples of eukaryotic cells are plant and slim capsule. animal cells. These cells are characterised by the following features: b) The cytoplasm of prokaryotes is surrounded by a single cell membrane, a) They are relatively large in size, ranging and all metabolic processes such as from microscopic to macroscopic. protein synthesis, respiration, and replication take place within the b) They have true or well organized cytoplasm. nuclei with nuclear membranes. c) Genetic material in the form of a c) They have large and numerous single circular DNA located in the ribosomes with the sedimentation speciﬁed region within the cytoplasm. speed of 80s (The 's' stand for the This controls hereditary functions of name Svedberg, but is also a unit of the cell. measurement). d) The ﬂagellum found in most aquatic d) They have membrane bound organelles, and soil bacteria aids in movement such as mitochondria and plastids. by a unique process of spinning on an axis like a propeller. e) The cell walls, if present, are chemically composed of cellulose e) The pili, a structure located on the and/or chitin. cell wall help bacteria to increase the chances of survival by undergoing f) They have large, helical DNA which conjugation or by enabling anchoring is associated with histone protein to to its host or substrate. form chromosomes. f) The mesosomes which are infoldings g) Cilia and ﬂagella, if present, arise from of the cell surface membrane which basal bodies and contain microtubules act as sites of respiratory enzymes. that are arranged in a “9+2” pattern. g) Granules of food stores are used as The plant cell respiratory substrates. Plant cells are eukaryotic and present in organisms of the kingdom Plantae. They 1.3.2 Eukaryotic cells have a true nucleus along with specialized The term Eukaryote comes from two structures called organelles that carry Greek words eu meaning ‘true’ and out different functions. Plant cells differ karyon meaning ‘nucleus.’ Eukaryotic 6 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 6 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology from the cells of other organisms in GOFVOERRNONMLEINNTE PURSOEPOENRLTYYa green pigment used for photosynthesis. that they have cell walls, chloroplasts, Other vital organelles found in the plant and central vacuoles. Therefore, the cells include mitochondria, endoplasmic distinctive features of plant cells include reticulum, ribosomes and golgi vesicles. the presence of cell walls containing Mitochondrion acts as a powerhouse of cellulose, hemicelluloses and pectin, and the cell; because it releases energy used the presence of chloroplasts capable of for all cell activities. performing photosynthesis. The Endoplasmic Reticulum (ER) is a Structure of the plant cell large folded membrane system found in The general structure of the plant cell the cytoplasm of the cell. Some ER are can be viewed by using an electron associated with ribosomes while others microscope (Figure 1.4). A plant cell has are not. The ER that are associated an outer layer surrounding the cell, called with ribosomes are known as Rough a cell wall. It is composed of cellulose, Endoplasmic Reticulum (RER), whereas which is a stiff carbohydrate. The cell wall those not associated with ribosomes are provides protection, structural support known as Smooth Endoplasmic Reticulum and mechanical strength to the cell. The (SER). presence of cellulose also helps the plant cell to maintain its regular shape. The Ribosomes are the organelle responsible cell wall has perforations that connect for protein synthesis within a cell. Hence, cytoplasm of the neighbouring cells called the RER provides a surface for protein plasmodesmata. Beneath the cell wall, synthesis while the SER provides a surface there is a cell membrane, which is semi- for transportation of liquids and nutrients permeable. Cell membrane controls the in the cell. There are small vesicles in the passage of materials in and out of the cell. cytoplasm called Golgi vesicles. These are The adjacent cells are usually bound to responsible for storage and transportation one another by a thin layer called middle of secretions of the cells. In addition, the lamella. plant cell has a large central vacuole which is responsible for storage of nutrients and The cytoplasm is a ﬂuid content that ﬁlls the water. The nucleus is a vital part of the cell giving its shape; it contains proteins and cell, as it controls all cell activities such as dissolved ions used in cellular activities. growth, cell division, DNA replication and It is a place where all cell organelles its transcription to RNA. It also contains are housed. Most of the plant cells have hereditary material which transmit traits large organelles called chloroplasts. from parents to the offsprings. Chloroplasts contain chlorophyll which is BIOLOGY FORM 5 KIWANDANI.indd 7 7 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Cell wall Plasmodesma Middle lamella Cell walls of adjacent cells Nuclear pole Free ribosomes scattered Nuclear envelope through cytoplasm (two membranes) Nucleus Rough endoplasmic Nucleolus reticulum GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Chloroplast Chromatin Heterochromatin Euchromatin C(twhloormopelmasbteerannvee)lope Granum Smooth endoplasmic reticulum Mitochondrion Cell surface membrane Cytoplasm Golgi vesicle Golgi apparatus Microtubule – often near Cell sap Vacuole to cell periphery Tonoplast Figure 1.4 A generalised structure of a plant cell as seen under electron microscope Activity 1.1 Observation of a plant d) Mount the specimen at the centre of cell under a light microscope the microscope slide. Materials e) Add a drop of iodine solution. Onion bulb, a light microscope, f) With the help of a needle, place the microscope slide, slide cover, petri dish or watch glass, iodine solution, water, cover slip gently. Make sure there are forceps, a needle, and a knife or surgical no air bubbles under the cover slip. blade or scalpel. g) Observe the specimen under the light Procedure microscope at low, medium, and a) Slice the onion longitudinally into high power objectives. The images tend to be smaller under low power small parts by using a knife or objective lens. However, if more scalpel. magnification is needed, change b) Using forceps, remove the thin objective lenses to medium and high transparent inner lining. power. Structures such as nucleus, c) Put a specimen on a watch glass or cytoplasm, chloroplasts, vacuole, petri dish containing some water to cell wall, and cell membrane can be prevent shrinking. clearly seen. 8 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 8 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Question GOFVOERRNONMLEINNTE PURSOEPOENRLTYYcell, the cytoplasm of the animal cell is jelly-like ﬂuid ﬁlling the cell and it Draw what you have observed and houses all cell organelles. The cytosol compare your diagram with that of or cytoplasmic matrix is a ﬂuid found in Figure 1.4. the cell organelles, such as mitochondria and ribosomes. The cytosol is a site of Safety precaution metabolic activities in the cell organelles. Be careful when working with sharp Mitochondria are called the powerhouses objects such as needle, knife and of the cell; since they release energy in surgical blade. the form of ATP through the process of respiration. The produced energy is used The animal cell to run metabolic activities of the cell. Animal cells are eukaryotic cells with The nucleus is the central part containing a membrane bound nucleus. Unlike the the hereditary (genetic) material. It also eukaryotic cells of plants and fungi, animal controls cell activities such as growth, cell cells do not have a cell wall. Animal cell division, DNA replication, and protein comprises of different cell organelles and synthesis. cell structures which perform specific functions necessary for the cell. The cell Ribosomes are the smallest organelles organelles have a vast range of functions responsible for protein synthesis in the to perform. The animal cells contains cell. Some ribosomes are located on the centrioles, endoplasmic reticulum, Golgi surface of the endoplasmic reticulum apparatus, lysosomes, microfilaments, which is a large folded membrane system microtubules, mitochondria, nucleus, in the cytoplasm. Like plant cell, animal peroxisomes, plasma membrane, cell has rough endoplasmic reticulum and ribosomes, cilia, and flagella. smooth endoplasmic reticulum. Moreover, the animal cell has small vesicles in the Structure of the animal cell cytoplasm known as Golgi vesicles which The outer boundary of the animal cell are responsible for the storage of enzymes is a cell membrane; which is selectively and formation of lysosomes. Lysosomes permeable to substances and controls the are small structures in the cytoplasm which exchange of materials between the cell contain digestive juices responsible for and its environment. Beneath the cell breaking down of old cell parts. There are surface membrane, there is a protoplasm also long structures called microtubules or which is made up of cytoplasm and the microﬁlaments. These are responsible for nucleus (Figure 1.5). Like in the plant all cell movements, and they provide the cell with cytoskeletal support. BIOLOGY FORM 5 KIWANDANI.indd 9 9 10/10/2019 14:05

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10 Exocytosis of secretory product Micrivillus Biology for Advanced Level Secondary Schools Secretory vesicle or secretory granule Pinocytotic vesicle forming BIOLOGY FORM 5 KIWANDANI.indd 10 FOGolgi vesicles Pinocytotic vesicle GOV R OGolgi apparatus Smooth endoplasmic reticulum Microtubule ERNMNLINEMitochondrion Lysosome ENT USERough endoplasmic Free ribosomes P Oreticulum Two centrioles ROPENRLTYYCell surface membrane Nuclear envelops (two membranes) Nuclear pores Nucleus FOR ONLINE USE ONLY Nucleolus DO NOT DUPLICATE Student’s Book Form Five Heterochromatin Euchromatin 10/10/2019 14:05 Cytoplasm Figure 1.5 A generalised structure of animal cell as seen under electron microscope

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Activity 1.2 Observation of an animal GOFVOERRNONMLEINNTE PURSOEPOENRLTYYExercise 1.2 cell under a light microscope 1. a) Draw and label the structure of plant Materials and animal cells as they are seen A plastic spoon, a light microscope, under high power magnification of slides, cover slips, a needle, and light microscope. methylene blue. b) Compare and contrast the two cells Procedure in (a) above. a) Gently scrub the inside of your cheek 2. Describe the composition of cell with a plastic spoon to obtain a cell cytoplasm and its functions. sample. Plastic spoons are used to avoid damaging the cheek cells. 3. Explain how the discovery of the electron microscope improved b) Place the cheek cells sample on a knowledge on cell structure. clean slide. 4. Describe the contribution of each c) Add a drop of methylene blue and of the following scientists in cell mix using a pointed needle. biology: d) Cover the specimen with a cover a) Robert Hooke (1665). slip. Make sure that there are no air b) Theodor Schwann and Mathias bubbles under the cover slip. Schleiden. e) Observe the specimen under the light microscope at low, medium, and high Structure and functions of the cell power objectives. You will see that, In general, a cell consists of cell at the low power objective, the cells membrane, the nucleus and the cytoplasm. appear very small; in contrast, at the Every cell in the body is enclosed by a high power objective, they appear to cell membrane. The cell membrane is be relatively larger. the protective barrier that surrounds the cell, which separates the material outside Question the cell (extracellular), from the material Draw what you have observed and inside the cell (intracellular). It is the compare your drawing with that of barrier that maintains the integrity of a cell Figure 1.5. and controls passage of materials into and out of the cell. Apart from cell membrane, Safety precautions other cells such as plant and fungal cells 1. Be careful when working with sharp have an additional outer layer called a cell wall. It is formed on the outside of the objects such as needle, knife and surgical blade. 2. Do not share instruments used to obtain cell sample. BIOLOGY FORM 5 KIWANDANI.indd 11 11 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools cell membrane to give the cell an extra GOFVOERRNONMLEINNTE PURSOEPOENRLTYYStructure of the cell membrane support, protection, as well as efficiency The cell membrane is made up of proteins and regulates exchange of materials. and lipids (phospholipids). Protein molecules are embedded in the layers of The nucleus is the largest cellular the phospholipids. Phospholipids form a structure, located inside eukaryotic cell bilayer structure which is fundamental to and acts as the control centre of a cell. the selective permeability function of the The material between the cell membrane membrane. Each phospholipid molecule and the nuclear envelope is known as consists of a hydrophobic (water hating) cytoplasm. Within the cytoplasm lies tail of two fatty acids and the hydrophilic an intricate arrangement of fine fibres (water loving) phosphate head. In the and thousands of miniscule but distinct cell membranes, phospholipids arrange structures called cytoplasmic organelles themselves in a layer of two molecules and cytoplasmic inclusion such as stored thick (bilayer), with their hydrophobic tails nutrients, secretory products, droplets and pointing inwards, away from the water pigment granules. Cytoplasmic organelles both inside and outside the cell, while the are small structures that are suspended hydrophilic heads face outwards. There in the cytoplasm of the cell. Examples are two models suggested to describe of cytoplasmic organelles include: the structure of the plasma membrane, endoplasmic reticulum, ribosomes, namely Danielli-Davson’s model (1935) mitochondria, plastids, vacuole, lysosome, and Fluid Mosaic model (1972). microbodies, cytoskeleton, and Golgi apparatus. Each type of organelle has a Danielli-Davson’s Model definite structure and a specific role in the According to Danielli and Davson, the cell. Cytoplasmic inclusions do not have membrane is structurally composed of two any membrane or specific shapes. chemical substances made up of proteins and lipids that form trilaminar layers Plasma membrane (Figure. 1.6). The outer and inner layers This is also called plasmalemma or cell are made up of protein molecules which membrane. It surrounds most of the cell sandwich the phospholipids bilayer. The organelles, separates the contents of the heads of phospholipids are polar, oriented cell from the external environment, and towards the protein layers to form the controls the exchange of materials. In hydrophilic region. animal cells, plasma membrane is the outermost layer, whereas in plant cells it is located beneath the cell wall. 12 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 12 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Protein layer Hydrophilic phospholipid head Hydrophobic phospholipid tail Phospholipid bilayer Figure 1.6 Model of plasma membrane as proposed by Daniel and Davson The model explains the presence of polar GOFVOERRNONMLEINNTE PURSOEPOENRLTYYThe Fluid Mosaic Model head (hydrophilic) and non-polar tail The model was proposed by Seymour (hydrophobic) in the phospholipids. The J. Singer and Garth L. Nicolson in proteins bilayers are continuous and are of 1972. According to this model, protein the same size. The model did not explain molecules are dispersed and inserted into a how material enters or leaves the cell. The phospholipid bilayer, which is hydrophilic model also indicate that the membrane is when exposed to water (Figure 1.7). This static, never change its structure and water provides maximum contact of hydrophilic passes freely between the adjacent protein regions and heads of phospholipids with molecules. The protein bilayers are on the water while providing the hydrophobic outside part, while phospholipids bilayers part with a non-aqueous environment. are at the middle part (intermediately). The Due to the ﬂuid nature of phospholipids model explains the presence of proteins and the arrangement pattern of protein and phospholipids. Moreover, this model molecules in the phospholipid bilayer, the does not explain how cell recognizes model is referred to as the Fuid Mosaic external signals and due to this weakness, Model. further studies were conducted and a new model was developed. This was the Fluid Mosaic Model. BIOLOGY FORM 5 KIWANDANI.indd 13 13 10/10/2019 14:05

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE Glycoprotein (a branch of carbohydrate attached to protein) Glycolipid (a branch of carbohydrate attached to lipid) Peripheral Phospholipid head protein Phospholipid layer Phospholipid Phospholipid tail bilayer Cholesterol Channel protein with pore Protein on one side of the membrane Trasmembrane protein Figure 1.7 Structure of a plasma membrane as per Fluid Mosaic Model Lipids and lipid-soluble substances are GOFVOERRNONMLEINNTE PURSOEPOENRLTYYFunctions of the plasma membrane allowed to cross the hydrophobic region a) It covers the surface of every living cell while non-lipids are not allowed to cross. Large molecules, such as glucose, and acts as a barrier which separates fatty acids, glycerol and amino acids the cytoplasm from extracellular are repelled by the hydrophobic region environment. and therefore, they diffuse through b) It allows passage of some materials special transport proteins called channel in and out of the cells (selective proteins and carrier proteins by facilitated permeability). diffusion. c) It facilitates the transmission of nerve impulse in the nervous system. The strength of the model is that, it d) It functions as a receptor site for realizes the presence of the phospholipid hormonal and neural transmission of bilayer and protein layer. It also realizes chemical stimuli. the presence of pores in the membrane e) It aids cell-to-cell recognition when and the presence of cholesterol in the membranes of two cells come together. membrane. The model explains the f) It serves as a base for attachment of presence of polar head (hydrophilic) the cytoskeleton in some organisms and non-polar (hydrophobic) tail in and as the cell wall in others. Thus, the phospholipids. Furthermore, the model cell membrane supports the cell and explains the presence of glycolipid, as maintains its shape. receptors that allow the cell to respond to chemical messengers which regulate Adaptations of the cell surface the activities of the cell. It is true that the membrane membrane is a dynamic (ever-changing its The cell membrane is specialised to its structure) with phospholipids in constant functions due to: motion. The weakness of the model is that a) Presence of glycolipids, glycoproteins it does not indicate or explain the presence of electrolytes in the plasmalemma. and phospholipids for detection of stimuli, such as antigens and antibodies. 14 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 14 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology b) Presence of hydrophilic pores for Cell wall passage of polar substances. Plant cells, fungal cells, and bacterial cells are surrounded by fairly rigid, non-living c) The phospholipid bilayer facilitates walls called cell walls (Figure 1.8). The the passage of fat soluble substances. chemical composition of cell walls among these organisms differs. The plant cell wall d) Presence of microvilli increases the is made up of cellulose. The fungal cell surface area for absorption. wall is made up of chitin. The bacterial cell wall, is made up of peptidoglycan e) Presence of proteins with speciﬁc called murein. shapes makes the membrane a receptor site for chemical stimuli such A cell wall is a protective layer around the as hormones. plasma membrane. It also determines the shape of plant cells. Originally, the cell f) Presenceofglycolipidandglycoprotein wall in plants is a product of cytoplasm. enable the membrane to bind to the The cytoplasmic organelles such as membrane of a neighbouring cell, that the endoplasmic reticulum and Golgi is, cell-to-cell recognition. apparatus play a very important role in the formation of cell walls. The formation of g) Presence of cholesterol disturbs a new cell wall usually takes place in a the close packing of phospholipids. dividing cell immediately after the nuclear This keeps them more ﬂuid and division. maintains stability and ﬂexibility of the membrane over a wide range of temperature. Exercise 1.3 GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 1. Describe the structure of a Structure of the cell wall plasma membrane as proposed by Plant cell wall, which is made up of Danielli-Davson model. cellulose and strengthened by other polysaccharides; is a protective layer 2. Describe the structure of a around the cell surface membrane. The cell membrane as envisaged primary cell wall in plants is composed by Jonathan Singer and Garth of cellulose, hemicelluloses and pectin. Nicolson in the Fluid Mosaic This primary wall is laid down during cell Model. division in plants. The primary cell wall thickens into secondary cell wall. During a) Explain why membranes are secondary thickening some cells undergo generally referred to as fluids. ligniﬁcation (hardening) whereby lignin is deposited in all cellulose layers. Lignin b) Name the chemical constituents cements and anchors ﬁbres together, of membranes and enumerate making the cell wall very hard and the role of each. increases tensile strength. Suberin and cutin are also found in the cell wall during 3. How is the cell membrane adapted secondary thickening. These are waxy to its function? materials acting as a water proof coat 15 BIOLOGY FORM 5 KIWANDANI.indd 15 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools which helps to prevent excessive water loss from the plant. Middle lamella is a thin layer of pectin materials (calcium and magnesium) which joins neighbouring cell walls together. Close group of Adjacent primary cell walls of two cells plasmodesmata (primary Middle lamela pit field) – primary cell walls are thinner in this area as a result of slower growth TS before lignification Plasmodesma ‘Pit cavity’ TS after lignification Secondary wall of lignin Primary cell walls Simple pit ‘Pit membrane’ – middle lamella plus two thin primary walls GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 1.8 Structure of a cell wall Functions of the cell wall therefore, they allow movements of a) It provides mechanical support and materials to long distances. strength to cells and the plant as a f) Cell walls possess small pores or whole, due to presence of lignin. pits through which the materials can pass from one cytoplasm to another b) It maintains the shape of the cell, since (symplastic movement). the cell wall is rigid. g) Cutin and suberin deposits prevent c) It prevents the osmotic bursting loss of water from the cell surface of the cell by inhibiting excessive through evaporation. endosmosis due to its capability to resist expansion. h) The cell walls of root endodermal cells are suberized to form casparian d) It protects the plant cells against strips. These, among other functions, pathogens and water loss due to the regulate the amount of water to be presence of waxy cutin on the cell admitted into the plant. wall. i) Cell walls of some cells store food. e) The walls of xylem vessels, tracheids and phloem sieve tubes are tubular; 16 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 16 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Exercise 1.4 GOFVOERRNONMLEINNTE PURSOEPOENRLTYYCytoplasmic organelles Cytoplasmic matrix contains numerous 1. Describe the composition of the membranous internal structures called cell wall in living organisms. organelles. Organelles can be deﬁned as tiny distinct parts with specialised 2. Explain the functions of lignin and structures and functions found inside suberin in the plant cell. the cell. The organelles are sub- cellular structures with characteristic 3. Give the name of the structure morphological forms, distinctive chemical which joins neighboring cell walls. constitutions and deﬁnite functions. The organelles perform speciﬁc functions Cytoplasm and cytoplasmic organelles such as oxidative phosphorylation and (sub-cellular units) generation of energy in the form of ATP in The space between the cell membrane the mitochondria, formulation and storage and the nucleus is ﬁlled with translucent, of carbohydrates in chloroplast, protein homogenous and colloidal ﬂuid called synthesis in ribosomes of the rough a cytoplasmic liquid. The latter is an endoplasmic reticulum and concentration aqueous substance containing different and packing secretions in Golgi apparatus. types of cell organelles, water and mineral Other functions include synthesis of lipid salts. It also contains organic compounds, and hormones in smooth endoplasmic such as carbohydrates, lipids, proteins, reticulum, degradation of macromolecules nucleic acids and enzymes. in the lysosomes, regulation of all cellular activities by nucleus, and organisation of Functions of cytoplasm spindle apparatus by centrioles. a) It provides medium for chemical The nucleus reactions such as glycolysis to take The nucleus is a functional unit of a cell. place. It is a membrane-bound structure, located b) It stores useful materials such as at the periphery of the cell membrane starch, glycogen, and lipids. more or less to the centre of the cell and it c) It stores waste materials such as contains the cell’s hereditary information. nitrogenous wastes. It controls all cellular activities and is d) Movement of materials takes place the most prominent organelle in the cell. within the cytoplasm. The cell nucleus is bounded by a double e) It harbours and organises cell membrane called the nuclear envelope. organelles that perform different It is a selectively permeable membrane, functions such as protein synthesis allowing some materials to pass in and out in ribosomes and lipid synthesis in and separates the contents of the nucleus smooth endoplasmic reticulum. from the cytoplasm. The envelope regulates the ﬂow of molecules into and out of the nucleus through nuclear pores. The pores allow exchange of substances between 17 BIOLOGY FORM 5 KIWANDANI.indd 17 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools the nucleus and cytoplasm. The pore has GOFVOERRNONMLEINNTE PURSOEPOENRLTYYFunctions of the nucleus a deﬁnite structure formed by fusion of a) It controls all metabolic activities of the outer and inner membranes of the envelope. The nucleus contains chromatin, the cell. consisting of DNA which is bounded by basic proteins called histones. During b) It contains hereditary information of nuclear division, chromatin stains more the cell, hence, it transmits genetic intensely and becomes more conspicuous information to the new cell. because it condenses into more tightly coiled threads called chromosomes. c) It takes part in the formation of However, some remains tightly coiled ribosomes and RNA, thus it controls and continue to stain intensely and this is protein synthesis. called heterochromatin. It is seen as a dark patch, usually occurring near the nuclear d) It controls cell division when required envelope. The remaining loosely coiled since DNA replication is essential for chromatin is euchromatin. It contains cell division. DNA which is genetically active during interphase. Exercise 1.5 The nucleolus 1. Describe the structure of the The nucleolus is a cellular structure nucleus of a cell. present in the nucleus of a eukaryotic cell. The nucleolus appears as a rounded 2. Explain the role of nucleolus. and darkly stained structure inside the nucleus. It contains nucleolar organisers 3. Why is the nucleus said to be the that synthesise ribosomes by transcribing controller of all cellular activities? and assembling ribosomal RNA (Figure 1.9). The nucleoli vary in number from Endoplasmic reticulum one to many nucleoli within a single cell The endoplasmic reticulum is a network nucleus of a plant or an animal cell. of flattened membranes bound sacs called cisternae. Some of the endoplasmic Ribosomes reticula are encrusted with ribosomes and termed Rough Endoplasmic Reticula Rough endoplasmic (RER), while those without ribosomes are reticulum known as Smooth Endoplasmic Reticula (SER). The quantity of both rough and Nucleolus smooth endoplasmic reticula in a cell can slowly interchange from one type Chromatin to the other, depending on the changing metabolic activities of the cell. Nucleoplasm Nuclear pore Nuclear Rough endoplasmic reticulum (RER) envelope The surface of the rough endoplasmic reticulum contains protein-manufacturing Figure 1.9 Structure of a nucleus ribosomes, giving it a “rough” appearance 18 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 18 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology (Figure 1.10a). However, the ribosomes the endoplasmic reticulum once a speciﬁc bound to it at any one time are not a stable protein-nucleic acid complex forms in the part of this organelle’s structure as they are cytosol. This special complex forms when constantly being bound and released from a free ribosome begins to translate the the membrane. A ribosome only binds to mRNA. Ribosomes Cisternae Cisternae (a) (b) Figure 1.10 The structure of endoplasmic reticulum (a) RER (b) SER Functions of rough endoplasmic GOFVOERRNONMLEINNTE PURSOEPOENRLTYYwhich are involved in metabolism of reticulum lipids such as steroids and glycogen. The The rough endoplasmic reticulum has the smooth endoplasmic reticula are generally following functions: found in adipose cells, interstitial cells, a) They are sites for protein synthesis, and glycogen storing cells of the liver. They also occur in conduction ﬁbres of due to the presence of ribosomes. the heart, spermatocytes and leucocytes. The muscle cells are also rich in smooth b) They provide pathways for endoplasmic reticulum known as the transportation of materials through the sarcoplasmic reticulum. cell, such as proteins synthesized on the ribosomes. c) They provide a large surface area for Functions of smooth endoplasmic chemical reactions to take place. reticulum a) For synthesis, secretion, and storage Smooth endoplasmic reticulum (SER) This type of endoplasmic reticulum of lipids, carbohydrate and other non- possesses smooth walls, because the protein products. ribosomes are not attached to its membranes (Figure 1.10b). The smooth endoplasmic b) It contains enzymes which breakdown reticulum occurs mostly in those cells chemical substances in liver cells. c) For synthesis of steroids which later form hormones. 19 BIOLOGY FORM 5 KIWANDANI.indd 19 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools d) It increases the surface area for although it can change from one form to chemical reactions in the cell to take another depending on the physiological place. conditions of the cells. The matrix contains few small ribosomes (70s), phosphate e) It is involved in the formation of Golgi granules, respiratory enzymes (such as bodies. ATP synthase) and small mitochondrial DNA which is circular and naked (Figure Exercise 1.6 1.11). 1. Describe the structural differences Mitochondrial DNA between smooth and rough Outer membrane endoplasmic reticulum. Ribosome 2. Outline the functions of endoplasmic Matrix reticulum. Phosphate granule 3. Explain how the RER and SER are Inter membrane space adapted to their roles. Inner membrane Cristae Stalked particles Porins in the outer membrane Mitochondrion GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 1.11 A structure of a mitochondrion A mitochondrion (plural mitochondria) is an organelle bound by double membranes Functions of mitochondria and it is found in eukaryotic cells. a) It is a site for aerobic respiration, hence Mitochondria have been described as ‘the powerhouses of the cell’ because releases energy in the form of ATP. they generate most of the cell’s chemical b) It is an intermediate site for synthesis energy originally contained in respiratory substrates. This energy is liberated in the of important biomolecules such as form of adenosine triphosphate (ATP). chlorophyll, cytochromes, steroids, and fatty acids. The structure of the mitochondrion c) The mitochondrion can store and Each mitochondrion is bounded by two release calcium ions when required. highly specialised membranes. Thus, it is Hence, it regulates calcium ion a double membrane organelle. The outer concentration in the cell. membrane is quite smooth, it has many copies of a transport protein called porins, Adaptations of mitochondria which forms large aqueous channels The mitochondrion is specialised to its through the lipid bilayer. On the inside is function because: the inner membrane separated from the a) The outer membrane contains lots outer membrane by a space, measuring 6 - 8 nm. The inner membrane is deeply of porins that allow the passage of folded into infolding known as cristae, molecules for respiration. which project in the matrix space. b) The inner membrane is highly folded Generally, the organelle has an oval shape, into cristae that increase its surface area. c) The membranes are permeable to allow the passage of all diffusable 20 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 20 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology materials. This allows raw materials inGOFVOERRNONMLEINNTE PURSOEPOENRLTYYare subdivided into three different types, and products out. namely amyloplasts, proteinoplasts, d) The matrix contains appropriate and elaioplasts. Each of these has a enzymes used in respiratory pathways distinctive function. For instance, such as Kreb’s cycle. amyloplasts are responsible for storage a) Presence of windows or fenestra in the of starch, proteinoplasts are responsible membranes facilitates the passage of for storage of proteins, while elaioplasts materials in and out. are responsible for storage of fats and oils which are needed by plants. They are also Plastids used for synthesis of amino acids and fatty These are membrane bound organelles acids. found in the cells of plants, algae, and other eukaryotic organisms. They often Chloroplasts. These are most commonly contain pigments and the type of pigment known plastids which play an essential determines the cell colour. They are role in enabling plants and some mainly responsible for activities related algae to make their own food through to making and storing food. The plastids photosynthesis. They are found in green include chromoplasts, gerontoplasts, parts of plants, mainly leaves and in some leucoplasts, and chloroplasts. other organisms such as photosynthetic bacteria and green algae. The term Chromoplasts. Pigmented plastids found chloroplast comes from two Greek words: in ﬂowers, aging leaves, and fruits such chloros, meaning ‘green’ and plast, as tomato and red pepper. They contain meaning ‘form’. It contains green pigment carotenoid pigments; mainly red, orange known as chlorophyll, enzymes and other or yellow which give different colours molecules that function in photosynthesis. seen in different parts of the plant. They assist in pollination and seed dispersal. Structure of chloroplasts The contents of chloroplasts are portioned Gerontoplasts. Plastids that develop from from the cytosol by an envelope consisting the chloroplasts of the leaves or other of two membranes separated by a very parts of the plant that are going through narrow inter-membrane space. Inside the ageing process (senescence) or are the chloroplast is another membranous converted into different organelles. This system in the form of ﬂattened sacs called occurs when such parts of the plant are no thylakoids or lamellae. In some regions, longer carrying out photosynthesis. thylakoids pile up like a stack of coins to form grana (singular, granum). The ﬂuid Leucoplasts. Colourless plastids found in outside the thylakoids is the stroma, which non-photosynthetic parts of the plant such contains the chloroplast DNA, ribosomes as roots, seeds, and bulbs. They are used (70s), starch granules as well as many for storage of starch, lipids, and proteins photosynthetic enzymes. The chlorophyll particularly in roots and tubers. They and carotenoids are present in thylakoids and grana (Figure 1.12). BIOLOGY FORM 5 KIWANDANI.indd 21 21 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Chloroplast Outer membrane Lipid droplet envelope Inner membrane Starch grain Free ribosomes Stroma Polysome Chloroplast DNA One granum Figure 1.12 Structure of the chloroplast Thylakoid Intergranal lamella (one thylakoid) Functions of the chloroplast GOFVOERRNONMLEINNTE PURSOEPOENRLTYYd) Proteins embedded in the grana hold a) The chloroplast is the fundamental photosystems and their chlorophyll in proper position for harvesting light. site for the photosynthesis process. e) The stroma contain enzymes needed b) It is the site for protein synthesis, due to catalyse the reactions in the light to the presence of ribosomes in the independent phase of photosynthesis. stroma. f) Contains chloroplast DNA for self- c) It stores starch and lipids for plant replication and inheritance. use. g) They have ribosomes needed for Adaptation of the chloroplasts protein synthesis. Chloroplasts are specialised for their function as follows: Exercise 1.7 a) They have permeable membranes 1. What are the differences between which allow movement of raw mitochondria and chloroplasts? materials in and products out. 2. Explain why chloroplasts and b) The presence of numerous grana mitochondria are considered as provides a large surface area for prokaryotic cells in the eukaryotic photosynthetic pigments, electron cells. carriers and ATP synthase involved in the light dependent reaction. 3. Draw and label a diagram of each of the following organelles: c) Arrangement of photosynthetic a) Chloroplast pigments in photosystems allows b) Mitochondrion maximum absorption of light energy. 22 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 22 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Vacuoles GOFVOERRNONMLEINNTE PURSOEPOENRLTYY cell (autolysis). Plant vacuoles Vacuoles are membrane bounded sacs can function in the same way as in which are found within the cytoplasm lysosomes of animal cells as they both of a cell. The vacuoles of plant cells are participate in an automatic cell death bounded by single membranes called by autolysis. This process occurs when tonoplast. These vacuoles are formed the tonoplast ruptures and releases its when vesicles released by the endoplasmic contents (enzymes) into the cytoplasm reticulum and Golgi apparatus merge which digests the entire cell. together. Young plants consist of a number of smaller vacuoles which during growth d) They play vital role in primary growth, and development, they fuse to form a large since the pressure exerted by fusion central permanent vacuole. Therefore, in a of small vacuoles leads to elongation mature plant cell, cytoplasm is displaced of the cells. Hence, this increases the and seen as a thin layer near the periphery length of a plant organ. of the cell surrounding the large central vacuole. The central positioning of the e) They contain anthocyanins which vacuole push the nucleus more or less to provide colour to ﬂowers, fruits, the periphery or near to the cell surface and buds. These pigments facilitate membrane. At this stage, the vacuole is pollination and seed dispersal. ﬁlled with cell sap, which contains water, phenol, mineral salts, alkaloids, pigments, Ribosomes sugars, and proteins. Animal cell lack Ribosomes are tiny organelles found in vacuoles, but if present they are small the matrix of mitochondria, chloroplasts, and temporary, associated with storage of and cytoplasm of the cells. They occur in food and other materials to be secreted, both, prokaryotic and eukaryotic cells. In transported or removed. Example, food prokaryotic cells they are found freely in vacuole or vesicle (phagocytotic or the cytoplasm, whereas in the eukaryotic pinocytotic vesicles). cells they are either attached to the outside of the endoplasmic reticulum (or nuclear Functions of vacuoles envelope) or occur freely in the cytoplasm. Vacuoles in plant cells play the following Structurally, each ribosome is made up of roles: two sub-units, a small sub-unit and a large a) They support herbaceous plants and sub-unit (Figure 1.13). Basing on their size and sedimentation coefficient, there herbaceous parts of woody plants by are two types of ribosomes. These are: providing an osmotic system which creates a pressure potential. a) 70s ribosomes: These are relatively smaller, with sedimentation coefﬁcient b) They act as temporary stores for of 70s and molecular weight of 2.7x106 different substances, such as food, Daltons. They occur in prokaryotic enzymes, and waste materials. cells, such as in blue-green algae and bacteria.They also occur in eukaryotic c) They have hydrolytic enzymes which cells organelles, such as mitochondria destroy dead cells or the entire plant and chloroplasts. 23 BIOLOGY FORM 5 KIWANDANI.indd 23 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools b) 80s ribosomes: These have the “translate” the message contained in sedimentation coefﬁcient of 80s the mRNA codes. and the molecular weight of 40x106 Daltons. The 80s ribosomes occur in c) They have enzymes that catalyse the eukaryotic cells. synthesis of peptide bonds. The ribosomes of mitochondria and GOFVOERRNONMLEINNTE PURSOEPOENRLTYYLysosomes chloroplasts are always smaller than Lysosomes are membrane-enclosed cytoplasmic ribosomes and are comparable organelles that contain an array of enzymes to prokaryotic ribosomes in both size and capable of breaking down all types of sensitivity to antibiotics. biological polymers proteins, nucleic acids, carbohydrates, and lipids. The word Large subunit lysosomes come from the two words lyso means ‘digestive’ and soma means ‘body.’ Small subunit They are also referred to as suicide bags since they undergo self-destruction, hence Figure 1.13 Structure of ribosome the digestion of the entire cell (autolysis). They mostly occur in animal cells and Functions of ribosomes few or rare in plant cells. Lysosomes a) Ribosomes are sites of protein are not present in bacteria and mature erythrocytes, while a few of them occur synthesis; they provide surface in muscle cells. Leucocytes, especially area or space for polypeptide chain granulocytes, are particularly rich sources construction and enzymes for the of lysosomes. In addition, they are synthesis of peptide bonds between numerous in the epithelial cells of lungs amino acid monomers. Hence, they and uterus. are known as protein factories. The ribosomes are adapted for protein Structure of lysosomes synthesis, as they have ribosomal RNA Lysosomes are round, with vacuolar (rRNA) which provides attachment structure which remains ﬁlled with dense points for both messenger RNA material and bounded by a unit membrane. (mRNA) and transfer RNA (tRNA). They consist of digestive enzymes, b) Ribosomes have receptor sites on the which are synthesized in the ribosomes small sub-unit where mRNA binds of the rough endoplasmic reticulum. The itself and they are able to “read” and enzymes, which always have acidic pH, are transported to the Golgi apparatus for modiﬁcation. The Golgi apparatus in the cytoplasm concentrates and packs the modiﬁed enzymes in the Golgi vesicles, which pinch off as lysosomes. Their shape and density vary greatly from cell to cell and time to time. 24 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 24 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Functions of lysosomes GOFVOERRNONMLEINNTE PURSOEPOENRLTYYany other chemical aggregates and once The main functions of lysosome include engulfed, they are contained within the heterophagy, autophagy and autolysis. autophagosome (autophagic vacuole). The latter can then fuse with lysosomes, Heterophagy which result in the release of lysosomal This is a process whereby lysosomes acid enzymes to degrade the contents of perform the intercellular digestion of the autophagosome. The products of the materials that are gathered from outside degradation include amino acids, among the cell by endocytosis, which are other molecules and all of them are pinocytosis (taking in liquid materials) and released back into the cytoplasm and re- phagocytosis (taking in solid materials). The used in metabolism as well as in building endocytotically ingested food material is macromolecules. collected in a membrane bounded vesicle called heterophagosomes (pinosomes or Autolysis phagosomes) and eventually fuse with Autolysis is more commonly known lysosomes to form phagolysomes in which as self-digestion, which refers to the the engulfed material is digested. Example destruction of a cell through the action of when bacteria are ingested by phagocytosis, its own enzymes. Lysosomes break down the ingested bacteria are packed in a to release its contents (enzymes) which phagocytic vesicle (phagosomes).This digest various organelles and ﬁnally the vesicle fuses with a primary lysosome, entire cell in certain pathological conditions. forming a secondary lysosome. Thereafter, This process is known as autolysis or self- enzymes of the lysosome digest the bacterial destruction of the cell. macromolecules. Exocytosis or extracellular digestion Autophagy Exocytosis is the process responsible Autophagy allows the orderly degradation for breaking down damaged cellular and recycling of cellular components. components and some unwanted proteins This process occurs when cytoplasmic which are expelled out of the cell. One components become enclosed in a double of the causes of aging is that, in long- membrane (phagophore) to form a lived cells the types of metabolic waste compartment known as autophagosome that cannot be broken down accumulates for degradation (Figure 1.14). This is and lysosomes may release them outside the regulated mechanism of the cell that the cell by exocytosis. For example; the disintegrates unnecessary or dysfunctional enzymes of lysosome are released during components. Autophagy starts with the the replacement of cartilage by bone during formation of a phagophore from the development. Also lysosomes of certain membrane; this expands and engulfs the cells such as spermatozoa discharge their molecules or “cargo” for degradation. The enzymes outside the cell during fertilization cargo can include redundant organelles or process. BIOLOGY FORM 5 KIWANDANI.indd 25 25 10/10/2019 14:05

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE Phagocytosis Food vacuole Digestion Secretion of Autophagy hydrolytic enzymes Lysosomes Plasma membrane Golgi apparatus Transport vesicle Rough endoplasmic reticulum Figure 1.14 Lysosomal functions Lysosomes are adapted to their functions GOFVOERRNONMLEINNTE PURSOEPOENRLTYYMicrobodies due to the presence of hydrolytic enzymes which catalyse degradation of unwanted Microbodies are small, spherical organelles cellular substances. In addition, lysosomes bounded by a single phospholipid bilayer have the membranes that isolate hydrolytic membrane which contain a matrix of enzymes from the rest of the cytoplasm. intracellular materials such as catalase This prevents unnecessary autolysis. (peroxidase) enzyme and other proteins (Figure1.15). They are present in almost Exercise 1.8 all eukaryotic cells and are mostly seen near the ER, and sometimes near mitochondria 1. Why are lysosomes said to be and plastids. They can be distinguished suicide bags? from other cell organelles by their contents. Microbodies include peroxisomes, 2. Describe the structure and functions glyoxysomes, and glycosomes. Peroxisomes of lysosomes. are particularly predominant in the liver and kidney cells of vertebrates, while in plants 3. Giving reasons, mention the parts they are found mostly in plant cells where of your body which are expected to photorespiration occurs. Glyoxosomes have large number of lysosomes. are specialized microbodies found in plants, particularly in fat storage tissues of germinating seeds and in filamentous 26 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 26 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology fungi. Glycosomes are microbodies which the peroxisomes. They are found in few contain glycolytic enzymes in its matrix, species of protozoa such as Trypanosoma. and they are believed to have evolved from Figure 1.33 Structure of the zwitterion Crystalline core Lipid bilayer Figure 1.34 Formation of dipeptide molecule linked by the peptide bond Figure 1.15 Structure of microbody Functions of microbodies GOFVOERRNONMLEINNTE PURSOEPOENRLTYYd) Microbodies also help in conversion a) Microbodies such as peroxisomes of stored lipid in germination oil seeds and liver cells into glucose in found in plant and animal cells the process called gluconeogenesis. are involved in the breakdown of poisonous hydrogen peroxide to Golgi apparatus water and oxygen in the presence of The name of this organelle was derived peroxidase enzyme. from its founder, Camillo Golgi, in 1898. He identified it in the nerve cells of the owl and cat. This happened long before the discovery of the endoplasmic reticulum. b) The peroxisomes contain enzyme Golgi apparati are involved in important glycolic acid oxidase that oxidises cellular functions, such as biosynthesis glycolic acid, a product of of polysaccharides, packaging of cellular photosynthesis, to glyoxylic acid, by synthetic products, production of the process called photorespiration. exocytotic vesicles, and differentiation of cellular membranes. It occurs in all cells, c) In plants, there are special microbody except in the prokaryotic cells and in called glyoxysomes. These are the cells of certain eukaryotes, such as fungi centre for the glyoxylate cycle, and bryophytes. It also does not occur which involves conversion of fats in cells of mature sieve tubes of plants, into carbohydrate, especially in spermatozoa, and in red blood cells. germinating seeds. BIOLOGY FORM 5 KIWANDANI.indd 27 27 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Structure of the Golgi bodies Golgi apparatus is associated with small, It is disc-shaped; consisting of central, spherical sac-like structures called Golgi ﬂattened, plate-like, compartments or vesicles. These contain various secretions cisternae (Figure 1.16). It is a modiﬁed such as hormones, mucus or enzymes, and smooth endoplasmic reticulum. The they are future lysosomes. Incoming transport vesicle Cisternae Lumen Secretory vesicle Newly forming vesicle Figure 1.16 Structure of Golgi apparatus GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Functions of the Golgi bodies Cytoskeleton The functions of Golgi bodies include the These are complex network of protein following: ﬁlaments and microtubules which exist a) They form lysosomes. in the cytoplasm of eukaryotic cells. It anchors proteins or organelles, such b) They concentrate and pack as nucleus to their ﬁxed location. The secretions, such as enzymes. cytoskeleton consists of microtubules, microﬁlaments and intermediate ﬁlaments c) They are involved in transformation (Figure 1.17). of spermatids into mature spermatozoa. d) They are involved in formation of primary cell walls in plants. 28 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 28 10/10/2019 14:05

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FOR ONLINE USE ONLY Cytology DO NOT DUPLICATE Microfilaments Intermediate filaments α − Tubule Actin Keratin β − Tubule Microtubes Figure 1.17 Structures of the cytoskeletons Microtubules GOFVOERRNONMLEINNTE PURSOEPOENRLTYYMicroﬁlaments These are tubular structures made up of These are much narrower than microtubules, arranged globular tubulin. They are found being only about 5-7 nm in diameter. in the cytoplasm of animal and plant cells. They are thread-like structures, arranged They occur in cilia, ﬂagella, centrioles, in sheets or in bundles beneath the cell the cortex of meristematic cells, and basal surface membrane. They are chemically bodies. composed of a large amount of actin, hence their name actin filaments. Actin Functions of microtubules filaments, usually in association with a) They determine the shape of the cell. myosin, bring about many types of cell movements. For example the contractile b) They form a framework along which proteins (actin and myosin) lead to the plant cell wall is laid down. contraction and relaxation of muscles. c) In cilia and ﬂagella, they help beating Functions of microﬁlaments of rhythmic movements. a) They determine the shape of cells; d) They bring about movement of since they offer a cytoskeletal support. chromosomes during anaphase in nuclear division. b) The cleavage of animal cells during cytokinesis is brought about by the e) Since they are tubular, they transport constriction of a ring of microﬁlaments materials from one part of the after nuclear division. cytoplasm to another. c) They are responsible for any f) They are involved in the movements movement that the cell makes; due to of other cell organelles such as Golgi the presence of actin and myosin that vesicles, lysosomes, and mitochondria. influence muscle cells contraction and For example, the movement of Golgi relaxation. vesicles towards the center to form cell plate during the formation of a primary cell wall in plant cells is brought about by microtubules. 29 BIOLOGY FORM 5 KIWANDANI.indd 29 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Intermediate filaments centrioles in the cytoplasm which usually These structures are found between lie at right angles to each other close to microtubules and microﬁlaments. the nuclear membrane. In cross section, They provide shapes of cells and act as each centriole is seen to contain nine intercellular tendons, preventing excessive groups of microtubules with three tubules stretching of the cells. in each group (Figure 1.18). During cell division, the centrioles divide and migrate Centrioles chromosome in opposite poles of the A centriole is a cylindrical organelle cell where they act as a focus for spindle found in animal cells, algal cells and formation. Centrioles also produce the fungal cells, but not in cells of higher basal bodies from which cilia and flagella plants. Animal cells contain a pair of develop. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY (a) (b) Figure 1.18 Structure of centriole (a) side view and (b) cross section Exercise 1.9 Comparison of prokaryotic and 1. What do you understand by the eukaryotic cells term cytoskeleton? Common features which can be found in 2. Explain the functions of microtu- prokaryotic and eukaryotic cells are as follows: bules and microﬁlaments in plant a) Both have cell membranes that and animal cells. 3. Describe the structure, location and separate the cell’s interior from its functions of centrioles in animal surrounding environment. cell. b) Both have a cytoplasm that consists of a jelly-like region within the cell in 30 which other cellular components are floating. c) Both have ribosome particles that synthesize proteins, and the genetic material of the cell. The prokaryotic and eukaryotic cells also differ in many aspects as elaborated in the Table 1.1. Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 30 10/10/2019 14:05

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FOR ONLINE USE ONLY Cytology DO NOT DUPLICATE Table 1.1 Differences between prokaryotic and eukaryotic cells Criteria/ Feature Prokaryotic cells Eukaryotic cells Cell type Mainly unicellular (some Mainly multicellular (except kingdom Nucleus cyanobacteria may be Protoctista which have many multicellular). unicellular organisms). Have no true nucleus. Have a true nucleus, bound by a double membrane. Double membrane Have no double bound organelles membrane bound Have many double membrane bound organelles. organelles, such as mitochondria, DNA chloroplasts, and nucleus. Have circular DNA. Have helical or linear DNA. Have naked DNA. Have DNA associated with proteins Ribosomes Have small andGOFVOERRNONMLEINNTE PURSOEPOENRLTYYknown as histones and is organised simple ribosomes (70s into chromosomes. Cytoplasm ribosomes). Have larger and more complex Cell size Have only one type of ribosomes (80s ribosomes). Functional organelles, that is, the compartments ribosomes. Filled with a large and complex collection of organelles, many Cell wall Small in size of them enclosed in their own Cilia and ﬂagella membranes. Have only one membrane Cell division (the plasma membrane) Relatively large in size. Reproduction enclosing all of the cell’s Have many different functional internal contents. compartments divided by membranes. Mureinic cell wall. Cellulose or chitinous cell wall. Do not arise from basal Arise from basal bodies and have 9+2 bodies and lack micro- arrangement of microtubules. tubules. Involves mitosis, meiosis or both. Involves binary fission or budding. Involves meiosis during gamete formation. No meiosis. Transfer of DNA is done by conjugation only. BIOLOGY FORM 5 KIWANDANI.indd 31 31 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools 1.3.3 Cell differentiation Signiﬁcance of cell differentiation Cell differentiation has the following Cellular differentiation is the process signiﬁcance: of cell transformation from one form to a) It modiﬁes cells to suit their functions another. It leads to the development of specialised types of cells for carrying out more efﬁciently. This means that, speciﬁc functions. This process involves during differentiation the cell becomes biochemical and structural changes. equipped with structural and/or The differentiated cells become more chemical changes to enhance its specialised than the undifferentiated ones. efﬁcient. In most cases differentiation occurs GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Examples include: during the development of a multicellular organism, as it changes from a simple i) Spermatozoa are packed with zygote to a complex system of cell types numerous mitochondria and or tissues. The process continues to acrosomal enzymes. They also have adulthood; as adult stem cells divide and ﬂagella. All these features facilitate create fully differentiated daughter cells efﬁcient fertilisation of egg cells. during tissue repair. Differentiated cells change in size, shape, membrane potential, ii) Female gametes (egg cells) have metabolic activity, and responsiveness numerous microvilli for absorption to signals. Cell differentiation leads to of food from follicular cells. They cell specialisation, which in turn leads to also have a large proportion of division of labour that improves efﬁciency cytoplasm which contains food of the organisms. Examples of specialised reserve for the developing embryo. cells in animals are sex cells, nerve cells, red blood cells, and epithelial cells; and iii) Nerve cells have features like in plants are xylem, phloem, root hair, myelin sheath and nodes of Ranvier, and parenchyma cells. Figure 1.19 shows which facilitate rapid transmission root hair cell as an example of specialised of impulses. The synaptic vesicles plant cell. contain neurotransmitters that aid in synaptic transmission of impulses. Cell wall iv) The cells in xylem vessels and Cytoplasm tracheids are hollow, and have ligniﬁed cell walls for efﬁcient Vacuole carriage of water and dissolved mineral salts. Nucleus b) It enables cellular organization, as a Figure 1.19 Root hair cell way of forming different tissues and organs (organogenesis) through the expression of a specific set of genes within the body to perform more specialized and complex tasks. c) It forms the basis for embryonic stem cell research, whereby researchers 32 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 32 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology can identify stem cells, which can Exercise 1.10 be used in the future to deal with the conditions that require transplanting, 1. Explain features which are found such as kidney transplanting. in both prokaryotic and eukaryotic d) It helps in the future treatment of cancer cells. patients by enabling measurement of the cancer progress at cellular level, 2. Using examples, explain the concept where the cytopathologists term of cell differentiation. ‘grade’is used as a marker to determine how differentiated cell in a tumor is. 3. Explain why cell differentiation is generally referred to as a cellular Activity 1.3 Observation of a division of labour. specialised root hair cell 4. What is the importance of cell differentiation in animals and plants? Materials GOFVOERRNONMLEINNTE PURSOEPOENRLTYY1.4 The organic constituents of cells Onion roots, surgical blade, iodine (Biochemistry) solution, petri dish, dropper, light The cells are composed of water, inorganic microscope, and microscope slides. ions and organic molecules (carbon- containing compounds). Water is the most Procedure abundant molecule which constitutes large a) Takethe onion root, and use a surgical part of cells, constituting about 70% of the total mass. It also interacts with other blade to cut it transversely into very constituents in the biochemistry of life. The thin slices. organic components of the cells include: b) Put a slice on the petri dish, and add Carbohydrates, proteins, lipids, enzymes, one drop of iodine solution using a nucleic acids and regulatory substances dropper. such as hormones and vitamins. c) Transfer the stained slice to the microscope slide. 1.4.1 Carbohydrates d) Observe the stained slice under a Carbohydrates are among of the fundamental light microscope. classes of macromolecules found in living organisms. These are molecules which Questions contain the carbonyl compound (aldehyde 1. What conclusion can you make and ketone derivatives). They are primary products of photosynthesis, and energy from what you have observed? providing substrates for various organisms 2. What are the features that including mammals. Carbohydrates contain three elements, namely carbon, hydrogen, characterise a specialised onion and oxygen, in which hydrogen and oxygen cell? are in the ratio of 2:1 (two hydrogen atom Safety precautions Observe safety precautions when working with sharp objects such as knife and surgical blade. 33 BIOLOGY FORM 5 KIWANDANI.indd 33 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools and one oxygen atom). This ratio or dihydroxyacetone, ribulose, and fructose proportion of hydrogen to carbon is the sugars. Carbohydrates can be oxidised to same as in water, hence the name hydrate yield energy. For example, the oxidation of of carbon. The general empirical formula glucose during respiration. for carbohydrates is Cx (H2O)y where by x and y are variables. C6H12O6 + 6O6 6CO2 + 6H2O + Energy Properties of carbohydrates Aldoses and ketoses are reducing They are either simple sugars or compound compounds; they have a tendency of sugars. The latter are formed by condensation reducing Copper (II) in Benedict’s solution of the former. For example; starch is formed into Copper (I), which precipitates as a red by condensation of several glucose units. solid substance of Copper (I) oxide. They have one hydrated carbon (CH2O), hence the name carbohydrates. The ratio Classes of carbohydrates of hydrogen to oxygen in a carbohydrate Carbohydrate can be classiﬁed according molecule is always 2:1. They are derivatives to the number of basic sugars or saccharide of polyhydroxyl alcohols and can be units present in a molecule. These classes polyhydroxy aldehydes with an aldehyde include the following: group H-C=O,examples are glyceraldehyde, ribose, glucose, and galactose sugars. a) Monosaccharides They can also be polyhydroxy ketones with a ketone group (C=O), examples are b) Disaccharides c) Polysaccharides - GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Table 1.2 Major types of carbohydrates and their sources Type Examples Sources Monosaccharides Fructose Sweet fruits and honey. Glucose Fruits, such as grapes, coconut water, and sweet potatoes. Disaccharides Galactose Milk and dairy product. Polysaccharides Sucrose Sugar cane and carrots. Lactose Milk. Maltose Malt, such as radicles of germinating cereals. Starch Yam, irish potatoes, sweet potatoes, and green banana. Cellulose Cell walls of various plant cells. Chitin Cell walls of fungal hyphae, and the exoskeleton of arthropods such as insects, crabs, and prawns. 34 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 34 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Monosaccharides (Single sugars) GOFVOERRNONMLEINNTE PURSOEPOENRLTYY such as erythrose and threose. These are the simplest carbohydrates, Their empirical formula is having only one sugar or saccharide C4H8O4. molecule, which cannot be hydrolysed into small molecules. They are classiﬁed Pentoses They contain ﬁve carbon atoms according to two different characteristics; in their molecules, examples the placement of its carbonyl group and are ribose, deoxyribose, the number of carbon atoms it contains. As ribulose and arabinose. Their for the ﬁrst characteristic, if the carbonyl empirical formula is C5H10O5. group is an aldehyde, the monosaccharide is an aldose and if the carbonyl group is Hexoses These are monosaccharides a ketone, the monosaccharide is a ketose. containing six carbon atoms in Monosaccharide are further classified their molecules, such as glucose, according to the number of carbon atoms fructose, and galactose. Their they contain, therefore, monosaccharides empirical formula is C6H12O6. with three carbon atoms are called trioses; They are the most common those with four carbon atoms are called monosaccharides. tetroses; those with ﬁve carbon atoms are called pentoses; and those with Heptoses They contain seven carbon six carbon atoms are called hexoses. atoms in their molecules. Their These two systems of classiﬁcation of empirical formula is C7H14O7. monosaccharides are often combined. For example, glyceraldehyde an Properties of monosaccharides aldotriose (a three-carbon aldehyde), Most of the monosaccharides have a sweet ribose is an aldopentose (a ﬁve-carbon taste. They exist in a crystalline solid form at aldehyde), glucose is an aldohexose (a room temperature and are extremely soluble six-carbon aldehyde), dihydroxyacetone in water; despite their high molecular is a ketotriose (a three-carbon ketone), weights. The presence of large number of ribulose is a ketopentose (a five-carbon OH groups makes the monosaccharides ketone) and fructose is a ketohexose (a much more water soluble than most other six-carbon ketone). molecules of similar molecular weight. Moreover, all monosaccharides are reducing Trioses These are the smallest sugars; as they have free aldehyde or ketone molecules of monosaccharides group. They reduce mild oxidizing agents, which contain three carbon such as Tollens’, Fehling or Benedict’s atoms in their molecules. reagents. Examples are glyceraldehyde and dihydroxyacetone. Their Open chain and ring forms of pentose empirical formula is C3H6O3. and hexose sugars Pentose and hexose sugars can exist in both Tetroses They are monosaccharides open chains (straight structures) and ring containing four carbon atoms structures. Example furanose or furan ring has five membered ring, and pyranose or 35 BIOLOGY FORM 5 KIWANDANI.indd 35 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools pyran ring has six membered ring structures. oxygen atom of carbon number 5 joins to These aromatic ring forms are the most the carbon number 1 bearing the aldehyde stable and used to form disaccharides and and transfer its hydrogen to it and break the polysaccharides. The ring form occurs in bond to form the OH either above or below polayqsuaecocuhsarsiodleusti.oTnhaendricnagnffoorrmm otwccouirssominearsquetohuesrsionlgu.tiTohneaondxycgaennfoisrmpatrwt oofistohme errisngwhich arewahlipchaar(eαe)itahnedr ablpehtaa (αβ) oirsobmetaer(sβ.)Tishoemαersf.ormanids wcahrebnonthneuhmybderrox6yslti(cOkHs )upgroouutpoofnthcearbon atoTmhenuαmfboerrm1isprwojheecnts tbheelohwydthroexryinl g(OwHh)ile rβinfgo.rmThiesswamhenprtohceeOssHocgcruoruspinognalcaacrtboosne.atom numgrboeurp 1opnrocjaercbtosnabatoovme tnhuemrbinegr .1PpernotjoescetssugTahres omnalyydfioffremrenthce bfievtwe emenemgablearcetdosreinagndwhen thebirelcoawrbtohne raitnogmwnhuilme βbefror1mjoisinwshweniththtehOe Hoxyggeluncaotsoemisotfhceadribfofenrennutmobrieern4ta, taionneoxfamthpelier is as shogwronuipnornibocaserbaonnd adteoomxynruibmobse rsu1gparrosje(cFtisgurhey1d.r2o1xyalagnrdoubp).inTchaerboonnlynduimffbeerren4c(eFitghuarteexists betawbeoevne trhibeorsienga.nPdendteoosxeysruibgoasrse msuagyarfoirsmtha1t.2d0ecoxanydribd)o.sIen fsruugcatorsela, cthkescaorxbyogneynl girnoucparbon numthbeefriv2e. mHeemxobseersedcarninfgorwmhebnotthhesiirxcaanrbdofnive ims ienmcbaerrbeodnrninumg.bFeorr2e, xsoamthpelreinggluicsofsoermcaend exist in atwtoomisnoummebresro1f jsoiixnsmwemithbethreedoxriynggesn(aαt-ogmlucobsye tahnedoβx-yggluecnosaeto).mThoef fcoarrmboantionnumofbreirng5 form is owfhceanrbothnenuomxybgeern4,aatnomexaomfpclearibs oasnshnouwmnberjo5injionignswtioththcearbcoarnbnounmnbuemr b2e,rle1adbineagritnog the batThlehdelictb1eeonha.dehw2asrtiry0bwaftifdmobtadeehenoreeeaeesnonanenprndxuitrrndaymiobobngr)crtboid..reibTeseaTsodernnshhsets2eaeoaeof.noetcxoisHrdncoyxuulnieryydgtrixsbgseoadoooerfihisfnnsxyfteleheyadsigrerscrseaciiokubnprlagsagocanhecaersoynttrfeotxdsohostsryrafo(eomugtF.txgeeihiTtyagbxnelrhuoiasrigenrtitnihessrdnoognubltitOarpaynhhebnHeeaicoddnkarvfiiifcorcenntfbaarhegomrrtcerbh,bnaeaioeobrntatbnnoictbroooeniennnnmndcuubgooammentmftoituosbwbfmemfueeβesorrrbe-rαanfe64nmn-rurfus(mg1rrFcttuiaihntibicclsoeggaektspuoc.rsOertrsW2ooeueH(jspFiehw1esciee.ogh2tpanieuuti1nrhldttoredheceojbwreegfea1callOhnt.toub2heedHwcoe0ndodvrs)eie.noIginsr. fruscitxosaen,dthfievceamrbeomnyblergerdourpinigs. iFnocraerxbaomn pnluembee)r. 2F,rusocttohsee rcianngailssofofromrmedtbhye pthyeroonxoysgeeansatom of gclaurcboosne ncuamn beexris5t jionintwinog iwsoitmh ecrasrboofnsinxumibnegr l2u,colesaed. ing to the formation of furan ring. WhmeenmtbheereOdHriningsc(aαr-bgolnucaotosme onr uβm-gbluecro1sei)s. projected below the ring, it becomes α-fructose whTilheewfohremn aOtiHoninofcarirnbgonfoartmomisnwumhebnerth2eis projected above the ring is β-fructose (Figure 1.21 e). Fructose can also form the pyronose as in glucose GOFVOERRNONMLEINNTE PURSOEPOENRLTYY (a()a) (b) (b) FiguFreigu1r.2e 11.2O0pOepnenchcahianinaanndd rriinnggfofromrmofo(af)(raib)orsiebaonsde (abn) dde(obx)yrdibeoosxeyribose 36 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 36 10/10/2019 14:05

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(a) (b) FOR ONLINE USE ONLY Figure 1.21 Open chain and ring form of (a) ribose and (b) deoxyribose DO NOT DUPLICATE Cytology Disaccharides (double sugars) They are formed through condensation of two monosaccharides; examples include sucrose, maltose, and lactose. They are composed of two monosaccharide units bound together by a covalent bond known as a glycosidic bond. They are formed via dehydration (condensation) reaction resulting in the loss of a hydrogen atom from one monosaccharide and a hydroxyl FigFuirgeu1r.e211.2(c0) (Oc)peOnpcehnacinhaainndarnindgrisntrguscttruurcetsuorefsgolufcosegroup from the other. The formula of Figure 1.21 (c) Open chaignluacnodsreing structures of glucose disaccharides is C12H22O11. Although there are numerous kinds of disaccharides, a handful of disaccharides are particularly notable. Sucrose is the most abundant disaccharide, and the main form in which carbohydrates are transported in plants. It is composed of one glucose molecule and one fructose molecule. Lactose, a disaccharide composed of one galactose molecule and one glucose molecule, occurs naturally in mammalian milk. Other notable disaccharides include maltose which is made up of two glucose molecules linked by 1, 4 –glycosidic bond. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY FFigiguurree11.2.201(d(d))OOppeennaannddrrininggffoorrmmooffggaallaaccttoossee Properties of disaccharides Figure 1.21 (d) Open and ring form of galactose Disaccharides are composed of two molecules of monosaccharides linked to each other by glycosidic bond. Like monosaccharides, disaccharides are sweet in taste and crystalline water soluble compound. All disaccharides cannot pass through the plasma membrane of the cell, since there is no carrier enzyme that can carry disaccharides to move across the plasma membrane. Among disaccharides, maltose and lactose are reducing sugars, while sucrose is a non-reducing sugar. Figure 1.21 (e) Open chain and ring form of fructose Maltose (malt sugar) FigurFeig1u.2r1e (1e.)20O(pee)nOcpheanincahnadinrianngdforirnmg ofofrfmrucotfose fructose Maltose is a double sugar which occurs naturally in roots and radicles of germinating cereals, such as maize, sorghum and ﬁnger tose (malt sugar) 37 otsoese(misaaltdsouugbalre)sugar which occurs naturally in roots and radicles of germinating cereals, seasismaadizoeu,bsloergsuhguamr wanhdicﬁhnogcecrumrsilnleat.uArarltliyﬁicniarloloyt,sitainsdmradieclueps boyf gcheremmiincatlincogmcebrienaltsio, n 10/10/2019 14:05 awsomaa-igzelu,BcIsOooLsrOegGhYuunFmOitRsMa. n5DdKuIﬁWrinAngNgDeArtNhmIi.isnidlcldeot3m.7Abirntiaﬁticoianll-yO, Hit igsrmouapdeaut pcabrybochnesm1icaanldco4mobfinthaetiotwn o

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools millet. Artiﬁcially, it is made up by chemical a molecule of water is lost (Figure 1.21). combination of two a-glucose units. During Maltose is a reducing sugar since it has this combination -OH group at carbons a free aldehyde group in its molecule. In 1 and 4 of the two glucose residues, are one of the glucose units, the aldehyde at involved in formation of oxygen covalent carbon 1 has been used in the formation of bond called glycosidic bond. Since it is the bond, while in the second glucose unit, formed between carbons 1 and 4, then the aldehyde at carbon 1 remained intact, it is termed a 1, 4-glycosidic bond. This since the carbon involved in the formation tsheecopfnorodrmcgeasltusicoionnsvoeofultvhneeits,bcothonenddaiesldnteshahatytidoaent ,paotthsceitarierobfnoor4ne.,1 reomf tahineebdoinndtaicst,thsaint caet pthoesictiaornbo4n. involved in second glucose unit, the aldehyde at carbon 1 remained intact, since the carbon involved in the formation of the bond is that at position 4. Figure 1.22 Chemical combination of two a-glucose units to form maltose Figure 1.21 Chemical combination of two a-glucose units to form maltose Sucrose (cane sugar) cThheiTSms uhiiscicsaraloiscdseoomu(aFcbbiagliendunoeraseutusib1gou.lang2er2aotrfCsh)uhaggtelumanrcaioctausthelraca(oltalmynnboaaicnltducaourtiasroeslnlysionufgstarwter)omamcaaostni-logdelncfufucrsiluousecsgetoaoruflssnewcoiat(asnactetoekornpefditlosoaernsnmletossasms.ttuIiago(tlFtanioirs;gs)e.muthDraeeudr1erif.n2oug2pre)t.,bhye reacotScioucnucr,rsothseien(–csOatneHemgssurogouafrp)sautgcaarrbcoann1e opflagnlutsc.osIet anSdutchraotsaet ciasrabonno2n-orfefdrucitnogsescuognatribbuetceatuostehe formisTahtmiiosandiseoafutdphoeub1by,l2ec-sghulegymacroicsthiadalitccnobamtounrbdail.nlyTathoioecncrueroascftiinoinstteilmsacasklsosof ascunogynadraeccnatsinaveteiopnlrae;ndttuhs.ecriInet fgiosrgmer,aoaduemp.uoplTebhcyuele of wgclauhtecemor siiecsa(llaocnsotma(lbFdiiongasuteiroesnu1go.fa2r3g))lu.acnSodusecfrr(ouasncetaoilsdeoas(eansounga-alrdre)deahunycdidnefgrugscurtoogsuaepr (baaektceactuoassreebosiutnglaa1rc)k.osDf uagrnilynugcaotchsteieve redukrceeitanocgsteiognsrou, utghpae.r)–T.OhDHeuagrlridnoeughpytahdteecargrerbaoocuntpi1oanotf, cgtahlurebcoo–sne 1aanondfdthgkalteuatcotoncsaerbgaonrnodu2kpoeftaoftrnucecatrgobsroeuncpo2natrotifbcuaftrebuotcontoth2seeof frucOtfoHosremgharotaivuoenp toahftetcihraer–1bO,o2Hn-g1glyrcoofuspgidlciucocnbotosrneibdau.ntTidnhegthrtaeoat tchtiehofnaovirsematalhsteoioicrno–onOdf eHthnsegagtrioloyuncp;otshcieodrniectfrobirboeu,ntadin.mgotleocuthlee aot fcwarabtoernis2 losft f(rFuicgtuorsee1c.2o3n)t.riSbuuctreosteoisthae nofno-rremduactiionng osufgtahrebgelcyacuosesiditiclabcoksnda.ny active forerdmuactiinogngorofutph.eT1h,e2-agldlyechoysdiedgicrobuopnadt.cTahrbeon 1 of glucose and ketone group at carbon 2 of fructose have their –OH group contributing to the formation of the glycosidic bond. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 1.23 Chemical combination between glucose and fructose to form sucrose LThaicstoissefo(FmuingiFdlukigreuesxur1cegl.2u1a3.sr2i)2CveChlehymemiinciactalhlcecoommmbibliiknnaaottiifoonnmbbaeemttwwmeeeaenlnsgglaulnucdocoseisneanamdnidflrkufrcputorcsoteodstuoecfttoosr.fmoLrsamucctsrooussceeroissethe only carboLhaycdtorasete(mofilkmsilukgawrh) ich is synthesized by mammary gland during lactation. It is derived fromThthise iscofonudnednseaxtciolunsioveflygainlacthtoesme ilakndof gmluacmomsealslinankdedinbmyil1k, p4ro-dugcltysc. oLsaicdtiocsebiosntdhe(Foniglyure 1.24c).arbohydrate of milk which is synthesized by mammary gland durSitnugdelnatc’staBtoiookn.FIotrmis Fdieverived f3ro8m the condensation of galactose and glucose linked by 1, 4 - glycosidic bond (Figure 1.24). BIOLOGY FORM 5 KIWANDANI.indd 38 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Lactose (milk sugar) during lactation. It is derived from the This is found exclusively in the milk of condensation of galactose and glucose mammals and in milk products. Lactose linked by 1, 4 - glycosidic bond (Figure is the only carbohydrate of milk which 1.23). is synthesized by mammary gland FiguFriegu1r.2e41.C2h3eCmheicmaliccaolmcobminbaintiaotniobnebtewtweeeennggaalalaccttoossee aannddgglluuccoosseetotofoformrmlalcatcotsoese Polysaccharides (multi-sugars) GOFVOERRNONMLEINNTE PURSOEPOENRLTYYmonosaccharides, linked together by Polysaccharides are polymer carbohydrate glycosidic bonds. They are large molecules molecules, composed of long chains of which are often insoluble in water and exist monosaccharide units bound together by in non-crystal form. glycosidic bonds. On hydrolysis, they give their constituent monosaccharides. Starch They range in structure, from linear to Starch is a polymer of hexose sugar (α highly branched molecules, examples glucose) that can be extracted as a white include storage polysaccharides such as powder. It is a major storage carbohydrate of starch and glycogen as well as structural plants, and it is a product of photosynthesis. polysaccharides such as cellulose and Chemically, starch is a polymer of repeated chitin. Starch is the main storage of a-glucose units that are bonded together polysaccharides in plants. It is made up of by glycosidic bonds. This polysaccharide two polymers, amylose and amylopectin is a mixture of two substances; amylose while in animals and fungi, glycogen is and amylopectin. Amylose unit is a linear, the main storage form of polysaccharides. helical chain which consists of around 500 In plants, cellulose is a structural to 20,000 monosaccharides connected by a constituent of their cell walls while in (1-4) glycosidic bonds between the glucose fungi and most arthropods, chitin is the units. Amylopectin differs from amylose in structural constituent of the cell wall and being highly branched, and has short side exoskeleton respectively. chains of about 30 glucose units linked with α (1-6) glycosidic bonds in addition Properties of polysaccharides to 1,4-glycosidic bonds (Figure 1.24). Polysaccharides are complex carbohydrate Amylopectin molecules may contain up polymers, consisting of several to two million glucose units. BIOLOGY FORM 5 KIWANDANI.indd 39 39 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Branch CH2OH CH2OH HH OH HH OH O OH H O OH H H OH H OHO -(1,4) Linkages -(1,6) Branch point H2COH H2COH H2COH CH2OH CH2OH CH2 CH2OH OH OH OH HH OH HH OH HH OH H H OH HO OH OH O OH H O OH H O OH H OH HO O OH n OH H OH H OH H OH H OH α (1-4a )(1g-4l)ygclyoccoicdidiicc bboondnd Main chain (a) (b) Figure 1.24 Structures of (a) amylose and (b) amylopectin Glycogen from a pair of molecules of glycogen in a Glycogen is the form in which protein which acts as a primer at the core of polysaccharide is stored in animals and the structure. Glycogen can be converted fungi. It is often called an animal starch, back into glucose when energy is needed and it is stored mainly in liver and skeletal through the process called glycogenolysis. muscles. Like starch, it is made up of Glycogen is easily converted back to a-glucose molecules and exists as granules. glucose in order to provide energy for Structurally, it resembles amylopectin, body activities. When glucose cannot be except that it is more branched, and its stored as glycogen or used immediately chains are shorter (Figure 1.25). The for relese of energy, it is converted into glucose chains are organized globularly fat. like branches of a tree. They originate GOFVOERRNONMLEINNTE PURSOEPOENRLTYY FigFuigreur1e.216.2S5trSuctrtucretuoref golfygcloygceongmenomlecoulelecule Cellulose thousands of b-glucose units, joined Cellulose is an important structural together by 1, 4-glycosidic bonds, to form polysaccharide of plants, which largely long, unbranched chains. Many chains run constitutes the chemistry of the cell wall. parallel to each other and have cross linkages It is chemically composed of several between them (Figure 1.26). These help to 40 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 40 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology give cellulose its considerable stability to used for manufacturing of fabrics. Rayon, make it a valuable structural material. It is a product of cellulose extract is used in the major component of the plant cell walls, manufacturing of industrial belts, tyre cods where it plays structural role. and clothing. Cellulose derivatives have various uses, for example; cellophane is Cellulose’s structural strength has made it used in packaging, and celluloid is used a valuable raw material in manufacturing for manufacturing of photographic ﬁlm. various industrial products, such as cotton, Other cellulose products include paper which is a pure form of cellulose. It is also and explosives. Figure 1.26 Structure of celluloseGOFVOERRNONMLEINNTE PURSOEPOENRLTYY Chitin Figure 1.27 Structure of cellulose cellulose, has its repeating units joined in β Chitin is an extracellular structural (1,4) linkages. However, the two differ in polysaccharide found in large quantities that, the hydroxyl group (-OH) of chitin at in the body covering cuticle of insects carbon atom number two (C-2), is replaced by and exoskeletons of crustaceans. Chitin is –NH.CO.CH3 (acetyl-amino) group. It is also found in smaller amounts in sponges, thus a result of an amino sugar, glucose molluscs, annelids and cell walls of fungi. amine, combining with an acetyl group Also, been identified in the cell walls of (CH CO-). Chitin, is therefore a polymer some green algae. Its structure and chemistry of acetyl, glucose and amine (Figure 1.27). are similar to those of cellulose. Chitin, like Figure 1.28 Structure of chitin 41 BIOLOGY FORM 5 KIWANDANI.indd 41 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Glucosamine ring CH2 Acetamide CH2 CO CO CH2OH H NH CH2OH H NH HH OH HH HH OH HH OH OH H H H H H H H H H NH CH2OH β-1,4-glycosidic H NH CH2OH O C bond CH2 OC Chitin CH2 Figure 1.27 Structure of chitin Chitin has also been proven to be useful GOFVOERRNONMLEINNTE PURSOEPOENRLTYYDifferent methods can be used to test for for several medical and industrial the presence of starch, reducing sugars and purposes.Chitin is used as a flocculating non-reducing sugars (Table 1.3). agent for waste water, wound-healing agent, a thickener and stabilizer for foods a) Biochemical test for starch and pharmaceuticals. Also, it used as a binder for dyes, fabrics, and adhesives, The presence of starch in biological materials and a sizing and strengthening agent for can be tested by using Iodine solution. The paper. In butterfly wing scales, chitin is use of iodine to test the presence of starch often organized into stacks of nano-layers is one of common experiments. A solution or nano-sticks made of chitin nanocrystals of iodine (I2) and potassium iodide (KI) in that produce various iridescent colours by water has a light orange-brown colour. If is thin-film interference. added to a sample that contains starch, the color changes to a dark blue (or blue black). Biochemical test for carbohydrates In the absence of starch, the orange-brown Carbohydrates are carbon compound colour of the aqueous solution remains. that have polyhydroxy aldehydes and polyhydroxy ketones, with reducing The basis of the test properties. Carbohydrates may be present The Iodine bound inside the helical structure as isolated molecules or they may be of the amylose forms a dark blue colour. physically associated or chemically bound The reaction is due to the formation of to other molecules. The specific test for a polyiodide chains (complex) from the particular type of carbohydrate is based reaction of starch and iodine. The amylose in on the presence of specific component of starch forms helices where iodine molecules carbohydrate or the reducing properties are assembled, forming a dark blue colour resulting from aldehyde or ketone groups. (Figure 1. 28). 42 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 42 10/10/2019 14:05

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FOR ONLINE USE ONLY Cytology DO NOT DUPLICATE Amylose Iodine complex (iodide ions) Figure 1.28 A helical structure of amylose bound the iodine molecule b) Biochemical test for reducing sugars The common test for reducing sugar is Benedict’s test. Fehling’s reagent is not All monosaccharides and some disaccharides, commonly used because it is corrosive and including maltose and lactose (with toxic. In this test, Benedict’s solution makes exception of sucrose), are reducing sugars; use of the ability of these sugars to reduce as one of the two units may have an open- copper (II) into copper (I). The test involves chain form with an aldehyde group. the use of an alkaline solution of Copper This means that they carry out a type of (II) Sulphate (CuSO4) which is reduced to chemical reaction known as reduction. insoluble Copper (I) oxide (Cu2O). In the The characteristic property of reducing absence of reducing sugar, the blue colour sugars is that, in aqueous medium, they of the Benedict’s solution remains. generate one or more compounds containing GOFVOERRNONMLEINNTE PURSOEPOENRLTYY an aldehyde group. An aldehyde can be The basis of the test the source of electrons that reduces ions. Benedict’s solution contains copper The oxidizing agent must be capable of sulphate. Reducing sugars reduce soluble oxidizing aldehydes, but not alcohols. Such blue copper sulphate; containing copper oxidising agents include Benedict’s solution (II) ions (Cu2+) to insoluble red-brown (CuSO4/citrate), Fehling's reagents (CuSO4/ copper oxide containing copper (1). tatrate), and Tollen's reagent [2[Ag(NH3)2]+]. However, sucrose, in which the anomeric Cu2+ + e- Cu+ carbons of the two units are linked together, are non-reducing disaccharides since neither Blue solution Brick red ppt of the rings is capable of opening. Such disaccharides do not have a free reducing group and are therefore non-reducing sugars. c) Biochemical test for non-reducing sugar A non-reducing sugar is a carbohydrate that is not oxidized by a weak oxidizing agent in basic aqueous solution. 43 BIOLOGY FORM 5 KIWANDANI.indd 43 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Table 1.3 Test for starch, reducing sugar and non-reducing sugar Food Observation Inference sample to be Procedure tested Starch Iodine test Blue-black colouration is Starch present. observed. Place 2 ml (cm3) of 1% starch solution in a clean and dry test tube. Add 3 drops of iodine solution (No heating is required). Alternatively, add the Iodine solution to the solid form of starch. Reducing Benedict’s test The initial blue Reducing sugar colouration of the sugar present. Place 2 ml of a solution mixture turns green, containing reducing sugar then yellowish to solution in a clean and dry orange and may ﬁnally test tube. form a brick- red precipitates. Add 2 ml of Benedict’s solution, and heat gently to boil. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Non- Place 2 ml of non- reducing The initial blue Non – reducing sugar (such as sucrose) colouration of the reducing sugar sugar solution in a clean and dry mixture turns green, then present. test-tube. yellowish to orange and may ﬁnally form a brick- Add 1ml dilute hydrochloric red precipitates. acid, heat gently, then allow to cool. Carefully, neutralize with 1 ml of sodium hydroxide solution. Add 2 ml of Benedict’s solution and heat to boil. 44 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 44 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology In basic aqueous medium, non-reducing GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Procedure sugars do not generate any compounds containing an aldehyde group. Due to a) Prepare two solutions, one from that, it cannot donate electrons to other sweet potatoes and another one molecules; hence, cannot act as a reducing from coconut pulp. agent. Sucrose is the most common non- reducing sugar. The linkage between the b) Carry out biochemical test using glucose and fructose units in sucrose, which the given reagents and apparati to involves aldehyde and ketone groups, is investigate food substances present responsible for the inability of sucrose to in each of the solutions. act as a reducing sugar. A non-reducing sugar does not reduce copper (II) sulphate; Question therefore, there is no direct test for it. State roles of each food substance found However, if it is first hydrolysed to its in the tested solutions. constituent monosaccharides, it will then give a positive Benedict’s test results. Functions of carbohydrates a) Monosaccharides, such as hexoses The basis of the test A non-reducing sugar (sucrose) can are used to form disaccharides and be hydrolysed by heating with dilute polysaccharides which are other types/ hydrochloric acid to give glucose and forms of carbohydrates. fructose, both of which are reducing sugars. b) Carbohydrates are the chief energy The solution is neutralized with dilute sources in living organisms because sodium hydroxide or potassium hydroxide they are oxidised to give energy. For so as to give the reducing sugar results with example, glucose is the most common the Benedict’s test on heat. respiratory substrate which when completely oxidised, yields about 38 Activity 1.4 Biochemical test for ATP. carbohydrates c) Trioses such as glyceraldehyde and dihydroxyacetone are used Materials as intermediates in respiration, Sweet potatoes, coconut seed, apparati photosynthesis and other carbohydrate (test tubes, test tube racks, test tube metabolic processes. During holder and brush, beaker, scalpel or respiration (during glycolysis), surgical blade, measuring cylinder, six carbon sugar splits to form droppers, mortar and pestle), reagents dihydroxyacetone phosphate and (Benedict’s solution, iodine solution, phosphoglyceraldehyde which enters dilute hydrochloric acid, dilute sodium the cycle, whereas during dark hydroxide solution, and distilled water), reaction of photosynthesis the formed and a source of heat. phosphoglyceraldehyde becomes a source of lipids and proteins. 45 BIOLOGY FORM 5 KIWANDANI.indd 45 10/10/2019 14:05

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Biology for Advanced Level Secondary Schools GOFVOERRNONMLEINNTE PURSOEPOENRLTYY FOR ONLINE USE ONLY DO NOT DUPLICATE d) They are the sources of other food substances, such as a triose sugar in Activity 1.5 Biochemical test for plants. carbohydrates e) Pentose sugar, such as ribose and 1. Suppose you have been provided with deoxyribose sugars used in the the following for a practical work: synthesis of nucleic acids. Ribose is a a) Solution K containing starch constituent of Ribonucleic acid (RNA) b) Benedict’s solution and deoxyribose is a constituent of c) Dilute hydrochloric acid Deoxyribonucleic acid (DNA). d) Sodium hydroxide solution e) Rubber bands for stimulating f) Ribose sugar is also used in the saliva secretion synthesis of ATP and coenzymes, such as NAD and NADP. Questions 1. Show step by step, how you would g) Carbohydrate such as ribulose (a five carbon sugar) forms Ribulose go about testing for starch. biphosphate, which is used as 2. It is advised that, before collecting carbon dioxide acceptor during light independent stage of photosynthesis. saliva, one should rinse his or her mouth with clean safe water. What is h) In association with proteins and the signiﬁcance of this? phospholipids, they form structural 3. Comment on the ﬁnal colour change parts of a membrane. of the solution. i) They form structural parts of Exercise 1.11 organisms, examples: cellulose in plant cells and chitin in exoskeleton of 1. With illustrations, differentiate between arthropods. monosaccharides and disaccharides. j) They are important constituents of 2. Explain the roles of carbohydrate in the connective tissues in animals. human body. k) Cellulose ﬁbres in edible fruits and 3. Show how two glucose units are otherfoods help to prevent constipation combined to produce maltose. Give in humans. details of chemical reactions involved and the bond formed. l) Flower nectar contains sugar, which is important in the process of pollination. 4. Can sucrose reduce Copper (II) in Benedict’s solution? Give an annotated description of your answer. 5. Show how the structure of α-glucose is maneuvered to produce β-glucose, galactose and fructose. 46 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 46 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology 1.4.2 Lipids chemical composition as simple lipids, Lipids are made up of carbon, hydrogen, compound lipids, and derived lipids. and oxygen in which the content of oxygen is always smaller compared to carbon and a) Simple lipids or homolipids hydrogen. Lipids are important constituents These are esters of fatty acids and various of the diet, because they are the source of alcohols. Such lipids include fats and high energy value. Natural fats and oils are oils (whose alcohol is glycerol) and compounds of glycerol and fatty acids. They waxes which contain alcohols higher are esters which are formed as the result than glycerol. Fats differ from oils in that of the reaction between organic acids and they contain fatty acids with saturated alcohols. hydrocarbon chain. In oils, fatty acids contain unsaturated hydrocarbon chains. Formation of lipids At room temperature, oil is liquid, while Lipids are esters formed by the reaction fat is solid. Fatty acids have a general between fatty acids and alcohols. In simple formula of CH3 (CH2)nCOOH where 'n' is lipids such as fats and oils, the alcohol a whole number. Stearic acid is a common involved in the reaction is glycerol. The fatty acid in animals’ adipose tissue. The formation of lipids is by condensation fats and oils are triglycerides, formed reaction; therefore, a molecule of water by the combination of one trihydroxyl is lost. This forms a covalent bond called alcohol, (glycerol), and three fatty acid ester bond. molecules. In this process, three molecules of water are lost and the ester bond is Types of lipids formed (Figure 1.29). In the year 1943, Bloor proposed the classification of lipids based on their GOFVOERRNONMLEINNTE PURSOEPOENRLTYY H O Ester bond + 3H20 H-C-O-H HO H - O - C- R H-C-O-H O HCOCR O H-C-O-H H - O - C- R H O HCOCR O H - O - C- R HCOCR H Glycerol + 3Fatty acids Triglyceride + 3Water Figure 1.29 Formation of triglyceride BIOLOGY FORM 5 KIWANDANI.indd 47 47 10/10/2019 14:05

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE b) Compound lipids or heterolipids These are esters of fatty acids with compound lipids contain fatty acids, alcohols that possess additional alcohols, and other compounds, such groups which may be derived from as phosphorous, amino-nitrogen and other acids other than fatty acids. The carbohydrates as shown in table (1.4). Table 1.4 Compound lipids Phospholipids or These contain a phosphate group. Their glycerol forms ester bond with phosphatides phosphoric acid and two fatty acids (Figure 1.30). They usually contain one hydrophilic head and two hydrophobic tails. They are called polar lipids and are amphipathic in nature. Glycolipids Glycolipids are compound lipids with carbohydrates. These lipids include also certain structurally related compounds comprising of gangliosides, sulpholipids, and sulfatides groups. Sphingolipids or Sphingolipids occur mostly in the cells of the brain. They do not phosphosphingosides contain glycerol in their molecules; instead, they contain amine alcohol (sphingosine or sphingol). For instance, the myelin sheath of the nerve ﬁbres contains a lipid known as sphingomyelin, which contains sphingosine and phospholipids in its molecules. Terpenes are mostly found in plants. Examples of terpenes are natural rubber and gern oil. GlycerolGOFVOERRNONMLEINNTE PURSOEPOENRLTYYHydrocarbons (fatty acid tails)Hydrophilic head HO Hydrophobic HCOC tails O O OHCOC OP O C O C H OH Figure 1.30 Structure of the phospholipid c) Derived lipids Steroids. These do not contain fatty acids. Derived lipids are substances derived from and are non saponiﬁable and not hydrolysed simple and compound lipids by hydrolysis. on heating. They are widely distributed The most common derived lipids are in animals, where they are associated steroids, terpenes, and carotenoids. with physiological processes. Examples: hormones, oestrogen, progesterone and testosterone. 48 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 48 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Terpenes. They are essential oils in plants GOFVOERRNONMLEINNTE PURSOEPOENRLTYYBiochemical test for lipids found particularly in conifers, citrus Lipids are nonpolar and do not dissolve trees and some insects. They are used for in polar solvents, such as water. They formation of aroma into medicine, such as only dissolve in nonpolar solvents, such aromatherapy, perfume and food additives. as benzene, ether, absolute alcohols, and These include certain fat soluble vitamins, chloroform. This property makes the lipids such as vitamins A, E, and K. to be tested effectively by adding nonpolar dye, which can easily be absorbed by a Carotenoids. These are widely distributed nonpolar lipids. Lipids can be tested using in both plants and animals. They are several methods, including that which exclusively of plant origin. Due to the involves the use of Sudan III solution, the presence of many conjugated double bonds, grease spot test and emulsification test they are coloured red or yellow. Examples (Table 1.5). are lycopene, carotenes, and xanthophyll (oxygenated derivatives of carotenes). The basis of the tests Fat globules are stained red with Sudan III Properties of lipids solution. Being less dense than water and Lipids are either liquids or non-crystalline insoluble in water, a red stained oil layer solids at room temperature. Pure fats or oils floats on the surface of water. In addition, are colourless, odourless, and tasteless. with grease spot test, fats or oil droplets They are less dense than water and are create a translucent spots on the paper on esters of alcohols and acids. Simple lipids, warming. As already known that, lipids are such as fats are esters of fatty acids and immiscible with water, therefore addition glycerol. Lipids are insoluble in water, of water to a solution mixture of lipids but soluble in organic solvents such as and ethanol results into emulsion of tiny ether, toluene and chloroform. They can droplets in the water, which reflect light, be hydrolysed by alkaline compounds giving a white opalescent appearance. into their constituents’ components by the Emulsification process is permanent and process known as saponiﬁcation. Simple complete in the presence of emulsifying lipids such as fats and oils are hydrolysed agents, such as bile salts, soap and protein. by the lipase enzyme into fatty acids and This process is important in fat digestion glycerol. Lipids contain either saturated or in the intestine, as the emulsifying agents unsaturated hydrocarbon chains and have (bile salts) lower surface tension of the a high caloriﬁc value due to the presence lipids and increase the surface area, hence of large number of hydrogen atoms in their easily acted by digestive enzymes. hydrocarbon chains. They are poor heat and electric conductors. Forthis reason, they are functional parts of nerve cells and skin sub-cutaneous layer. BIOLOGY FORM 5 KIWANDANI.indd 49 49 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Table 1.5 Biochemical test for lipids Food sample to be Procedure Observation Inference tested Sudan III test A red- stained oil Lipids Lipid (fat or oil) present. Put 2 ml of a solution containing layer separates lipid in a clean and dry test tube. on the surface of solution. Add 3 drops of Sudan III solution and shake vigorously. Then allows the mixture to settle for 1 minute. Grease spot test A permanent Lipids translucent spot on present. Rub a drop of the sample on to a the paper. piece of paper. Lipids present. Allow time for any water to evaporate. Warm gently in order to speed up the process or reaction. Emulsification test Lipids becomes Put 2 ml of absolute ethanol in a finely divided clean and dry test tube, and then add and is dispersed in water when 2 ml of lipid. shaken with water Shake vigorously to dissolve the it forms a cloudy lipids. Then add equal volume of white suspension cold water.GOFVOERRNONMLEINNTE PURSOEPOENRLTYY (emulsification). Functions of lipids e) Since lipids are less dense than water, a) They are structural component of they aid in buoyancy in the aquatic animals such as whales. membranes. Examples: phospholipids and glycolipids. f) They are precursors of important body requirements such as vitamin D and b) They insulate the body against heat sex hormones. loss. For example, fats found in the sub- cutaneous layer of the skin are an g) They protect internal vital organs such insulating blanket. as heart and kidneys. c) They are sources of energy; therefore, h) They form protective layers against they are used as alternative respiratory water loss for example waxes in plants. substrates when carbohydrates are completely exhausted. i) They facilitate fast conduction of nerve impulses, as they are integral d) They are sources of metabolic water. parts of myelinated nerve ﬁbres. This is an important source of water for animals found in arid and semi- j) They are components of some enzyme arid areas such as camels. systems. 50 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 50 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology k) They form plasma proteins, such Exercise 1.12 as lipoproteins which facilitate transportation of lipids in the aqueous 1. Give an account on the properties environment of the body. of lipids. Activity 1.6 Biochemical test for lipids 2. Classify lipids based on their chemical composition. Materials 3. Describe the structural functions Groundnuts, test tubes, test tube racks, of lipids in living organisms. test tube brush, beaker, measuring cylinder, droppers, mortar and pestle, 1.4.3 Proteins reagents Sudan III solution and distilled Proteins are large biomolecules or water. macromolecules, consisting of one or more long chains of amino acids. A Procedure molecule contains carbon, hydrogen, a) Prepare a solution from the nuts oxygen, nitrogen, sulphur and sometimes phosphorous. The amino group (NH2) using the materials provided. provides protein’s basic nature, and the carboxyl group (-COOH) gives the acidic b) Carry out a biochemical test to nature of the amino acid. The R-group is identify food substance(s) present known as the side chain which represents in the solution using the reagents the hydrogen atom or any other group such provided. as the alkyl group (Figure 1.31). Proteins differ from one another, primarily in their c) Record your observations. sequence of amino acids, which is dictated GOFVOERRNONMLEINNTE PURSOEPOENRLTYYby the nucleotide sequence of their genes and which usually results in protein folding into speciﬁc three-dimension structure that determines its activity. H HO H N C C OH Amino group R Carboxylic acid group Side chain Figure 1.31 Structure of the amino acids BIOLOGY FORM 5 KIWANDANI.indd 51 51 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Properties of the amino acids ion and becomes positively charged. Each They are colourless, crystalline solids which amino acid has its own pH value at which it are soluble in water but insoluble in organic exists in its neutral zwitterionic form. This solvent such as ether, chloroform, and pH at which the amino acids are electrically acetone. They are amphoteric compounds as neutral is termed as an Isoelectric point they have both acidic and basic properties. (I.E.P). In the alkaline medium, when the In neutral aqueous solutions, they exist as pH of the I.E.P increases, the amino group dipolar or zwitterions. On one side, the dissociates, releasing hydrogen ions, (H+), acidic carboxyl group has a tendency of the amino acid thus becomes negatively donating hydrogen ion (proton); therefore, charged. In the acidic medium, (when the it dissociates, to release hydrogen ion and pH is lowered), the carboxyl group accepts becomes negatively charged. On the other hydrogen ions, and the whole structure side, the basic amino group has a high afﬁnity becomes positively charged (Figure 1.32). to hydrogen; therefore, it accepts hydrogen GOFVOERRNONMLEINNTE PURSOEPOENRLTYY FiguFriegu1re.313.32SStrturuccttuurreeoof tfhethzewizttweriiottnerion Formation of proteins combination of this type extends the All proteins are formed by condensation length of the chain to form a polypeptide of amino acids to give peptide chains. The chain, which usually contains hundreds of condensation reaction occurs between amino acids. Polypeptides may be linked the amino group of one amino acid and by other forces such as disulphide bridges, the carboxylic groupFiogfuroeth1e.3r 3aSmtriuncoturheyodfrothgenzwbiotntedr,iohnydrophobic interaction acid to form a dipeptide molecule linked and ionic bonds. by peptide bond (Figure 1.33). Further Figure 1.34 Formation of dipeptide molecule linked by the peptide bond Figure 1F.i3g4urFeo1r.3m3aFtoiromnatoiofndoifpdeippetpidtideemmoolleeccuulelelinlkinedkebydtbheyptehpetidpeebpotnidde bond 52 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 52 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Structure of polypeptide GOFVOERRNONMLEINNTE PURSOEPOENRLTYYbonds plays a considerable role in shape The structure of polypeptide molecule is and stability of the polypeptide molecule. determined by amino acids sequences and its configuration. For each particular type Disulphide bond of protein, the chain of amino acid makes This is formed between side chains of up a polypeptide molecule of a specific cysteine (amino acid containing sulphur) shape. This shape is very important in and keeps parts of polypeptide intact and the functioning of the protein, especially maintains its stability. If two molecules enzymes. The type and the three- of cysteine line up alongside with each dimension configuration of a polypeptide other, the neighbouring sulphur can be molecule, is stabilised by the interactions oxidized to form a disulphide bridge. of five different types of bonds (Figure A disulphide linkage may be formed 1.35). between the cysteine residues of the same polypeptide chain or different polypeptide Peptide bond chains of a functional protein. Disulphide This is a bond formed between carboxyl bonds stabilize the tertiary or quaternary group (-COOH) of one amino acid and structures of the protein. amino group (-NH2) of another amino acid. A polypeptide molecule has a free Ionic bond amino group at one end, and a carboxyl The bond occurs between the positively group at the other end. and negatively charged side chains of amino acids that come in contact with Hydrogen bond each other. Normally ionic bond is Hydrogen bond is a bond that is formed formed between ions of opposite charges in the polypeptide chain between from ionized acid (-COO-) and basic amino acid and side (R) groups. The (-NH3+) groups of the amino acids. The bond is an electrostatic attraction availability of ionized carboxylic group between the hydrogen atom and another (COO-) and amino group (-NH3+) at electronegative atom. Hydrogen bond the side chain of amino acid, and at the forms between the carbonyl (C=O) of one terminal of polypeptide chain may form amino acid or the amino group (N-H) of ionic interactions, which help to make another amino acid. Hydrogen present in a polypeptide molecule of a particular hydroxyl (-OH) group or amino group shape. (-NH2) of amino acids, become slightly electropositive. Therefore, hydrogen Hydrophobic interaction bond is a partially electrostatic attraction This is considered to be among the major between the hydrogen (H) atom which is driving force for the folding of globular covalently bound to a more electronegative proteins in aqueous environment. Some atom or group, such as nitrogen (N) and R groups of amino acids are non-polar as oxygen (O). Although hydrogen bonds they have equal number of charges from are very weak, the absolute number of amino and carboxyl groups. The non-polar R groups are hydrophobic and they repel 53 BIOLOGY FORM 5 KIWANDANI.indd 53 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools from water. In a long polypeptide chain, usually insoluble in water as well as in other aqueous media. Fibrous proteins there are many such non-polar amino acids aid in protection and structural support. Examples of fibrous proteins include which may occur adjacent to each other. collagen (tendons, bones, and other In an aqueous environment such as inside connective tissues), myosin (found in the cell, the linear polypeptide will fold muscles) and keratin (found in nails, into a particular shape that hydrophobic horns, hairs, fur, and feathers). amino acids come in contact with each other, while excluding water due to its hydrophobicity. Van der Waals interactions (dispersion forces) act between hydrophobic side branches Hydrogen Polypeptide backbone bond Disulphide link Ionic bond Figure1.34 Bonds in a polypeptide molecule Figure 1.35 Structure of fibrous proteins (α-keratin) Categories of proteins Due to their complexity, it is difﬁcult to Globular proteins. These proteins have classify protein molecules into a single, tertiary structure, in which the polypeptide well deﬁned category. They can be classiﬁed chains are tightly folded to form the according to their structure, composition, spherical shape (Figure 1.36). They level of organisation, and functions. are soluble in water. Examples of such proteins include enzymes, antibodies, and some hormones, such as insulin. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY a) Classiﬁcation of proteins based on their structure Based on their structure, proteins are categorized as ﬁbrous, globular, and intermediate proteins. Fibrous proteins. These proteins form Figure 1.36 Structure of globular proteins long polypeptide chains, cross linked at intervals, forming long ﬁbres or sheets (Figure 1.35). Their shapes resemble long ribbons or ﬁbres. Fibrous proteins are mostly found in animals, and are 54 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 54 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Intermediate proteins. These are ﬁbrous, Simple proteins. These are proteins made soluble proteins. A good example of up of only amino acids, and are mostly intermediate proteins is ﬁbrinogen, which globular. When decomposed by acids, forms an insoluble ﬁbrin during blood these proteins liberate their constituent clotting. amino acids. Examples of simple proteins are albumins, globulins, and histones. b) Classiﬁcation of proteins based on Conjugated proteins. These are proteins their composition made up of amino acids and other organic compounds. They have a non-amino Based on their composition, proteins can acid group termed as prosthetic group. be classified as simple and conjugated or Examples of conjugate proteins and their complex proteins. prosthetic groups are shown in Table 1.6. Table 1.6 Conjugate proteins, their prosthetic groups, and locations Name Prosthetic group Location Phosphoprotein Phosphoric acid Casein of milk and vitelline of egg yolk. Glycoprotein Carbohydrate Cell membrane, and mucin (component of Nucleoprotein Nucleic acid saliva). GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Lipoprotein Lipid Component in the structures of viruses, chromosomes and ribosomes. Cell membrane and lipids transported in blood as lipoprotein. c) Classiﬁcation of proteins based on the polypeptide chain (Figure 1.37). Its their level of organisation sequence is determined by the sequence of nucleotide bases of the DNA in the genetic There are four types of proteins based code. The amino acid sequence determines on the level of structural organization, the positioning of different R-groups namely primary, secondary, tertiary, and relative to each other. The positioning also quaternary structures of proteins. determines the way the protein folds and the ﬁnal structure of the molecule. Primary structure of proteins. The primary structure of protein is a linear sequence of amino acids that make up BIOLOGY FORM 5 KIWANDANI.indd 55 55 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools N-Terminus (amino end) Gly Pro Thr Gly H3N+ Thr Gly Glu Leu Pro Cys Lys Ser Met Val Lys Val LeuAspAla Val ArgGly Ser COO- Pro Ala C-terminus (carboxyl end) Figure 1.37 The primary structure of proteins Secondary structure of proteins. The to produce the secondary structure. The secondary structure of proteins refers to regular pattern is due to the hydrogen bond the regular folding pattern of β-sheets and formation between atoms of the amino acid α helix of the polypeptide chain (Figure and backbone of the polypeptide chain. It 1.38). The linear unfolded structure of the includes components of hairs, claws, nails, polypeptide chain assumes a helical shape and the skin. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Hydrogen bond Hydrogen bond (a) (b) Figure 1.38 The secondary structure of proteins (a) alpha helix and (b) beta plate Tertiary structure of proteins. The of the polypeptide chain is folded into a tertiary structure of proteins is the three- compact globular structure. The folding dimensional structure formed by the of the polypeptide chain is stabilized by bending and twisting of the polypeptide weak, non-covalent interactions. These chain (Figure 1.39). The linear sequence interactions are hydrogen bonds and 56 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 56 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology electrostatic interactions. Hydrogen bonds covalent bonds, also contribute to the are formed when hydrogen atom is shared with two other atoms. Hydrophobic formation of the tertiary structure. interactions, disulphide linkages and Examples of tertiary structure proteins are enzymes and antibodies. - +- - -- Figure 1.39 The tertiary structure of proteins Quaternary structure of proteins. GOFVOERRNONMLEINNTE PURSOEPOENRLTYYhaemoglobin which is the oxygen Some proteins contain more than one carrying component of the blood, is made polypeptide chains. This association of up of four polypeptide chains; 2α-chains, polypeptide chains refers to the quaternary each containing 141 amino acids, and 2β structure of proteins and each polypeptide chains, each containing 146 amino acids chain is called a subunit. The subunits (Figure 1.40). can be similar or different. For example, β-chain Fe2+ Heme α-chain Figure 1.40 The quaternary structure of proteins BIOLOGY FORM 5 KIWANDANI.indd 57 57 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools d) Classification of proteins according or synthesis to the site of utilization or to their functions storage and membrane transport proteins Proteins can be classified into different which transport substances across the cell categories depending on their physical and membranes. chemical structures as well as their location in the cell. They can also be grouped based Nutrient and storage proteins. These on the metabolic functions they perform in are proteins which provide reservoirs of the body as follows: essential nutrients to a growing embryo. A good example is the albumin of an egg Enzymes proteins. These are biological white, used as an amino acid source for the catalysts which are mostly protein in developing embryo. Casein, the protein of nature. They are the most varied and highly milk, is the major source of amino acids specialised proteins with catalytic activity. for baby mammals. Ferritin is an iron- Virtually, all the chemical reactions of binding protein; which stores iron in the organic biomolecules in cells are catalysed liver. Moreover, plants store proteins in by enzymes, resulting into increased reaction seeds, where seeds of many plants store rate. Enzymes such as urease, catalase, and nutrient protein for growth of embryonic lactase catalyse a variety of body reactions. plants such as wheat, rice, maize, and bean. Structural proteins. These are proteins GOFVOERRNONMLEINNTE PURSOEPOENRLTYYContractile or motile proteins. These which aid in strengthening or protecting proteins function in the contractile tissues. biological structures. These protein act They include actin, myosin, and tubulin as supporting filaments, cables or sheets proteins. They are important for movement to give biological structure, strength, and of body parts. Contractile proteins are protection. Collagen is an example of the responsible for undulation of the cilia and structural protein of the bone and connective flagella, which propel many cells. tissue. Collagen and elastin provide a fibrous framework in animal connective tissues, Defence proteins. These are proteins which such as tendons and ligaments. Keratin is defend the body against invaders, such the structural protein of hairs, horns, finger as antibodies, ﬁbrinogen and thrombin. nails, feathers and other skin appendages These are highly specialized proteins of animals. that recognize and combine with foreign substances like viruses, bacteria and destroy Transport or carrier proteins. These them. Fibrinogen and thrombin are blood proteins are involved in transportation of clotting proteins which protect the body ions and other substances. Examples of such against excessive bleeding. proteins include haemoglobin, the iron- containing protein of blood, which transports Regulatory proteins. They regulate oxygen from the lungs to other parts of gene expression and cellular or metabolic the body, serum albumin which transports activities of an organism. These include fatty acids in the blood, lipoproteins, which hormones, such as, insulin hormone which carry lipids from the site of absorption is secreted by the pancreas, helps in the 58 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 58 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology regulation of the blood sugar concentration GOFVOERRNONMLEINNTE PURSOEPOENRLTYY and (NH4)2SO4. Decrease in solubility that regulates the metabolism of cells. occurs due to competition between salt Transcription factors are proteins that and protein molecules for water as well regulate gene expression. Some repress gene as a decrease in charge on the protein expression by binding to target genes and molecule. activating their transcription. The examples of such protein include lac repressor and e) Proteins are also coagulated by heat and catabolite activator protein (CAP). Lac agents like strong acids, alkali, alcohol, repressor is a DNA-binding protein which acetone, urea and salts of heavy metal. inhibits the expression of genes coding for proteins involved in the metabolism of f) Proteins are speciﬁc in their reactions lactose in bacteria, whereas CAP promotes and substrates they act upon. This transcription at several sites as it affects property is clearly illustrated by the metabolism of sugars and amino acids, enzymes. protein folding, toxin production and pilus synthesis. g) Proteins are colloidal in nature, that is, they can be hydrolysed into their amino Receptor proteins. Receptor proteins are acid constituents. built into the membrane of a nerve cell and they detect chemical signals released h) They can be denatured or changed from by other nerve cells. Other proteins act their natural state by heat or chemicals. as chemical messengers within the brain throughout the body. They are involved Denaturation of proteins in the cell’s response to chemical stimuli. A protein is said to be denatured, if it loses its natural three-dimension conformation Properties of proteins or shape. This change may be temporary Proteins have the following properties: or permanent, but the amino acid sequence of the protein remains intact because a) They are colourless, tasteless, and the peptide bonds are not cleaved. amphoteric in nature as they have both Denaturation results in the alteration of acidic and basic properties derived from physical properties of a protein in terms of –COOH and –NH2 groups respectively. solubility and other criteria. However, the protein in this situation can no longer carry b) They exhibit characteristic isoelectric out its normal biological functions. The points and have buffering properties. causes of this condition include heat and radiation, organic solvents and detergents, c) They are large molecules; hence, highly concentrated salts and strong acids they have high molecular weight. and alkalis. Denaturation is also caused by For instance, haemoglobin has the heavy metals, urea solution and mechanical molecular weight of about 68,000 g/mol. forces. d) Proteins differ in their solubility in Heat and radiations, such as ultra violet water, some are insoluble, example rays and infra-red. These supply kinetic keratin while others are highly soluble energy which causes strong vibrations such as albumin. Soluble protein can be precipitated from solution by addition of certain salts example NaCl 59 BIOLOGY FORM 5 KIWANDANI.indd 59 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools of protein molecules. These result into GOFVOERRNONMLEINNTE PURSOEPOENRLTYYFor example, stretching of hair breaks breaking down of ionic and hydrogen the hydrogen bonds in the keratin helix. bonds that are weaker than peptide bonds, The latter is extended and the hair is resulting into coagulation of such protein stretched. If released, the hair returns to molecules. its normal length. However, if it is wetted and then dried under tension, it keeps Organic solvents and detergents. These its new length. This is the basis for hair reagents disrupt hydrophobic interactions styling. Many liquid proteins denature and form bonds with hydrophobic (non- and precipitate when they are vigorously polar) groups. Consequently, this disrupts agitated because of incorporation of hydrogen bonds resulting into denaturation. air bubbles and adsorption of protein An example of such chemical substances molecules to the air-liquid interface. is methyl alcohol, which is used as a disinfectant to clean the skin before General functions of proteins injection. The alcohol denatures proteins a) They are essential building materials in bacterial cell walls. of the body. For that reason, they Highly concentrated salts, strong acids, are needed for proper growth and and alkalis. These compounds disrupt the development. This explains why ionic bonds, resulting into coagulation of kwashiorkor victims experience proteins. If such proteins remain mixed stunted growth. with these reagents for a long time, peptide bonds may also break down. b) They are used as alternative respiratory substrates when both carbohydrates Presence of heavy metals such as and lipids are completely exhausted. mercury (Hg), silver (Ag), and lead (Pb). Cations of such metals tend to form c) They absorb excess ﬂuids in the body. strong bonds with the negatively charged For example, kwashiorkor victims carboxyl groups on the proteins, leading to have swollen lower parts of their the disruption of ionic bonds. The protein’s legs and some parts of hands due to polarity is reduced and its insolubility accumulation of excess ﬂuids, this becomes high, hence precipitated as an condition is called oedema. insoluble metal protein. d) They form structural components Urea solution. Urea tends to disrupt of body parts. For instance, keratin hydrogen bonds. Being amide-like, it is a structural protein of hair, horns, forms hydrogen bonds of its own via hooves, and nails. distorting the unique conﬁguration of the protein molecule. e) They are structural components of membranes. For example, globular Mechanical forces. Physical movement protein and glycoprotein which form of proteins may break hydrogen bonds. the cell surface membrane. 60 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 60 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology f) They take part in various metabolic GOFVOERRNONMLEINNTE PURSOEPOENRLTYYBiochemical test for proteins Proteins are complex organic structures processes in the body, for example made up of polypeptide chains of amino enzymes that catalyse different acids, which have different amino physiological activities in the body. acid sequences and three dimensional configuration to define a particular type g) Proteins such as hormones have of protein. An amino acid is a class of the following roles: act as chemical organic compounds with a carboxyl messengers and regulate body group (-COOH), an amino group (NH2) metabolites. Examples of such and a side group, all attached to a central proteins are insulin and glucagon, carbon atom. Proteins differ from each which regulate the level of blood other in terms of their type, number and sugar in mammals. sequence of amino acids that make up the polypeptide backbone. Therefore, h) Proteins such as anti-bodies protect different proteins have different molecular the body against infections. structures, nutritional attributes and physiochemical properties. There are i) Proteins such as myosin and actin are several methods used to test for proteins. contractile; therefore, they interact to The most common method is chemical bring about contraction and relaxation method. Chemical method relies on the of muscles, hence, the movement of properties of amino acids or peptide bonds body parts and locomotion of animals. that are common to all proteins. The biuret test is a chemical assay that is widely used j) Proteins such as haemoglobin and to detect the presence of proteins and myoglobin transport oxygen in the amino acids in a sample. The test relies blood. on a color change to confirm the presence of proteins. If proteins are present, the k) Proteins such as ﬁbrinogen are sample will turn violet (Table 1.7). important for blood clotting, hence, they help in healing wounds by The basis of tests forming ﬁbres over injured parts to Biuret test is the chemical test used to prevent excessive loss of blood and detect the presence of peptide bond as a water, and entry of germs. general test for detection of proteins. In the presence of dilute copper (II) sulphate l) Proteins such as ovalbumin of egg (CuSO4) in alkaline solution (medium), white and casein of milk are storage nitrogen atoms in the peptide chain form in function. For example albumin a purple complex with Copper (II) ions supplies food to a developing embryo. (Cu2+). m) Proteins help to build and improve the body immune system. This explains why children suffering from kwashiorkor are vulnerable to various opportunistic diseases. BIOLOGY FORM 5 KIWANDANI.indd 61 61 10/10/2019 14:05

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Table 1.7 Biuret test for protein Food sample to be Procedure Observation Inference tested A purple Protein Protein Prepare a solution of egg albumen. colour present. develops Place 2 ml of egg albumen solution in a slowly clean and dry test tube. Add 2 ml of dilute Sodium hydroxide solution and mix. Then add 2 drops of 1% of Copper (II) sulphate solution and shake (No heating is required). Activity 1.7 Biochemical test for GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 2. Explain the nutritional roles of the proteins food substance(s) present in the food sample. Materials Exercise 1.13 Fresh milk, test tube, test tube rack, test tube brush, beaker, measuring cylinder, 1. Proteins are said to be amphoteric and dropper, 1% Copper (II) sulphate in nature, what is the biological solution, and dilute sodium hydroxide importance of this? solution. 2. Explain the medical importance of Procedure protein denaturation. a) You are provided with a beaker 3. Classify proteins on the basis of containing fresh milk. structure and function. b) Using the apparati and reagents 1.4.4 Enzymes provided, design an experiment Enzymes are complex, three dimension and carry out biochemical tests to globular proteins that are made up by living identify the food substances present cells. They are biological catalysts, since in it. they alter the rate of different physiological processes in living organisms. They are c) Tabulate your results in a usual way also found in natural secretions, such as to show the procedures followed, plant juices, milk and the digestive juices observations made, and inferences where they catalyse several metabolic drawn. reactions or processes taking place in the Questions 1. What is the basis of test for the food substance(s) present in the food sample provided? 62 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 62 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology living cells. A compound with which the reaction. By acting as catalysts, enzymes enzyme combines is called a substrate. lower the activation energy. Activation The substrate ﬁxes itself in an active energy is the minimum amount of energy site of the enzyme whose shape is ideal that is required to activate a substrate for accommodating it. The active site molecule to a condition in which they can is a group of amino acids comprising undergo biological transformation (Figure the region of the enzyme into which 1.41). the substrate ﬁts in order to catalyse the Free energy (G) Energy of Activation energy (EA) reactants without enzymes Activation energy (EA) with enzymes Change in free energy (AG) Energy of products Progress of reaction Figure 1.33 Structure of the zwitterion Figure 1.41 Activation energy for an enzyme-catalysed and an un-catalysed reaction GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Mechanisms for enzyme action enzyme - substrate interaction. The two Several steps of enzymic action result in molecules form a temporary structure the formation of products. There are two called an enzyme-substrate complex as theories which explains the mechanism of an intermediate product of substrate to enzymic action. These are the lock and key be converted into product. The products hypothesis and the induced fit hypothesis. have different shapes from the substrates; In the lock anFdigkueryeh1y.3p4otFhoersmisa,tiaonneonfzdyimpeeptidtehemreofloecreu,leolninckeedthbey pthreodpuecpttiidse fboornmded, it holds the substrate as a lock holds the escape from the active site, leaving it key, while the induced ﬁt hypothesis, the free for accommodating other substrate active site expands and contracts to form molecules. BIOLOGY FORM 5 KIWANDANI.indd 63 63 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Lock and Key theory In this analogy, the lock is the enzyme and The theory states that, as the key ﬁts in the key is the substrate. Only the correctly one lock, the same happens to a substrate sized key (substrate) ﬁts into the key hole which ﬁts only in one active site of the (active site) of the lock (enzyme). Smaller enzyme to form an enzyme-substrate keys, larger keys, or incorrectly positioned complex (Figure 1.42). The speciﬁc action teeth on keys (incorrectly shaped or sized of an enzyme with a single substrate can be substrate molecules) do not ﬁt into the explained using a Lock and Key analogy lock (enzyme). Only the correctly shaped ﬁrst postulated in 1894 by Emil Fischer. key opens a particular lock. Key (substrate) Lock (enzyme) Substrate Active site Enzyme Lock-key Enzyme substrate complex complex GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 1.42 A model explaining the lock and key hypothesis Induced fit theory because the enzyme has been distorted too The induced-ﬁt theory assumes that the much. Other molecules may be too small substrate plays a role in determining to induce the proper alignment. Therefore, the ﬁnal shape of the enzyme; thus, the they cannot react, since only the specific enzyme is partially ﬂexible (Figure 1.43). substrate is capable of inducing the proper This explains why certain compounds alignment of the active site. can bind to the enzyme but do not react 64 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 64 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Enzyme Substrate entering the active site of enzyme Free enzyme + Substrate ES Enzyme-substrate complex Enzyme-products complex Free enzyme + Products ES EP P E Figure 1.43 Model of induced fit theory Factors governing rate of enzyme GOFVOERRNONMLEINNTE PURSOEPOENRRaLteTYofYreaction Maximum reaction rate activity Several factors affect enzyme activities. Rate approaching These include substrate concentration, maximum rate enzyme concentration, temperature, and pH level. Rate increases directly with substrate concentration a) Substrate concentration At fixed concentration of enzymes, an Substrate concentration increase in substrate concentration will increase the rate of reaction. This is Figure 1.44 The effect of substrate because more substrate molecules will concentration on the reaction rate of enzyme be colliding with enzyme molecules. Therefore, more products will be formed b) Enzyme concentration at a time. However, after a certain The rate of any enzyme catalysed reaction concentration, any increase will have directly depends on the concentration of the no effect on the rate of reaction, since enzymes. Provided that, the temperature and all enzyme’s active sites have bound to other conditions are suitable for reaction and substrate, and the remaining substrate will there are excess substrate molecules, the rate be unable to bind to enzymes. of the reaction is directly proportional to the concentration of enzymes. If the amount This point is called enzyme saturation of the substrate is restricted, it may limit point. Thus, extra substrates have to wait the rate of the reaction. Likewise, addition for the enzyme to release the product of more enzymes cannot increase the rate. and become free to accommodate other Therefore, the graph tails off as shown in substrate (Figure 1.44). Figure1.45. 65 BIOLOGY FORM 5 KIWANDANI.indd 65 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Product concentration With 2x enzymes from fitting together exactly. Finally, the enzyme will become denatured, and it will With 1x enzymes GOFVOERRNONMLEINNTE PURSOEPOENRLTYYno longer be functional, hence decreasing the rate of reaction. With no enzymes However, below normal temperature, Time enzymes become less active due to reduction in speed of molecular movement. Figure 1.45 The effect of enzyme concentration When the temperature is lowered below on the reaction rate of enzyme controlled reaction or near freezing point, the enzymes are said to be inactive. This condition will last c) Temperature when the higher temperature above the Generally, increase in temperature freezing point is restored. increases the kinetic energy that molecules possess, implying more random collisions Therefore, as the temperature increases, between molecules per unit time. Since the rate of reaction also increases due enzymes catalyse reactions by randomly to increased kinetic energy. There is a colliding with substrate molecules, temperature range at which the rate of increasing temperature will increase the enzyme’s action is maximum. This is rate of reaction, leading to more products. called an optimum temperature. Below However, increasing temperature also this temperature, enzymes are less active. increases the vibration energy that Contrary, above the optimum temperature, molecules have; speciﬁcally in case enzymes are denatured. All enzymes work of enzyme molecules which put strain within a range of temperature specific to on the bonds that hold them together. the organism. In human, the optimum As temperature increases, more bonds, temperature for many enzymes lies around especially the weaker hydrogen and ionic 40 °C and denaturation occurs at about 60 °C bonds, will break because of this strain. (Figure 1.46). However, enzymes of some Breaking of bonds within the enzyme will other organisms have different optimum cause the active site to change in shape. temperatures. For example thermophilic This change in shape means that the active bacteria such as Thermus aquaticus have site is less complementary to the shape of optimum enzymatic temperature ranges the substrate; therefore, it is less likely from 51 °C to 80 °C and in Archaea the to catalyse the reaction. The change in optimum enzymic temperature ranges from shape prevents the enzyme and substrate 41 °C to 122 °C. 66 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 66 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Optimum temperature is usually Enzymes around 40 °C denature at high temperatures so Rate of reaction rate falls rapidly 0 10 20 30 40 50 60 Temperature °C Figure 1.46 Effect of temperature on the rate of an enzyme-controlled reaction The effect of temperature on the rate of solutions have pH values below 7, and reaction can be expressed as temperature basic solutions (alkalis) have pH values coefﬁcient, Q10. According to the Q10 rule, above 7 while the pH of 7 is termed as the rate of a physiological process or ‘neutral’. Hydrogen (H+) and hydroxyl (OH-) ions are charged, therefore, they reaction doubles for every 10 °C rise in interfere with hydrogen and ionic bonds temperature, if the temperature is within that hold together an enzyme, since they the range that can be tolerated by a living will be attracted or repelled by the charges system. A mathematical expression is created by the bonds. This interference presented below: causes a change in shape of the enzyme GOFVOERRNONMLEINNTE PURSOEPOENRLTYYand, consequently, its active site. Most Q10= rate of reaction at (X+10) °C enzymes are sensitive to pH and have rate of reaction at X °C specific ranges of activity. Different enzymes have different optimum pH Where: X is the initial temperature values; hence, the bonds within them are influenced by H+ and OH- ions at different Thus, within the range of 0 - 40 °C, Q10 of pH value. Thus, the shape of their active an enzyme controlled reaction is 2. site is most complementary to the shape of their substrate. This means that the rate of the enzyme’s action doubles for every 10 °C rise in temperature. d) pH At optimum pH, the rate of reaction is The pH scale measures the acidity and maximum. Any change in pH, above basicity of a solution. pH is a measure or below the optimum, will quickly of hydrogen ion (H+) concentration. cause a decrease in the rate of reaction, It is therefore a good indicator of the since more enzyme molecules will have hydroxy ion (OH-) concentration. Its active sites whose shapes are not less values ranges from 1 to 14. Lower pH complementary to the shape of their values implies higher H+ concentration substrates (Figure 1.47). Slight changes and lower OH- concentration. Acidic in pH above or below the optimum do not cause a permanent change to 67 BIOLOGY FORM 5 KIWANDANI.indd 67 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools the enzyme, since the bonds can be protein groups that are associated with the reformed. However, extreme changes in enzyme are known as prosthetic groups. pH can cause enzymes to be denatured Only apoenzyme and cofactor together are and permanently lose their functions. active as a catalyst. The cofactor is either Enzymes in different locations have inorganic ions, usually metal ions such different optimum pH values, since their as Fe2+, Mg2+, Cu2+, Cl- or small organic environmental conditions may differ. molecules such as haem, biotin, Flavine For example, the enzyme “pepsin” adenine dinucleotide (FAD), Nicotineamide functions best at pH value of around adenine dinucleotide (NAD). They may 2 and is found in the stomach which also be vitamins called coenzymes. Some contains hydrochloric acid. “Carbonic enzymes need both, a metal ions and a anhydrase” which is a key enzyme in all coenzyme to become active. living organisms works best at pH value of around 7, and “chymotrypsin” which Metal ion and/or coenzyme is found in small intestine works best at pH value of around 9. Apoenzyme + Cofactor = Active enzyme activity Enzymes inhibitors (%) There are many molecules that can interfere 100 with enzymes activity either by reducing or destroying their actions. These molecules Pepsin Carbonic Chymotrypsin are called enzyme inhibitors. There are anhydrase two main groups of inhibitors: competitive and non-competitive inhibitors. In either 0 GOFVOERRNONMLEINNTE PURSOEPOENRLTYYtype, inhibitors are either reversible or 0 7 pH irreversible. Reversible inhibitors generally bind to an enzyme with weak bonds, such Figure 1.47 The effect of pH on the rate of an as hydrogen bonds, which are easily enzyme-controlled reaction broken. The effect of these inhibitors to the enzyme is temporary, such that, when Enzyme cofactors they are detached, the enzyme regains its Many enzyme-catalysed reactions require normal functioning. Contrary, irreversible more than just an enzyme and its substrate. inhibitors are strongly bonded to the Some enzymes require a particular enzyme in such a way that an enzyme and ion or even a small molecule known as the inhibitor cannot be separated without cofactor. Cofactors are small, non-protein damaging the enzyme. components of enzymes that are needed for their efﬁcient activity. These substances are Competitive inhibitors resemble substrates, stable at high temperatures and vary from therefore, they compete with the substrates simple inorganic ions to complex organic for the active site of an enzyme molecule compounds. In such enzymes, the protein part is called an apoenzyme and the non- 68 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 68 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology (Figure 1.48a). When the inhibitor remains they neither compete for nor attach to ﬁxed to the active site, the enzyme is the active site of the enzyme. They ﬁx prevented from working normally, as the themselves elsewhere on the enzyme substrate cannot move into the active molecule. In so doing, they completely site. The substrate is then prevented alter the shape of the enzyme molecule from binding to the same active site and in such a way that the active site cannot therefore, decreases the enzyme affinity to accommodate the substrate. Since the other substrates. The effects of competitive inhibitor does not compete with the inhibitors decrease with increased substrates for the active site of the enzyme, concentration of substrates. A good example an increase in substrate concentration does of the competitive inhibitors is malonic not reduce the effect of the non competitive acid, which competes with succinic acid inhibitor. An example of non-competitive for the active site of a respiratory enzyme, inhibitor is cyanide, which attaches itself succinic dehydrogenase. to copper prosthetic group of cytochrome oxidases, thereby inhibiting respiration Non-competitive inhibitors are substances process (Figure 1. 48b). that do not resemble substrates. Therefore, Substrate Inhibitor Active site Substrate EnzymeGOFVOERRNONMLEINNTE PURSOEPOENRLTYYEnzyme Inhibitor Substrate Inhibitor blocks Conformation active site change of active site (a) (b) Figure 1.48 Inhibitors (a) competitive (b) non-competitive Enzyme regulation in which metabolic pathways in the cells Regulation of enzymatic activity is an are regulated involve allosteric enzymes important biological activity in controlling which are designed to change the shape different metabolic processes. Enzymes and are regulated by the compounds are important for regulation of different which act as non-competitive inhibitors. metabolic activities, such as biochemical The regulation of these enzymatic pathways, homeostasis, gastro intestinal activities includes; end-product inhibition, digestion and growth. The common way zymogens and genetic control. BIOLOGY FORM 5 KIWANDANI.indd 69 69 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools End-product inhibition control. If a given GOFVOERRNONMLEINNTE PURSOEPOENRLTYYthey are synthesized, so that they cannot physiological process involves several steps attack the pancreas. and various intermediates, the end product of the pathway may inhibit the enzyme at Genetic control. This is the regulation of the start (Figure 1.49). In this example, the enzymatic activity by control of the synthesis product “Y” acts as an inhibitor to enzyme of the enzyme. The synthesis of enzymes is “a” (ea). If the level of product Y falls, the regulated by genes. Genes carry the code for inhibition is reduced. If the level of Y rises making enzymes. These mechanisms, which above normal, inhibition of “ea” increases; are controlled by hormones can accelerate therefore, the level of Y is reduced. In this or decelerate enzyme synthesis. The genetic way, homeostatic control of Y is achieved. control strategy is particularly useful for This mechanism is termed as negative enzymes which are needed only at certain feedback, because the information from stages of development. Depending on the the end of the pathway which is feedback genetics and other environmental factors, to the start has a negative effect; that is the the body can produce many enzymes during high concentration of Y reduces its own a lifetime. As body ageing commences, the production rate. The enzymes that are body tries to automatically conserve its inhibited in this way are called allosteric decreasing resources and produces fewer enzymes. These enzymes can have more enzymes of all types. When this lifetime than one shape. One shape renders the enzyme potential is reached, the body can enzyme active (by allosteric activator), no longer sustain life. Death occurs because another renders it inactive (by allosteric nothing takes place in the body without inhibitor). enzymes. Enzymes constitute the ‘`life force” which powers the whole system in Inhibition (negative feedback) the organism’s life expectance. Intermediate compounds Properties of enzymes They are proteins (globular proteins) in (Substrate) U ae V Web ed X ed Y (Product) nature and biocatalysts, as they lower the activation energy of the reaction they Figure 1.49 End product inhibition of enzyme catalyse. They are never used up, never affected by the reaction they catalyse, Zymogens (proenzymes) control. Some meaning that it remains unchanged at the enzymes are synthesized in inactive forms end of reaction. Since they are proteins, that differ in composition from the active enzymes are coded for by DNA. They forms. Activation of such enzymes, known have active sites where the substrates are as zymogens or proenzymes, requires accommodated; and the sites have speciﬁc a chemical reaction that either adds or shapes which make them to be speciﬁc to splits off part of the molecule. Some not only the substrates they act upon, but enzymes that digest proteins, examples: also the reactions they catalyse. They are trypsinogen, chemotrypsinogen, and sensitive to temperature and pH changes, proelastase are produced in the pancreas. and they can also be affected by enzyme These enzymes must be inactive when 70 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 70 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology and substrate concentration. They are very carbondioxide and water to form carbonic efﬁcient, thus, they are needed in a very acid in tissues where the concentration of small amount; this means that a small carbon dioxide is high. In the lungs, where amount of enzymes acts on large quantities the concentration of carbon dioxide is low, of substrates. Enzymes work reversibly; the same carbonic anhydrase, catalyses the meaning that they catalyse reversible dissociation of carbonic acid into carbon reactions. For example, an enzyme carbonic dioxide and water. anhydrase catalyses the combination of Classiﬁcation of enzymes In 1964, the International Union of Biochemistry (IUB) introduced a system of classifying enzymes based on the type of reactions they catalyse. This system recognised six major functional classes of enzymes. a) Oxidoreductases which catalyse redox reactions (biological oxidation and reduction reactions) by the transfer of hydrogen, oxygen, or electrons from one molecule to another. Example; Ethanal + NADH + H+ dehydrogenase Ethanol + NAD+ Hydrogen is simultaneously lost from NADH and gained by ethanal. NADH is oxidised to NAD+ and ethanal is reduced to ethanol. b) Transferases which catalyse the transfer of a group from one compound to another. Example; Glutamic asid + Pyruvic aminotransferase α-ketoglutaric acid + alanine GOFVOERRNONMLEINNTE PURSOEPOENRLTYY The R-group on the amino acid, glutamic acid, is exchanged with the R-group on a keto acid, pyruvic acid. A new amino acid, alanine is formed along with a new keto acid, α-ketoglutaric acid. c) Hydrolases which catalyse the splitting of a large substrate molecule into two smaller products in the presence of water (hydrolysis process). Example; Glucose + Galactose Lactose + Water Lactase The disaccharide, lactose, is broken down into two monosaccharide residues by the lactase enzyme in the presence of water. All digestive enzymes fall under this category. d) Lyases which catalyse the removal of a chemical group by the process other than hydrolysis. Example; Pyruvic acid decarboxylase Ethanal + Carbon dioxide BIOLOGY FORM 5 KIWANDANI.indd 71 71 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Pyruvic acid is converted into ethanal and carbon dioxide by breakage of its double bond. e) Isomerases which catalyse rearrangement within a molecule, converting one isomer to another. For example, glucose-1-phosphate is converted into glucose- 6-phosphate in the presence of the phospho-hexo-isomerase enzyme. The position of the phosphate group in the glucose-1-phosphate molecule is changed to form the isomer glucose-6-phosphate. CH2OH Phospho-hexo-isomerase CH2OPO32- H OH H OH H H OH H OH H HO OH HO OOPOP3O23-2- H OH H OH Glucose - 6 - phosphate Glucose - 1 - phosphate f) Ligases which catalyse the joining of two molecules by forming a new chemical bond, and it requires energy from the breaking down of ATP. An example of such enzymes is amino acyl-tRNA systhetase which catalyses the formation of amino acid-tRNA complex during protein synthesis. Exercise 1.14 GOFVOERRNONMLEINNTE PURSOEPOENRLTYY1.4.5 Adenosine Triphosphate (ATP) ATP is a nucleoside triphosphate used in 1. Describe the factors governing cells, often called the “molecular unit of enzyme activity. currency” of intracellular energy transfer. It belongs to a category of high energy 2. Explain how the lock and key compounds that release energy when hypothesis illustrates specificity of the bond between the second and third enzymes. phosphate is broken. The presence of these high energy bonds makes it possible 3. Classify enzymes on the basis of for ATP to store and release energy for reactions they catalyse. cellular reactions. 4. Explain why substrate concentration Chemical composition has no effect on non-competitive ATP consists of adenosine (composed of inhibition. an adenine ring and a five carbon sugar, ribose sugar) and three phosphate groups 5. Explain why at temperatures (triphosphate) (Figure 1.50). ATP is above 40 °C, mammalian enzymes highly soluble in water and is quite stable do not function efficiently? in solutions with pH ranging between 6.8 and 7.4, but easily hydrolysed at extreme 72 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 72 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology pH. Therefore, ATP is best stored as an is synthesised during light dependent anhydrous salt. It is also considered as phase of photosynthesis. In this case, the energy currency of the cell and life, when light of appropriate wavelength because all cells need this energy molecule strikes on the chlorophyll, its electrons in order to perform their functions in the get excited, as they gain excess human body. energy. In this state, they are boosted to high energy levels. As the electrons Formation of ATP move downhill back to ground state, One molecule of ATP contains three they lose the gained excess energy, phosphate groups, and is produced by a which is used to combine ADP and wide variety of enzymes, including ATP Pi to form ATP. This process is called synthase, from adenosine diphosphate photophosphorylation (refer section (ADP) or adenosine monophosphate 5.2). (AMP) and various phosphate group b) Respiratory phosphorylation, which donors. is the cellular process involving two stages. The ﬁrst stage is substrate Adenine level phosphorylation in which ATP is synthesised in the cytoplasm, by Phosphate groups glycolytic pathway. The second stage is oxidative phosphorylation, which occurs in the electron transport system in the inner mitochondrial membranes. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Ribose Roles of ATP Figure 1.50 The chemical structure of ATP provides energy for the following: a) Synthesis of macromolecules, such as adenosine triphosphate polysaccharides from monosaccharides, Synthesis of ATP proteins from amino acids and DNA ATP is synthesised when an inorganic replication. phosphate, Pi, is energetically bonded to b) Active transport across the plasma adenosine diphosphate, ADP. The amount membranes in the cell, example: of energy required in this process is sodium-potassium pump. 30.6kJ. c) Cellular movements, such as cilia action in trachea and fallopian tubes, Condensation spindle ﬁbers during cell division and muscle contraction. 30.6 kJ + ADP + Pi ATP + H2O d) Production of useful secretions by vesicles. The processes that yield ATP, therefore, e) Activation of important molecules, involve phosphorylation. They are of two such as glucose, which is activated into types: glucose-6-phosphate during respiration. a) Photosynthetic phosphorylation, ATP 73 BIOLOGY FORM 5 KIWANDANI.indd 73 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Exercise 1.15 GOFVOERRNONMLEINNTE PURSOEPOENRLTYYrelatively large amount of heat energy to freeze. Thus, this property is important in 1. What is ATP? maintaining natural states of cell contents. Water has a density of 1000 kgm-3 or 1 gcm-3 at 2. Brieﬂy explain the process of standard temperature and pressure. However, ATP formation. the density decreases with a decrease in temperature. Thus, frozen water (ice) ﬂoats 3. What is the importance of ATP in on liquid water. Water has a high surface our daily life? tension and cohesive force. Cohesive force is the force by which individual molecules 1.5 Water as a constituent of the cell stick together. Water is the most abundant molecule in a cell, constituting about 80% of total Water being liquid at room temperature, volume of cell. The liquid part of the cell provides a liquid environment inside the is called cytosol. Generally, without water, cells. Example glycolysis and synthesis of life would not exist on this planet as water proteins that take place in the cytoplasm. supports metabolic reactions. Additionally, water has a high latent heat of vaporisation. This means that Properties of water water needs a lot of energy to evaporate Water is an excellent solvent for polar hence, helps in cooling the body through compounds such as ionic substances, like sweating. salts, and non-ionic substances like sugars. It has a high heat of vaporization due to Roles of water hydrogen bonds which hold molecules The roles of water in living organisms can together. Latent heat of vaporization means be categorized as follows: a measure of the heat energy required to overcome the attractive forces between The metabolic role of water molecules and make them to escape in a) It is used for hydrolysis of many form of a gas (vaporize). This property is significant in minimizing water loss from substances, such as proteins into the body and cooling it. amino acids, fats into fatty acids and glycerol. In the hydrolytic processes, Water has high heat capacity which is the water is brought in by enzymes or heat required to raise the temperature of hydrolytic reagents such as mineral 1 kilogram of water by 10C. By having acids. high heat capacity means that, increase in heat energy can lead to relatively small b) It is the medium for all cellular rise in temperature. Also water has a high metabolic processes, for instance, heat of fusion. It requires a relatively large water is an important raw material for amount of energy to melt its solid state (the photosynthesis. ice). Conversely, liquid water must lose a c) It facilitates diffusion of materials across surfaces; for example, for passage of food solutions into blood stream across the walls of the ileum. 74 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 74 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Cytology Water as solvent GOFVOERRNONMLEINNTE PURSOEPOENRLTYYc) Water found in humours of the eye Water is a universal solvent; it readily helps to maintain the eye’s shape. dissolves other substances, hence it is used for the following purposes: d) The mammalian foetus is supported a) For transportation of various and protected by an amniotic ﬂuid, which is largely water. substances from one part of the body to another. These are carried by blood e) Water provides support (habitat) to and other ﬂuids in solution. aquatic organisms such as ﬁsh. b) For removal of metabolic wastes, such Other functions as nitrogenous waste products. These Other functions of water include the excretory wastes are removed from the following: body in the form of solution in water. a) It controls body temperature in Water as a lubricant mammals. Evaporation of sweat from Due to its viscosity property, water takes the body surface has the cooling effect. part in lubricating body parts which b) It is an agent for dispersal of seeds, slide past each other. It makes various larvae, and male gametes of animals lubricating ﬂuids in the body; example: and lower plants such as Bryophytes. mucus, which aids movements in animals c) In mammals, ﬂuids in the inner ear are such as snails. It also lubricates internal important for hearing and balance. parts, such as gut walls in animals, the synovial ﬂuid (which lubricates Exercise 1.16 movements in joints of vertebrates) and pleural ﬂuid (which lubricates movements 1. Explain the role of water in plants of lungs during breathing). and animals. Supporting role of water 2. Water is said to be the universal The supporting role of water is made clear solvent. Substantiate. in the following examples: 3. Explain the properties of water. a) In animals such as annelids and nematodes, water exerts a hydrostatic pressure which helps to support and maintain their structure. This is known as the hydrostatic skeleton. b) Osmotic inﬂux of water into plant cells generates turgor pressure which supports herbaceous (non-woody) plants. The turgor pressure also supports primary growth in woody plants. BIOLOGY FORM 5 KIWANDANI.indd 75 75 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Revision questions 6. Describe the difference in molecular structure between cellulose and 1. Why is a mitochondrion said to be starch. a cell within a cell? 7. Name the bond(s) formed between 2. Explain the prokaryotic nature of neighbouring glucose molecules in the mitochondrion and chloroplast. starch and cellulose. 3. Chloroplast, mitochondria, and 8. Explain why amylase, the enzyme bacteria have features in common. that catalyses the hydrolysis Substantiate. of starch, will not catalyse the hydrolysis of cellulose. 4. Explain the role of the following cell organelles: 9. Compare the lock and key hypothesis and the induced ﬁt a) Lysosomes hypothesis of enzymes’ action. b) Endoplasmic reticulum c) Ribosome 10. Outline the uses of ATP in the d) Golgi apparatus metabolic activity of the cell(s). 5. With the aid of diagrams, differentiate a bacterial cell from a plant cell. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 76 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 76 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE TwoChapter Principles of classification Introduction Planet Earth contains different kinds of organisms, ranging in size from microorganisms to macroorganisms. Due to the existing diversity of organisms, it is difficult to clearly understand their characteristics and how they are related in evolutionary terms. Classification helps in identification of organisms that share common characteristics and traits. In this chapter, you will learn about the concept of classification, classification systems, categories of classification, taxonomic ranks, nomenclature and taxonomic keys. 2.1 The concept of classification GOFVOERRNONMLEINNTE PURSOEPOENRLTYYThe process of grouping organisms based on their common or shared characteristics The science of classification of living is called classification. For organisms to be classified uniformly across the world, a set organisms dates back to 384-322 BC, of principles, procedures, and rules must be when the ﬁrst taxonomist, Aristotle observed. The principles of classiﬁcation initially classified organisms into two were pioneered by Carolus Linnaeus and major groups, namely animals and plants. published in the 18th century in his book With advances in science and technology, “Systema Naturae”. In that publication classification has constantly been dynamic a simple way of naming organisms was and more reﬁned. For example, by using also explained. The science of classifying electron microscope and molecular organisms is termed taxonomy and the techniques, taxonomists have classified scientist who classifies organisms is known organisms into five kingdoms namely as a taxonomist. Taxonomy involves Monera, Protoctista, Fungi, Plantae, and placing organisms into their respective Animalia. Considering the fact that the groups and sub groups called taxa without number of organisms occupying the earth considering evolution. The science of is large, it has been difficult for scientists placing organisms in their respective taxa to study each individual organism. Since that reflect their evolutionary history is called systematics. related organisms share some common features, scientists group related organisms together so that they can easily study their characteristics. BIOLOGY FORM 5 KIWANDANI.indd 77 77 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Importance of classiﬁcation of of one species is named differently in organisms different places. Zea mays is a scientiﬁc The importance of classiﬁcation name for maize. In America, maize is organisms is summarised as follows: also known as corn but in Britain corn is wheat which sounds confusing. a) It helps to reduce large number of However, Zea mays worldwide will groups of dissimilar organisms into only refer to different names of what small number of manageable groups we call maize in Tanzania. of organisms with more features in common. For example, all species of d) It helps to show evolutionary ﬂower producing plants are placed relationship between organisms. The under division Angiospermophyta. classiﬁcation of organisms is mostly Similarly, all species of non ﬂowering based on evolutionary history and plants are placed in division relationship among them. This makes it Coniferophyta and all spore producing easy to understand how organisms are plant species with conductive tissues related interms of their evolutionary are placed in division Filicinophyta. history. A Leopard (Panthera pardus) Once plant species are grouped in this and Lion (Panthera leo) which are way, it makes it easy to understand both classiﬁed under family Felidae their life cycle. and genus Panthera have a lot of features in common. These are hairs, b) It makes easy to classify all known GOFVOERRNONMLEINNTE PURSOEPOENRLTYY mammary glands, and other various organisms and predict the placement morphological features. It is therefore of the yet to be discovered based on most likely that they share a common already known features. For example, ancestor. if a new plant species with ﬂowers is discovered today it will be placed e) Organisms grouped in the same taxon, under division Angiospermophyta. such as at genus level, normally have Similarly, if it produces ﬂowers, leaves, many common features. For example, berries and stems with stipules as all plant species under genus Coffea those of coffee plants; it will be placed resemble coffee plants in many aspects, under the coffee family Rubiaceae. such as leaf type, leaf arrangement Furthermore, if it has more features on stems, ﬂower type, and stipules. in common with Coffea arabica it They all differ from members of will deﬁnitely be placed under genus cotton plants, genus Gossypium on the Coffea, making its classiﬁcation same features. This kind of grouping simple and less time consuming. therefore simpliﬁes description of organisms because understanding of c) Classiﬁcation simpliﬁes communication features of just one individual within a among taxonomists worldwide. This is certain group/taxon can give an insight because, taxonomically, an organism into all other members within the same is assigned only one name, unlike taxon. the use of common names in which 78 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 78 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Principles of classification f) It paves a way towards understanding GOFVOERRNONMLEINNTE PURSOEPOENRLTYYLinnaeus in the 1700s. This taxonomist other disciplines, such as ecology, retained the two major groups or kingdoms medicine and pharmacy. For example, of organisms, Animalia and Plantae. plants of the same genus may Linnaeus introduced several taxa under have similar ecological or growth each kingdom to accommodate groups requirements. Ecologically, all of organisms sharing more common plants under the bean/legume family characteristics in which resemblance among (Leguminosae/Fabaceae) have the organisms increased hierarchically down ability to harbour Nitrogen ﬁxing the groups. He classiﬁed organisms based bacteria. Likewise, members under the on their shared natural features. same genus may produce secondary metabolites or biochemicals with Since then, classiﬁcation has been very similar medicinal or pharmacological dynamic, and has gone through five systems. properties. These are artificial, natural, phyletic, phenetics and phylogenetics or cladistics. 2.2 Classiﬁcation systems In artificial approach, only one or a few Organisms can be grouped in many ways observable characteristics were used. for convenience of studying them and Natural approach grouped together to fully appreciate their comparative individuals reflecting how they occur evolutionary relatedness. Traditionally, in nature. This approach did not reflect all organisms were grouped by Aristotle evolutionary history though it used many as either animals or plants with just characteristics. Natural approach was a few sub groups in each group. This followed by phyletic approach based on classiﬁcation had shortfalls as it did not Charles Darwin’s publication; “The origin consider the evolutionary relationship of species by means of natural selection” among organisms grouped together. For and the development of modern theory example, grouping into one or single of chromosomes. In phyletic system group of all ﬂying animals such as birds, organisms were classified from simple to bats, moths and butterﬂies, as done by complex, reflecting evolutionary history. Aristotle was taxonomically misleading. However, assigning of ancestral or derived This is because bats are actually mammals status was done subjectively. Phyletic was with hairs on their bodies and they differ followed by phenetic approach. Phenetics from birds which have feathers. They uses many characteristics and mathematical also differ from the butterﬂies, which are algorithms to group similar organisms in insects. A penguin which has feathers same cluster and different organisms in would be difﬁcult to classify it with birds different clusters. As in natural system, into the same group as it lacks the ability phenetics does not consider evolutionary to ﬂy. history. The most recent approach is known as phylogenetic. This approach The controversy of classiﬁcation was partly resolved by the taxonomist Carolus 79 BIOLOGY FORM 5 KIWANDANI.indd 79 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools bring together organisms that share derived GOFVOERRNONMLEINNTE PURSOEPOENRLTYYfrom spore producing medicinal plants. characters in groups called clades. Clades Thus, the medicinal value attached to these thus are made up of organisms that share plants cannot sufﬁce their placement in one the most recent ancestor. group because they have no shared natural features. This limits the application of this The change from one approach to the next classiﬁcation system despite its significant was influenced by advances in science and merits. Artificial system cannot group technology leading to use of new source individuals that are evolutionary related. of taxonomic data, methods of analysis As a result all classfication systems that and weaknesses observed in previous does not reflect evolutionary history are approach. Phylogenetic approach use DNA considered to be artificial. markers and different computer software and analysis programs. Merits of artificial system of classiﬁcation Types of classification systems a) It is simple to identify and classify There are two major systems of classification; artificial and natural system organisms since newly discovered of classification. organisms with just a few known information can be easily ﬁtted in. It Artificial system of classiﬁcation therefore takes short time in placing an This system of classification uses a few organism into its group. easily observable characteristics to classify organisms for easy and quick comparison or b) It is stable; it does not change with time study. Examples of artiﬁcial classiﬁcation or discovery of new organisms given its could be when grouping all animals as fauna broad nature of classiﬁcation. and all plants as ﬂora, or when grouping all organisms on the basis of their body size as c) It is less expensive; since it uses microorganisms and macroorganisms. Other few observable features to group the examples are when grouping animals as organism. ﬂying and non-ﬂying animals, edible versus non-edible plants, spices versus non-spices d) This system does not require special plants, predators versus prey animals, and classiﬁcation techniques or skilled medicinal versus non-medicinal plants. As personnel. noted from the above examples, this system of classiﬁcation neglects natural relationship Demerits of artificial system of existing among these groups of organisms. classiﬁcation For instance, birds and bats are all ﬂying a) It does not consider evolutionary animals, but the former have feathers while the latter have hairs and mammary glands. or phylogenetic relationship among Similarly, medicinal plants producing organisms. Closely related organisms ﬂowers, seeds, and fruits are different under the artiﬁcial system are most likely to be placed in different groups while unrelated organisms such as bats and birds may be grouped together because both have wings. This makes 80 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 80 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Principles of classification the system somewhat misleading GOFVOERRNONMLEINNTE PURSOEPOENRLTYYMerits of natural system of because, phylogenetically, organisms classiﬁcation belonging to one group would be a) It allows organisms which are expected to have originated from a common ancestor. genetically and evolutionarily related to be grouped in the same taxon, the b) It provides only a limited characteristics evolutionary relatedness increases down or information about each member. For the hierarchy. This clearly implies that example, organisms such as viruses, organisms grouped together at genus bacteria and some fungi are grouped level will be more evolutionarily related as microorganisms because they than those grouped at family level. are microscopic. This classiﬁcation has ignored other features like their b) This classiﬁcation system considers modes of feeding, reproduction, homology of all characters of organisms and cell structure. Use of these which makes it easy to predict features necessitate grouping of these information about missing links in microorganisms in different groups. the course of evolution of organisms even though there is no fossil evidence c) It does not allow the prediction of to substantiate the link. For example, information, hence it limits recent some taxonomists have predicted advancements in taxonomy. that ﬂowering plants evolved from Pteridosperms, a seeded fern which is d) It does not incorporate new discoveries. not existing. New species cannot be easily added to the existing groups. c) It allows critical thinking and development of inquiry minds. The natural system of classiﬁcation Although description based on The natural system of classiﬁcation morphological, physiological, anatomical, is the system of grouping organisms and embryological features of a newly based on natural features they have in discovered species has to be done before common, particularly those that reflects a decision on its proper placement to a the evolutionary relationship. Characters taxon is reached. that show evolutionary relationship are shared derived ones which are many and d) It is accurate, since it involves plenty are shared aross members of one group of scientiﬁc research to gather enough With advances in science and technology, information before the actual placement the natural system of classification has of an organism to a particular taxon is incorporated anatomical, embryological, decided. serology, physiological, and molecular characteristics and techniques in grouping Demerits of natural system of organisms. classiﬁcation a) It makes classiﬁcation of organisms tedious, expensive and time consuming. It is very difﬁcult, since it 81 BIOLOGY FORM 5 KIWANDANI.indd 81 10/10/2019 14:06

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Biology for Advanced Level Secondary SchoolsGOFVOERRNONMLEINNTE PURSOEPOENRLTYY FOR ONLINE USE ONLY DO NOT DUPLICATE requires much information to place the organisms into their respective groups. b) Observe each specimen carefully Newly identified organisms are thus and use the provided hand lens not easily classiﬁed. where necessary, then answer the questions that follow. b) It is not stable; it changes with the increasing diversity of organisms and Questions new discoveries based on expanding 1. Record any three observable knowledge, science and technology. It was the discovery of the light features of each specimen. microscope that led to the discovery of kingdom Protista. Later, with 2. Classify all the specimens into two the invention of the scan electron major groups, citing the criteria microscope, it made it easy to separate used to classify them. Archaeae and Eubacteria into different groups within the same kingdom 3. Using the features recorded in Monera. number 1 above, classify the collected organisms into any three c) Given the wealth of information, broad groups and state the criteria knowledge, techniques, and skills used to classify them. required to classify organisms, natural classiﬁcation is limited to taxonomic 4. Classify all the specimens into experts. five groups. Give reason for your classification. Activity 2.1 Classification of living organisms 5. Give any two reasons to justify the placement of the species in the Materials above five groups. Earthworms, a Pinus branch, a fern plant (Dryopteris sp. or Pteridium 6. Brieﬂy comment on the aquilinum), a grasshopper, a butterﬂy, evolutionary relationship among a young maize plant, mature bean the organisms placed in the same plant, a mouse, grass (Panicum sp. or group as in question 5. Hyparrhenia sp.), a houseﬂy, tilapia, a hand lens, a note book, pen, and pencil. Safety precautions Necessary precautions should be Procedure observed when collecting specimens a) Collect the above mentioned from the school surroundings and nearby environment since there might specimens. be dangerous organisms like snakes, bees, thorn plants, and allergens. 82 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 82 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Principles of classification 2.3 Taxonomic ranks GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Kingdom: Animalia The classiﬁcation system by Carolus Linnaeus in 1700s introduced a systematic Phylum: Chordata way of grouping organisms stepwise, from a very broad group of organisms called Class: Mammalia Kingdom to narrow level of individual organism called species. Linnaeus, Order: Primates recognizing the natural variations existing among organisms divided them Family: Hominidae into ﬁve broad groups. He arranged them hierarchically from the broadest to Genus: Homo the smallest in terms of the number of organisms in each. Originally, these groups Species: Homo sapiens were Kingdom, Class, Order, Genus (singular) Genera (plural), and Species. Figure 2.1 Classfication of human being However, later on, two more groups were introduced. The ﬁrst introduced group Organisms placed under the same taxon was called Family, which was created have features unique to that group; thus, by Michael Adanson in 1763, and it was they can be used to describe the entire group. allocated between order and genus. The For example, members of same species have second group termed Division or Phylum the largest number of characters that are (singular) phyla (plural) was introduced more similar and often reproduce fertile by Ernest Haeckel in 1866 and it was offspring. Lions fall in the species Panthera assigned between kingdom and class, leo, leopard in Panthera pardus, and tiger making seven hierarchical groups namely Panthera tigris. Thus lion, leopard and Kingdom, Phylum, Class, Order, Family, tiger are different species in the same Genus, and Species (Figure 2.1), which genus Panthera. The genus comprises of are still being used by taxonomists today. relatively more closely related organisms Phylum is used in animal classification with similar morphology, structure, and Division in plant classification. The reproductive organs and most importantly, system in which organisms are classified evolutionary history compared to those hierarchically from kingdom to species at the higher ranks. However, they can level is called a taxonomic hierarchy or not interbred to produce fertile offspring. taxonomic ranking. Any named group Members of different related genera fall in or rank within the hierarchy such as one family, families is one order and related kingdom or phylum is referred to as taxon orders into one class. Related classes are (singular) taxa (plural). A taxonomic rank placed in one phylum/division and related is therefore a level at which an organism phyla in a kingdom. Kingdom Plantae, for example, contains four divisions, is placed within the hierarchy. namely Angiospermophyta (Angiosperm), Coniferophyta (Gymnosperm), Pteridophyta or Filicinophyta (Ferns and their relatives), and Bryophyta (Moss). 83 BIOLOGY FORM 5 KIWANDANI.indd 83 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Kingdom Animalia is made up of Polifera, Exercises 2.1 Cnidaria, Platyhelminthes, Nematoda and its relatives (the round worms), Annelida, 1. Differentiate between artificial and Arthropoda, Molusca, Echnodermata, natural systems of classification. Chordata and several other smaller phyla. Organisms at the rank of kingdom have a 2. Explain the concept of “ranks” as few features in common compared to the used in classification. organisms at lower ranks. This book will focus on five selected phyla of Kingdom 3. Explain what would be the problem Animalia, namely, Platyhelminthes, if organisms were not grouped into Nematoda, Annelida, Arthropoda, and ranks. Chordata. 2.4 Nomenclature Importance of taxonomic hierarchy in The process of assigning scientiﬁc names classification to organisms is called nomenclature. The a) It provides a standard method to be biological nomenclature uses two names that is the generic name representing the followed by taxonomists in assigning name of the genus and specific name new scientific names to a newly representing the species name. The Swedish discovered species. This makes it easy taxonomist Carolus Linnaeus (1707- to classify or group organisms. 1778) is acknowledged for using binomial system consistenty. The word binomial b) It provides a classification system is a combination of two Greek words bi- of living organisms which expresses nomina which literally means ‘two-names.’ natural or evolutionary relationship Binomial nomenclature follows a set of among the members of the same group agreed rules and principles. and between various organisms. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY c) It provides smooth communication 2.4.1 Rules used in binomial among the taxonomists, while avoiding nomenclature confusion and repetition of species Binomial nomenclature is governed by names. nomenclatural codes, which provide details of rules necessary in giving d) It simplifies access to information on scientiﬁc names for various broad groups various organisms across the taxa. of organisms, such as animals, plants, fungi algae, bacteria, and virus. For example, the code of nomenclature for wild plants is called the International Code of Botanical Nomenclature (ICBN) while for animals is called the International Code of Zoological Nomenclature (ICZN). The rules used in binomial nomenclature are as follows: 84 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 84 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Principles of classification a) The name of an organism should come GOFVOERRNONMLEINNTE PURSOEPOENRLTYYh) If the binomial name is cited more from its generic and speciﬁc name. than once in a paper or report, the For example human being belongs genus name can be abbreviated the to genus Homo and species sapiens; second time it is written in the same hence, its scientiﬁc name should be document. In this case, the ﬁrst letter Homo sapiens. Sweet potato belongs of the genus is written in a capital to genus Ipomoea and species batatas; letter and separated from species its scientiﬁc name should therefore be name by a dot. For instance, Panthera Ipomoea batatas. lupus can be written as P. lupus or the bacteria Escherichia coli as E. coli. b) The full scientific name should The abbreviation “spp.” is used to include name of the author; the represent several species. In this case, person who was the first to publish the genus, but not the abbreviation, is the name effectively. For example, italicized or underlined. For instance, Rana temporaria L, where L stands Hyparrhenia spp. implies several for Linnaeus means Linnaeus was the species of the genus Hyparrhenia such person who effectively published this as Hyparrhenia rufa, Hyparrhenia name. collina, and Hyparrhenia variabilis. On the other hand, if the actual c) A speciﬁc epithet may be taken from speciﬁc name cannot be ascertained any source and may even be composed or speciﬁed, an abbreviation “sp” arbitrarily. followed by a dot is placed after the generic name, but it is not italicised d) An organism can bear only one correct while the generic name is italicised or scientific name, which is the earliest underlined, for example, Hyparrhenia effectively assigned to it, if several sp. names had been given to it earlier. Activity 2.2 Binomial nomenclature e) The ﬁrst name of the binomial, that is the generic name, always begins with Materials a capital letter and the entire species Solanum incanum (thorn apple or name is written in small letters as in bitter ball or bitter apple), Solanum Pennisetum mezianum. nigrum (black nightshade or Hound’s berry), Solanum tuberosum (irish f) All binomial names should be written potato plant). in the Latin language. If the name is hand written, it should be underlined Procedure separately or italised in case of a print a) Collect the following specimens form. For instance, the scientiﬁc name of a leopard can be written as Panthera from the school surroundings or pardus when hand written or Panthera nearby environment: Solanum pardus when printed. incanum, Solanum nigrum, and Solanum tuberosum. g) Any scientiﬁc name is not legitimate, unless it is accompanied by a suitable b) Name the genus in which the three description and a diagnosis which collected species belong. reflects only the unique characteristics of the species. 85 BIOLOGY FORM 5 KIWANDANI.indd 85 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools c) Using a magnifying glass where curcas seeds and jatropha curcas necessary, observe each of stem cuttings. the collected plant specimens and state any three natural a) Write correctly the names of morphological features justifying the species to be ordered before the placement in their respective submitting to TTSA. genus. b) Using your knowledge on the Questions rules of binomial nomenclature 1. Which two features would you use explain the violated rules in the above names. to justify the placement of each of the three plants to their species? c) Provide a comprehensive list of the species names to be submitted 2. What two characteristics to TTSA. differentiate the three species from each other. 2. What do you understand by the following terms: 2.4.2 Signiﬁcance of scientiﬁc names GOFVOERRNONMLEINNTE PURSOEPOENRLTYY a) Nomenclature The use of scientiﬁc names is very important for the following reasons: b) Binomial nomenclature. a) They simplify communication 3. Citing examples of species worldwide. This is because only one from your local environment, valid name is used for each living outline the rules used in binomial organism. nomenclature. b) The system provides uniformity 4. Explain the significance of in naming organisms worldwide. scientific naming of organisms. This helps to avoid confusion and ambiguity. 2.5 Taxonomic keys There are several ways of identifying an c) Scientific names are not influenced by unidentiﬁed organism. Identification is language barrier or region as common naming an organism based on existing names. classfication. The easiest way is by consulting and directly asking an expert such Exercise 2.2 as a taxonomist with profound knowledge and experience in identification. Also, by 1. Assume that you are a taxonomist comparing the unidentiﬁed organism with and you want to order some plant authentically identified specimen stored species from Tanzania Tree Seeds in museums for animals or herbaria for Agency (TTSA) for the home plant specimens. The other way is to use garden; the species to be ordered a local ﬁeld guide in which pictures and/ are Lantana camara, Hibiscus sp. or drawings of organisms coupled with with red ﬂowers, any ﬁve panicum species, delonix Regia, jatropha 86 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 86 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Principles of classification explanations are available for comparison. GOFVOERRNONMLEINNTE PURSOEPOENRLTYYb) Each of the collected specimens is Moreover, taxonomic keys may be used for carefully examined, and its easily identification of unidentiﬁed organisms. observable features are identiﬁed and recorded in a notebook. Taxonomic keys are tools or devices used by taxonomists for a quick identiﬁcation c) A table listing the specimens in one of organisms. The identification is based column and characters to be studied on permanent contrasting phenotypic in the other is created. features. Phenotypic features, also known as morphological features, include features d) From the table, study the recorded such as hairs, stipules, shape, number of specimen features carefully and appendages, and segments. In order to determine a general pair of exclusion identify an organism using taxonomic character which can be used to keys, all readily observable features of divide the entire group of collected the unknown organisms are recorded ﬁrst. specimens into two. These are later matched with diagnostic features of a named taxon. e) Subdivide each of the obtained groups into two more groups using The diagnostic features are characteristics shared or common features. unique to a particular taxon or rank. They differ from those of an organism belonging f) The second group is subdivided to a different taxa. Diagnostic features further into two other smaller groups therefore depict natural phylogenetic or based on their common features. evolutionary relationship, and they are reﬂective of features used in both artiﬁcial g) The smaller groups are continuously and natural systems of classiﬁcation. subdivided into two groups using contrasting pairs of statements or Taxonomic keys enable organisms to be couplets until all of the specimens are identiﬁed into their appropriate taxon and identified. it increases familiarity of taxonomist with the identiﬁed organisms; since it involves h) If the constructed key is numbered, careful investigation of the presence allocate the number of couplet to be or absence of particular structures and considered next after each step to the manifestation of present characteristics. last step in which the specimen is identiﬁed. i) Write down the couplets in a special pattern to get a desired framework for a particular key. Procedures for construction of Types of taxonomic keys taxonomic keys There are various types of diagnostic keys a) The organisms to be identiﬁed used in taxonomy. The most common and simple key used for identification of are collected and displayed for a organisms is called dichotomous key. This thorough observation of identiﬁable type of key was pioneered by a French features. The collected organisms, taxonomist, Jean Baptiste Lamark in such as, animals and plants are called specimens. 87 BIOLOGY FORM 5 KIWANDANI.indd 87 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools 1778. Dichotomous is a Greek word which could be leaf shape, stem texture such as literally means ‘divided into 2 branches’ or woody or herbaceous and ﬂower-colour. ‘cut in half.’This kind of key is constructed In constructing dichotomous keys, features using two statements with contrasting used in describing organisms must be features and mutually exclusive choices at permanent but not temporal or transitional a branching point. The pair of statements is features, such as those emanating from called leads or couplet, and they provide two seasonal variations or growth of an organism alternatives at each branching, each leading based on how couplets are organised in to a subsequent statement until an organism directing the user from one choice to the is identiﬁed. As one moves down the key, next. Two types of dichotomous keys are a large group of organisms with diverse recognised. These are indented key and bracketed or simple numbered key. features is reduced to a smaller group and ﬁnally to an individual organism or taxon. The couplets can be organised using Indented dichotomous key numbers as in numeric keys or letters. It is worth noting that the characteristics used In indented dichotomous key pairs of in dichotomous keys may be quantitative or contrasting statements are successively qualitative. The former can be exampliﬁed indented, with equal distance from the left. by features such as number of petals, leaf Each statement (or lead) starts with the same size, and petiole size, while the latter character being described, and they both begin with the same noun, such as leaves, corolla, and petiole. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Example: Indented dichotomous key for five plant species 1a. Flowers present 2a. Leaves small Abelia grandiflora 2b. Leaves large 3a. Flowers red, petals free Hibiscus rosa-sinensis 3b. Flowers red, petals connate into tube Delonix regia 1b. Flowers absent 4a. Tree with needle-like leaves Pinus sylvestris 4b. Shrub with leafy fronds Dryopteris filix-mas 88 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 88 10/10/2019 14:06

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Bracketed dichotomous keys FOR ONLINE USE ONLY In bracketed dichotomous keys, sets of DO NOT DUPLICATE couplets are kept together (bracketed), and they start at the same level near the Principles of classification margin. The couplets must be assigned numbers or letters. The user is provided with a pair of lead for identiﬁcation of unidentiﬁed organism or taxon and is directed by numbers to a subsequent lead, if the selected lead does not provide the answer. Example 1: Bracketed dichotomous keys for five plant speciesGOFVOERRNONMLEINNTE PURSOEPOENRLTYY 1a. Flowers present................................................... 2 1b. Flowers absent.................................................... 3 2a. Leaves small........................................................ Abelia grandiﬂora 2b. Leaves large........................................................ 4 3a. Tree with needle-like leaves................................ Pinus sylvestris 3b. Shrub with leafy fronds....................................... Dryopteris filix-mas 4a. Flowers red, petals free....................................... Hibiscus rosa-sinensis 4b. Flowers red, petals connate into tube.................. Delonix regia Example 2: Bracketed dichotomous keys for seven animal species (Figure 2.2) 1a. Organism has a backbone……………………….2 1b. Organism does not have a backbone……………3 2a. Organism has wings…………………………….4 2b. Organism does not have wings………………….5 3a. Organism has antennae ……………………….. Grasshopper 3b. Organism does not have antennae………………Spider 4a. Organism has feathers…………………………..Bird 4b. Organism has hair……………………………….Bat 5a. Organism has legs………………………………6 5b. Organism does not have legs……………………Snake 6a. Organism has a shell…………………………….Turtle 6b. Organism does not have a shell………………….Frog BIOLOGY FORM 5 KIWANDANI.indd 89 89 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools (a) (b) (c) (d) (e) (f) (g) Figure 2.2 Animals (a) grasshopper, b) frog (c) turtle (d) spider (e) bird (f) bat, and (g) snake Revision questions GOFVOERRNONMLEINNTE PURSOEPOENRLTYY8. Why is scientific naming of organisms important? 1. What is biological classification? 9. Citing one example for each, 2. Explain any four drawbacks of outline rules governing binomial artificial system of classification. nomenclature. 3. Elucidate the advantages of natural 10. You are provided with fresh specimen system of classification. of (a) Phaseolus vulgaris (bean), (b) Solanum tuberosum (irish potato), 4. With examples, briefly explain why (c) Solanum incanum (bitter ball), it is important to classify organisms. (d) Solanum lycopersicum (tomato) and (e) Solanum aethiopicum (bitter 5. Explain the significance of taxonomic tomato) with flowers (Figure 2.3). hierarchy in classification. i) Examine characteristics of each 6. Explain with examples, scientific plant species such as the stem and technological advantages texture, leaf blade size, leaf paralleled with the taxonomic shift blade margin, flower colour, size from artificial to natural system of of calyx, and size of corolla. classification. ii) Construct bracketed and 7. Explain the challenges of assigning indented keys for identification scientific name to a newly of the provided specimens. discovered organisms. 90 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 90 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Principles of classification (a) (b) GOFVOERRNONMLEINNTE PURSOEPOENRLTYY (c) (d) (e) 91 Figure 2.3 Specimens for question number 10 10/10/2019 14:06 BIOLOGY FORM 5 KIWANDANI.indd 91

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools ThreeChapter organismsComparative studies of natural groups of Introduction In comparative studies of natural groups, organisms are classified on the basis of their shared characteristics and common ancestry. The grouping is done in relation to physiology, embryonic development, and phylogenetic relationship. In this chapter, you will learn the six groups of organisms, namely Viruses, Monera, Protoctista, Fungi, Plantae, and Animalia. 3.1 General overview of classification GOFVOERRNONMLEINNTE PURSOEPOENRLTYYIn 1866, the third kingdom of unicellular The natural groups of organisms are the organisms, Protista was put forward by broad categories of organisms formed Ernest Haeckel after its long placement by placing together organisms which under kingdom Animalia since it was ﬁrst are naturally or evolutionarily related discovered by Antoine van Leeuwenhoek for comparative purposes. This enables in 1674. The discovery of the scanning taxonomists across the world to compare electron microscope facilitated microscopic for various reasons how individual groups studies, and it made it possible to discern of organisms are related. The number of Eukaryotes (organisms with distinct natural groups of organisms, for example nucleus) from Prokaryotes (organisms at kingdom level has been steadily lacking a clearly deﬁned nucleus but have increasing since the 18th century, when their DNA lying free in the cytoplasm). Carolus Linnaeus introduced the natural This led to the establishment of kingdom classiﬁcation system from which kingdom Monera, in which all types of bacteria were Animalia (multicellular heterotrophs) and grouped. The placement of multicellular Plantae (multicellular autotrophs) were eukaryotic saprophytic organisms such as conceived. This system was adopted by mushrooms, yeast, and Rhizopus was still many taxonomists and gained a wider contradicting, because they were erratically popularity over the artiﬁcial system of classiﬁed under kingdom Plantae or Protista. classiﬁcation. This prompted Robert Whitaker to propose kingdom Fungi in 1969 under which all 92 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 92 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms multicellular saprophytes were grouped, Beijerink named the isolated extract ‘virus’ making ﬁve kingdoms. However, molecular a Latin word, meaning toxic or infectious. studies by Carl Woese in the 1970s revealed Viruses are therefore infectious particles, cellular structural differences among thought to have genomes detached out prokaryotes based on membrane structure, of eukaryotic or prokaryotic cells. Thus, ribosomal RNA, lipid compounds, among a virus can be deﬁned as a fragment of others. This necessitated the splitting of nucleic acid (single or double stranded kingdom Monera also called Prokaryota DNA or RNA), surrounded by a protein into Archaebacteria and Eubacteria. In coat and capable of replicating once 1982, about a decade later, Margulis and they are inside a living cell. Generally, Shwartz proposed a classiﬁcation system viruses are too minute; they are smaller which adopted the ﬁve kingdoms, namely than bacteria and cannot be seen by a the Prokaryotae and four Eukaryote light microscope, but they can be viewed kingdoms. However, that was not the end, under the electron microscope. The latter because recent molecular work has further has simpliﬁed an understanding on the revealed phylogenetic relatedness among characteristics of viruses, including their protists which lead to yet another kingdom, shapes and ways in which they interact Chromista. with their hosts. In 2015, Cavalier Smith and others introducedGOFVOERRNONMLEINNTE PURSOEPOENRLTYYCharacteristics of viruses biological taxonomy of 8 kingdoms namely; a) They are the smallest organisms with Eubacteria, Archaebacteria (Archae), Archezoa, Protozoa, Chromista, Fungi, size ranging from 17 nm to 300 nm. On Plantae, and Animalia. Biological taxonomy average, they are 50 times smaller than of 8 kingdoms has introduced a taxonomic bacteria, which range in size between rank called domain above the kingdom. 0.1–10 µm. Three domains of life, namely domain Archaea, Bacteria and Eukarya, are thus b) They are simple in structure with a recognised. Domain Archaea includes fragment of nucleic acid which is either Archaea bacteria which are the most DNA or RNA, enclosed in a protein primitive bacteria with cell wall containing or lipoprotein layer. Most animal and pseudomurein but lacking a peptidoglycan bacterial viruses have DNA, but other cell wall. Domain bacteria consist of all animal and plant viruses have RNA. true bacteria, while Eukarya encompasses all Eukaryotic organisms thus bringing c) Viruses lack cellular structure together the kingdoms Protoctista, Fungi, organisation, hence they are acellular. Plantae, and Animalia. d) Viruses can reproduce in a living cell only, that is, inside the cell of a living host. 3.2 Viruses e) Most viruses are infectious; they can The ﬁrst viruses were isolated in 1852 cause diseases to their hosts. They show as infectious extract from tobacco plants a high degree of host cell speciﬁcity, as suffering from tobacco mosaic. In 1898, they can recognise and infect speciﬁc 93 BIOLOGY FORM 5 KIWANDANI.indd 93 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools types of host cells. For example, a GOFVOERRNONMLEINNTE PURSOEPOENRLTYYa number of characteristics similar to those virus causing disease in plants will of living organisms as follows: not cause disease in animals and vice- a) They possess nucleic acid; either DNA versa. However, the same viruses can cause disease to different species in the or RNA, which is a genetic material same group of organisms. A virus called helping the virus to produce identical H5-N1 that causes a fatal bird’s ﬂu was copies of itself. recently discovered to cause infection and death in humans. b) They penetrate through a host cell by the help of enzymes derived from the f) In the absence of a host, viruses can protein coat on the cell surface of the crystallize outside a living medium host cell. and assume features of non-living organisms. c) They are able to multiply or reproduce inside the host cell. g) The ability of a virus to reproduce inside the cell and crystallize in the absence of d) They are able to undergo mutation in a living host places them between living response to host internal changes, and and non-living organisms. they respond rapidly. h) Viruses are obligate endoparasites e) They possess capsid, which is a protein because they can live and replicate coat embracing nucleic acids. inside their host cell only. f) They show speciﬁcity to hosts and 3.2.1 Classiﬁcation of viruses have the ability to infect the host Generally, classiﬁcation of viruses has been cell and take control of its metabolic challenging due to their characteristics activity. while inside or outside the host cell. Several other attributes of viruses intensify the Non-living characteristics of viruses difﬁculties experienced by taxonomists As non-living organisms, viruses have the in classifying them because they are very following characteristics; microscopic nucleocapsids (they are smaller than a molecule), lack cellular organisation a) They do not replicate on their own and (acellular) and lack certainty in evolutionary lack cellular structures hence unable history despite having fragments of to carry out any life processes when genetic materials such as DNA or RNA. outside the host cell. Thus, they do not fit precisely into the established biological classification system b) They do not have any enzyme system as they possess both living and non-living such as respiratory enzyme, hence characteristics. they lack energy releasing processes. Living characteristics of viruses c) While outside the host cell, viruses While inside the host cell, viruses possess are inert, but retain their ability to replicate, if they invade a host cell. Viruses are therefore crystalline in the absence of a host cell. When they exist as individual particles outside the host cell, they are called virions. 94 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 94 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms d) They are ﬁlterable; therefore, they can GOFVOERRNONMLEINNTE PURSOEPOENRLTYYClassification according to the host range pass through a bacterial proof ﬁlter includes plant viruses which infect plants paper. only. Examples include; Tomato leaf curl virus that infect tomatoes and Tobacco e) They are resistant to very high mosaic virus which infect plants like tobacco temperatures due to lack of enzymes. and other plants including tomato, potato, Normally, at high temperatures, orchid and blackcurrant, and cauliflower enzymes are denatured and thus render mosaic virus which infect cauliflower plant. them useless. In this type also there are animal viruses which infect animals only, examples include Viruses can be classified based on a influenza virus and Herpes simplex virus number of factors including; phenotypic which infect human. Also, there are bacteria characteristics, such as type of nucleic acid, viruses that infect bacteria, for example; host organisms, type of disease they cause, bacteriophage such as lambda (l) phage mode of replication, and morphology. In the (a lysogenic virus which is less virulent classification according to type of nucleic whereby the host and a phage can exist acid, there are RNA and DNA viruses. together for many years), enterobacteria RNA virus is a virus that has RNA as its T2, and T4 phages (lytic viruses which genetic material, normally single-stranded infect the bacteria known as Escherichia RNA, but some viruses may form double coli). Likewise, there are insect viruses helix intra-stranded complimentary base which affect insects only, and these include; pair of RNA. Viruses infect both plants Baculovirus, Sacbrood virus, Entomopox and animals, examples are Tobacco Mosaic virus and Granulosis virus. Virus (TMV) which infects plants, influenza virus, hepatitis virus, and polio virus which Based on the type of disease they cause, infect humans. A type of RNA virus known viruses can be classified as; measles virus; as Retrovirus has a peculiar character of cause measles, polio virus; cause polio, inserting a copy of its RNA into DNA of and rabies virus; cause rabies. According to the host cell by reverse transcription process morphology there are different categories and changing the genetic material of that based on the symmetry of capsid which cell, example is Human Immunodeficiency include helical and icosahedral viruses, Virus (HIV). On the other hand, DNA virus the helical morphology consists of helical is a type of virus whose genetic material array of capsid proteins wrapped around a is DNA rather than RNA. The DNA may helical filament of genetic material, example be either double or single stranded. These TMV, whereas in icosahedral the protein viruses infect animals and plants. Examples subunits are arranged in a form of hollow, include herpes virus, smallpox virus, quasi spherical structure, example; Herpes chickenpox virus; which infect animals, simplex virus. and tomato yellow leaf curl virus; which infect plants. BIOLOGY FORM 5 KIWANDANI.indd 95 95 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools 3.2.2 General structure of viruses with the genetic material (DNA or RNA), Viruses are composed of fragments of constitute a nucleocapsid. Some viruses genetic material (DNA or RNA), which may have additional envelope of lipoprotein forms a nucleic acid core. The DNA (lipid rich protein) around the capsid. The contains a few genes and can either be lipoprotein layer is usually derived from the single or double stranded. The nucleic acid cell membrane of the host cell. The viruses core is enclosed by a protein coat called with this layer are called enveloped viruses, capsid as in bacteriophage. The capsid is examples are inﬂuenza and herpes viruses. made up of small identical protein sub units Those with no envelope are referred to as called capsomeres which are structures that naked viruses, for instance, bacteriophage or enable viruses to crystallize and assume simply a phage; viruses that attack bacteria a non-living matter. The capsid, together (Figure 3.1 a, b and c). Capsid Envelope protein Nucleic acid Nucleic acid Protein (DNA) Viral envelope Reverse (c) Sheath transcriptase Base RNA Capsule protein Tail Matrix protein (a) (b) GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 3.1 Structure of (a) Bacteriophage (b) the Human Immunodeﬁciency Virus (HIV) and (c) Tobacco mosaic virus (TMV) 3.2.3 Viral replication (HIV) show uniqueness at a certain stage Viral replication involves formation of of their replication due to ability to convert viruses during the infection process, and they their RNA back into a DNA copy. Some replicate only when in living cells; that is the viruses called lytic phages kill host cells viruses must first get into the host cell before immediately after they enter. On the other viral replication can occur. Replication hand, other viruses such as lambda phages between viruses differ significantly and may remain dormant for a long time after depends on the type of genes in them. For inserting their DNA into the host DNA, example, most DNA viruses gather in the but they may eventually be activated to nucleus while most RNA viruses develop complete their life cycle. These types of merely in the cytoplasm. viruses are described as lysogenic phage and the dormant stage is called prophage. The The life cycle of a bacteriophage viral replication therefore, occurs in two In principle, viral life cycle is the same major stages or phases, namely; lysogenic in all bacteriophages. Retroviruses such and lytic phases or cycles as summarised as Human Immunodeﬁciency Viruses in Figure 3.2, and Figure 3.3 respectively. 96 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 96 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms a) Lysogenic cycle divides. However, the phage is not virulent When a phage contacts a bacterium, its tail at this stage but dormant, and bacterial cells ﬁbers attach to receptor sites on the bacteria may exist together with the dormant phage and it sheds its protein coat outside the DNA for many generations. This dormant host cell. The viral DNA is incorporated in or latent stage of the phage is also termed as the bacteria chromosomes (simple circles prophage and the host’s cell as a lysogenic of DNA) and is replicated along with it. cell. The viral DNA released may enter Therefore, replicated copies of viral DNA a virulent pathway called lytic cycle, if will be produced each time the bacteria cell activated (Figure 3.2). Phage Phage DNA Bacterial cell The DNA of phage is injected into Bacterial the bacterial cell cell DNA The DNA of phage becomes incorporated into bacterial DNA The bacterial cells divided to produce two cells whose DNA still incorporates the DNA of the phage GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Each cell continues to divide many times to give large numbers of cells which may, under special circumstances, enter a lytic phase whereby phage replication takes place. Then, cell bursts (lysis) and the phage particles escape. Figure 3.2 The life cycle of a lysogenic phage b) Lytic cycle cell machinery, replicates more repeatedly, When a phage particle approaches the host and codes for its new coat proteins. New cell, it attaches to the host wall and injects viral proteins and new virus particles are its genetic material. Other lysogenic viruses assembled. As a large number of new may be activated to enter the lytic cycle; viral particles is produced, the phage also this occurs when their genetic materials are produces lysozymes containing digestive already inside the host cell. They undergo enzymes which digest the host cell. This replication and produce more phages, makes the host cell to burst and release disrupting the host’s DNA as a result, the phages. Due to the digestion of the host phage DNA takes control of the bacterial cell caused by the phage, this phase is 97 BIOLOGY FORM 5 KIWANDANI.indd 97 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools termed as lytic phase from the word lysis with the bacteria DNA while in a lytic cycle, meaning ‘digest’. The host cell lysis and the viral DNA and the host DNA replicate release of phages mark the culmination separately within the host cell resulting in of the lytic phase (Figure 3.3). The newly many copies of the virus being produced produced phages are capable of infecting a very quickly. Also, the lysogenic cycle does new bacteria and the cycle starts over again not lyse the host cell straight away while as lysogenic cycle with or without a break in the lytic cycle, the host cell is lysed or or dormant stage. destroyed. The lysogenic and lytic cycles can be Phages that replicate using both lytic and distinguished due to the fact that, in lysogenic cycles are called temperate phages lysogenic cycles, the spread of the viral while phages that replicate only through the DNA occurs through the usual bacteria lytic cycle are called virulent phages. reproduction as their DNA has incorporated Phage Phage particle approaches bacterial cell Bacterial cell Phage attached to bacterial wall. DNA is Empty protein coat injected into bacterial cell and protein ‘ghost’ is left outside Phage DNA GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Phage DNA inside bacterial cell multiplies using bacterial nucleic acid and other substances absorbed by bacterium Phage DNA induces formation of protein coat. Eventually bacterial cell burst (lysis) releasing about 200 exact copies of original phage Figure 3.3 The life-cycle of a lytic (virulent) phage 98 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 98 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Retroviruses GOFVOERRNONMLEINNTE PURSOEPOENRLTYYdevastating epidemics in human societies, These are special groups of viruses as they are highly infectious and relatively that contain an enzyme named reverse easy to produce. transcriptase, which is capable of synthesizing a DNA copy from the virus Advantages of viruses RNA. This is unlike the usual transcription a) Viruses are widely applied in in which RNA is synthesized from a fragment of DNA. Literally, the term retro preparation of vaccines against means ‘reverse or going back.’ Hence, animal diseases. Currently, there is a retroviruses were so named due to their number of vaccines against deadly ability to undergo this reverse transcription human diseases such as poliomyelitis, process in producing DNA copies from measles, and yellow fever. RNA. These copies can be incorporated randomly into chromosomes of the host b) Viruses such as bacteriophages play DNA. It is in this group where the Human a great role in marine ecology and Immunodeﬁciency Virus (HIV), Hepatitis carbon cycling. B viruses and Herpes viruses belong. The retrovirus DNA is known as provirus. c) Viruses are important in the field of Provirus can be injected in the host DNA molecular and cell biology; they help and remain dormant for a long time prior to in manipulating and investigation expression and formation of its new RNA. At of cells, hence providing valuable this stage, the host does not portray any sign information about the aspects of cell of infection. This explains why it sometimes biology. takes a long time for people infected with HIV to develop AIDS symptoms. However, d) Some viruses are used in biological when provirus is incorporated into the host studies. Example, the enzymes reverse cell DNA, it may activate host genes to transcriptase discovered in retroviruses produce RNA which will be packaged are currently widely used in various inside the retrovirus particles and delivered aspects in genetic engineering. together with retroviral RNA to the next infected cell. The retrovirus binds on T- e) They stimulate the synthesis and helper lymphocytes and destroys them and release of interferon in the body. This cripples the immune system. suppresses the viral replication and stimulates the activity of cytotoxic 3.2.4 Economic importance of viruses cells. Though viruses have some disadvantages; as they cause diseases to organisms by being f) They are used in gene therapy through endoparasites and infectious pathogens, genetic manipulation of somatic cells yet some have significant beneficial in of individuals as well as in production medical industry, biotechnology, research, of transgenic plants and animals. agriculture and ecology. Furthermore, viruses have been used as biological g) Certain pathogenic viruses can be used warfare (biological weapons) and cause as a pests control agent. Disadvantages of viruses a) Viruses are known to cause various diseases in living organisms, for example influenza, measles, ebola, AIDS, chickenpox, and herpes in 99 BIOLOGY FORM 5 KIWANDANI.indd 99 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools human, potato mosaic and tobacco GOFVOERRNONMLEINNTE PURSOEPOENRLTYYnucleus or without a true nucleus. Although mosaic in plants, and newcastle in prokaryotes have no true nucleus, they still poultry. have diffuse area(s) of nucleoplasm called b) Some viruses can cause chronic nucleoid, containing genetic materials with infections; for example, the virus can no distinct nuclear membrane or envelope. replicate the entire life of the host, This is a very unique feature unifying all regardless of the presence of the host’s prokaryotes. It makes them distinct from defense mechanisms. This is common species of the other four kingdoms which in Hepatitis viral infection and in HIV. have membrane enclosed nuclei. Lack c) A host with chronic viral infections of membrane bounded nucleus makes can be a carrier of an infectious virus prokaryotic organisms evolutionarily the for lifetime. It can sometimes kill most primitive life forms. It is believed many cells, causing the organism to that the oldest prokaryote evolved about suffer ill effects. 3.5 billion years ago. Moreover, most organisms under this kingdom have a cell Exercise 3.1 wall containing peptidoglycan (Refer to Figure 1.3). 1. With examples, explain when and why viruses are considered to be a Prokaryotic organisms are diverse, and living and non-living organism. they constitute the largest group interms of abundance of organisms it encompasses. 2. Describe the life cycle of a Studies show that a gram of soil may contain bacteriophage, showing the main approximately 2.5 billion bacteria, while events of viral replication. a cubic centimeter of milk has more than 3,000 million bacteria. Organisms belonging 3. Brieﬂy explain why vaccines to this kingdom are very minute (1- 10 µm) against many viral diseases are to be seen without the aid of a microscope currently available but HIV and are thus termed as microscopic. This vaccination is still a challenge to is the reason why kingdom Monera was medical biologists. not among the two traditional kingdoms; Plantae and Animalia, as it was still difﬁcult 4. Giving reasons, brieﬂy explain in to see, identify, and characterise them. The which phase of the life cycle does discovery of the Monerans, therefore, came HIV replication occur. following the discovery of the microscope, particularly the electron microscope and 3.3 Kingdom Monera computer applications which revealed The kingdom Monera consists of unicellular the ﬁner details of the Monerans. This prokaryotes. Literally, the term prokaryote simpliﬁed the understanding of differences is a combination of two Greek words, across members of this kingdom, leading to pro meaning ‘before’ and karyo meaning the recognition of the three major divisions, ‘nucleus,’ which simply means before namely; division Archaea, Eubacteria, and Cyanobacteria. Earlier classiﬁcation 100 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 100 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms system splited Monera into two groups, methanogens (Methanobrevibacter in this case, all Archaea bacteria were ruminantium) which produce methane gas grouped under kingdom Archaebacteria in anoxic conditions in ruminant’s digestive while Cyanobacteria and Eubacteria were systems. These similar bacteria produce classiﬁed under kingdom Eubacteria or methane gas from cow dung which is used Prokaryota. as biogas, which is one of the renewable sources of energy. The members of kingdom Monera GOFVOERRNONMLEINNTE PURSOEPOENRLTYY3.3.1 Characteristics of monerans are cosmopolitan in distribution and predominant in all habitats, ranging from a) They are very microscopic unicellular aquatic; that is marine, brackish and fresh organisms, with an average diameter waters to terrestrial environments; such of 0.1-10 mm. as in the air, dust, soils, on plants and animals. They also range from parasitic, b) Their cells lack a well organised free living and symbiotic bacteria to animals nucleus, since they have no nuclear and plants. Some bacteria are saprophytes, membrane, and the nuclear materials especially decomposers, which are very are freely suspended in the cytoplasm. important in nutrient cycling. Nitrogen ﬁxing bacteria are found in symbiotic c) They lack cytoskeletons and association with leguminous plant roots membrane bound organelles, such as while the cyanobacteria form symbiotic mitochondria, plastids, and chloroplast. relationships called lichens with fungi. The photosynthetic Moneras have Parasitic prokaryotes include infectious photosynthetic lamella instead of bacteria such as Salmonella typhi that chloroplasts. causes typhoid and Vibrio cholerae which causes cholera, spend part or their entire d) They have few and smaller ribosomes, life in their hosts as facultative parasites 70s ribosomes. or obligate parasites respectively. The free living bacteria are capable of synthesizing e) They have small, circular DNA that their own food using energy obtained lacks the histone protein coat. from light or chemicals. The former is called photoautotrophic bacteria such as f) Most of physiological processes, such Purple sulphur bacteria, while the latter as respiration and food synthesis (for is called chemoautotrophic bacteria such the autotrophs), occur in membrane as Iron bacteria (Ferrobacillus). Some systems. prokaryotes such as Archaebacteria have interesting features such as the ability to g) The cell wall is composed of a survive in extremely harsh environments, carbohydrate-protein complex called such as very low oxygen concentration murein or peptidoglycan. (anoxic condition), high alkaline or acidic media, high salt concentration, and h) Most prokaryotes move using a beating extreme temperatures (in hot springs and ﬂagella, gas vesicles, and gliding volcanic domes) where other organism have mechanisms. Flagella, if present, lack completely failed to inhabit. For example, an internal 9+2 ﬁbril arrangement pattern. 101 BIOLOGY FORM 5 KIWANDANI.indd 101 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools i) They reproduce asexually by binary GOFVOERRNONMLEINNTE PURSOEPOENRLTYYare temperature-loving and acid-loving fission and sexually by conjugation, no archaeans (acidophils). They are found in mitotic and meiotic divisions, hence no hot springs and acidic conditions such as in spindle formation. hot springs and phosphoric or arsenic ponds. The third group is the extremohalophiles 3.3.2 Classiﬁcation of Monera which are salt loving archaeans found in The microorganisms in kingdom Monera salt lakes. Other classiﬁcation systems are considered as primitive organisms and treat Archaebacteria as a kingdom and the most ancient living forms on earth. This place the groups of archaea into distinct kingdom is divided into two main groups phyla or divisions while the entire group which are Archaebacteria (Extremophiles) of Archaebacteria in this text is regarded and Eubacteria (cyanobacteria and true as a division. bacteria). In this text, much emphasize will be devoted to Eubacteria. Division Eubacteria These include the true bacteria and the Division Archaebacteria cyanobacteria, also known as blue-green Under this group, bacteria are the most bacteria or blue-green algae, which are primitive and ancient members of kingdom photosynthetic. Members of this division Monera. Their cell wall chemistry differs lack true nuclei and they have a strong and from eubacteria as they lack peptidoglycan. rigid cell wall containing a polysaccharide Instead, they have lipids which are different called murein cross-linked by short chains in composition from other bacteria due to of amino acids. They have a variety of the presence of long chains of fatty acids shapes ranging from spherical, rod-like, with glycerol attached to it by ester linkage. and spiral or comma shaped. Additionally, Another unique feature of these bacteria is some are heterotrophs, living as pathogenic their ability to inhabit extreme environments parasites while others are free living in which other organisms cannot survive. autotrophs. Furthermore, eubacteria have These habitats include environments simple circular DNA which is not associated with extreme temperatures, saline, and with proteins to form chromosomes and acidic conditions. Others can survive in they use mesosomes for respiration. oxygen deprived or anoxic conditions. Because of their ability to survive in Cyanobacteria are grouped in the same extreme conditions, Archaebacteria division with other true bacteria, because are grouped into methanogens, which they share many features. For example, produce methane by reducing carbon- both possess prokaryotic cell structures, dioxide, for example, methanogens reproduction by binary ﬁssion, their cell (Methanobrevibacter ruminantium) wall contains peptidoglycan (murein), and found in ruminants’ digestive system. The have mucilaginous sheet. other group is hyperthermophiles which 102 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 102 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms In other classiﬁcation systems, cyanobacteria GOFVOERRNONMLEINNTE PURSOEPOENRLTYYThis staining based classiﬁcation of bacteria form a division of their own called Division was invented by Hans Christian Gram, a Cyanobacteria. This is because, unlike Danish microbiologist in 1884, and was bacteria, they have chlorophyll a for therefore named “Gram stain’s test.” This photosynthesis and they produce oxygen simple test classiﬁes bacteria into two broad during photosynthesis which resembles groups namely; Gram negative and Gram- algae more than bacteria. In addition, their positive (3.4 a and b). The Gram-positive chlorophyll lamellae and DNA lie free in bacteria appear blue to purple, because they the cytoplasm. Cyanophytes can occur as retain the crystal violet colour of the dye free living cells or as colonies. They have used to stain them. In contrast, the Gram- specialised cells called heterocyst which are negative bacteria do not retain the colour capable of ﬁxing Nitrogen. These bacteria of the stain (crystal violet). form blooms in ponds. Sometimes, they are found in symbiotic association called The staining differences are based on lichen with fungi. variation in the cell wall chemistry, particularly in the amount of peptidoglycan. Classiﬁcation of bacteria The Gram-positive bacteria have a Bacteria are single celled microbes, simple cell wall with a thick layer of with a simple cell structure that has no peptidoglycan (polysaccharides and nucleus or membrane bound organelles. protein). Moreover, due to differences Although genetic divergence specifies in cell wall constituents, the Gram- the evolutionary relationships of bacteria, positive bacteria cell wall is susceptible reaction to Gram stain, mode of nutrition, to lysozymes and antibiotics. The Gram- morphological, motility, and biochemical negative bacteria are resistant to antibiotics features of bacteria remain important in and lysosomes. This is because, although the identification and classification of these they have thinner cell walls, they are more organisms. Three major ways can be used complex, by having additional outer layer to identify bacteria; based on their cell wall on the outside of murein layer which is chemistry or composition which makes thin, smooth membrane-like containing them respond differently to Gram stain, lipid and polysaccharides that protect the difference in morphology of their cells, and bacteria from host’s lysozyme, as well mode of nutrition. as antibacterial enzymes found in tears, saliva and other body fluids. Examples of Classiﬁcation of bacteria based on Gram-positive bacteria include Bacillus their staining properties sp., Clostridium sp., Streptococcus sp., In this case, the bacterial cell is smeared on and Staphylococcus sp., while Gram- a microscope slide and stained with crystal negative bacteria include Escherichia coli, violet solution followed by iodine solution, Chlamydia sp., Neisseria sp., Salmonella and later washed with organic solvent such as sp., Treponema sp., and Azotobacter sp acetone or ethanol and counterstained with (Figure 3.4). a red dye called safranin or carbolfuschin. 103 BIOLOGY FORM 5 KIWANDANI.indd 103 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Gram-positive bacteria Outer Gram-negative bacteria membrane Peptidoglycan Cell wall Peptidoglycan Plasma membrane (a) (b) Figure 3.4 Structure of a bacterial cell wall (a) Gram-positive and (b) Gram-negative bacteria The framework of the protein that makes diffusion of the staining solution (see the the peptidoglycan materials of the cell three dimensional detailed view of the wall is a porous network that allows Gram-positive bacteria in Figure 3.5). Cell wall Plasma membrane Protein Figure 3.5 Structure of a bacterial cell wall (detailed view of the cell wall) GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Activity 3.1 Identification of Gram- solution or gentian violet, and let it positive and Gram-negative bacteria stand for one minute. Materials c) Decolourise by adding alcohol, drop by drop until no further stains come Dried smears of bacteria, gentian violet out. or iodine solution stain, alcohol, red dye (safranin/ carbolfuschin), and d) Counterstain by flooding the smear watch glass. with a red dye such as safranin or carbolfuschin and let it stand for Procedure about 40-45 seconds. a) Place an air dried smear on a watch e) Observe the colour change and glass. explain your results. b) Gently flood the smear with iodine 104 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 104 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Classiﬁcation of bacteria based on binary ﬁssion simultaneously. Four shapes their morphology of bacteria exist, namely cocci, bacilli, Bacteria can be classiﬁed according to spirilla, and vibrio or comma-shape. their morphology or shapes, which are diverse, ranging from rod-like to comma- Cocci (singular coccus) like shapes. They can exist singly or These are spherical-shaped bacteria. in a series of interconnected individual They may exist as a single cell, while cells called colonies. This should not be others may exist in pairs, forming a confused with multicellular organisms, double-celled (diplococcus) organism. because each cell is capable of carrying out The diplococus may be surrounded by a all its essential life processes, and each can capsule, for example the pneumococcus survive independently if separated from bacteria (Diplococcus pneumoniae) a the colony. The cells normally associate to causative agent of pneumonia. They may form a colony after binary ﬁssion, as the also occur in chains of interconnected two resulting cells adhere to each other. individuals or in bunches (cluster cells) Some bacteria cells associate in tubular such as Streptococcus and Staphylococcus sheaths, forming ﬁlaments which undergo respectively (Figure 3.6 a, b, c, and d). (a) (b) (c) GOFVOERRNONMLEINNTE PURSOEPOENRLTYY(d) Figure 3.6 Structures of cocci bacteria (a) single-celled (b) double-celled (c) colon and (d) chain Bacilli (singular bacillus) forming endospores with various shapes, These are rod-shaped bacteria which may position and size, examples include oval occur singly as in Escherichia coli; a common spore without swelling at the center like gut-living symbiont and Salmonella typhi in Bacillus anthracis, and spherical spore which causes typhoid fever. The bacilli may with a swollen terminal like in Clostridium occur in chains as seen in Nitrogen ﬁxing tetani; the causative of tetanus or with sub- bacteria (Azotobacter) and the anthrax terminal swollen example Clostridium causing bacteria (Bacillus anthracis). botulinum the causative of botulism (Figure The bacilli usually have a tendency of 3.7 a, b and c). BIOLOGY FORM 5 KIWANDANI.indd 105 105 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools (a) (b) (c) Figure 3.7 The structure of bacilli bacteria (a) single rods (b) chained rod and (c) Bacilli with endospores Spirilla (singular spirillum) GOFVOERRNONMLEINNTE PURSOEPOENRLTYYVibrio Bacteria in this group have a long cylinder This group of bacteria includes various cell, coiled into a spiral or helical body. curved bacteria which appear superﬁcially The individuals under this group are also like a comma. That is why they are called spirochaetes; their name came sometimes named as comma-shaped from the fact that they contain distinctive bacteria. These bacteria possess a single double membrane, and most of which ﬂagellum which is used in locomotion as have long helically coiled structure seen in Vibrio cholerae (Figure 3.9). (corkscrew-shaped or spiraled). They are also characterised by presence of unique Figure 3.9 The structure of a comma-shaped axial ﬁlaments composed of ﬂagella, bacterium running from one end of the cell, where they are directly attached to the cell wall. Classification of bacteria based on The ﬂagella are used for locomotion. their mode of nutrition Bacteria under this group include free Bacteria obtain their food from their living bacteria found in water and muds environment in different ways. Some of as well as parasitic spirochaetes such as them can synthesise their own food using Treponema pallidum that causes syphilis energy from the sunlight, while others in humans (Figure 3.8). use chemicals as their energy source. Some of the bacteria cannot synthesize Figure 3.8 The structure of a Spirillum bacterium their own food and they rely on other organisms as their source of food. Thus, in this regard, bacteria are classified into 106 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 106 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms photoautotrophs, chemoautotrophs, and GOFVOERRNONMLEINNTE PURSOEPOENRLTYYare pathogenic as they obtain their foods chemoheterotrophs. by living in or on other organisms thereby causing diseases and even death of their Photoautotrophs hosts. Some bacteria live permanently Photoautotrophs bacteria need light as on or in their host (obligate parasitic their source of energy in manufacturing bacteria), while other bacteria’s life cycles their food. The light is trapped with the depend on multiple host (facultative aid of chlorophyll 'a' and carotenoid parasitic bacteria). Other bacteria live in pigments. This type of photosynthesis a mutual (symbiotic) relationship with is much simpliﬁed compared to that of other organisms where by both partners plants. Examples include blue-green benefit from the association. Examples of bacteria. symbiotic association include; Rhizobium bacteria that live in the root nodules of Chemoautotrophs leguminous plants, and also have ability These bacteria acquire their energy by to fix nitrogen into useful compounds oxidising simple inorganic substances, but like nitrates which are needed by these not from sunlight as in photoautotrophs. plants, and Escherichia coli which live The obtained energy is used to synthesise symbiotically in the human gut and food in the presence of carbon dioxide. contribute to the formation of vitamin B Important nitrogen ﬁxing bacteria such as and K. Nitrosomonas and Nitrobacter belong to this group. Others include Iron bacteria 3.3.3 Bacterial reproduction which oxidise Iron two (Ferrous Iron) to Bacteria reproduce both sexually and Iron three (Ferric Iron), and the energy asexually; sexual reproduction involves released from oxidation is utilised during two organisms/cells exchanging their food synthesis. genetic materials (not gametes, as they have no reproductive structures) and Chemoheterotrophs produce daughter cells which differ in their All bacteria which cannot manufacture genetic materials from that of the parental food on their own as they lose the ability to cells. Sexual reproduction involves the photosynthesize in the course of evolution process of genetic recombination through are heterotrophs (heterotrophic bacteria). cell to cell contact (Conjugation), while in They are named “chemo” heterotrophs, asexual reproduction the cell divides by when they obtain energy for their growth binary fission to form two daughter cells from organic compounds such as proteins with similar genetic materials as that of and glucose. Chemoheterotrophs can the parental cell. be further categorised into saprotrophs, parasites and mutualists. The saprotrophs Asexual reproduction in bacteria obtain their food from dead and decaying Most bacteria reproduce asexually. A organic matter, majority of them are single bacterium can reproduce asexually decomposers, which are very important by binary ﬁssion which involves division in nutrient recycling. Parasitic bacteria of one bacterium into two bacteria (Figure 107 BIOLOGY FORM 5 KIWANDANI.indd 107 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools 3.10). In this process, the dividing cell Sexual reproduction in bacteria elongates and if the cell is spherical, the Sexual reproduction in bacteria is primitive elongation is very much restricted. A rod- in the sense that it does not involve union shaped bacterium elongates to almost of gametes as commonly seen in other double its size. Then, the protoplasmic organisms, particularly the eukaryotes. mass divides into two equal halves by a The reproduction simply involves transverse wall or constriction. The cell combination of genetic material by the division is preceded by the replication of process called genetic recombination. DNA. The two daughter cells soon grow This process involves the primitive form to maturity and divide further. of sexual reproduction called conjugation (the transfer of DNA between two cells Cytoplasm which are in direct contact). One of the Parental cell with its circular DNA DNA Cell wall two cells (male) donates while the other Cell replicate its DNA (female) receives genetic material. The The cytoplasm elongates ability to donate the genetic material is separating the daughter DNA controlled by the bacterial gene found molecules in a special type of plasmid called sex Cross wall start to be formed factor which also codes for the formation of a small tubular structure called pilus, Cross wall completely formed connecting the two bacterial cells. Through Two daughter cell are this pilus, the genetic material is injected formed to one or more recipient(s) at a time. This kind of exchange is essential especially GOFVOERRNONMLEINNTE PURSOEPOENRLTYY during unfavorable condition, and they Figure 3.10 Bacterial reproduction by binary produce more resistant cells (Figure 3.11). fission Donor Pilus Recipient 1. Formation of pilus 2. Pilus connects cells 4. Fragment of donor DNA 3. Donor DNA replicated by rolling incorporated into recipient cycle method and transferred Figure 3.11 Sexual reproductions in bacteria 108 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 108 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms 3.3.4 Economic importance of monerans such as leaf litter, dead logs and animals Bacteria have a wide range of economic into simple substances like nutrients which importance; ranging from beneﬁcial to can be easily absorbed by other plants. detrimental effects to humans and other This process is called decomposition and organisms. Furthermore, many bacteria it ensures nutrients recycling. It is vital to serve important roles in both industries and agriculture. nature because it unlocks nutrients locked Advantages of monerans in dead bodies of other organisms and makes them available to others. a) Production of vinegar GOFVOERRNONMLEINNTE PURSOEPOENRLTYYe) Treatment and purification of Some bacteria, such as those of genera waste water or sewage Acetomonas and Acetobacter are used in Bacteria can be used in treating and making vinegar (for vinegar fermentation), purification of water or sewage in whereby ethanol is partially oxidised into oxidation pond, by reducing the bulky of ethanoic acid (vinegar). wastes and converting them into simpler forms which can be easily handled in the b) Manufacturing of dairy products subsequent stages in a stabilisation ponds In this case, bacteria such as Streptococcus (lagoon). Examples of decomposers lactis are employed in preparation and include Streptomyces sp. and Bacillus sp. preservation of commercial butter, cultured milk, and cheese from cream milk. The f) Making flavour, aroma and curing bacteria species Streptococcus thermophilus of agricultural products and Lactobacillus bulgaricus are frequently Bacteriaare used for production of different used in preparation of yoghurt by inoculating dairy flavour compounds, such as butyric fresh milk with a starter culture containing acid, lactic acid and diacetyl in mixed Brevibacterium linens in order to produce cultures of Lactobacillus acidophilus and the appealing smell in cheese. Pediococcus pentosaceus. Some bacteria such as Bacillus subtilis have been used to c) Manufacturing of amino acids, bring about several physio-chemicals and proteins, and starch sensory changes in soybean foods to make In the manufacture of amino acids, some it highly digestible and nutritious. Bacillus bacteria such as Monococcus glutamis are subtilis which dominate traditionally used. Industrial proteins such as amylase fermented soy foods have typical taste, are produced by bacteria such as Bacillus texture and aroma which is popular in polymysa. Asian and African countries. Certain bacteria such as Bacillus megaterium d) Decomposition of organic matters can be used in curing off the bitterness in Most bacteria are chemoheterotrophs leaves of tea and tobacco. which obtain their food from dead or decaying organic matter. In so doing, such bacteria reduce heaps of dead substrates 109 BIOLOGY FORM 5 KIWANDANI.indd 109 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools g) Nitrogen fixation and nitrification GOFVOERRNONMLEINNTE PURSOEPOENRLTYYbacteria of genus Pseudomonas are used in the soil in cleaning oil-contaminated water as they Some bacteria, besides being decomposers feed on oil spills. are important in ﬁxing atmospheric nitrogen into a form that can be utilised by plants j) Biodiversity studies by the process known as nitrogen fixation. Bacteria may be one of the most abundant Examples of nitrogen fixing bacteria are and species-rich groups of organisms, Azotobacter, Clostridium, and Rhizobium. that mediate many critical ecosystem Some bacteria convert ammonia into processes. They contribute signiﬁcantly nitrates in the soil by the process known to the global biodiversity, given the as nitrification. Nitrosomonas convert existence of numerous species of bacteria. ammonia into nitrite which later gets The position and role of each species oxidised to nitrates by Nitrobacter. The in the ecosystem cannot be underrated. two processes are important in agriculture, Cyanobacteria initiated early life on land because nitrogen is one of the elements as they were the ﬁrst organism to produce required by plants in large quantity for oxygen from photosynthesis. Such oxygen growth and other physiological processes. was used by early aerobic organisms. Nitrogen contributes largely in improving agricultural yields. k) Medical application Some bacteria such as Streptococcus are h) Bioindicator in detecting water used in the process of manufacturing pollution antibiotics, such as Streptomycin. Cyanobacteria blooms in ponds can Streptococcus lactis ferments milk to be used as bioindicator, since they are produce lactic acid which prevents growth sensitive to water pollution. Changes in of harmful bacteria in the stomach, by abundance of cyanobacteria in aquatic maintaining the acidic environment in the ecosystems can serve as indicators of stomach. Lactic acid prevents bacterial water pollution. vaginosis, thus preventing urinary tract infection (UTI). Starch, in the form of i) Biotechnology and genetic amylose, is produced for industrial uses engineering by bacteria. For example Escherichia coli Bacteria can be used to alter and replicate or E. coli are used in the mass production genes that are then introduced into of asparaginase enzyme which has also plant or animals. Bacterial systems lend a medical application in chemotherapy themselves to genetic manipulation in part against lymphoblastic leukemia. because of their rapid reproduction rates. Thermus aquaticus (Taq) is a thermal stable l) Symbiotic association with other bacterium which is used to produce DNA organisms polymerase. DNA polymerase enzyme is Some bacteria such as cyanobacteria live in used in amplification of short segments of association with fungi in which the former DNA through polymerase chain reaction synthesise food through photosynthesis (PCR). Some genetically engineered 110 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 110 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms and supply it to fungi, while fungi provide GOFVOERRNONMLEINNTE PURSOEPOENRLTYYb) In farm animals, some diseases such as support and protection from dehydration anthrax in cattle, avian tuberculosis in to cyanobacteria. Some non-pathogenic poultry, and black leg in sheep, goat and bacteria live on human skin and are cattle are caused by bacteria including important in destroying the bad bacteria Bacillus anthracis, Mycobacterium that live in symbiotic association with avium, and Clostridium chauvoel human. For example, Staphylococcus is respectively. among skin microbiota (skin flora) that live symbiotically with human skin, protecting c) Some bacteria cause diseases in the host from pathogenic bacteria.In plants, resulting into crop destruction, addition, Ruminococcus bacteria that live for example; corky root in lettuce, symbiotically with ruminant animals, halo blight in beans, and bacterial breakdown the plant fibres (cellulose) into pith necrosis in tomatoes are caused monosaccharides, and E.coli in human by bacteria such as Rhizomonas intestines synthesises vitamin K. suberifaciens, Pseudomonas syringae Pv. Phaseolicola, and Pseudomonas m) Biological control corrugate respectively. Bacteria are potentially used in several biological control methods in agriculture d) Foods with high protein content are and public health programs as bio often decomposed by bacteria leading pesticides. For example, some bacteria are into food spoilage. For example, the soil dwelling Gram-positive, commonly smell coming from rotten eggs or any used as biological pesticides. They other protein-containing foods results infect and kill the destructive organisms, from decomposition of protein by including caterpillar of some butterﬂies proteolytic bacteria. and larvae of some insects. An example of a soil dwelling Gram-positive bacterium e) During the process of bioleaching, is Bacillus thuringiensis. some bacteria such as Thiobacillus oxidise sulphides to form sulphuric Disadvantages of monerans acid and Hydrogen ions (H+) which a) Pathogenic bacteria cause diseases in can leak into the ground and turn surface and ground water into acidic, humans. For instance; Vibrio cholerae hence water pollution; which is an cause cholera, Treponema pallidum; environmental destruction. syphilis, Shigella dysenteriae; shigellosis, Salmonella typhi; f) Bacteria called Clostridium botulinum typhoid fever, Entamoeba histolytica; can release toxin in imperfectly canned dysentery, Mycobacterium tuberculosis; food. tuberculosis, and Escherichia coli cause urinary tract infection (UTI). BIOLOGY FORM 5 KIWANDANI.indd 111 111 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Exercise 3.2 GOFVOERRNONMLEINNTE PURSOEPOENRLTYYcelled eukaryotes constituted kingdom Protoctista. 1. Brieﬂy explain why the Carolus Linnaeus classiﬁcation system Recent phylogenetic studies have shown was silent about kingdom Monera. that even Protoctista is no longer a group of naturally related organisms. This makes 2. Describe the general and it difﬁcult to clearly deﬁne kingdom distinctive features of division Protoctista. For example, protoctists such Eubacteria. as algae have chloroplasts; hence, they are photoautotrophs. Amoeba is a heterotroph, 3. Citing the signiﬁcance of each, while slime molds and water molds explain two ways by which are saprophytes sharing many features bacteria reproduce. in common with fungi than with other protoctists. It is for this reason, kingdom 4. Give any four reasons to justify Protoctista is deemed controversial by the placement of cyanobacteria contemporary taxonomists. This is why the under division Eubacteria. classiﬁcation system has advanced from ﬁve to eight kingdoms. Members under 5. Why some taxonomists separate kingdom Protoctista have been separated Cyanophytes from division into two kingdoms, namely Protozoa and Eubacteria and place them in Chromista. More recently, they have been division Cyanobacteria. separated into three kingdoms: Protozoa, Chromista, and Archezoa. However, this 6. Using relevant examples, explain text will focus on Protoctista as a kingdom the ways in which bacteria are for convenience. ecologically and economically important. Protoctists can be deﬁned as unicellular eukaryotic organisms other than fungi, 7. Explain with examples, why plants, and animals. Evolutionarily, bacteria are said to be successful members in high kingdoms such as Fungi, colonisers. Plantae and Animalia, have their ancestors in the Protoctista kingdom. Therefore, 3.4 Kingdom Protoctista protoctists are eukaryotes consisting of In the early classiﬁcation of living organisms unicellular and multicellular members. into four kingdoms, all organisms which The multicellular protoctists consist of an could not ﬁt into kingdoms Fungi, Plantae assembly of similar cells such as Spirogyra. and Animalia were placed under kingdom The major difference between protists and Protista. This made kingdom Protista very protoctists is that the former consists of diverse, as it accommodated both unicellular only unicellular microscopic organisms prokaryotes and eukaryotes. Later, with the (protozoans) while the later is the mixture use of molecular taxonomy, prokaryotes of unicellular and multicellular organisms. were separated from Protista to form a Studies based on the base sequence of group of unicellular organisms lacking a well organised nucleus. These were placed under kingdom Monera, while all single- 112 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 112 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms mitochondrial and chloroplast DNA indicate GOFVOERRNONMLEINNTE PURSOEPOENRLTYY majority of protoctists, although some that members of kingdoms Fungi, Plantae members lack sexual reproduction. and Animalia have their ancestors in the Asexual reproduction occurs by binary kingdom Protoctista. ﬁssion (in which one nucleus divides), multiple ﬁssion (in which many nuclei Characteristics of protoctists divides into multiple daughter cells), a) Organisms under this kingdom are or budding (in which a new cell grows on the surface of the mother cell). nucleated; that is, all are eukaryotes. During all these types of asexual b) Some protoctists are unicellular while reproduction, an organism replicates its nucleus and divides to form new others are multicellular. organisms. Sexual reproduction in protoctists is still primitive, given that c) They lack tissue differentiation. it is mainly a recombination of genetic material. d) Protoctists are adapted to both, aquatic and terrestrial habitats. i) Some protoctists are parasites, while others are free living organisms. e) They have various types of vesicles The free living members are either that perform different functions. autotrophs (such as Spirogyra) These include their increased surface or heterotrophs (such as Amoeba area to facilitate exchange of materials proteus). needed for their survival. For instance, contractile vacuole helps protoctists Classiﬁcation of protoctists to discharge excess water taken by Classifying protoctists has been a osmosis. They also have food vacuole, difficult task due to their high diversity. as in Paramecium, which helps them Traditionally, protoctists were subdivided in digestion of engulfed food particles. into several groups based on their physical similarities to higher kingdoms of f) Their cell surfaces are diverse, ranging Animals, Plants and Fungi. This text will from just a plasma membrane as in deal with six selected phyla of Protoctista Amoeba, to a stiffer surface as in namely; Rhizopoda, Zoomastigina, Euglena to ensure the integrity of the Apicomplexa, Euglenophyta, Oomycota, cell. and Chlorophyta. g) Many protoctists are involved in Phylum Rhizopoda endo-symbiotic relationship with Rhizopoda is a broad group of protozoan other organisms. A good example amoeboid organisms placed in kingdom is a radiolarian which harbors other Protoctista. The shape and organization photosynthetic protoctists. These of pseudopodia are among the main protoctists, through photosynthesis, characteristics that are used to classify synthesise food that is shared by both, while the radiolarian in turn confers protection and provide some metabolites to the other symbiont. h) Both asexual and sexual types of reproduction are common in the BIOLOGY FORM 5 KIWANDANI.indd 113 113 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools members of phylum Rhizopoda. This GOFVOERRNONMLEINNTE PURSOEPOENRLTYY f) They possess contractile vacuole that phylum comprises of all forms of amoeba carries out osmoregulation. Normally, including parasitic and free living amoeba. ﬂuids in the amoeba cell are relatively Parasitic amoeba include Entamoeba more concentrated which allow more hystolytica which feeds on cells of water to ﬂow to their body in response the human colon, and cause amoebic to osmotic gradient. Amoeba in turn dysentery also (amoebiasis). The disease pumps out this water using their is characterised by abdominal pains, contractile vacuole. nausea, vomiting, erosion of blood vessels of the gut and diarrhoea containing blood. Distinctive features of phylum Rhizopoda General characteristics of phylum Members of the group Rhizopoda have Rhizopoda the following features which distinguish They are found in sea water, fresh water, them from the rest of the protoctists. and in the soil. They can also be found in a mud shallow pond and slow ﬂowing a) They have pseudopodia, which are streams containing plenty of decaying used for both locomotion and feeding. organic matter. Such pseudopodia are constantly changing as amoeba moves and feeds. a) They are single-celled eukaryotes and Food particles and small organisms their cells have no deﬁnite shape. are engulfed using pseudopodia and digested in the food vacuoles. The b) They are unicellular whose bodies digested food is assimilated into the are surrounded by membranes. Their rest of the body. This type of feeding cytoplasms have two distinct regions, is called phagocytosis. Ingestion is the plasmasol (inner) and plasmagel by endocytosis and egestion is by (outer). exocytosis. c) Most of them are free living, forming b) The food vacuole and the oil droplets of important links in the food chains. They amoeba confer a granular appearance feed on plant and animal materials. to the endoplasm. In contrast, others are parasitic or infectious to animals, including human c) They possess a contractile vacuole, being; some human pathogens such as which carries out osmoregulation. Entamoeba histolytica cause amoebic When the contractile vacuole reaches dysentery. a certain size, it fuses with the cell membrane where water is released d) They reproduce asexually by binary outside the cell. ﬁssion. e) They move by using pseudopodia; d) Their cytoplasm has two distinct hence, amoeba and other protoctists regions; viscous outer layer ectoplasm using this mode of locomotion are (plasmagel) and more ﬂuid internal called pseudopods. endoplasm (plasmasol). 114 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 114 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Structure of Entamoeba histolytica low oxygen concentration, since they Entamoeba histolytica has a regular body live in areas with low oxygen supply which changes constantly. The body in the large intestine. is covered by a thin semi-permeable e) They have rapid binary ﬁssion and membrane called plasmallema or plasma production of a large number of membrane; and it is differentiated into cysts to ensure their existence and two distinct portions; an outer ectoplasm perpetuation in alternative hosts. (plasmagel) and an inner endoplasm f) They can feed on various foods, (plasmasol). In the endoplasm, there is ranging from bacteria to blood cells, a prominent nucleus which is enclosed and digest them with their enzymes. by a nuclear membrane. They possess pseudopodia for locomotion and feeding Exercise 3.3 by engulfing food substances (Figure 3.12). 1. Give reasons as to why some Ectoplasm Food vacuole taxonomists consider Protoctista Endoplasm as an obsolete kingdom. Pseudopodia Nucleus 2. Explain the reason why both Ingested red Monera and Protoctists are single- Ingested blood cells celled organisms but belong into bacteria different kingdoms. Plasmalema Figure 3.12 Structure of Entamoeba histolyticaGOFVOERRNONMLEINNTE PURSOEPOENRLTYY 3. Describe any ﬁve features which make Amoeba a specialised form Adaptations of Entamoeba to its mode of protoctists. of life 4. What is the economic importance Some amoeba such as Naegleria are free of Entamoeba? living; they can live in different habitats such as on the bottom of ponds and lakes, Phylum Zoomastigina whereas others like Entamoeba exhibit a This phylum consists of ﬂagellated parasitic mode of life. Parasitic amoeba parasitic protoctists. It contains free- have the following adaptations to their living organisms, some are symbionts, mode of life. such as protozoans which live in the gut a) They can form cysts which resist of termites and digest cellulose in the wood eaten by the termites, and some digestive agents in the stomach. are parasites. Examples of parasitic organisms found in this phylum include b) They lack contractile vacuoles, since Trypanosoma gambiense; a parasite they live in isotonic state with the causing African sleeping sickness. host’s gut ﬂuid. c) They live where there is a plenty of food supply from their host. d) They are physiologically tolerant to BIOLOGY FORM 5 KIWANDANI.indd 115 115 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools General characteristics of phylum Structure of Trypanosoma Zoomastigina The genus Trypanosoma contains a large a) The phylum Zoomastigina contains number of parasitic species which infect wild animals, domesticated animals and organisms such as Trichonympha and humans. Trypanosoma is divided into Trypanosoma, which have one or two several sub-genera based on morphological ﬂagella. differences. Different species of trypanosomes are transmitted by insects. b) The members of this phylum are Examples include; Trypanosoma cruzi, heterotrophic; single-celled organisms. Trypanasoma brucei and Trypanosoma gambiense which is a causative agent of c) It comprises of both free-living and sleeping sickness in humans. This parasite parasitic organisms. Free-living is common in west and central Africa, its Zoomastigina are found in ponds and vector is a tsetse ﬂy, Glossina palpalis. It is puddles with plenty of organic matter about 15µm long, and 1µm wide, pointed while a few such as Trypanosoma are at both ends and bears a prominent ovoid parasites. nucleus in the central region. It is enclosed in a strong pellicle which maintains the d) Some have undulating membrane. body shape. The entire body is covered by a wavy undulating membrane. Along e) Most of them reproduce by a simple the edge of the membrane is a ﬂagellum binary ﬁssion. attached posteriorly to a small granule known as a blepharoplast (basal body). f) The body is overlaid by a semi-rigid Anteriorly, the ﬂagellum projects in front pellicle. of the body as a short, ﬁne slash, and immediately posterior to the basal body, Distinctive features of phylum there is a prominent granule, a parabasal Zoomastigina body (Figure. 3.13). Zoomastigina species differ from the other members of the kingdom Protoctista by being the only heterotrophic unicellular eukaryotes with one or more flagella. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Free flagellum Kinetoplast Undulating membrane Parabasal body Pellicle Cytoplasm Nucleus Figure 3.13 Structure of a Trypanosoma 116 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 116 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Adaptations of Trypanosoma spp. to GOFVOERRNONMLEINNTE PURSOEPOENRLTYYPhylum Apicomplexa their mode of life This phylum consists of eukaryotic Trypanosoma spp. are highly adapted to unicellular organisms, which are spore parasitic mode of life in their hosts due forming parasites of animals. They are to possession of the following adaptive also known as sporozoans; an example features: is the parasite Plasmodium which cause malaria in humans. a) They have large surface areas to volume ratio. This is important for General characteristics of phylum absorption of oxygen and food from Apicomplexa their hosts. a) Most of them possess a unique type of b) They live isotonically within the plastid called an apicoplast, used for blood plasma of their hosts. They piercing host cells. lack contractile vacuoles and osmoregulation does not take place. b) They are unicellular and spore forming organisms. Almost all species c) They have rapid reproductive rate by are obligate endoparasites of animals, binary ﬁssion which ensures that large except nephromyces which live number of parasites are produced. symbiotically in marine animals. Large number of these parasites is potentially important especially c) They have an infectious stage known in adverse conditions where some as sporozoite. parasite formed die, but some will remain. d) They reproduce asexually by schizogony and sexually by sporogony. d) They have a hard pellicle that protects cytoplasmic structures and restricts e) The parasite changes its shape action of digestive agents of the host. depending on the host it inhabits. For instance, it is sickle shaped in e) They are able to remain dormant in salivary glands of mosquito, while it their host’s cells of liver and spleen is spherical or amoeboid in liver cells during adverse conditions. This of humans. ensures existence of the species. f) They are non-motile. g) They form resistant spores after fertilisation. Exercise 3.4 Distinctive features of phylum Apicomplexa 1. Explain the distinctive features of Organisms in the phylum Apicomplexa the phylum Zoomastigina. differ from other groups by the following features: 2. Describe the structure of a a) They have a plastid called apicoplast, Trypanosoma. which is used for piercing host cells. 3. Normally, areas infested by tsetse flies are not suitable for human b) They reproduce asexually by settlement. Justify. schizogony in the human body and 117 BIOLOGY FORM 5 KIWANDANI.indd 117 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools sexually by sporogony in the mosquito. GOFVOERRNONMLEINNTE PURSOEPOENRLTYYLife cycle of Plasmodium c) They change their shapes depending The parasite in the form of sporozoites enters the blood stream of the human on the host it inhabits. For instance, being after a mosquito bite. It then travels plasmodium is sickle shaped in to the liver and invades it (Figure 3.15). salivary glands of mosquito, while it is The sporozoites grow, divide and produce amoeboid in liver cells of human. many haploid forms called merozoites or schizozoites in liver cells. The merozoites Structure of Plasmodium in the liver cells exit and re-enter blood The Plasmodium is oval shaped, and stream, where red blood cells are invaded. lacks contractile vacuoles and locomotory The merozoites multiply in the red blood organs. The apical end is a bridged cone- cells by asexual reproduction. In the red shaped projection demarcated by the polar blood cells, they develop into schizonts rings. A single mitochondrion is generally (feeding stage), which rupture the cells, present at the posterior end and the Golgi releasing newly formed merozoites which apparatus is unremarkable. Just beneath then invade other red blood cells. Some the inner membrane, there is a row of of the merozoites in infected blood cells, microtubules which originate from the leave a cycle of asexual replication. polar end of the apical end and continue to Instead of replicating, the merozoites the posterior end. Attached to the nucleus, in these cells develop into sexual forms there is an endoplasmic reticulum, a of the parasite called male and female network of membranous tubules within gametocytes. The cycle in mosquito the cytoplasm (Figure 3.14). Additionally, starts when the mosquito bites an infected there are the rhoptries, which are the human and ingests gametocytes. The male specialized secretory organelles. and female gametes fuse to form diploid zygote, which develops into moving Golgi apparatus ookinete. The ookinete burrows in the Nucleus midgut wall of mosquito, forming oocyst Endoplasmic reticulum on the other side. Growth and division of each oocyst produce numerous active Mitochondrion haploid forms called sporozoites. After 8 to 15 days (depending on the species), the Rhoptries oocyst bursts, thus releasing sporozoites into the body cavity of the mosquito, Microtubules from where they travel to, and invade the mosquito salivary glands. The cycle Figure 3.14 Structure of a Plasmodium of human infection re-starts when the mosquito taking a blood meal injects the sporozoites from its salivary glands into the human blood stream. 118 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 118 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Sporozoites to Hepatic cell salivary gland Merozoites Mature liver schizont Oocyst Erythrocyte Mosquito Ruptured Erythrocytic schizont midgut erythrocyte Zygote Macrogamete Microgamete Gametocyte Figure 3.15 The life cycle of a Plasmodium Adaptations of Plasmodium to its mode GOFVOERRNONMLEINNTE PURSOEPOENRLTYY blood, mosquito’s crop, haemocoel and of life salivary glands assures their existence Plasmodium, a parasite that causes malaria in the mentioned parts. invades the human red blood cells as an e) They have gametocytes which can resist essential step of its complex life cycle; it mosquito’s digestive enzymes, and they has the following adaptive features to its have adapted to high reproductive rate mode of life: by schizogony in liver cells, repeated schizogony in red blood cells, and a) Presence of a well developed chemotactic sporogony in the mosquito salivary responses which enable them ﬁnd glands, to ensure their survival. their way to the liver cells, then to the human red blood cells, gut epithelium, Exercise 3.5 and eventually, to the salivary glands of mosquitoes. 1. Distinguish between Apicomplexa and other protoctists. b) They have enzymes which enable them to penetrate through the host cells such 2. Describe the reproductive cycle of as liver and red blood cells of human a Plasmodium. as well as crop and salivary glands of mosquitoes. 3. Plasmodium is able to survive in its two different hosts. Justify. c) Plasmodium has an extremely simple structure, which enhances its sheltered life within the bodies of the two hosts. d) The ability to adjust their osmotic pressure in relation to the mammalian 119 BIOLOGY FORM 5 KIWANDANI.indd 119 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Phylum Euglenophyta GOFVOERRNONMLEINNTE PURSOEPOENRLTYYDistinctive features of phylum This phylum comprises of unicellular aquatic Euglenophyta algae, most of them live in freshwater; Members of the phylum Euglenophyta many possess flagella and are motile. The are distinguished from other phyla by the outer part of the cell consists of firm but following features: flexible layer called a pellicle or periplast, a) They have pyrenoids for storage of which cannot properly be considered a cell wall. Some euglenoids contain chloroplasts starch. that contain chlorophyll 'a' and 'b'; the b) They have eye spot (photoreceptor) photosynthetic pigments, as in the phylum chlorophyta. Others are heterotrophic and for detection of light intensity. can ingest or absorb their food. Food is c) They possess both plant and animal stored as paramylon. Reproduction takes place by longitudinal cell division. The characteristics (Figure 3.16). Plant most common organism in this phylum is characteristics include; presence of photosynthetic protozoan such as Euglena, chloroplasts containing chlorophyll, usually found in water bodies like ponds. pyrenoids, and utilization of nitrites or ammonia as sources of nitrogen. General characteristics of phylum Animal characteristics include; Euglenophyta possession of myonemes (muscle- like a) They have chloroplasts which contain strands), and ﬂagella for locomotion (euglenoid movement), utilization of chlorophyll for photosynthesis. amino acids, peptones or polypeptide as a source of nitrogen, presence of b) Most of them are found in fresh water; gullet with sphincter and reservoir for only few are marine dwellers. ingestion of food. c) They are protected by pellicle which Flagellum surrounds the cytoplasm, since they Eye spot lack cell wall. This enables the cells to change shape because they move Reservoir around by euglenoid movement by the Contractile aid of myonemes. vacuole d) They have two ﬂagella. One of them Chloroplast is short, while the other is long; these Nucleus arise from the bottom of a reservoir. Pellicle e) They have eye spot (photoreceptor) for detection of light intensity. Figure 3.16 Structure of the Euglena f) They have pyrenoids for storage of starch. g) They sometimes feed heterotrophically by using the gullet. 120 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 120 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Adaptations of Euglena GOFVOERRNONMLEINNTE PURSOEPOENRLTYYoccur as saprotrophs; living on decayed Euglena is able to survive freely in its matter or parasites living on higher environment due to presence of the plants and can be aquatic, terrestrial or following adaptive features: amphibious. Oomycetes play an important a) It has chloroplast which contains role in the decomposition and recycling of decaying matter. Members of this chlorophyll for photosynthesis. phylum are fungi-like protoctists such as b) It sometimes behaves as heterotroph Phytophthora, Puccinia and Pythium. due to possession of a gullet with General characteristics of phylum sphincter and reservoir. Oomycota c) It can swim using ﬂagella. a) They are filamentous protoctists d) It has a ﬂexible pellicle for maintenance of shape and aiding in euglenoid which must absorb their food from movement. the surrounding water or soil, or may e) It possesses contractile vacuole for invade the body of another organism osmoregulation. to feed. f) It has a high (rapid) rate of multiplication during favorable conditions and forms b) They are mostly parasites of plants, cysts under unfavorable conditions to example Phytophthora infestans ensure survival. which causes serious diseases such as g) It has a photoreceptor for detection of potato blight disease. light conditions. c) They reproduce sexually by oogamy Exercise 3.6 in which male and female gametes fuse to form an oospore. 1. Euglena is believed to be the origin of both plants and animals. d) The general body is organised into Explain. mycelia with aseptate or coenocytic hyphae. 2. Draw a well labelled diagram of Euglena. e) They have cell walls made up of cellulose. 3. Explain the adaptations of Euglena to its mode of life. f) They have a tubular structure called a haustorium used for absorption of Phylum Oomycota nutrients from the host (Figure 3.17). The phylum includes fungus-like organisms, which are also referred to as Distinctive features of phylum Oomycota “water molds”. Normally oomycetes may Oomycota can be distinguished from other members of the group by the following features: a) They have sporangia which produce zoospores. b) Zoospore have two flagella attached to a ventral groove; the anterior flagellum BIOLOGY FORM 5 KIWANDANI.indd 121 121 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools is a tinsel while the posterior one is a angles. The mycelium grows both intra- and whiplash type. intercellularly. During intercellular growth, it develops finger like haustoria inside the Structure of Phytophthora neighbouring host cells, which are normally The vegetative body of Phytophthora the mesophyll cells of the plant leaves. consists of mycelium which is abundantly The haustoria absorb nutrients from the branched where septa may develop in the leaf cells. The hyphae possess sporangium older parts and at the base of sex organs. which produces spores (Figure 3.17). The mycelium branches arise at right Haustorium Leaf mesophyll cell Intercellular hyphae Lower epidermis Sporangiophore Guard cell Stoma GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Sporangium Figure 3.17 Structure of Phytophthora infestans, growing on an infected potato leaf Adaptations of Phytophthora to its mode c) It has haustoria with a large surface of life area for penetration into the plant cells and absorption of nutrients from them. The Phytophthora have the following adaptations to their mode of life: d) The haustoria secrete enzymes which a) Formation of cysts during unfavourable help the parasite to penetrate its host cell. conditions ensures its survival. e) It has spores which withstand the b) Ability to reproduce both sexually and adverse conditions, such that, under asexually, with a high reproductive favourable conditions, they germinate output, increases its chances of to Phytophthora infestans. survival. 122 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 122 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Exercise 3.7 GOFVOERRNONMLEINNTE PURSOEPOENRLTYYChlorophytes are heterogeneous in their pigmentation, shapes, and size. They range 1. Outline the general characteristics of from microscopic, simple and unicellular Phytophthora infestans. such as Chlorella and Chlamydomonas to giant multicellular macroalgae. Although 2. Why does Phytophthora infestans they resemble eukaryotic plants in many belong to kingdom Protoctista? ways, they have no true roots, stem or leaves and do not produce seeds. The simplest 3. Explain the effects of Phytophthora structure is unicellular, but they may exist infestans to plants and show how in colonies or in ﬁlaments of several distinct the spread of this parasite can be cells. Others may be multinucleated with controlled. interconnected cells that lack cross walls as in Volvox and Oedogonium respectively. Phylum Chlorophyta This section will focus on the characteristics Members of this phylum were formerly of chlorophytes, structure, and adaptations classiﬁed as plants. They include of Spirogyra. unicellular non motile alga (Chlorella and Acetabularia), a unicellular motile General characteristics of phylum alga (Chlamydomonas), ﬁlamentous alga Chlorophyta (Spirogyra) and a thalloid marine alga, a) They are adapted to aquatic (Ulva). In other classiﬁcation, chlorophytes are placed under kingdom plantae, since environments ranging from fresh to they are more phylogenetically related to marine water, for example, their sexual plants. They are regarded as ancestors of reproduction relies on water as they plants, because they have photosynthetic produce motile sperms which have to pigments such as chlorophyll 'a', 'b' and 'β' move in water medium to fertilise the carotenoids as well as xanthophylls, which egg. are characteristics of plants. Additionally, they possess photosynthetic apparatus called b) They are photoautotrophs and have pyrenoid for condensation of glucose to chlorophyll 'a' and 'b' and other starch, which is the same as photosynthetic photosynthetic pigments such as product in plants. Under this phylum there carotenoids used in photosynthesis. are important species of high economic importance including sources of agar and c) They have cell walls made up of phycocolloids, which are widely used in cellulose. textile, pharmaceutical, and food industries. Chlorophytes are primarily aquatic, and are d) They store carbohydrates in the form the primary source of energy and oxygen of starch. to marine heterotrophs. Few are found in special habitats in terrestrial environments. e) They possess large vacuole for osmoregulation. f) They occur in a great range of sizes and forms, including unicellular, ﬁlamentous, colonial and thalloid forms. 123 BIOLOGY FORM 5 KIWANDANI.indd 123 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools g) They reproduce both sexually and GOFVOERRNONMLEINNTE PURSOEPOENRLTYYDistinctive features of phylum asexually; sexual reproduction involves Chlorophyta specialised cells called sporocytes Chlorophytes are distinguished from other which undergo meiosis to produce species of Protoctists by the following haploid motile or ﬂagellated cells called features zoospores. These grow mitotically to a) They have spiral chloroplasts with form a gamete producing body called gametophyte, capable of producing pyrenoids. either male or female reproductive cells (gametes). Female gametes b) They have central suspended nucleus can be either larger than male ones with cytoplasmic strands. (anisogamous) or similar (isogamous) morphologically. Female and male c) They show an isomorphic and gametes are ﬂagellated, they can swim haplontic alternation of generations. and unite to form a diploid zygote which settles and grows mitotically to form a Sturcture of Spirogyra multicellular body called sporophyte Spirogyra is a genus of filamentous green which can again produce sporocytes. algae which have helical or spirally The gametes, if not fertilised, lose their arranged chloroplast as a characteristic ﬂagella and grow into a new gamete- feature of this genus.They have thin strands producing body. Asexual reproduction of cytoplasm in which the prominent occurs by vegetative fragmentation nucleus is suspended, and their spiral where individual cell or short chains chloroplasts embedded in the cytoplasm of cells separated from the main body bear the structure called pyrenoid for starch are capable of growing into a new body. storage. The cell wall contains cellulose at the inner layer, and the outer layer h) Life cycle of chlorophytes is diverse. contains pectin, which is responsible for For instance, Ulva shows an the slippery surface of algae. Surrounding isomorphic alternation of generations the cell wall, there is mucilage, which in which sporocyte-producing body thickens the cell membrane, store water called sporophyte generation is and food. Moreover, Spirogyra has long, morphologically identical to gamete- unbranched filaments with cylindrical producing body called gametophyte cells that are joined end to end. Each cell generation. Ulothrix shows haplontic has a central vacuole. The cells are long life cycle, in which sporophyte and thin filaments, and sometimes these and gametophyte generation are filaments develop root-like structures for morphologically different. attachment to the substrate (Figure 3.18). 124 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 124 10/10/2019 14:06

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Cell membrane FOR ONLINE USE ONLY Cell wall DO NOT DUPLICATE Pyrenoid Comparative studies of natural groups of organisms Cytoplasm Procedure Mucilage Nucleus Vacuole GOFVOERRNONMLEINNTE PURSOEPOENRLTYYa) Collect fresh Spirogyra from fresh Chloroplast water ponds or slow moving water Figure 3.18 Structure of a Spirogyra streams, and put it into a watch glass. Adaptations of Spirogyra to its mode of life b) Add a drop of water on a clean slide Spirogyra is able to live and thrive in its using a dropper, and using an ofﬁce environment due to the following adaptive pin pick a few threads of Spirogyra features: and mount them on the slide. a) It has pyrenoids for storage of starch. b) It has a large vacuole for osmo c) Separate the strands using a pin to remain with a few threads. Cover regulation. your specimen with a coverslip. c) It has chlorophyll 'a' and 'b' for d) Place the slide under a light photosynthesis, hence it is an autotroph. microscope for observation. d) It has mucilage layer to protect it from e) Notice the wide variety of desiccation and infection. chloroplast types and the small, e) It has a cellulose cell wall for strength round, colorless pyrenoids on some or all the larger chloroplasts. and protection. f) Based on your observation, draw Activity 3.2 Observation of Spirogyra and label the diagram of Spirogyra under a light microscope showing the pyrenoids, spiral chloroplast, mucilage, cytoplasm, Materials and nucleus. Fresh Spirogyra, microscope, slides, slide cover, dropper, office pin, watch Exercise 3.8 glass, and beaker containing water. 1. Draw and describe the structure of Spirogyra. 2. Describe ways in which Spirogyra is adapted to its mode of life. 3. Explain the role of Spirogyra in oxygen balance in fresh water habitat. 4. With examples, explain why taxonomists sometimes regard Spirogyra as a plant. BIOLOGY FORM 5 KIWANDANI.indd 125 125 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Economic importance of kingdom GOFVOERRNONMLEINNTE PURSOEPOENRLTYYf) Algae species produces oxygen useful Protoctista for aerobic respiration, particularly Protoctista are mostly aquatic organisms in the aquatic environment which is found in sea, fresh water and moist soil. utilised by other aquatic organisms. Many are also found in the form of plankton and some live in the bodies of g) Some are used in agriculture as good animals as parasites. Some members of sources or fertilizer. For example, the kingdom Protoctista plays an essential liquid extracts from the brown algae role in the ecosystem that can benefit supply potassium and trace elements humans and other creatures. However, such as zinc. some members are important pathogens and can bring harm to living organisms. In h) Some algae serve as a source of agar, some cases, Protoctista might be a source used in the pharmaceutical industry of pollution in lakes and coastal shores. in preparation of culture media for growing microbes, such as bacteria Advantages of kingdom Protoctista and fungi. Protoctists have the following economic importance: i) Some protoctists such as algae are a) Algae are edible and nutritious to milled or ground to obtain powder which is used as a thickener, binder, humans and other animals. Some gelling or stabilising agents in the species are cultivated and harvested manufacture of various products such for consumption by human being. Red as cosmetics, paints, tooth paste, and algae are rich in vitamins and minerals. ice cream. Carrageenan, a polysaccharide extracted from red algae, is used as j) Some protoctists such as Entamoeba thick agent in ice cream and other coli; a non-pathogenic species of genus foods. Entamoeba, can exist as a commensal parasite in the human gastrointestinal b) Giant kelp forests (Large brown algae) tract and feed on pathogenic bacteria. are rich ecosystems, providing food and shelter for many organisms. Disadvantages of kingdom Protoctista a) They cause pollution; the red algae c) Trichonymphs are flagellates that live in the intestines of termites. These cause water pollution called the algal protozoans break down cellulose in bloom which may hinder boating and wood into carbohydrates that termites recreation. can digest. b) They cause diseases to human beings; d) Algae and Euglena are primary for instance, Amoebiasis is caused producers in aquatic ecosystems. Most by Entamoeba histolytica, malaria is species are primary sources of food for caused by Plasmodium species (like aquatic organisms such as ﬁshes and Plasmodium malariae, Plasmodium zooplanktons. vivax, and Plasmodium falciparum). e) Some Protoctists are used as ﬁsh baits. c) Some members of the kingdom cause diseases to animals; for 126 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 126 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms example Trypanosoma brucei causes parasitic or saprophytic. Fungi produce Trypanosomiasis (sleeping sickness) extracellular enzymes which digest almost to humans, Trypanosoma vivax causes everything including protein and starch. The Nagana disease in cattle. end products of digestion are absorbed by special structures called haustoria (plural) d) Some members cause diseases or haustorium (singular). Some fungi are to plants. A good example is parasites, as they obtain nutrients directly Phytophthora infectans which infect from other living organisms such as plants tomato and potato plants. and animals. They have cell walls made up of chitin, unlike plant cell walls which are 3. 5 Kingdom Fungi made up of cellulose. Organisms under this Organisms belonging to this kingdom are kingdom store carbohydrate in the form of those originally placed in kingdom Plantae glycogen like animals, but not starch, as in under the two kingdom classiﬁcation chlorophytes and plants. system. The early placement of fungi under kingdom Plantae was due to the They have a variety of shapes and sizes morphological appearance of some fungi, extending from microscopic to macroscopic. particularly the mushrooms which resemble Sexual reproduction in fungi involves two plants. The microscopic fungi were not haploid nuclei of compatible mating hyphae yet known by then, since the microscopes strains that unite to form a zygote which were not yet invented. It was discovered later grows into a new fungal body. Asexual later that fungi differ from plants in several reproduction is accomplished by production ways, hence they were placed in their own of asexual spore which, under favorable kingdom, and most of them had economic conditions, germinates and grows to form importance. Through mycology (a study of new haploid fungal hyphae. Examples fungi), over 100,000 species of Fungi have of organisms in this kingdom include been described. It is estimated that there are mushrooms, yeasts, Penicillium, bread over 1million species of Fungi waiting for mould, and toadstool. identiﬁcation. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Fungi are eukaryotic, unicellular or Position of kingdom Fungi multicellular multinucleate organisms, As explained earlier, the position of fungi in made up of a mass of branching and delicate classiﬁcation was one of the controversial thread-like structures called hyphae, which arguments. It was previously not clear collectively constitute fungal bodies called whether fungi should be classiﬁed as an mycelium. Depending on the species, some animal or as a plant, because they have hyphae may have cross walls called septa, some features in common for both plant dividing hyphae into many cells with one or and animal groups. more nuclei. In some species, the cytoplasm is continuous without cross walls. Fungi Similarities between fungi and animals are thallophytes, lacking chlorophyll, Similar to animals, fungi have the hence nutrition in these organisms is either following features: BIOLOGY FORM 5 KIWANDANI.indd 127 127 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools a) They have chitin as a structural GOFVOERRNONMLEINNTE PURSOEPOENRLTYYPhylum Zygomycota carbohydrate in the cell wall. This is Fungi belonging to this phylum produce a feature typical of animals such as asexual resting spore called zygospore, arthropods; example insects. which is produced when two opposite mating strains come close together and their haploid b) They store carbohydrates in the form nuclei unite. The zygospores are resistant of glycogen. to breakage but they are light, hence they can be dispersed by wind and water. The c) They are heterotrophs. Thus, they structure of zygospore is capable of keeping cannot manufacture their own food the fungus over a long period of dormancy. since they are either saprophytes or Cells within the zygospore undergo meiosis parasites. The parasitic fungi can be to form haploid spores and when released facultative or obligate. in favorable conditions they germinate to form a new hyphae or mycelium. This Similarities between fungi and plants phylum comprises of saprophytic fungi Similar to plants, fungi have the following such as Mucor and Rhizopus stolonifer; a features: common bread mould. Zygomycetes can also reproduce asexually by spores born a) Their cells have cell wall. out of sporangia. Some zygomycetes are parasites in plants, insects, and animals. b) Some fungi have vegetative bodies that are superﬁcially differentiated General characteristics of phylum into shoot-like and root-like systems. Zygomycota a) They produce a characteristic sexual c) Most fungi’s growth is restricted to apical cells. resting spore called zygospore. d) They are non-motile. b) They are eukaryotic organisms, with aseptate hyphae that have e) They reproduce sexually by formation well developed branching mycelia. of spores such as ascospore in yeast Aseptate means without septa or and basidiospores in mushrooms. Some cross walls, and are sometimes called fungi reproduce asexually by producing coenocytic. spores such as sporangiospore. c) They undergo both sexual and asexual f) They lack centrioles in their cells. reproduction. Sexual reproduction is by conjugation; this involves fusion Fungi are heterogeneous kingdom of two haploid nuclei from the two consisting of several phyla. However, mating hyphae or strains to produce despite many ways in which fungal zygospores. Asexual reproduction organisms are distinct, the major criterion occurs via haploid spores released used in grouping them into their respective from sporangia. groups is their reproductive structures. Within the kingdom Fungi there are three d) They are saprophytes since they feed phyla, namely; Zygomycota, Ascomycota, on dead decaying organic matter by and Basidiomycota. 128 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 128 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms undergoing extracellular digestion. c) They undergo sexual reproduction However, some zygomycetes are involving two gametangia to produce parasitic on plants, animals, and a resting spore known as zygospore. insects. Structure of Rhizopus e) Their hyphae have three distinct parts, The body of Rhizopus consists of branching namely sporangiophore, stolon, and mycelia composed of three types of hyphae; rhizoids. stolons, rhizoids, and normally branching sporangiophores (a stalk that arises from the Distinctive features of phylum vegetative hypha), and sporangia (asexual Zygomycota spore-forming structures) arise from stolons Members of the phylum Zygomycota have opposite to rhizoids (Figure 3.19). Stolons the following features that differentiate are the horizontal creeping hyphae that them from other phyla: interconnect the upright growing hyphae. The sporangiospores are produced inside a) They have aseptate hyphae which the spherical structure called sporangium lack cross walls between adjacent which is supported by the columella. cells. They are therefore coenocytic in structure. b) Their cytoplasm is continuous and multinucleate. Sporangium GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Sporangiospores Collumela Apophysis Sporangiophore Mycellium Stolon Rhizoids Figure 3.19 Structure of a Rhizopus BIOLOGY FORM 5 KIWANDANI.indd 129 129 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Adaptations of Rhizopus to their mode Activity 3.3 Observation of Rhizopus of life Members of Rhizopus are saprophytic, and Materials can grow and survive on various organic Bread, petri or dissecting dishes, hand substrates including bread, mature fruits, lens or light microscope, and slides. and vegetables. They are able to acclimatize themselves to their environment due to the Procedure presence of the following adaptive features: a) Take one slice of bread in a dish. b) Leave it exposed on a bench for ﬁve a) Pressure in columella makes the sporangium burst to release haploid to seven days, until black hairy-like spores. Each individual spore upon structures appear on the slice. falling on conducive environment can c) Use a hand lens or a light microscope germinate to a new hyphae body. These to observe the specimen on the slice. asexual spores are produced in large Carefully observe the upright hyphae quantities; even in harsh conditions with black spherical structures at when the environment is dry, they ensure their tips. a quick spread of the species. b) They have rhizoids for anchorage on the Questions substrate and absorption of nutrients. 1. Draw a well labelled diagram of c) Their hyphae show chemotropism; in the observed specimen. response to the digested food substances. 2. State the functions of each d) They produce thick-walled resistant, structure in the diagram you have dormant zygospore. This enables the drawn. spores to withstand unfavourable and adverse conditions. 3. Identify the specimen by its common name. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY e) The wall of sporangium is so brittle that Phylum Ascomycota it easily breaks off to release the spores These are ascocarp forming fungi such as and ensure their multiplication. yeasts (Saccharomyces), Aspergillus, and Penicillium. The ascocarp are cup-like f) Under asexual reproduction, they structures containing small sacs which produce large number of spores to produce spores known as ascospores, ensure survival of the species. resulting from sexual reproduction. Besides sexual spores, ascomycetes produce asexual g) The spores are small and very light, spores called conidia, which develop at and the sporangia are raised up to aid the tips of specialised hyphae called dispersal of spores by wind. conidiophores. This is the most diverse group with about 30,000 described species. 130 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 130 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Organisms in this phylum form many c) They have a fruiting body containing colourful cup shaped growths called morels several sac-like structures called asci on decaying logs of trees, fruits, crops, (singular ascus) which produce haploid and foods. Most ascomycetes have highly spores called ascospores. These spores branched hyphae. They are thus mycelia can germinate to form new haploid except yeasts, which are unicellular. hyphae. Yeast shows a number of differences in GOFVOERRNONMLEINNTE PURSOEPOENRLTYYd) They possess conidia which are morphology, reproduction, and cell structure, found at the apex of hyphae called when compared to other ascomycetes. conidiophores which produce millions Besides lacking hyphae, yeast does not of resistant spores used in asexual have ascocarp, hence they are sometimes reproduction. referred to as hemiascomycetes; meaning “half ascomycetes,” to distinguish them e) Sexual reproduction is accomplished by from euascomycetes or true ascomycetes mating of compatible hyphae forming a that have hyphae and ascocarp. They dikaryotic hyphae; that is hyphae with extracellularly secrete and produce enzymes two nuclei in their cell. The nuclei will such as protease (protein digesting enzymes) fuse only after the formation of ascus. and cellulase (cellulose digesting enzyme). The diploid nucleus will later undergo These kinds of enzymes make this group meiotic and mitotic divisions to form very destructive to animals, and plants. ascospores. However, some ascomycetes such as yeast are widely used in brewing industries for f) Some ascomycetes such as yeasts are production of alcohol through fermentation, unicellular and reproduce asexually by while others are used in bakery and textile budding (new cells form on the surface industries. of the old ones). General characteristics of phylum Distinctive features of phylum Ascomycota Ascomycota The following are the distinctive features a) Their mycelium is made up of tightly of the phylum Ascomycota: woven septate hyphae except yeasts, which are unicellular. a) They have specialised spore producing structures called ascocarps. b) They are heterotrophic saprophytes; in contrast to other members are parasites. b) They reproduce asexually using conidia For example, Candida albicans are formed on the tips of conidiophores; in infectious ascomycetes which cause some members asexual reproduction is mouth thrush. In plants, they are through budding. responsible for powdery mildew which infects cereal grains. c) Some are unicellular heterotrophs, and lack typical hyphae, for example Saccharomyces. BIOLOGY FORM 5 KIWANDANI.indd 131 131 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Structure of Saccharomyces apparatus, vacuoles and ribosomes which are found within the cytoplasm (Figure Saccharomyces are flat, smooth, and 3.20). The cell walls of Saccharomyces moist. They are unicellular, and they lack are elastic, determine the shape of the hypha. They have eukaryotic organelles cell, and provide osmotic and physical such as mitochondria, ribosomes, Golgi protection. Cytoplasm Scar of attachment Cell wall Nucleus to parent cell Vacuole Cytoplasm Cell membrane New cells attached Chitin cell wall to parent cell Nucleus Mitochondrion Food reserves such as glucose and oil Vacuole (a) (b) Figure 3.20 Structure of Saccharomyces (a) a single cell (b) a budding cell Adaptations of Saccharomyces to its GOFVOERRNONMLEINNTE PURSOEPOENRLTYYe) Spores’ ability to remain dormant in mode of life unfavourable conditions ensures their existence. Saccharomyces species have the following adaptive features that enable them suit to f) Some Saccharomyces are facultative their mode of life: anaerobes. They have an ability to respire anaerobically or aerobically, a) They store carbohydrates in the form which ensures survival in both aerobic of glycogen for use during shortage of and anaerobic conditions. food supply. Activity 3.4 Observation of yeast cells b) They have permeable cell walls to allow under light microscope entry of nutrients that are obtained from external digestion. Thus, they Materials can absorb simple monosaccharides Yeast cells, water, beaker, stirring rod, and vitamins directly from their dropper, slides, and microscope. environment. Procedure c) They secrete extracellular enzymes a) Put some yeast in a beaker contain- such as sucrase and cellulase for digestion of carbohydrate, and ing small amount of water, then stir protease for digestion of protein. to get a suspension. d) They have high reproductive rate through budding, to produce new cells hence increase in number. 132 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 132 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms b) Add a drop of suspension using a GOFVOERRNONMLEINNTE PURSOEPOENRLTYYcereals, among other plant species. dropper, put it on a clean slide. Saprophytic basidiomycetes include the edible mushroom Agaricus campestris while c) Observe the specimen under a light others like Amanita virosa are poisonous. microscope. In addition, symbiotic association called mycorrhizae are common between Questions basidiomycetes and roots of higher plants. 1. Draw and label a diagram of the speci- This phylum got its name due to the men under observation. presence of a characteristic club shaped structure known as a basidium (plural 2. Classify yeast to phylum level. basidia) from which basidiospores are produced. Basidiospores are characteristic Exercise 3.9 sexual reproductive structures of basidiomycetes. Individual basidia 1. In which ways are Ascomycetes are fused to form basidiocarp, which similar to and yet different from is the most spectacular and familiar Zygomycetes? stage of most basidiomycetes such as mushrooms. Species in this phylum have 2. With examples, explain why yeast septate hyphae with distinct small pores. (Saccharomyces cerevisiae) is not Haploid hyphae of basidiomycetes like a good representative of phylum mushrooms fuse to form a dikaryotic Ascomyota, but it is still classiﬁed mycelium called stipe, growing upright under the same phylum. and culminate into an umbrella-like cap called basidiocarp in which the hyphae 3. Describe the adaptations of yeast to are tightly packed. The hyphae tips are its mode of life. swollen forming a characteristic club-like structure (basidia) in which the dikaryotic 4. In which ways are Ascomycetes nuclei fuse and later meiotically divide to economically important in our daily form four haploid basidiospores. These life? are ejected out of the basidia through four ﬁngerlike projections at the tip of each Phylum Basidiomycota basidium. Each spore can germinate to This phylum consists of basidiomycetes form new haploid hyphae. Evolutionarily, which contains about 25,000 species. It basidiomycetes are more closely related to is the most common and widely known ascomycetes than to the other phyla. The phylum of kingdom fungi. Organisms in basidia function in a similar way as ascus. this kingdom include mushrooms, bracket fungi, puffballs, smuts, rust and toadstools. General characteristics of phylum Some basidiomycetes are parasites, while Basidiomycota others are saprophytes. Bracket fungi cause a) They have a characteristic cap-like damage to plants. For example Puccinia graminis causes wheat rust; smuts infest structure called basidiocarp, which 133 BIOLOGY FORM 5 KIWANDANI.indd 133 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools contains numerous club-like structures b) Hyphae have septa with distinctive known as basidia from which pores. haploid, sexually reproduced spores (basidiospores) are produced. Structure of Agaricus Members of Agaricus consist of a stalked b) Sexual reproduction in most fruiting body with pileus on its top (a basidiomycetes results into the fleshy cap), which in turn bears numerous formation of dikaryotic hyphae radially arranged gills on its basement. The vegetative mushroom body is also called c) They have septate hyphae. mycelium. The underground hyphae have minute threads called rhizoids, as a group d) Some basidiomycetes are saprophytes are also known as mycelium threads. They while others are parasites. are located underneath the fruiting body, and they store and supply the nutrients to Distinctive features of phylum the mushroom. These structures anchor Basidiomycota the mushroom to the substrate, while the Members of phylum Basidiomycota stipe (stem) make it stand upright (Figure possess some features which differentiate 3.21). Cup (volva) is found below the them from the other phyla. These features stem while the ring (annulus) surrounds include: the stem. a) Basidium formed at the tips of hyphae is a characteristic sexual spore producing structure in which union of dikaryotic nuclei occurs, followed by meiosis to produce haploid basidiospores. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Cap (pileus) Ring (annulus) Gills (lamellae) Cup (volva) Stem (stipe) Mycelium thread (rhizoid) Figure 3.21 Structure of an Agaricus 134 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 134 10/10/2019 14:06

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Adaptations of Agaricus to its GOFVOERRNONMLEINNTE PURSOEPOENRLTYY FOR ONLINE USE ONLY saprophytic mode of life DO NOT DUPLICATE Comparative studies of natural groups of organisms Members of the genus Agaricus are adapted to saprophytic mode of life. The b) Observe the specimen using a hand adaptations of Agaricus to its mode of life lens or under a low power of the are as follows: light microscope. a) They have ability to secrete a variety c) Take note of the gills radiating out of hydrolytic enzymes for extracellular from the stalk (stipe) like the spokes digestion of various organic matters. of the wheel. b) They possess rhizomorphs which are d) Examine part of the gill under high responsible for absorption of nutrients power and note the presence of tiny from the substratum. club-shaped basidia lining one side of the gill. Sometimes, small ﬁnger- c) They have stipe for upward transport like projections at the tips of basidia of nutrients to reach cap cells. are visible in which black spots ‘basidiospores’ are found. d) They store carbohydrates in the form of glycogen for use during shortage of Questions food supply. 1. Draw and label the structure e) They are able to grow and survive on under observation. different substrata to increase chances of survival. 2. Outline the adaptive features of the specimen to its mode of life. f) They produce large numbers of very tiny and resistant basidiospores which Safety precaution are easily dispersed and resistant to harsh conditions. Some mushroom species are poisonous when consumed, so be careful when g) They have pileus or cap made up dealing with mushrooms. of closely packed hyphae to confer protection to the gills. Activity 3.5 Observation of a mushroom Economic importance of Fungi Although some fungal species are Materials pathogenic that may cause disease in plants Fresh or preserved mushroom, hand lens and animals. Most fungi are saprophytic or light microscope, petri dish, and a and not pathogenic to plants and animals pair of gloves. are important to human life at many levels. Fungi play an important role in medical Procedure industry, agriculture, research and in the a) Wear a pair of gloves on your hands ecosystem. and collect a fresh or preserved specimen of mushroom and put it in a petri dish. BIOLOGY FORM 5 KIWANDANI.indd 135 135 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Advantages of kingdom Fungi GOFVOERRNONMLEINNTE PURSOEPOENRLTYY which is used in many aspects of cell biology and biochemistry to a) Some members of the kingdom elucidate various molecular events involved in epigenesis, cell fusion and Fungi such as Agaricus species are development. source of food to human being. For example Agaricus bisporus are the i) Fungi, particularly the genetically most important edible mushroom engineered ones, can be used in commercially cultivated world-wide. bioremediation to degrade some They are rich source of nutrients such pollutants in the environment. as proteins, carbohydrates, lipids, They are useful in detoxiﬁcation of minerals, fibres, and vitamins. They poisonous substances such as cyanide can be used as nutritional supplements which is removed from cassava by to humans. They can also be used for medical therapy: as antimicrobial, moulds, such as Rhizopus. anticancer, and antioxidant roles. Other animals such as ants and millipedes j) Saprophytic fungi are used as feed on fungi. scavengers in sewage treatment to clean the environment. Some fungi b) Yeasts are used in fermentation to with the ability to digest cellulose are produce alcohol in brewing industries. used in waste papers’ disposal. c) Fungi are important in production of k) Some fungi are grown for commercial organic acids and organic solvents production in order to extract pigments such as acetic acid, lactic acid, amyl, which are used in the preparation of isoamyl alcohol, and glycerol. various dye materials. d) Saprophytic fungal communities are l) Some fungi can be used in biological important in the soil as they decompose control as they obtain their food dead organic matter and recycle by destroying other organisms like nutrients locked in dead plants and amoeba, rotifers, and nematodes. In animals thereby improving soil fertility. addition, entomogenous fungi are parasitic on insects and other small e) Some members of the kingdom anthropods such as mites and spiders. Fungi are used in producing medicine (antibiotics) such as penicillin from m) They are involved in symbiotic Penicillium sp., and ephedrine extracted mycorrhizal association with roots from yeast. of vascular plants in which they increase the plant roots’ surface area f) They are sources of important hormones for absorption of nutrients of nutrients, such as gibberellins obtained from while, in turn, the fungi get some of Gibberella fujikuroi. This hormone the photosynthesized food from plants. regulates vegetative and fruit growth in plants. n) They are used in biological studies as specimens, for instance Rhizopus, g) They are important in cheese industry Saccharamyces, and Agaricus. and in production of some enzymes such as amylase. Disadvantages of kingdom Fungi a) Some fungi produce toxins that can h) They are used in research such as biochemical genetics; a good example affect plants and animals, for example is Neurospora crassa (ascomycetes) 136 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 136 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms some fungi are so poisonous that GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 4. Explain why the placement of when consumed by mammals they can fungi under the kingdoms Plantae cause death. An example of poisonous and Animalia was confusing early mushrooms is Amanita. taxonomists. b) Some fungi cause diseases, for example, 5. Brieﬂy explain why ascomycetes ringworms (dermatophytosis or tinea) and basidiomycetes are evolutionarily are fungal skin infection in animals and related. smuts in plants. 3.6 Kingdom Plantae c) Foods such as grains, tubers, and fruits Plants can be broadly deﬁned as can be destroyed by saprophytic fungi multicellular eukaryotic photoautotrophs. such as Mucor and Rhizopus if not well They contain chloroplasts which have stored. chlorophylls 'a' and 'b'. Some plants contain photosynthetic pigment called carotenoid d) Saprophytic fungi deteriorate organic which is used for photosynthesis. Their materials such as leather, natural cells have cell walls made up of cellulose fabrics, and damp timber, example and have large permanent vacuoles. Plants mold leather, mildew and wet rot fungi. store carbohydrates in the form of starch. They reproduce sexually by production of e) When accidentally consumed in food, spores and vary from primitive to advanced some fungal species affect the nervous plants. The most primitive plants such as system and may cause hallucinations, Bryophytes produce spores which are of example an invasive fungus called the same kind and size (homospores) and Cryptococcus may cause a serious the plants are termed homosporous. On the inflamation of brain and spinal cord, other hand the advanced plants, including a the condition known as cryptococcal few species of ferns and all seed producing meningitis. plants are heterosporous, as they produce two types of spores: micro and macro spores. f) Some fungi such as the Penicillium, Plants exhibit alternation of generations in which are used in pharmaceutical and which a haploid gamete producing phase cheese industries, cause various types called gametophyte generation alternate of allergic conditions to some people. with the diploid spore producing phase called sporophyte generation. Plants are Exercise 3.10 sessile, meaning that they have limited locomotion but show curvature movements. 1. With examples, explain how Their vegetative body is divided into root mycology and its application and shoot systems. can be an important step towards industrial revolution in Tanzania. 2. Give reasons to justify the position of fungi in their kingdom. 3. What is the single important factor considered in classifying fungi into different phyla? Give an example for each phylum. 137 BIOLOGY FORM 5 KIWANDANI.indd 137 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Plants are believed to have evolved from GOFVOERRNONMLEINNTE PURSOEPOENRLTYYto produce seeds, and ﬂower formation. an aquatic ancestor which was probably Among others, these features have led to the Ulotricales algae stocks. Life on land started classiﬁcation of plants into four divisions, about 0.5 billion years ago when the earliest namely Bryophyta, Filicinophyta (or plants started to establish their life on land. Pteridophyta), Coniferophyta (or Pinophyta) The earliest plants were very tiny and were and Angiospermophyta. not well differentiated in roots, stem, and leaves. In addition, they had no vascular 3.6.1 Division Bryophyta tissues. Water was absorbed to their bodies Bryophytes are the most primitive terrestrial by simple diffusion. They produced motile plants. They resemble the most advanced sperms which restricted their habitats to wet algae species in certain ways especially their areas or seasonally wet areas. dependence on water in sexual reproduction and lack of conducting tissues. Unlike algae, Early plants slowly adapted to terrestrial they form a zygote which is protected in habitat by developing features such as the female reproductive structure called cuticle to protect them from desiccation, archegonium that safeguards the zygote development of roots and vascular against physical damage and desiccation. system for water uptake and movement, Most bryophytes have poor vegetative and translocation of food. Furthermore, differentiation because they are thallose in sexual reproduction, fertilisation was (or thalloid). The lack of conducting tissues taking place inside the female reproductive (xylem and phloem) in bryophytes, unlike structure called archegonia, within which in other divisions of plants, is a challenge zygote development occurs. This was in terrestrial environments where water is important to protect the delicate zygote limited. from desiccation. The most advanced plants overcome dependence on water in However, water can simply be absorbed over reproduction by producing special tubes their surface as they have various structural called pollen tube to carry sperms to the features to ensure the absorption of water female reproductive organs for fertilisation. falling on their surface. For instance, their Plants can reproduce asexually in various leaf-like structures are overlapping, and ways, including through the use of gemmae have small warts on them to delay escaping as in bryophytes, and using various other water. In addition, they do not grow tall, types of vegetative reproduction such as hence, water can rise by capillarity, and fragmentation and cuttings. they also have rhizoids for anchorage and easy absorption of water and mineral salts Members of the kingdom Plantae are from the soil surface. Bryophytes include heterogeneous in many features. Among mosses, hornworts, and liverworts. key aspects used in the classiﬁcation of plants is alternation of generation. The Traditionally, bryophytes were classified features characterising each phase of into two classes, namely Musci and generation are: types of spores, spore Hepaticae. Members of class Musci include producing features, vascular tissue, ability moss plants (Funaria sp.), while members 138 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 138 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms of class Hepaticae include liverworts (PelliaGOFVOERRNONMLEINNTE PURSOEPOENRLTYYh) Asexual reproduction is by sp). A recent classiﬁcation splits bryophytes fragmentation in which a small part into three classes, namely Hepaticopsida can detach from the mother plant to (Liverworts), Bryopsida (Mosses), and form green multicellular reproductive Anthoceropsida (Hornworts). bodies of different shapes called gemmae. Gemmae is formed in gemma General characteristics of division cups on the leaf surfaces, stem apex Bryophyta or inside the cells. Each gemmae can a) They show alternation of generations germinate to form a new gametophyte upon falling on a suitable substrate. in which the haploid gametophyte generation is dominant over the diploid i) They contain photosynthetic pigments sporophyte generation. (chlorophyll) as that of higher plants. b) The sporophyte is attached on the Distinctive features of division gametophyte generation, and it depends Bryophyta upon it for support and nutrition. Bryophytes possess the following features which differentiate them from members c) The gametophyte generation is of other divisions: anchored by ﬁlamentous rhizoids which provide support and used for a) They lack conducting tissue such as absorption of water and mineral salts. xylem and phloem. d) They lack vascular tissue, meaning b) They do not possess true stem, that they have no xylem and phloem. leaves, and roots. They have rhizoids instead of roots and they also lack e) They have a thallus body which shows cuticle; therefore, absorption of water low level of differentiation; hence, and mineral salts in species such as they lack true leaves, stems, and roots. liverworts takes place over the whole surface of the plant by diffusion. f) They have a sporophyte generation, which produces homospores. Upon c) They have a dominant gametophyte landing on a conducive environment, generation, on which sporophyte the spores can germinate to form generation is attached and depends on the gametophyte generation on gametophyte for food and support. which male and female reproductive structures develop. They undergo d) They are homosporous and their sexual reproduction which involves haploid spores germinate into multicellular sex organs called a characteristic structure called antheridia (male sex organs) and protonema, which are ﬁlament of cells archegonia (female sex organs). that later grow to form gametophytes. g) They are found mainly in damp and shady environment because their sexual reproduction depends on water, which facilitates mobility of their sperms. BIOLOGY FORM 5 KIWANDANI.indd 139 139 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Structure of Funaria sp. water and mineral salts. The greenish part A mature Funaria plant is structurally of the plant (that is the stem-like structure erect, measuring only a few centimetres and leaf-like structure), and the rhizoids above the ground. It is clearly constitute a gametophyte body (Figure differentiated into stem-like and root-like 3.22). The sporophyte has a capsule which systems. The stem-like structure bears encloses the spores and their sex organs leaf-like structures that are arranged (antheridia and archegonia) which are spirally along it. At the base of the “stem” borne at the tips of stem-like structures. are tuft of adventitious rhizoids that are Funaria hygrometrica is the most common used for anchorage and absorption of moss species. Sporophyte (2n) Capsule Gametophyte (n) Annulus Peristome Spores Operculum (capsule lid) Calyptra Seta Leaves GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Main axis Rhizoids Figure 3.22 Structure of a Funaria Reproduction of Funaria on the surface. The sperms produced have A mature gametophyte of genus Funaria two ﬂagella (bi-ﬂagellate spermatozoids); consists of short stem-like structure in hence, they can swim towards the egg which antheridia and archegonia are (oogonium) located in the archegonium. borne at the tips of the male and female Fertilisation takes place inside the stems respectively. Sexual reproduction archegonium to form a diploid zygote. requires water which is an essential It keeps growing while still inside the medium for sperm swimming from the archegonium to form a stalk-like structure male gametangium (antheridium) to called seta which is a young sporophyte. female gametangium (archegonium). This structure later matures and produces Normally, when it rains, these small stem- capsule on its tip. This means the entire like structures become ﬂooded, saturated, sporophyte (seta and capsule) grows on swollen, and they burst to release sperms the gametophyte, where it is supported and 140 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 140 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms supplied with food. The capsule produces spores which, once released, can germinate to form another gametophyte. The cycle repeats over again (Figure 3.23). Sporangium Meiosis Leaf gametophyte Sporophyte (2n) Seta Spores (n) Gametophyte (n) Gametophyte Protonema (n) Gametophyte Embryo Antheridium Rhizoid (2n) sperm (n) Egg (n) Fertilization Sperm Archegonium Egg ArchegoniumGOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 3.23 The life cycle of a Funaria Activity 3.6 Observation of moss plant greenish part and a small stalk growing on it; bearing a small club- Materials like structure at the top. Moss plant, hand lens or light microscope, and petri dish. Questions 1. Draw a well labelled diagram of Procedure a) Collect fresh moss plants from damp what you have observed. areas, wet walls, or tree barks. 2. Compare your diagram with that b) Take a single moss plant and put it of Figure 3.22. on a petri dish. c) Observe the specimen using hand lens or light microscope. Note the BIOLOGY FORM 5 KIWANDANI.indd 141 141 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Adaptations of Funaria to its mode of Exercise 3.11 life Members of Funaria have the following 1. Brieﬂy explain how bryophytes adaptive features: have managed to overcome various challenges in terrestrial a) They have chlorophyllous “leaf-like habitats. structures” for photosynthesis. 2. Explain why bryophytes are b) They have limited heights to overcome regarded as amphibious plants. problems associated with lack of vascular tissues. Water and mineral 3. Outline the distinctive features of salts can move up by capillarity in division Bryophyta. their short stems. c) They possess rhizoids for anchorage GOFVOERRNONMLEINNTE PURSOEPOENRLTYY3.6.2 Division Filicinophyta on soil as well as absorption of water (Pteridophyta) and mineral salts. Members of division Filicinophyta are called pteridophytes. Examples of d) Male gametes, antherozoids, are pteridophytes include ferns. Pteridophytes biﬂagellate for swimming into inhabit damp shady environments, such archegonia. as on the ﬂoor of moist forests and river banks. About 1100 species of ferns are e) They produce small and light spores currently identiﬁed. Ferns are related to that are easily dispersed to allow bryophytes in several ways, indicating colonization of new areas. that they might have probably descended from bryophytes. For example sexual f) The spores are tolerant to long reproduction in pteridophytes depends on periods of unfavorable conditions water like in bryophytes. Moreover, like due to the presence of a thick wall bryophytes, the pteridophytes’ zygotes are with sporopollen in one of the major retained and develop inside the multicellular chemical component (polymers) on archegonium. However, unlike bryophytes, the outer wall of the spores. pteridophytes exhibit alternation of generation in which the sporophyte g) They have elongated seta to expose generation is dominant over gametophyte the capsule to air for easy dispersal of generation which is relatively reduced and spores. dependent on sporophyte. Ferns are also heterogenous in size and shape, ranging h) Archegonia secrete chemical from ﬁliform ferns to tree like ferns which attractants which attract antherozoids can grow to approximately 20 metres tall to swim towards the egg during and with broad leaves known as fronds. A fertilisation. fern tree called Cyathea manniana is very common in most parts of the eastern arch 142 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 142 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms mountain forests of Tanzania such as the or petiole. Characteristically, the young Udzungwa scarp forest reserve. This fern leaves show a tightly rolled structure can grow to a height of about 5 metres. called circinate leaves or croziers which Ferns have conducting tissues (xylem and later unroll to reveal fronds with a stalk phloem) which are not well developed and or petiole at the base. The bases of the are sometimes termed as tracheophytes. fronds are covered with dry brown scales While most pteridophytes are homosporous, called ramenta for protection of young some of the fern species produce two types leaves against drought. The frond has a of spores (heterosporous). Besides the midrib called rachis, which bear leaﬂets pteridophytes, which are regarded as true called pinnae on both sides and small ferns, other plant species called fern allies rounded sub-divisions of pinnae called are not true ferns, though they relatively pinnules (Figure 3.24). resemble pteridophytes in various ways. For example they disperse by shedding spores The mature frond bears specialised to initiate an alternation of generation. An reproductive structures called sori (clusters example of a common fern is Dryopteris of sporangia) on the lower surface of the filix-mas, found in damp woods and other frond. The sporangia contain spores; shady places. therefore, sporangia bearing leaves are called sporophyll (sporo meaning spore Structure of Dryopteris sp. and phyll meaning leaves). The Dryopteris A mature fern plant has an underground species have poorly developed vascular creeping stem called rhizome. This bears tissues with simple xylem elements for adventitious true roots for anchorage and the mechanical support and transport of absorption of water and mineral salts from water and mineral salts, while phloem the soil. It has broad leaves called fronds elements are mainly for the translocation attached to the rhizome by a long stalk of synthesized food. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Leaflet (Pinna) Fronds Sorus Rachis Young leaf Crozier Petiole (stalk) Rhizome Adventitious roots Figure 3.24 Structure of Dryopteris sp. showing sori at the lower side of the frond BIOLOGY FORM 5 KIWANDANI.indd 143 143 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Reproduction in Dryopteris (antheridia and archegonia), and rhizoids. The diploid sporophyte generation have The archegonia produce female gametes a cluster of sporangia (sori) in which while the antheridia produce ﬂagellated the spore mother cell undergoes meiotic male gametes which swim to the archegonia division to produce haploid spores. When in the presence of water to fertilise the egg, the sporangia mature they break and release forming a zygote. The zygote develops the spores. In favorable conditions, the to form a sporophyte generation with a spores germinate into a small green heart- horizontal stem (rhizome) and leaves. The shaped structure called prothallus forming gametophytes shrink and degenerate (Figure a haploid gametophyte generation, bearing 3.25). male and female reproductive structures Spores Young Prothalus gametophyte Antheridium Meiosis Sporangium Archegonium Zygote Eggs Sperm MatureGOFVOERRNONMLEINNTE PURSOEPOENRLTYY sporophyte New sporophyte Fertilization Young fern Gametophyte Figure 3.25 The life cycle of a fern plant (Dryopteris) Adaptations of Dryopteris to its mode of c) They have stomata which facilitate life gaseous exchange. Dryopteris possess the following features d) They have xylem responsible for which enable them to adapt to their transportation of water and dissolved environment: minerals and also they have phloem for translocation of manufactured food. a) They have chloroplasts containing chlorophyll for capturing light energy e) Rhizomes play part in storing food needed for photosynthesis. and propagating new plants, and can remain viable in the soil for a long time b) They have roots for anchorage and to ensure survival. absorption of water and mineral salts. 144 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 144 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms f) They have a well-developed and GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Exercise 3.12 independent sporophyte generation, since the gametophyte withers and 1. You are consulted by a friend who is dies as the young leaves of sporophyte raising ferns in his garden for the ﬁrst grow. time. He needs your advice on what appropriate measures he should take g) They have cuticle in their leaves to to rescue his fern plants, that appear to prevent excessive water loss. have a lot of dust brown spots on the lower side of the leaves, which were h) Archegonia secrete chemical which not there when they were young. Based attracts antherozoids to swim towards on your knowledge of ferns, advice him the egg during fertilization. accordingly. Activity 3.7 Observation of fern plants 2. Give reasons as to why ferns are considered to have evolved from Materials bryophytes. Mature fern plant (Dryopteris sp.) and hand lens or light microscope. 3. In which ways are ferns more adapted to terrestrial environment than Procedure bryophytes? a) Collect a mature fern plant (Dryopteris sp.) from a damp 3.6.3 Division Coniferophyta shaded area such as in the forest, Coniferophyta is a division of kingdom ﬂoor or water canal or river bank. Plantae which belongs to a broad group of non-ﬂowering seed bearing plants, referred b) Uproot the plant with a small part to as gymnosperms. The word gymnosperms of the rhizome and roots. originated from a combination of two Greek words Gymno meaning ‘naked’ and sperma c) Carefully examine the collected meaning ‘seed.’ Theophrastus was the ﬁrst fern plant. Take note of the fronds person to use this term in his book “Enquiry (leaves) arising from the horizontal into plants” referring to plants producing stem (rhizome). naked seeds. Under gymnosperms, there are four groups namely: d) Turn the frond and observe its lower side with the aid of a hand lens or a a) Conifers; the cone bearing plants such light microscope. Note small dark as cypresses; example: Cupressus or brown patches on the lower side species (Figure 3.26), pines; example: of mature fronds. Each discrete Pinus sylvestris, and Spruce; Picea patch is called sorus. species, which are the most abundant Gymnospermous species. Question Draw a diagram to show the morphology of the specimens provided and indicate the sporophyte, frond, sorus, rhizome, and rhizoids. 145 BIOLOGY FORM 5 KIWANDANI.indd 145 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools b) Cycads, the palm like plants. GOFVOERRNONMLEINNTE PURSOEPOENRLTYYalong the slopes of Mount Kilimanjaro in c) Gingkos, exampliﬁed by only one Tanzania. Globally, coniferophytes are common in the North-western part of the extant species, the Gingko biloba, United States, the northern hemisphere, which is regarded as a living fossil, and China. because the majority of species in this division are extinct. Characteristics of division d) Gnetos such as Welwitschia sp. Coniferophyta restricted to deserts in Namibia and a) They are non-ﬂowering, seed bearing Angola. plants, producing naked seeds which Figure 3.26 A photo of cypress tree among the are not enclosed in ovaries or fruit popular Christmas tree tissues. b) Sexual reproduction involves Source: TAFORI, 2019 microspores (male gametophyte) and megaspores (female gametophyte) Species belonging to this division are which are found in male and female evolutionarily, more advanced than cones or strobili respectively. pteridophytes. They have more advanced c) Fertilisation does not require water; vascular tissues, and they do not require instead, they develop pollen tubes water for fertilization. The presence of which carry sperms to the ovule for a highly reduced gametophyte and seed fertilisation. formation also makes them evolutionarily d) They have poor xylem with only more advanced than ferns. Coniferophytes tracheids as conducting elements but are very abundant in the cold and moist no vessel elements. This is the reason regions such as the southern highlands and why most coniferophytes produce soft wood. e) Their phloem tissues lack companion cells; instead, they are associated with albuminous cells. f) Leaves are reduced into spiny or needle-like leaves to minimize water loss through transpiration. Exceptions are Gingkos and Cycads. Distinctive features of division Coniferophyta Presence of the following features in members of division Coniferophyta differentiate them from members of other divisions: 146 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 146 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms a) The plants bear cones from which GOFVOERRNONMLEINNTE PURSOEPOENRLTYYannual rings of the xylem. The constituent microspores (pollen grains) and tissues of these species have resin canals megaspores (ovules) are produced. which run vertically and laterally along the stem. The bark, has secondary phloem, b) The pollen grains are winged to which is relatively thick and does not have provide buoyance, hence they are companion cells, but albuminous cells that wind pollinated. perform the same function as the companion cells. c) They have seeds which are not enclosed within the ovary; thus, no The trunk has a tap root system with ovaries, and no formation of fruits. lateral roots in different directions. Roots of some Pinus form symbiotic association d) Their xylem lacks vessel elements but (mycorrhizae) with fungi. Young shoots has only tracheids as the conducting have two types of leaves; small scaly elements. leaves on the main stem and leaves on the dwarf shoots. In addition, the plant has e) Their phloem tissues are associated foliar spars which develop into normal with albuminous cells instead of branches. The fertile plant bears female companion cells. and male reproductive cones which are distinct when mature. The male cones f) The majority produce resin in special are relatively soft or herbaceous and ducts called resin canals. Such resin is small while female cones are woody and useful in wound healing and deterring relatively larger. Usually, male cones are browsers. borne on the lower branches while female cones are borne on the upper branches g) Most are evergreen plants with needle- (Figure 3.27(b)). The leaves enclosing the like shaped leaves. cones are called sporophylls. For instance, microsporophylls are associated with Structure of Pinus male cones, whereas megasporophylls are The sporophyte consists of roots, stem and associated with female cones. branches, bearing needle-shaped leaves which appear in clusters of two to ﬁve. These clusters are called fascicle. Their leaves are dark green with cuticle, sunken stomata, and resin canals in the mesophyll. Their stems develop relatively wider Female cone Seed Female cone Male cone (a) (b) 147 Figure 3.27 General structure of (a) female cone and seeds and (b) Pinus plant 10/10/2019 14:06 BIOLOGY FORM 5 KIWANDANI.indd 147

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Reproduction of Pinus female cones, mainly through the process called pollination. The sporophyte generation is dominant, Once the pollen grain has landed on the more pronounced, and varies in form female cones, the pollen tube is formed and grows, carrying two male sperms to or habit. They include shrubs and trees, the archegonium and penetrate the ovule via a small hole called micropyle. In female consisting of roots, stems and leaves- cones inside the ovule, the megasporocyte produces four haploid nuclei through bearing branches. The gametophyte meiotic division. One of these cells develops into megaspore. The nucleus of megaspore is highly reduced (only a few cells). undergoes mitotic division to form a small female gametophyte where by two or three They are heterosporous, producing archegonia are present; each with one egg cell. During fertilisation one of the sperms microspores which are pollen grains fertilises the egg to form a zygote while the (male gametophyte) and megaspores other sperm degenerates. The zygote later (female gametophyte). Male cones bear develops to form a seed embryo which is microsporangium with microsporocyte a sporophyte in resting condition (Figure which produce microspores by meiotic 3.28). division, which give rise to light winged pollen grains (microspores). The nucleus within the pollen grain divides mitotically to form a pollen tube nucleus and a generative nucleus which later divides by mitosis to form two sperm nuclei. These pollen grains are transferred to mature GOFVOERRNONMLEINNTE PURSOEPOENRLTYYSeed Stored food Ovule Seed coat Seed cone scale Embryo Wing Zygote Sporophyte Megasporangium Fertilization Microsporangium Megasporocyte Microgametophyte Integument Microsporocyte Sperm Meiosis Microspore Pollen grain Pollen tube Pollination Megaspore Archegonium Megagametophyte Figure 3.28 The life cycle of Pinus plant 148 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 148 10/10/2019 14:06

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Adaptations of Pinus to its mode of life GOFVOERRNONMLEINNTE PURSOEPOENRLTYY FOR ONLINE USE ONLY Pinus are able to adapt to their environment DO NOT DUPLICATE due to presence of the following features: Comparative studies of natural groups of organisms a) The root and shoot systems are well developed to provide the plant Activity 3.8 Observation of Pinus with a good contact to the soil and sporophyte and reproductive atmosphere. structures b) They have roots for absorption of Materials water and nutrients from the soil. Branches of pine (Pinus) plants with male and female cones, hand lens or c) The plant has mechanical tissues microscope. for support and vascular tissues for transportation of water and food. Procedure a) You are provided with branches of the d) They have an elaborate mechanism for reducing water loss through Pinus species, with male and female transpiration. This becomes possible cones. Examine the mature female due to presence of thick cuticle, cones which are relatively woody. needle-like leaves to reduce their At the base of each cone are two surface area and a reduced number of winged seeds; however, they might stomata pores. Additionally, their bark sometimes be missing, because they is coated with waxy material called fall off when mature, especially if suberin to reduce water loss. the cones are disturbed by wind or any other mechanical force. If seeds e) They produce lighter pollen grains, are missing, two small depressions, each with two wing-like structures showing the mark of where the seeds which make them to float in air, were attached should be seen. hence easily to be carried by wind for pollination. b) Carefully examine the male cones which are relatively small and much f) They can reproduce sexually without herbaceous compared to the woody necessity of using water, because the female cones. Normally, male cones transfer of male gametes to female are borne in clusters at the axils of gametes is through pollen tube, which lower branches. Take some pollen ensures reproduction in terrestrial grains from the male cones and environment where water is limited. mount a few in a drop of water on a slide for examination under the light g) The seeds are winged; hence, they can microscope to observe the wings on be easily dispersed by wind. each. Questions 1. Draw a diagram of the male and female cones. 2. Draw a diagram of the pine pollen grain and show the wings. 149 BIOLOGY FORM 5 KIWANDANI.indd 149 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Exercise 3.13 GOFVOERRNONMLEINNTE PURSOEPOENRLTYYﬁliformis are parasitic, hence they rely on other plants. Others grow as epiphytes on 1. Outline ways in which other plants without causing any harm. coniferophytes are advanced Angiosperms are the dominant plants in all compared to ﬁlicinophytes. habitats, ranging from terrestrial to aquatic environments, where plants such as water 2. Explain the distinctive features of lilies and sea grasses are abundant. Based on gymnosperms. duration, flowering plants are classified as annual, biannual or perennial. Annual plants 3. Explain the importance of wind in are normally herbs and grasses that live only the life cycle of coniferophytes. in one season. Biannual plant live for two seasons growing vegetatively in the first 3.6.4 Division Angiospermophyta season and flowering in the second season. Angiospermophytes are ﬂowering plants which are the most advanced and adapted Perennial plants live for three or more to terrestrial life. The word angiosperm seasons. Example of perennial plants is a combination of two Greek words; are trees. The angiosperm sporophyte Angeion which means ‘vessels’ or ‘carpels’ is dominant with gametophytes entirely and sperma which means ‘seeds.’ They conﬁned in it. The sporophyte consists of produce seeds enclosed in the ovary, which roots, the stem, branches, and leaves. The later matures to become a fruit. Thus, their gametophyte generation is represented only fruit is a mature ovary and the seeds in it by ﬂowers in which the male and female are fertilized ovules. Angiosperms resemble gametophytes are conﬁned. They have well coniferophyta in many aspects such as the developed vascular tissues with xylem ability to produce seeds. However, the containing tracheids and vessels which presence of ﬂowers and seeds enclosed in make the angiosperm wood harder than the fruit makes them distinct. Flowers and those of coniferophytes. The phloem on fruits have contributed signiﬁcantly to the the other hand contains companion cells success of angiosperms in their ecosystems. and sieve tubes. Flowers are diverse in colour, aroma and morphology. These have made it easy to Angiosperms are heterosporous. They attract different pollinators, instead of produce microspores (male gametophyte) relying solely on the wind. The ability to and megaspores (female gametophyte). produce seeds enclosed in the fruit is also Actually, the male gametophyte is the an adaptation to seeds’ dispersal by animals germinated pollen grain which is highly which feed on such fruits. reduced into three nuclei, namely two male nuclei and a pollen tube nucleus. Whereas, The number of angiosperm species is over the female gametophyte is found in the 257,000, existing in various sizes, shapes ovule’s embryo sac; the ovary is reduced into and forms, such as grasses, herbs, shrubs, vines, liana, suffrutescents and trees. Some of these plant species such as Cassytha 150 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 150 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms eight nuclei, namely three antipodal nuclei, Class Monocotyledoneae, such as maize, two polar nuclei, and an egg contained grass, millet, and sugar cane plants. Class between two nuclei called synergids (Figure Dicotyledoneae, such as bean plant, 3.29). Following pollination, the pollen mango, and orange plants. grain on the stigma develops a pollen tube A recent estimate of the number of carrying two sperm nuclei which grow ﬂowering plant species globally is down to the embryo sac via micropyle. One approximately 400,000, distributed into of the sperms fertilizes a haploid egg to form about 393 families. When partitioned a zygote which later develops to form an into their old two broad classes, a larger embryo. The second sperm fertilizes the two number of species are dicots, represented polar nuclei forming triploid nutritive tissue by 336 families. In contrast, monocots are called endosperm. This process is called represented by about 57 families. double fertilization, because fertilization Distinctive features of class occurs twice. A fertilized ovule becomes a Monocotyledoneae seed surrounded by two integuments (seed The following features possessed by coat) and the ovary develops into a fruit. members of the class Monocotyledoneae (Figure 3.30) differentiate them from Germinating pollen grain those of class Dicotyledoneae. Stigma Style a) Leaf venation is parallel in monocots Pollen tube and the leaf blade or lamina is elongated with dorsal and ventral surfaces more or less identical. Nucellus GOFVOERRNONMLEINNTE PURSOEPOENRLTYYOvary wall Embryo sac Antipodal nuclei b) The stem anatomy shows vascular Polar nuclei Synergids bundles scattered in the ground tissue and closed as they lack vascular Micropyle Ovum cambium, hence no secondary growth. Tube nucleus Sperm nuclei c) They have a ﬁbrous root system which Figure 3.29 An ovary arises at the base of the stem replacing the primary root. Classes of division Angiospermophyta d) The monocot seed’s embryo bears one Old system of classification recognised cotyledon. two classes based on the number of cotyledons; Monocotyledon and e) Flower parts are usually trimerous (in Dicotyledon. threes or multiple of threes). f) Pollen grains in the monocots mostly have one aperture. BIOLOGY FORM 5 KIWANDANI.indd 151 151 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Tassel Styles Leaf Silk Brace root or prop root Node Stalk Roots Figure 3.30 Structure of a monocot plant showing root and shoot systems Distinctive features of class GOFVOERRNONMLEINNTE PURSOEPOENRLTYY vascular bundles are open, that is, they Dicotyledoneae have a strip of cambium which gives Members of the class Dicotyledoneae rise to secondary growth. (Figure 3.31) differ from those of class Monocotyledoneae due to presence of the c) The primary root system is a persistent following features: and becomes thick tap root which develops lateral roots. a) Dicot leaves have net like or reticulate venation with the dorsal and ventral d) Their seed embryo has two cotyledons. surfaces of their leaf blade being distinct. e) Floral parts are normally tetramerous or pentamerous (in four or ﬁve or b) Their stems have vascular bundles multiples of four or ﬁve). which appear in a ring form. The f) Pollen grains in dicots mostly have three apertures. 152 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 152 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Flower Stem Leaf Tap root (Primary root) Bean pod Bean seed Figure 3.31 Structure of a dicot plant showing root and shoot systems Activity 3.9 Observation of cross GOFVOERRNONMLEINNTE PURSOEPOENRLTYYQuestions section of the stem and morphology of 1. Summarise in a tabular form monocot and dicot plants the morphological differences Materials between the two classes of the Monocot plant (grass or maize), dicot collected plants. plant (beans or Hibiscus) plants with their flowers intact, light microscope, 2. Draw and label each of the two surgical or razor blade, and slides. plants to display their root system, stem, leaf venation and ﬂower(s). Procedure a) Collect some monocot and dicot 3. Draw diagrams of the observed stem sections, indicating the plants with their ﬂowers from the vascular bundles. school environment. Make sure that you uproot the entire plant carefully 4. What are the differences between in order to display their root system the stem sections observed in (c)? clearly. Safety precautions b) Observe the morphological structure 1. Handle with care sharp objects like of the two classes of plants collected. surgical or razor blade to avoid c) Make a thin cross section of the stem cutting your fingers or hands. of monocot and dicot plants. Place 2. Be aware of some dangerous them on slides and observe one at a animals such as piercing insects time using light microscope. and snakes while collecting monocot and dicot plants. 153 BIOLOGY FORM 5 KIWANDANI.indd 153 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Structure of the ﬂower GOFVOERRNONMLEINNTE PURSOEPOENRLTYYTulipa genera. They may be separate or A ﬂower is interpreted as a modiﬁed leaf fused into a single outer sheath collectively of a plant which is highly specialised called calyx. for reproduction (Figure 3.32). It can be bisexual or unisexual, depending on a plant c) Petals species. Bisexual and unisexual ﬂowers These are normally located inside and are called complete and incomplete above the sepals, are brightly coloured ﬂowers respectively. Flowers have the and expand to form the most conspicuous following major parts: part of the ﬂower. As such, they serve to attract pollinators such as insects and birds, a) Receptacle which are essential for accomplishing the This is a swollen tip of a pedicel on which reproductive process. The petals may all ﬂoral parts are borne or attached. It has be separate or united in a single tube or limited growth, which ceases as the last united in several groups. The collective ﬂoral part is formed. The receptacle varies term for petals is corolla. In some ﬂowers, in shapes between members of one species both calyx and corolla are united to give a and another. The ﬂoral parts are arranged structure termed as “Perianth.” in whorls around the receptacle, as rings of calyx, corolla, androecium and gynoecium. d) Androecium When all these whorls are present, the This is a collective term for the male part ﬂower is termed as a perfect or complete of the ﬂower, and includes anther and flower, example, and flowers of cherries, ﬁlament. Anthers are usually bright orange roses, and orchids. In contrast, when one or yellow in colour. The anther and ﬁlament of the four whorls is missing, the flower together is termed stamen. The transverse is termed as incomplete flower. Examples section of the anther shows that it is made include; flowers of sweet corn and most up of 2-4 pollen sacs containing pollen grasses. The ﬂoral parts are inserted in the grains or microspores. The whole stamen following order from the base to the apex of can be regarded as microsporophyll bearing receptacle; the ﬁrst whorl is for the calyx, microsporangia. The fertile microsporangia the second whorl is for corolla, the third are born as pollen sacs at the distal end whorl is for androecium, and the fourth of the ﬁlament. When mature, the pollen whorl is for gynoecium. sac ruptures to release pollen grains (microspores or male gametophyte) which b) Sepals develop into male gametes. These are the lowermost or outermost structure, which are usually green, leaf- e) Gynoecium like in structure, protecting the developing This refers to the female reproductive ﬂower whilst the ﬂower is still a bud. As the parts of the ﬂower which consists of the inner parts of the ﬂower grow and expand, stigma, style, and ovary. These three parts sepals are pushed outwards. In some are collectively called pistil or carpel. instances, they may become expanded Gynoecium shapes vary in different and brightly more coloured, like petals. species as some have a single carpel or a Examples include the flowers of Aloe and 154 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 154 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms number of separate carpels, or a number characteristic of angiosperms. They of carpels fused in a variety of ways. The contain an embryo sac in which the female carpel is either single or united in a closed gametophyte is found. The distal end of the hollow container housing (ovary), with ovary bears a prolonged structure known as one or more ovules. The ovules which are style, which terminates in a sticky surface enclosed within the ovary bear a peculiar called stigma. Carpel Stigma Anther Style Androecium Ovary Filament Receptacle Petal Sepal Pedicel Figure 3.32 A generalized longitudinal section of an angiosperm flower Flowers have the basic parts mentioned GOFVOERRNONMLEINNTE PURSOEPOENRLTYY both gynoecium and androecium parts, above, but morphological variations while others have only one part. are common across plant species. These variations are based on the following Position of floral whorls at the receptacle attributes: As pointed out earlier, the position of ﬂoral parts at the receptacle varies across the a) The manner of insertion of the parts. species. Based on the arrangement of the ﬂoral leaves at the receptacle in relation b) The number of ﬂoral parts: Some to the position of the ovary, three types of ﬂowers have all four whorls while ﬂowers are recognised: others have less than four whorls. a) Hypogynous flower c) The freedom or fusion of ﬂoral parts: In this ﬂower, the calyx, corolla, and Some parts in some ﬂowers may be androecium arise from the lower position fused while other parts may not. of the ovary. This means that the calyx, corolla and androecium are inserted below d) The relative position of the ﬂoral parts the ovary that is the ovary is positioned on the receptacle; may be above or above them. The ovary is therefore said below the receptacle. to be superior as it occupies the highest position in the receptacle (Figure 3.33). e) The symmetry of the ﬂower: some Examples of hypogynous ﬂowers include ﬂowers have radial or bilateral Hibiscus, tulip and tomato ﬂowers. symmetry while others are asymmetrical. f) The distribution of the sexual parts within the ﬂower: Some ﬂowers have 155 BIOLOGY FORM 5 KIWANDANI.indd 155 10/10/2019 14:06

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE Anther Petal Ovary Sepal Thalamus Figure 3.33 Structure of a hypogynous flower b) Perigynous flower stamens, and the ovary is said to be half inferior. Examples include cherry and rose In this type of a ﬂower, the margins of flowers. The term “perigynous” emanates the thalamus grow upwards to form a cup from the nature in which other ﬂoral parts shaped structure called the calyx tube that encloses the ovary. However, it remains appear to enclose the ovary (Figure 3.34). free from it, carries with it sepals and GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Anther Ovary Petal Sepal Thalamus Figure 3.34 Structure of a perigynous flower c) Epigynous flower Anther In this ﬂower, the calyx, corolla, and Petal androecium arise above the ovary and completely enclose it. The ovary is therefore Sepal said to be inferior, while the rest of the Ovary ﬂoral parts are said to be superior (Figure 3.35). Examples of epigynous ﬂowers Figure 3.35 Structure of an include the cucumber, apple, guava, and epigynous flower passion ﬂowers. Student’s Book Form Five 156 10/10/2019 14:06 BIOLOGY FORM 5 KIWANDANI.indd 156

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Flower symmetry Line of A ﬂower can be dissected longitudinally symmetry to expose its internal parts for clear examination. One of the fundamental Figure 3.36 Structure of an actinomorphic aspects of a ﬂower plan is its overall ﬂower shape which is described as symmetry. A symmetrical ﬂower is the one that b) Bilateral symmetry can be divided along at least one plane A ﬂower is said to have bilateral symmetry in relation to perianth into two or more when it can be split into two identical halves identical parts which are mirror image of in one plane only. This type of symmetry each other. Although most ﬂowers have is caused by differences in size and shape a certain kind of symmetry, few ﬂowers of petals and or sepals as can be noted have no symmetry and are referred to as in pea and bean ﬂowers. Additionally, in asymmetrical ﬂowers. Three categories of some ﬂowers, some whorls may be fused ﬂowers’ symmetry are therefore recognized or some parts of an individual whorl may namely, radial symmetry or actinomorphic have different sizes compared to others in flower, bilateral symmetry or zygomorphic the same ﬂower (Figure 3.37). Bilaterally flower and asymmetric flower. symmetrical flowers are said to be irregular or zygomorphic. Example sweet pea. The a) Radial symmetry symbol used to represent them is ●|●. A ﬂower is said to have a radial symmetry GOFVOERRNONMLEINNTE PURSOEPOENRLTYY when it can be split vertically through the centre in any one of several planes to produce identical parts which are mirror images of each other. This type of symmetry applies when each part of the whorl is identical with all other parts. Normally each side can have one sepal and one petal. Radially symmetrical flowers are said to be regular or polysymetric or actinomorphic (Figure 3.36). Literally, actinomorphic means star like because the ﬂower can be divided into three or more identical parts. Most ﬂowers have actinomorphic symmetry, for instance the Hibiscus ﬂower. The symbol used to denote this type of symmetry is . Figure 3.37 Zygomorphic flower BIOLOGY FORM 5 KIWANDANI.indd 157 157 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools c) Asymmetric ﬂowers Floral diagrams These ﬂowers have no plane of symmetry, A ﬂoral diagram is a diagrammatic they cannot be divided into two equal halves representation of the transverse section of in any plane; this is because their parts are a ﬂower. It shows a plan of the ﬂower as spirally arranged, and good examples are viewed from above with each of its ﬂoral flowers of Cacti, Canna indica, and ginger. whorls represented by a series of centric cycles showing their number, arrangement, Methods of recording floral structure relative position and fusion. The axis of Flower features can be represented to the inﬂorescence is represented by a small reveal the arrangement and relationship of cycle at the top of the diagram which is the parts using three methods. These are then regarded as the posterior position a half-ﬂower diagram, ﬂoral formula, and of the ﬂower and bracts, if present. In ﬂoral diagram. principle, ﬂoral diagrams are never labelled, but standard symbols are used A half flower diagram (Figure 3.38b). Although such symbols This is a schematic representation of may not be representing physical structures, a ﬂower cut longitudinally along the they carry additional ﬂoral information median plane in relation to the main stem such as symmetry and orientation. Floral to provide an elevation view of the ﬂower. diagrams are useful in the identiﬁcation Normally, in regular ﬂowers, cutting along of ﬂowers, comparison of angiosperm this plane will result into two identical and taxa, reconstruction of fossil ﬂowers and opposite halves of the ﬂower. A half cut understanding the ontogeny and phylogeny ﬂower diagram shows exactly how the of angiosperms. ﬂoral parts are arranged in relation to each other (Figure 3.38a). GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Anther Plant axis Petal Sepal Filament Petal Style Stamen Ovary Sepal Figure 3.38 Representation of flower features (a) a half-flower diagram (b) floral symbols 158 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 158 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Procedure for construction of a floral h) The edges of fused sepals or petals are diagram connected by lines. a) In drawing a ﬂoral diagram, it should i) The two lips of bilabiate calyx or be noted that different ﬂoral whorls are corolla are joined by bulging lines. always represented in concentric circles starting with sepals on the outermost j) In epipetalous ﬂowers, where stamens circle, followed by petals, stamens and are fused with petals, both whorls are carpels towards the inner side. linked with small radial lines. b) Examine mature ﬂoral buds and pluck k) Count the number of stamens; note them off the mother axis after noting their cohesion and adhesion to other the anterior and posterior sides. ﬂoral parts and position in relation to petals, introse or extrose position; and c) The ﬂoral parts are drawn in a ﬂoral draw them inside the petals in the ﬂoral diagram, as they would appear in their diagram. Stamens are represented by transverse sections below the mother transverse sections of anthers (Figure axis. A small circle is drawn above the 3.39). Introse stamens face towards the ﬂoral diagram to designate the mother centre while extrose ones face towards axis; however, for the terminal ﬂowers, the petals. Staminodes are represented this circle is not shown. by an asterisk (*) or by a cross (x). d) In ﬂowers associated with bracts (bracteate flower), a section of bract is drawn. In contrast in bracteolate flower; bracteoles are drawn in section on the left and right sides of the diagram. GOFVOERRNONMLEINNTE PURSOEPOENRLTYYPosterior sidePlant axis Diagonal plane Gynaecium e) The number of sepals and their Lateral or Androecium arrangement in relation to the mother transverse Corolla axis or aestivation are drawn in transverse sections. The odd number Calyx of sepals and petals are drawn either posterior or anterior to the ﬂower (that Bract is, opposite the mother axis or opposite the bract, respectively) with its sepals Figure 3.39 The floral diagram with labeled and petals alternating. symbols f) In zygomorphic ﬂowers, sepals and Floral formula petals with unequal sizes are drawn. This is a representation of various ﬂoral parts using standardized symbols and g) The spurred sepals or petals are shown numbers. It depicts ﬂoral information by drawing a loop at their respective back. BIOLOGY FORM 5 KIWANDANI.indd 159 159 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools pertaining to symmetry; ﬂoral whorls GOFVOERRNONMLEINNTE PURSOEPOENRLTYY and corolla are fused and cannot be namely calyx, corolla, androecium and differentiated. gynoecium; their numbers; and how they relate to each other. Symbols used in A Represents Androecium or stamens. construction of ﬂoral formulae and their The letter A is followed by the number respective meanings are as summarised of stamens like A(5)+5 indicates a total below: of ten stamens in which ﬁve are free Represents radially symmetrical and ﬁve are fused. A means five free stamens. If the stam5ens are attached ﬂower (actinomorphic). to petals, their symbols are united with an arc line above them as in C͡ A. ●|● Represents a ﬂower with bilateral symmetry (zygomorphic). ∞ Represents a large and variable ♂ Represents unisexual male or number of whorls. It is used when the number is more than twelve in a staminate ﬂower. flower. Example A∞ means many free stamens and A(∞) means many fused ♀ Represents unisexual female or stamens. pistillate ﬂower. G Denotes Gynoecium or pistil. Each G is followed by the number of carpels Represents bisexual (hermaphrodite) like G1 or G2, which means one carpel ﬂower. and two free carpels respectively. The carpels may also be fused as in G(2) Br Represents ﬂower with bracts or free as in G4 implying two fused (Bracteate). and four free carpels respectively. A small line under the letter G indicates Ebr Represents ﬂower without bracts superior ovary while a small line (ebracteate). above it, such as Ḡ, indicates an inferior ovary. Brl Represents flower with bracteoles (Bracteolate). The following examples highlight how ﬂoral formula are constructed and interpreted. K Represents calyx; each K is followed by a number indicating the number of sepals; for example K5 represents ﬁve free sepals. If this number appears within brackets as in K(5), it denotes five fused sepals. C Represents corolla; each C is followed The above formula indicates that the by the number indicating number of ﬂower has radial symmetry, and it is petals for example C5 depicts five bisexual. It further implies that the ﬂower free petals. If this number is enclosed has ﬁve sepals, ﬁve petals, numerous by brackets as in C(5) it denotes five stamens and five carpels. The ﬂower has fused petals. no bracts and all whorls are free from each other that is, not fused. P Is used if sepals and petals are replaced by perianth. That is, calyx 160 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 160 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Floral formula of Lathyrus is; Floral formular of Ipomoea is; The Lathyrus ﬂower is zygomorphic, hermaphrodite, calyx with ﬁve fused sepals, corolla with ﬁve free petals, androecium with ten stamens (nine fused stamens and one free stamen); and a superior ovary with one free carpel. The Ipomoea ﬂower is actinomorphic, GOFVOERRNONMLEINNTE PURSOEPOENRLTYYFigure 3.40 A photo of a common Hibiscus plant bisexual, calyx with ﬁve free sepals, found in several places of Tanzania corolla with ﬁve fused petals, androecium with ﬁve free stamens united with petals, The floral formula of Hibiscus flower and gynoecium is superior with two fused derived from the individual with bracts carpels. (bracteate) and bracteoles (bracteolate), radial symmetry, bisexual, fused five Floral formulae and floral diagrams of sepals (calyx), free five petals (corolla) a selected flower fused with infinite androecium, and five The Hibiscus is a genus that belongs to fused gynoecium (hypogynous). the family Malvaceae (Figure 3.40). The genus is quite large, comprising of several Floral formula of Hibiscus hundred species that are native to warm temperate, subtropical and tropical regions throughout the world. Several species are widely cultivated as ornamental plants for their showy flower. Floral diagram of Hibiscus The schematic cross-section of Hibiscus flower is presented in structular form to express the arrangement of floral parts as projected in transverse or horizontal plane (Figure 3.41). BIOLOGY FORM 5 KIWANDANI.indd 161 161 10/10/2019 14:06

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE (a) Activity 3.10 Observation and Stamens Corolla recording ﬂower structures Stigma Calyx Epicalyx Materials Pedicel Hibiscus flower, common bean flower, Leaf maize flower and elephant grass flower, hand lens, and surgical or razor blade. (b) Procedure Corolla a) Collect two ﬂowers from each of Style Calyx the following plants; Hibiscus, Epicalyx common bean, maize, and elephant Ovary GOFVOERRNONMLEINNTE PURSOEPOENRLTYY grass. Pedicel b) Carefully observe each ﬂower using (c) a hand lens and state with evidence the classes to which each of the four plant species belongs. c) Use a surgical or razor blade to make a transverse section of each flower and examine its parts. d) Draw a transverse section of each flower and state their symmetry. e) Prepare a longitudinal section of the second ﬂower for each plant and draw well labelled diagrams. f) Write the ﬂoral formulae of bean, elephant grass, and maize ﬂowers. g) From your observation, what features do the four ﬂowers have in common? h) Explain the main differences between Hibiscus and grass ﬂowers Figure 3.41 Hibiscus flower (a) vegetative Safety precaution morphology (b) half flower diagram (c) floral Be careful when using surgical or razor diagram blades. 162 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 162 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Adaptation of Angiospermophytes to GOFVOERRNONMLEINNTE PURSOEPOENRLTYY For instance, some ﬂowers can live on land be pollinated by insects with long Angiosperms are the most recently proboscis or birds with long narrow evolved plants and are relatively the most beaks, only as they secrete nectar at adapted plants to terrestrial environment. the base of a narrow ﬂoral tube which Several factors have contributed to their is the right size of their corresponding survival, hence success on land; such pollinators. factors include: a) Flowers have contributed to the d) Stamens have also become modiﬁed through time to prevent self- diversiﬁcation of angiosperms fertilisation in order to increase throughout the time with adaptations genetic diversity that will eventually to specialised pollination conditions. enable them to inhabit a wider range The adaptations exhibited by any of habitats. Additionally, closed carpel given ﬂower depend on the type of allows adaptations to specialised pollinators the ﬂower is designed to pollination conditions and controls attract, and have evolved features to self-fertilisation. enable pollinators to recognise and locate them quickly. For instance, e) The male gametophyte in angiosperms bees can only see yellow, blue, and is highly reduced into three nuclei ultraviolet (UV) colors; therefore, bee (a tube nucleus and two sperm pollinated ﬂowers are yellow, blue or nuclei). This evolved to shorten the UV but not red. Butterﬂies detect red; duration of time between pollination accordingly, they can pollinate red and fertilisation. Thus, unlike ﬂowers. Moths, which are nocturnal, Coniferophytes, which takes about a pollinate brightly white coloured year for fertilisation to take place after ﬂowers, which can standout against pollination, in angiospermophytes darkness. begins fertilisation soon after pollination, which translates into seed b) Most plants have ability to make swift, seed formation, and species and supply some food in the form of perpetuation. nectar and advertise their presence to the pollinators by producing fragrant f) Their male gametes are transferred scent. They also have a way of putting through a special tube (pollen tube) pollen on the pollinators and easily to the female gametes for fertilisation. transferred to the ﬂower of the next The ability to reproduce sexually plant. without necessarily requiring water is an important feature in terrestrial c) To ensure pollination, angiosper- environment, where water is limited. mophyte ﬂowers have evolved ways of preventing non beneﬁcial pollinators g) Fruits produced by angiospermophytes from visiting their ﬂowers while are adaptations for dispersal by various embracing the beneﬁcial pollinators. agents such as wind, water, animals, and bursting. Animal dispersed 163 BIOLOGY FORM 5 KIWANDANI.indd 163 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools fruits have ﬂeshy mesocarp which GOFVOERRNONMLEINNTE PURSOEPOENRLTYY in all plant leaves. In addition, stems is edible or produces edible seeds or of monocots restrict excessive water have various kinds of hooks. Wind loss. dispersed fruits have structures for n) Deciduous trees shed their leaves buoyancy, such as wings. These have during dry season to reduce the rate provided angiosperms an opportunity of transpiration, hence, limiting water to increase their domination in the loss. terrestrial ecosystem. o) Asexual reproduction by vegetative propagation ensures rapid growth and h) Seeds produced by angiospermophytes maturity. have a highly nutritive tissue called endosperm, which provides food for Economic importance of plants the developing embryo, cotyledons, Plants are very important to the survival and sometimes, for the seedling when of other organisms; without plants our day it ﬁrst appears. to day life would have been impossible. Animals’ life is dependent on plants i) They have developed extensive root directly and or indirectly. However, there system for anchorage on land and are some plants with detrimental effects absorption of water and mineral salts. to life of animals. The following are Some plant roots have developed advantages and disadvantages of plants. symbiotic relationship described as mycorrhizae with Fungi to increase Advantages of kingdom Plantae the root surface area for absorption of a) Species in this kingdom are the chief nutrients and water from the soil. source of food for heterotrophs. Primary j) They have an advanced and elaborated consumers such as browsers and vascular system for transportation of grazers depend on angiospermophytes materials. For example, xylem has as their sole source of food. Likewise, both vessel and tracheids for efﬁcient human beings obtain various types water movement. of food such as vegetables, potatoes, sugar, cereals, and fruits from plants. k) They have stomatal pores for transpiration and gaseous exchange. b) They are important atmospheric These are modiﬁed in various ways to puriﬁers due to their ability to sequester reduce excessive water loss. carbon dioxide (CO2), thus reducing its concentration in the atmosphere. l) Control of evapotranspiration, Carbon dioxide is one of the depending on the environment in greenhouse gases; hence its reduction which a particular species is adapted in the atmosphere will in turn reduce to live. For example, xerophytes have the risks of global warming. Through sunken stomata; most of them are photosynthesis, plants produce oxygen restricted on the lower side. which is used by most of the organisms for respiration. m) They have cuticle, a thick waxy material covering the epidermal cells 164 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 164 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms c) Plants such as legumes have symbiotic ﬁbres from plants such as sisal are used relationship with nitrogen ﬁxing bacteria to manufacture mattresses and carpets. in their root nodules. These bacteria are White pines are extensively used for capable of ﬁxing unavailable nitrogen making boxes, furniture, ﬂoor, and from the atmosphere into available panel. forms, which can be absorbed by plants. k) Resins from pines are used for making d) They help to conserve water in the soil premier paints and varnish solvents by preventing excessive evaporation. ointments, wax, and shoe polish. For example, plant leaves and grasses are used as mulching materials covering l) They provide timber for various the soil surface to conserve water. purposes such as furniture making, poles for houses construction and e) Grasses and some trees have important electric supply. catchment value, because they have matted root networks that reduce lateral m) Forests attract tourists and thus aid in ﬂow of water, evaporation, and soil generating national income. erosion. n) Plant leaves such as grass, banana and f) Plant communities or vegetation such coconut leaves, are used in thatching as grasslands, woodland, and forests houses. provide habitats for wild animals. Additionally, bird species use plant o) Fern rhizome, root bark, and rhizome materials for construction of their nests. bark of certain species are used for growing Orchids. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY g) They are used in research and biological p) Some plants are source of medicine for studies. example Neem trees h) Plants are sources of traditional fuel Disadvantages of kingdom Plantae such as charcoal and ﬁrewood. In a) Some plants can produce metabolites Africa, for instance, approximately 90% of the population use charcoal as or accumulate toxic or poisonous a source of domestic energy. products which are dangerous to consumers (animals). Cassava plants i) Ferns and most Angiospermophytes are can accumulate cyanide, which grown as ornamental plants for indoor is toxic, if consumed by humans. and outdoor decoration, examples: true Jatropha curcas produces a toxic ferns, Hibiscus, cacti and roses. protein called curcin. Tea and coffee produce caffeine which in high doses j) They provide raw materials for may cause hypertension in humans. industrial purposes. Examples are cotton for making clothes, latex for b) Weed plants compete with food crops, making rubber, cellulose for making leading into low crop yield. ﬁber products such as ropes, and wood pulp for making paper. Additionally, c) Some plants are parasites to other 165 BIOLOGY FORM 5 KIWANDANI.indd 165 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools plant species. For instance, Cassytha Animals are mobile, they can move from ﬁliformis is a parasitic weed in crops such as mango, orange and cashewnut one place to another in search for food, trees; they cause serious crop loss and, consequently income loss. shelter, mates, and safety. Mobility in d) Some aquatic weeds can colonise water bodies and affect ecosystem as animals include movement of organs. well as hindering ﬁshing and boating activities. For example corals are sedentary animals Exercise 1.14 but their organs move to trap food. 1. Describe the distinctive features In most animals, body activities and of the kingdom Plantae. responses are coordinated by the nervous 2. With the aid of diagrams illustrate the differences between the two and endocrine systems. Higher animals classes of ﬂowering plants. reproduce sexually, involving haploid 3. Outline the distinctive features of the division Angiospermophyta. gametes. Most animals are triploblastic 4. With the aid of a well labelled organisms, meaning they have three body diagram, describe the structure of a ﬂower. layers (outer layer; an ectoderm, middle 5. Brieﬂy explain how Hibiscus layer; mesoderm, and endoderm as an ﬂower is adapted to cross inner layer); Examples of such animals pollination. include all multicellular animals, with the exception of certain invertebrates such as the cnidarians and sponges. Some are diploblastic, consisting of two layers of cells (ectoderm and endoderm); for example cnidarians (jellyfish, corals and sea anemones). Their body symmetry is bilateral, except phylum cnidaria that have radial symmetry and phylum, Porifera example sponges whose body regularly lack symmetry. Most animals have anterior and posterior ends, with oral and anal openings. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 3.7 Kingdom Animalia Kingdom Animalia is divided into Animals are a diverse group of organisms about twenty eight phyla including that make up the kingdom Animalia. This Polifera, Cnidaria, Platyhelminthes, kingdom comprises of animals, which Nematoda, Annelida, Arthropoda, Mollusca, are multicellular eukaryotic organisms. Echnodermata, Chordata and other smaller Most of them have high level of tissue phyla. The first eight phyla fall under the group of invertebrates (animals without differentiation and specialised body a backbone) while the ninth phylum, organs. They undergo heterotrophic Chordata, includes some invertebrates mode of nutrition; that is, they depend and vertebrates (animals having a on other organisms directly or indirectly backbone). This book will deal with five to obtain organic food. They digest food selected phyla, namely Platyhelminthes, internally, particularly in the gut and store Nematoda (Aschelminthes), Annelida, carbohydrate in the form of glycogen. Arthropoda, and Chordata. 166 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 166 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms 3.7.1 Phylum Platyhelminthes GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Fasciola hepatica (liver ﬂuke). Most This is a group of ﬂatworms. The worms members of this phylum are parasites can be free living or parasites. One of the while others are free living, for best-known example of ﬂatworms is the example: Planaria. tapeworm. Classiﬁcation of Platyhelminthes General Characteristics of phylum Common Platyhelminthes, fall into three Platyhelminthes classes namely; class Cestoda, Trematoda and Turbellaria. Class Cestoda consists a) They are dorsoventrally ﬂattened and of endoparasite animals such as the some are unsegmented worms. Most of tapeworms, including Taenia solium (the them have mouth and gut with no anus. pork tapeworm), Dipylidium caninum (the dog tapeworm) and Taenia saginata (beef b) They have ﬂame cells in the mesoderm tapeworm). Class Trematoda comprises for excretion and osmoregulation. of the ﬂukes; example, Fasciola hepatica (Liver ﬂuke) and the blood c) They are hermaphrodites with a flukes Schistosoma haematobium and complex reproductive system, which Schistosoma mansoni. Class Turbellaria prevents self-fertilisation, but favours consists of the free living worms such as cross-fertilization. Planaria. They are flat worms. d) They are triploblastic acoelomate Structure of a tapeworm animals, which have three body layers An adult tapeworm for example Taenia, (ectoderm, endoderm, and mesoderm) consists of a knob-like head or scolex, without a body cavity or coelom. equipped with hooks and suckers for attachment to the intestinal wall of e) Some have cilia on their outer surface the host; a neck region; and a series for locomotion, for example Planaria, of ﬂat, rectangular body segments (or others have cilia in larval stage, for proglottids), generated by the neck example miracidium larva in flukes, (Figure 3.42). The chain of proglottids but lack cilia in adult stage. may reach up to 15 or 20 ft (4.6–6.1 m) long. Terminal proglottids break off, f) They exhibit bilateral symmetry. and are egested in the feaces of the host. Nevertheless, the new ones are constantly g) They have a very simple nervous formed at the neck of the worm. As long system, with two nerve cords which run as the scolex and the neck are intact, the down on either side of the body. They worm is alive and capable of growing. have two simple brains called ganglia, Rudimentary nervous and excretory which are simple bundles of nerves. systems run the length of the worm, through the proglottids. However, there is h) Some have two eyespots that help in no digestive tract; the worm absorbs the sensing the presence of light. i) Some platyhelminths have hooks and suckers for attachment. Examples of platyhelminths are Taenia solium, Taenia saginata (tapeworms), and BIOLOGY FORM 5 KIWANDANI.indd 167 167 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools host’s digested food through its cuticle or g) It is well adapted to osmotic pressure outer covering. changes in the host’s body. Rostellum Mature proglottid h) It has ﬂame cells, which collect Hook excretory material from all parts of the body. Scolex Suckers Structure of a liver fluke Neck Morphologically, an adult liver ﬂuke, for example Fasciola, has a ﬂattened leaf Immature proglottid shaped appearance (Figure 3.43). In the anterior part, there is a triangular projection Figure 3.42 Structure of a Taenia with a mouth surrounded by oral suckers at its apex. Ventrally, at the base of the Adaptations of Taenia to its mode of life. projection, there are ventral suckers; and Taenia exhibits various special adaptations between the two types of suckers, there is to its parasitic mode of life as follows: a genital pore. Posteriorly, there is a minute a) It has scolex (head) with hooks and excretory pore. The body is enclosed in a tough cuticle, which is extended into suckers for ﬁxation and attachment on backward directed spines. Their muscle the host’s gut wall ﬁbres have small glands with minute ducts. The mouth runs into the oesophagus which b) It lacks alimentary canal because it branches into two blind parts. absorbs digested food materials from GOFVOERRNONMLEINNTE PURSOEPOENRLTYY its hosts. Oral sucker Mouth Head c) It has a thin and ﬂattened body, which Genital pore provides a large surface area for Flattened body Acetabulum gaseous exchange and absorption of (ventral sucker) digested food. Excretory d) Its body is covered by a living pore epidermal layer called the tegument which produces antienzymes to protect Figure 3.43 Structure of a liver fluke it from hosts’ digestive enzymes. Adaptations of the liver fluke to its e) It has a large number of ploglottids, mode of life which ensures production of a large Liver fluke possesses the following features number of eggs, hence high chance of that facilitate a parasitic mode of its life in survival. the host: f) It can respire anaerobically; therefore, it is able to live under low oxygen concentration, for example in the host’s gut. 168 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 168 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms a) It has suckers that provide a means of GOFVOERRNONMLEINNTE PURSOEPOENRLTYYb) Some members of Platyhelminthes attachment to the host. are used in biological studies as specimens; for example, Taenia and b) It has tegument with spines that Fasciola. prevent it from being washed away by bile; and also help the parasite to erode Disadvantages of phylum liver cells. Platyhelminthes Some members are parasites, which cause c) The tough tegument and secretions diseases to man and domestic animals. from the glands prevent the worm Examples include: from the effects of the host’s toxins. a) Taenia causes taeniasis; an intestinal d) The parasite secretes enzymes that tapeworm infection caused by eating help it to penetrate the liver cells at raw or undercooked contaminated various stages of its life cycle. beef (Taenia saginata) or pork (Taenia solium). e) It has mechanisms and chemicals that suppress the actions of the host’s b) Fasciola hepatica causes fascioliasis, digestive enzymes. which results into liver rot in sheep, cattle, and humans. f) It has a high reproductive potential and different multiplication phases c) Schistosoma haematobium and that balance its high mortality rate. Schistosoma mansoni cause They have two hosts, namely primary urinary and interstinal bilharzia hosts (example: sheep and humans) (schistosomiasis) respectively. and secondary host (example: fresh water snail called Lymnea sp.). 3.7.2 Phylum Nematoda They have several larval stages (Aschelminthes) (miracidium, sporocyst, redia, cercaria Nematodes or round worms are the most and metacercaria) which increase numerous multicellular animals on earth, the chances of survival and more and inhabit a wide range of environments. perpetuation. Many of them are parasites of animals (including humans) and plants. They may Economic importance of phylum cause serious diseases that are deleterious to Platyhelminthes human health and agricultural productivity. Some members of phylum Platyhelminthes The free-living species inhabit marine and play an important role in marine, freshwater freshwater environments, as well as the soils and terrestrial ecosystems, while several and sediments of all of the various types of species are harmful parasites to humans terrestrial biomes. Examples of Nematodes and other animals. include: Ascaris lumbricoides (the pig and human nematodes), Wuchereria bancrofti Advantages of phylum Platyhelminthes (infecting human lymphatic system), hook a) Some species of Platyhelminthes feed worms (blood-feeding parasite of human and other animals) and Meloidogyne on dead bodies of large organisms; incognita (plant root knot nematode). therefore, they decompose organic matter in the soil; for example, free living Planaria. 169 BIOLOGY FORM 5 KIWANDANI.indd 169 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Structure of Ascaris from being digested by the enzymes of Ascaris are round, slender unsegmented the alimentary canal of the host. worms with tapering bodies at both ends. b) It produces chemicals, which act as They are characterised by being tubes anti-enzymes to the digestive enzymes within tubes, referring to the alimentary of the host. canal, which extends from the mouth on the c) It has an alimentary canal, which opens anterior end to the anus, located near the at the mouth and anus. This enables the tail (Figure 3.44). They possess digestive, parasite to take food from the hosts’ nervous, excretory and reproductive digestive system. systems, but they lack distinct circulatory d) It possesses digestive enzymes in its and respiratory systems. The male and digestive system for the completion of female Ascaris differ in morphology, as male partially digested food from the hosts’ is smaller and more curved at its posterior alimentary canal. end than the female. They lack locomotory e) It has sensory papillae around its organs; movement is by undulating bodies mouth for detecting food present in the in dorso-ventral waves. elementary canal of the host. Mouth f) It respires anaerobically, and have low metabolic rate; hence, they are able to live inside the host’s intestine. Excretory g) It has high reproductive potential; thus, pore by producing large number of eggs, it ensures its survival and existence. Female GOFVOERRNONMLEINNTE PURSOEPOENRLTYY gonopore h) The pharynx has valves, which prevent Cloaca aperture regurgitation of the ingested food. Lateral line Penial spicules Economic importance of phylum Curved tail Aschelminthes Anus Members of Aschelminthes are associated Straight tail (b) with both advantages and disadvantages as follows: (a) Figure 3.44 Structure of Ascaris lumbricoides Advantages of phylum Aschelminthes (a) female and (b) male a) Nematodes, such as Ascaris are used Adaptations of Ascaris to its mode of in biological studies in different ways; life for instance, in laboratory practical Ascaris possesses some adaptive features studies. that enable it to adapt to its parasitic mode b) Some nematodes are used as biological of life. Thus: control agents for pest insects. They a) It has a tough cuticle, which protects it attack insects and kill or hinder their development. 170 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 170 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Disadvantages of the phylum f) They have a lip like extension on Aschelminthes the first segment above the mouth Some Aschelminthes are parasites and cause (prostomium). diseases in plants and animals. Examples include: g) They have nephridia as typical a) Wuchereria bancrofti that causes excretory organs. elephantiasis. This disease infects the h) They have central nervous system, human lymphatic system by blocking with paired cerebral ganglia in which it; resulting in the accumulation of the paired commissures around the gut lymph in legs, hands, and/or scrotal lead to a double ventral nerve cord, sacs. expanded to form a ganglion in every b) Ascaris lumbricoides causes ascariasis segment. in humans that may lead to obstruction in the gut and anaemia. Body plan of coelomates In annelids and other coelomates there is c) Meloidogyne incognita causes an extensive internal space or body cavity root knot galls in plants that drain called a coelom. This is the space between photosynthetic products; hence, affect the body wall and the alimentary canal plant growth and reduce yield. (Figure 3.45). 3.7.3 Phylum Annelida GOFVOERRNONMLEINNTE PURSOEPOENRLTYYFunctions of the coelom Members of this phylum are known as ringed The coelom has the following biological or segmented worms. This is a large phylum signiﬁcance to an organism: comprising of lugworms, earthworms, and a) It contains coelomic fluid which acts leeches. The species are adapted to various habitats; some members are aquatic, living as a hydrostatic skeleton. This is found in marine and fresh water, and others live in such organisms as earthworms. in moist terrestrial environments. b) It separates the alimentary canal from Characteristics of phylum Annelida the body wall so that the functions of a) They are triploblastic, coelomate the two parts take place independently. organisms. c) It allows the animal to grow larger. b) They have bilateral symmetry. d) The coelomic ﬂuid may function as a circulatory medium for transportation c) They are metamerically segmented. of food, gases, and excretory wastes. d) They have a definite outer covering e) It provides space for enlargement of called cuticle internal organs. e) They have chitinous hair-like structures f) In some animals, it plays an called chaetae (except in leeches), the osmoregulatory role. chaetae of polychaetes are found on structures known as parapodia. BIOLOGY FORM 5 KIWANDANI.indd 171 171 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Ectoderm Peritoneum Body Somatic wall mesoderm Splanchnic mesoderm Gut Wall Coelom Endoderm Gut Mesentery Gonad or Excretory organ Tubes leads to the exterior of reproductive system Figure 3.45 Transverse section of a generalised coelomate Classes of phylum Annelida GOFVOERRNONMLEINNTE PURSOEPOENRLTYYthe length of its body. It has a thin wet The phylum has three classes namely: skin through which gaseous exchange Class Polychaeta, which includes the takes place. There is a double transport marine bristle worms with many chaetae system composed of coelomic ﬂuid that and parapodia, examples are Nereis (the moves within the ﬂuid-ﬁlled coelom. The ragworm) and Arenicola (the lugworm). circulatory system is simple and closed. Class Oligochaeta which includes; the The worm has a central and peripheral earthworms and fresh water worms, that nervous systems. The central nervous have few chaetae without parapodia, system consists of two ganglia above for example Lumbricus (the common the mouth, one on either side, connected earthworm), Tubifex (fresh water earthworm to a nerve cord running back along its sometimes called sludge worm, or sewage length to motor neurones and sensory worm). Another class of annelida is class cells in each segment. A large number of Hirudinea which includes segmented worms chemoreceptors are concentrated near its with fixed number of segments, and have mouth. Circumferential and longitudinal neither chaetae nor parapodia; an example muscles on the periphery of each segment is Hirudo (the leeches). enable the worm to move. Similar sets of muscles line the gut and their actions move Structure of earthworm the food towards the worm’s anus. An earthworm is an elongated, tube-shaped, metamerically segmented organism (Figure Earthworm is a hermaphrodite, meaning 3.46). Its digestive system runs through that, the organism has both male and 172 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 172 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms female reproductive organs. Has an are openings of the vasa differentia (male opening of spermotheca, which is found opening). Additionally, earthworm has in segments 9, 10, and 11. Seminal ﬂuid clitella (singular clitellum) which secret from another worm is passed through a cocoon in which eggs are deposited. the opening during copulation. Ventrally, The mouth is overhang by a ﬂap called a on segment 14, there are very small prostomium. Movement is by means of slits, which are openings of the oviducts paired chaetae. (female opening) and on segment 15; there Segments Head Anus Clitellum (saddle) Figure 3.46 Structure of the earthworm Adaptations of earthworm to its mode GOFVOERRNONMLEINNTE PURSOEPOENRLTYYf) They are omnivorous; as they feed on of life live plant matters, fungi, bacteria and a) They have ideal shapes with chaetae microscopic animals. They also feed on dead organic matter from plants and for burrowing. animals. This feeding habit ensures sustainable food supply. b) They have gizzard for breaking up plant tissues. g) Under natural conditions, earthworms are less active; this limits oxygen c) They have clitellum, which holds consumption. together earthworms during copulation and forms an egg depositer structure h) They have looped surface vessels, called cocoon to ensure efﬁcient which facilitate absorption of oxygen provision of offspring during over a short diffusion distance. unfavourable conditions. i) Their haemoglobin has high afﬁnity to d) The mucus secreted helps to bind the oxygen. walls of burrows and helps the worm to pass through smoothly. j) The head is less elaborate. The worm has tactile and photoreceptive cells for e) They can thrust the earth aside when it locating food at night and sensing light is loose and consume it when it is tight. during the day respectively. This ability ensures burrowing under both conditions. k) They have chaetae that are used for movement. BIOLOGY FORM 5 KIWANDANI.indd 173 173 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Economic importance of Annelids pollutants from the soil and clean the Annelids are both ecologically and environment by transforming organic economically important; even though on wastes during feeding as a way of the other side, they have some drawbacks. waste management. Advantages of Annelids f) Their excretory wastes in form of a) They improve soil aeration, drainage casts increase cementing effects of soil particles; hence, increase water- channels and increase depth of the top holding capacity. soil through burrowing and mixing of soil layers. g) They are used as specimens in biological studies. b) They are used as bait in ﬁshing industry, for example earthworms. Disadvantages of Annelids a) They increase soil porosity and c) They are used as source of nutritious food rich in proteins and vitamins for aeration, which is detrimental to paddy ﬁsh and carnivorous birds. ﬁelds (rice plants in the ﬁeld). b) They damage young roots of the d) They are ecological decomposers; growing plants. hence, they contribute to nutrient c) Leeches are harmful to mammals, circulation; since they feed on reptiles, and ﬁshes as they suck blood. decaying organic matter. e) They are used for removing soil GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Activity 3.11 S1 S2 S3 Figure 3.47 Specimens S1, S2, and S3 174 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 174 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Examine the external features of GOFVOERRNONMLEINNTE PURSOEPOENRLTYYc) They have segmented bodies, which specimens S1, S2 and S3, (Figure 3.47) are arranged into regions, called and then answer the questions that tagmata comprising of the head, follow. thorax, and abdomen. The head of 1. Identify the specimens by their some arthropods such as arachnids and crustaceans is fused with the thorax to common names. form a structure called cephalothorax (prosoma). 2. In what kind of habitat would you expect to find specimen S3? d) Their body plan is bilaterally symmetrical. e) They have a ventral nervous system 3. What are the observable features; which make specimens S1, S2 and S3 and open circulatory system, which is differ from each other? dorsally positioned. f) They are triploblastic coelomate 4. Name the phylum and classes animals, which are metamerically to which each of the observed segmented. specimens belong. g) Their coelom is reduced and confined 3.7.4 Phylum Arthropoda to cavities of excretory organs and This is the largest group in the Kingdom reproductive ducts during their Animalia, with high species diversity. development and form another cavity Arthropods represent about three-quarters called haemocoel. of all known living organisms. Some of the well- known arthropods include insects, h) They have an open circulatory system. crustaceans, and arachnids. Arthropoda comes from two Greek words arthro that Classification of Arthropods means ‘joint’ and podos that means ‘foot’. Arthropods are classified into five classes Therefore, all arthropods have jointed namely; class Crustacea, which include appendages. Arthropods are found in almost crabs, class Arachnida, which include every known environment including marine, spiders and scorpions, class Chilopoda, for freshwater, and terrestrial ecosystems. example centipedes, class Diplopoda, for They vary extremely in their habitats, life instance millipedes, and class Insecta, which histories, and feeding habits. include cockroaches and grasshoppers. Characteristics of phylum Arthropoda Class Crustacea a) They possess a chitinous and Crustaceans form a large group of arthropods that include familiar animals such as crabs, sometimes calcareous exoskeleton, lobsters, prawns, shrimps, barnacles, and which may be rigid, stiff or flexible; crayﬁsh. Most crustaceans are marine shed during growth in some organisms. aquatic animals, other are found in fresh b) They have jointed, paired appendages water habitats, and a few are terrestrial, such as legs and antennae. 175 BIOLOGY FORM 5 KIWANDANI.indd 175 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools for example woodlice (Isopota) found in g) They have variable number of legs, leaf litter. sometimes up to ten legs and can be modified for swimming. Unlike Distinctive features of class Crustacea other arthopods, the legs and other Crustacea have distinctive features that appendages of Crustacea have two make them unique among other arthropods branches (they are biramous). as highlighted below: a) They possess two body division, which Structure of a crab A crab is covered with a thick exoskeleton are cephalothorax (the head fused with (carapace) composed of calcium carbonate. thorax) and abdomen. This means they are well protected against predators (Figure 3.48). The body is divided b) They have carapace or an exoskeleton into two parts: the cephalothorax and hardened with calcium salts which abdomen. The abdomen is entirely hidden acts as a protective shell. under the carapace; it may not be visible at all, unless the crab is turned over. The head c) They have heads bearing two pairs of bears two pairs of antennae. The animal antennae. is equipped with a pair of claws (pincers) which are the most important weapons with d) They have a pair of compound eyes at at least three functions: seizing, eating and the ends of movable stalks. subduing the prey. If the food is a shellﬁsh, then the pincers can exert force to open or e) They have at least three pairs of break the mollusc’s shell. Males also use mouthparts. pincers for or during ﬁghting. f) Gills are used for gaseous exchange, which are the outgrowth of the body wall or limbs. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Antennae Cheliped Propodus Eye Carpus Merus Walking legs Carapace Figure 3.48 Structure of a crab 176 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 176 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Class Arachnida Structure of a spider The arachnids represent the second The spider has two main body parts: a fused largest group of terrestrial arthropods head and thorax, called cephalothorax after the insects. The class includes the and abdomen (Figure 3.49). Most animals whose bodies are organised into external appendages are attached to the two tagmata called cephalothorax or cephalothorax. The appendages are legs, prosoma (fused head with thorax) and chelicerae, mouthparts, and pedipalps. On abdomen (opisthosoma). Most of them the ventral part of the abdomen are two are carnivores, except the mites, which are hardened plates covering the book lungs. herbivores. Members of this class include The spinnerets, which produce silk, are also spiders, mites, ticks and scorpions. located in the abdomen. Distinctive features of class Arachnida Walking Pedipalp Arachnids can be distinguished from other legs Chelicerae members of the phylum Arthropoda by the following features: Carapace a) Their bodies are divided into two Pedicel Abdomen regions; prosoma and opisthosoma, separated by a narrow waist-like Spinneret constriction. b) They lack antennae; alternatively, GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 3.49 Structure of a spider they use pedipalps to detect external stimuli. Adaptations of spider to its mode of c) They lack compound eyes, they only life have simple eyes. Spiders live in almost every habitat. They d) They lack true mouthparts; instead, are adapted to different environments they have two pairs of appendages born because: from prosoma. One pair, the chelicerae or poisonous fangs, is used for killing a) They have pairs of chericerae which preys or defending themselves; the produce silk for capturing preys. other pair called pedipalps holds the prey in place when the animal injects b) They have pedipalps for sensation. poison. c) They have four pairs of legs for e) Usually they have four pairs of locomotion.The hairy spiders have walking legs. stings used to paralyse prey and defend themselves. f) Their respiratory structures are book lungs or book gills or trachea. Subphylum Uniramia The centipedes (Chilopoda), millipedes (Diplopoda) and insects (Insecta) form a closely related group of arthropods. BIOLOGY FORM 5 KIWANDANI.indd 177 177 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools They have three features that distinguish a) They have a ﬂattened body with a them from other arthropods. The first is distinct head. However, other body possession of a single pair of antennae segments are similar, the trunk is not (crustaceans have two pairs and arachnids obviously divided into thorax and have none). The second is the presence of abdomen. strictly uniramus (unbranched) appendages. Thirdly, the cuticle is hardened using b) They have one pair of legs per segment. tanning process involving chemicals known as hydroquinones. It is made c) They are carnivores, feeding mainly waterproof using wax, and never has on insects and worms. calcium carbonate. For these reasons, the three classes are nowadays grouped d) Their ﬁrst trunk segments have together under \"Uniramia\". appendages, which are modiﬁed into a pair of poisonous fangs. Class Chilopoda This class consists of organisms found in Structure of centipede terrestrial environment. They are terrestrial Centipedes have a head bearing eyes, well- animals abundant in moist areas, such as developed one pair of mouthparts (jaws), leaf litters, under logs or rocks. An example and one pair of antennae (Figure 3.50). The of chilopoda are centipedes. body consists of many segments, each of which bears one pair of legs. The legs of Distinctive features of class Chilopoda the ﬁrst body segment are modiﬁed into The following features distinguish poisonous claws, and are used for defence centipedes from other members of the as well as for capturing and paralysing phylum Arthropoda: preys. They have tracheae used for gaseous exchange. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Segment Antennae Leg Eye Poisonous jaw Last pair of leg with hooks for defence Figure 3.50 Structure of a centipede Adaptations of the centipede to its a) They are fast moving animals; this mode of life helps them to catch their prey. Centipedes are adapted to a wide range of b) They feed on insects, spiders, and habitats because: worms, which they hunt and paralyse with a bite of their poisonous claws. 178 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 178 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms c) They have antennae for sensation. Structure of millipede d) They have poisonous claws for defence The millipede has elongated and cylindrical body in which each body segment bears and hunting. two pairs of legs. Millipedes are made up of a series of segments, whose number varies e) They have legs for locomotion. greatly from one species of millipedes to another (Figure 3.51). Many of the f) The last pair of legs has hooks for segments contain special glands that secrete defence. a noxious chemical to repel predators. The ﬁrst segment behind the head does Class Diplopoda not have legs, but the rest of the segments The class Diplopoda consists of members have legs. Towards the end, some of the with many legs; usually two pairs of legs segments have no legs. The number of per body segment. An example of a member legless segments varies from one millipede of class Diplopoda is a millipede. The head to another. Some species of millipedes have bears one pair of antennae and a pair of hair or spiny appendages protruding from mouthparts (jaws) while the trunk is not their bodies. Its head is on one end of its divided into thorax and abdomen. They are body, and is about the same diameter as scavengers that feed on decaying organic the adjacent segment. Also the head has a matter, like leaves and compost. pair of antennae that helps the millipede to sense the surrounding environment. One Distinctive features of class Diplopoda pair of mouthparts (jaws) is on the front Diplopods have unique features, which part of its head and the eyes are fixed above differentiate them from other Arthropods. its jaws. Most millipedes have simple eyes a) They have round bodies with clearly that provide basic vision, but not all types or species of millipedes have eyes. defined head, followed by other similarGOFVOERRNONMLEINNTE PURSOEPOENRLTYY segments. b) They have many legs; with two pairs of legs per segment. c) Most millipedes are herbivorous, feeding mainly on decaying vegetation. Figure 3.51 Structure of a millipede 179 BIOLOGY FORM 5 KIWANDANI.indd 179 10/10/2019 14:06

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE Adaptations of the millipede to its mode of life Activity 3.12 Millipedes have the following features that make them adapt to their environment: S5 a) They have many, short and strong legs S6 that enable them to burrow into the soil. b) They produce special secretions, which help them to moisturize dead organic matter on which they feed upon. c) A millipede tends to curl up into a tight ﬂat coil for self-defence, and protect their delicate legs inside an armoured exoskeleton. d) Millipedes produce an offensively odorous fluid (repugnatorial fluid) when provoked, this acts as a defence against predators. Class Insecta GOFVOERRNONMLEINNTE PURSOEPOENRLTYY S7 The class contains all insects and is the most diverse group of organisms on Figure 3.52 Specimens S5 , S6 , and S7 earth. Members of this class are found in all environments including fresh water Study specimen S5 , S6 , and S7 (Figure aquatic and terrestrial environments, but 3.52) carefully, then answer the very few are found in marine habitats. questions that follow: They differ in morphology and feeding 1. Identify specimens S5 , S6 , and S7 by habits. Although members of this group vary greatly, they have some common their common names. characteristics, which make them to 2. Name the classes to which belong into the same class. Members of this class have three pairs of walking legs, specimens S5 and S6 belong. three distinct body parts or regions and 3. List the observable features that one pair of antennae borne on the head. The antennae are used as sense organs have enabled you to place the two for detection of odour molecules in the specimens in (2) above into their air, changes in the concentration of water respective classes. vapour, sounds, and gauging air speed. Examples of insects include grasshopper, butterfly, house fly, cockroach, beetle, bees, ant, wasp, and termite. 180 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 180 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Distinctive features of class Insecta GOFVOERRNONMLEINNTE PURSOEPOENRLTYYmesothoracic legs and metathoracic legs Insects have the following features that respectively). The thorax also bears two differentiate them from other arthropods: pairs of wings in most adults insects. The body is covered by a rigid exoskeletons a) Their bodies are divided into three (cuticle) secreted by the epidermal layer. main regions or tagmata, namely the This occurs in jointed sections or plates to head, thorax, and abdomen. allow body movement. The exoskeleton is made up by a structural protein known b) They have three pairs of walking legs as chitin. It is coated with wax, which is on the thorax (one pair per thoracic impermeable to water. The exoskeleton segment). provides attachment for body muscles. Cockroaches are mostly dark brown or c) They usually have one or two pairs of reddish in colour. Male cockroach has a wings on the thorax, some members narrow abdomen an expanded tergum of may lack wings. the last visible segment, and has a pair of styles at the end of abdomen, while the d) They use the tracheal system as their female cockroach has a wide abdomen respiratory surface with segmental with a large podical plates used to carry spiracles. the ootheca, and lacks styles (Figure 3.53 a, b and c). e) They undergo metamorphosis during their development through the molting 3.7.4 Body systems in arthropods process. Like other animals, arthropods have various body systems which enable them f) They have a pair of compound eyes to perform and sustain their life processes. and simple eyes. These include: respiratory, circulatory, digestive, nervous, reproductive and g) They usually have three pairs of excretory systems. In this text, digestive mouthparts, which are maxillae, and reproductive systems will be dealt mandible, and labrum. with. Structure of a cockroach The body of a cockroach is elongated and segmented, divided into a head, thorax, and abdomen. The thorax is subdivided into three parts; prothorax, mesothorax and metathorax and each segment bears one pair of legs (prothoracic legs, BIOLOGY FORM 5 KIWANDANI.indd 181 181 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Jointed legs Antennae Head (a) Compound eye Thorax segments Antennae Fore wing Head Compound eye Abdomen segments Mouth parts Hind wing Cercus Antennae Head Compound eye Mouth parts GOFVOERRNONMLEINNTE PURSOEPOENRLTYYWalking legWalking leg Abdomen Abdomen Cercus Cercus Anal style (b) (c) Figure 3.53 Structure of a cockroach (a) dorsal view (b) male ventral view (c) female ventral view Digestive system of a cockroach and pharynx) are found inside the head The alimentary canal of the cockroach is capsule and not visible in the dissected long and coiled tubular structure starting at cockroach, while the other three part the mouth opening. It is divided into three are visible. The gizzard is muscular main parts, namely foregut (stomodaeum), and internally provided with six cutical midgut (mesenteron or ventriculus), and pointed teeth, for crushing the food. hindgut (proctodaeum). The foregut is differentiated into ﬁve parts: Buccal The midgut is short and tubular lined with chamber, pharynx, oesophagus, crop, and glandular endoderm. At the anterior end gizzard. The fist two parts (buccal cavity of midgut there are eight blind glandular 182 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 182 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms hepatic caeca (digestive/mesenteric Oesophagus Eye caeca) which increase the surface area for Crop Salivary duct absorption. The cells lining the mesenteron Salivary secrete enzymes. Most of the food nutrients gland are digested in the mesenteron and the end products of the digested food substances Salivary are absorbed by the cells of mesenteron receptacle and digestive caeca. The distal end of the midgut is indicated by the presence of Gizzard malpighian tubules which are excretory in Hepatic caeca function (Figure 3.54). Mesenteron The hindgut comprises of the ileum, Malphigian colon, and rectum. The ileum is short tubules Ileum Rectum and narrow and receives the openings Anal cercus of the malpighian tubules. On the other hand, colon is wider and longer than the Colon Tenth abdominal tergum rectum. The wall of the rectum is provided with six rectal papillae, which help in Figure 3.54 The digestive system of a female the absorption of water and salts. The cockroach digestive system terminates with the anal opening (anus) through which undigested Reproductive system of a male material is removed in process known as cockroach egestion. The male cockroach has a pair of anal styles; the external structure which differentiate the male cockroach from female. Testes are small lobed masses (lobules) lying laterodorsally in the fourth and fifth abdominal segments. There are two testes (one on the right and the other on the left), each joined to a slender vas diferens (plural vasa diferentia) which connect to the wider ejaculatory duct. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Lobules of testes Vas deferens Mushroom gland Ventral phallomere Ejaculatory duct Cercus Right phallomere Pseudo-penis Anal style Figure 3.55 The reproductive system of a male cockroach The testes produce sperms which transfered called spermatophore (sperm pouch). through the vasa differentia to the seminal There are three asymmetrical chitinous vesicle. All sperms from a seminal vesicle structures, called male gonapophyses or are collected together into a large bundle phallomeres; the right phallomere, the 183 BIOLOGY FORM 5 KIWANDANI.indd 183 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools left phallomere (largest) and the ventral chamber. A genital pouch or gynatrium is phallomere (smallest). These, together with divisible into a genital chamber in front and the pseudo-penis, form the organ used to the oothecal chamber behind. transfer the sperm pouch to the female during copulation (Figure 3.55). Female gonapophyses consist of three pairs of chitinous rods hanging from the roof Reproductive system of a female of the oothecal chamber into its cavity. cockroach They help in shaping the ootheca and The female organs consist of ovaries, depositing eggs in it. The ootheca of the oviduct, vagina, genital chamber, cockroach contains sixteen fertilised eggs, spermathecae, collateral glands, and female coated with the secretions (protein, and gonapophyses (ovipositor processes). dihydroxyphenol) of the colleterial glands. Ovaries of the cockroach are located The eggs are lying in two rows, each with laterally in the abdominal segments four, eight eggs. The female cockroach carries the five and six. Each ovary consists of eight ootheca for several days and finally protrude ovarioles. (Figure 3.56). more and more until it is deposited to the dark crevice, and for about six weeks, the One oviduct from each side open into a young cockroaches hatch out and grows genital chamber at a slit-like aperture. A pair into adult. of collateral glands also open in the genital Ovaries Filament GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Left collateral Egg chamber gland Pedicel Oviduct Common oviduct Spermatheca Right collateral gland Genital chamber Oothecal chambers Figure 3.56 The reproductive system of a female cockroach Dissection of a cockroach organism and on accurate descriptions of Animals are dissected to analyse the structure the body parts. Dissection involves attentive and function of their body components. isolation and removal of individual organs, Dissection provides the crucial opportunity accessing the area in which the organs are for students and other scientists to develop situated, and systematically removing the scientific observational skills. The methods anatomical connections of organ to its of investigating gross structure depend on surrounding. careful dissection or cutting apart, of an 184 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 184 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Dissection of a cockroach allows learning while the dorsal side (tergum) is facing of the location and appearance of internal upwards. organs; distinguishing among different types of tissues within an insect body e) Allow the wax to cool, and then the and to describe the major body systems. insect will be fixed (Figure 3.57). The following practical guidelines in dissecting a cockroach, permits the studies of internal features of the insect, including its heart, circulatory, digestive and reproductive systems. Materials necessary for the dissection of a cockroach include dissection kit, dissecting tray or board, a piece of thread, dissecting pins or office pins, scissors, fine-point forceps gloves and chloroform. General procedure for dissecting a Figure 3.57 Cockroach fixed for dissection cockroach a) Melt little wax in the centre of f) Since cockroach’s heart is on its dorsal side attached inside the terga and dissecting tray. nervous system is on its ventral side, when dissecting, cut either on its left or b) Wear a pair of gloves. right lateral side (pleural) from the last segment of the abdomen to the thorax. c) Cut the insect wings, antennae and legs close to their base. d) Place the cockroach in the melted wax or use dissecting pins, to place the cockroach on its ventral side (sternum) GOFVOERRNONMLEINNTE PURSOEPOENRLTYY (a) (b) 185 Figure 3.58 Fixed cockroach showing (a) lifted aside terga (b) pined terga 10/10/2019 14:06 BIOLOGY FORM 5 KIWANDANI.indd 185

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools g) Carefully lift the last abdominal tergum i) Remove fats to expose the gut and using a forcep, then cut one side of the other organs in the body cavity. abdomen. Work forward by lifting aside the terga with forceps and cut j) Cover your dissection with water to around the edge with small scissor bring the organs float up, prevent them or scalpel up to the base of the head from drying up and to enable them (Figure 3.58a). being seen clearly. h) Place a pin to hold the terga aside (you k) Loosen the gut, deflect to one side and can use an optical pin to clearly pin it pin it to display all the systems (Figure and ease observation of all parts in the 3.59). terga as well as those of the abdominal cavity (Figure 3.58b). Salivary gland Receptacle Oesophagus Crop Gizzard Hepatic Digestive caeca Mesenteron Colon Rectum Malphigian tubule Ileum Anal cercus GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 3.59 General view of the dissected cockroach l) Make sure the body wall is neatly Safety precautions pinned aside, the dissection is generally neat with all required features; avoid 1. Care should be taken when working damaging the organs and blocking the with live specimens and apparatus, ducts. including dissection kit tools. m) Carefully examine all internal parts 2. The working area, equipment and using a hand lens. instruments used must be thoroughly cleaned and decontaminated after 186 use, by using appropriate methods. 3. Good hygiene practices should be observed all the time; hands should be kept away from the mouth, nose, eyes, and face during and after dissection. Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 186 10/10/2019 14:06

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Hands should be thoroughly washed FOR ONLINE USE ONLY with soap or disinfectant immediately DO NOT DUPLICATE after conducting a dissection practical Comparative studies of natural groups of organisms session. 2. State the function (s) of each 4. All other safety laboratory rules labelled part. should be observed; the teacher or laboratory technician should guide 3. Explain how the central location the students. of a gizzard helps the organism in digestion. 4. Differentiate the crop from the digestive caeca. Activity 3.13 Dissection of a GOFVOERRNONMLEINNTE PURSOEPOENRLTYYNote: cockroach to display the digestive system 1. The diagrams should be well drawn, large enough, generally neat and Materials accurate. Fresh male or female cockroach, dissection kit, chloroform, dissecting 2. The caption should be well indicated; tray or dish with wax intact, source of when written on top of the diagram it heat, and water. should be capitalised and underlined, while when written below the diagram, Procedure the first later should be upper case and a) Collect a fresh male or female should not be underlined. cockroach. 3. Label lines should be indicated in pencil; should be straight without b) Prepare a dissecting tray or board arrows; and should not cross each and chloroform for anaesthetizing other. the specimen. 4. Labelling words should be on the c) Dissect the cockroach in a usual required parts and written using blue way; deflect the gut to your right or black ink. hand side, to fully display the digestive system. 5. The magnification of the diagram should correspond to the real Questions specimen. 1. Draw a diagram of your dissection and label only the parts of the digestive system. Compare your diagram with that of Figure 3.59. BIOLOGY FORM 5 KIWANDANI.indd 187 187 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Activity 3:14 Dissection of a cockroach GOFVOERRNONMLEINNTE PURSOEPOENRLTYYa) They possess a cuticle, which prevents to display the reproductive system water loss and makes them resistant to desiccation, predators, invasion Materials by parasites, as well as physical and Fresh male or female cockroach, mechanical injury. dissection kit, chloroform, dissecting tray or board with wax intact, source of b) They have modified and specialised heat, and water. mouthparts according to their feeding habits; their mouthparts have Procedure mandibles for cutting and chewing, a) Collect a fresh male or female piercing, and sucking as in mosquitoes. cockroach. With reasons identify c) They have a well developed and the sex of your specimen. efﬁcient respiratory system extending towards the individual cells in which b) Prepare a dissecting tray or dish gaseous exchange takes place. and chloroform for anaesthetizing the specimen. d) They possess ﬂexible jointed appendages which facilitate rapid c) Dissect the cockroach in a usual movement with minimum utilisation way and deflect the gut to the left of muscles. hand side of the animal, to fully display the reproductive system. e) They possess sensory organs such as antennae, compound eyes, and cerci, Questions which are capable of detecting slight 1. Draw a well labelled diagram of movements, sounds, or chemicals. your dissection. Compare your f) They undergo moulting (ecdysis) diagram with that of Figure 3.55 or process during development by Figure 3.56. removing their hard covers, and become soft to facilitate growth. 2. State the role(s) of each labelled part. g) Their small and flattened body shapes enable them to hide into small cracks 3. Classify the organism to the class and crevices, where they live. level. h) They possess coloured cuticle, which Adaptations of Arthropods to their provides camouﬂage against predators. environment Arthropods are the most abundant and i) Wings help them in dispersal and diverse group of organisms on earth. They colonization of new habitats. possess the following adaptive features, which help them to be a successful diverse Economic importance of Arthropods group: Arthropods play an important role in the world. However, not all arthropods are useful; some are harmful to other living organisms. 188 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 188 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Advantages of Arthropods GOFVOERRNONMLEINNTE PURSOEPOENRLTYYc) Some arthropods destroy crop plants; a) Insects such as bees and butterﬂies examples include locusts and the caterpillars of butterflies and moths. are useful in agriculture; as they act as pollinators; many plants depend on d) Some arthropods are parasitic to insects for pollination. mammals. Good examples of such arthropods are ticks, jiggers, and b) They are used in industries for bedbugs, which grip themselves on production of honey and wax human skin and suck blood. materials; for example honey bees. 3.7.5 Phylum Chordata c) Insects are used in biological control This is the third largest phylum in the of pests; in certain cases, insects have kingdom Animalia. The phylum comprises been very effective predators to reduce of all animals that at some point during the number of pests. For example, lady their lives, possess a hollow nerve cord beetles are used to kill aphids (the pest and notochord. insects that transmit viruses to plants). General characteristics of phylum d) Many arthropods are used as food; Chordata they are a good source of protein for a) They have a notochord at some stages humans and other animals. Example include shrimps and lobsters, crabs, of their development. Notochord is edible grasshoppers, locusts and a stiff, ﬂexible rod located dorsal to grasshoppers, and many larvae of the gut and ventral to the nerve cord. beetles and moths. In most chordates the notochord is replaced by a vertebral column e) Insects are used in research and (backbone) during adulthood. biological studies. b) They have visceral clefts which are slits perforating the body wall in the f) Insects such a as butterflies are valued pharynx. They are useful in ﬁshes for their beauty. and tadpole larva of amphibians for gaseous exchange as they use gills. In g) Many arthropods are used as indicators adult amphibians, reptiles, aves and of the quality of environment. mammals, the visceral clefts never develop gills. Disadvantages of Arthropods a) Some insects are vectors of animal c) They have endoskeletons made up of bone and cartilage. and plant diseases. For example, mosquitoes carry Plasmodium, which d) They have post-anal tail. cause malaria, and tsetse ﬂies carry Trypanosoma, which cause sleeping e) They have a dorsal hollow nerve cord sickness to human beings. Whiteflies found above the notochord and below carry Tomato yellow leaf curl virus the epidermis. In higher chordates, which cause chlorosis in plants. the anterior part forms a brain and the b) Some arthropods such as scorpions posterior part forms a spinal cord. and centipedes bite human beings, release their poisons causing severe pains. 189 BIOLOGY FORM 5 KIWANDANI.indd 189 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools f) They have ventrally positioned heart, GOFVOERRNONMLEINNTE PURSOEPOENRLTYYDistinctive features of class which is a pumping organ as it pumps Chondrichthyes blood. Moreover, they have closed Members of the class Chondrichthyes circulatory system. have the following unique features, which distinguish them from other fishes. g) They are triploblastic, coelomate a) They possess placoid scales (tooth- animals with bilaterally symmetrical body. like) covering their skin. b) They have cartilaginous endoskeleton. h) They have two pairs of pentadactyl c) They have five pairs of visceral clefts limbs or fins formed from more than one body segment. In higher chordates as separate gill slits for gaseous they are attached to the rest of the exchange,with no opercula or gill skeleton by pelvic and pectoral girdles. covers. d) They have ventral mouths. i) Some members (cartilagenous fish, e) They have heterocercal tail ﬁns bony fish, amphibians and reptiles) (asymmetric in shape), which prevent are poikilothermic organisms, in that them from sinking as they lack swim their body temperature depends on the bladder for buoyancy. environmental temperature changes f) They have paired ﬂeshy pectoral and while others (birds and mammals) pelvic ﬁns for swimming. are homeothermic organisms, as their g) They undergo internal fertilisation. body temperature remains constant regardless of the changes in external Structure of a shark environmental temperature. The body is more or less completely covered by placoid scales and has a Classes of phylum Chordata lateral line that runs along the side of its There are six classes of chordates namely; body for detecting water currents and Chondrichthyes (cartilagenous ﬁsh such wave intensity. Its pectoral fin is anterior as shark and rays), Osteichthyes (bony to the pelvic fins; usually the latter has ﬁsh such as tilapia and tuna), Amphibia claspers (pterygopodes) which are used (amphibians such as frog and toad), as copulatory organs in males, and the Reptilia (reptiles such as lizard, crocodile, caudal fin is heterocercal in shape. The and snake), Aves (birds such as hen, mouth is located ventrally with teeth, parrot, eagle, and pigeon) and Mammalia which are constantly replaced. It has small (mammals such as human, mouse, bat, eyes, which have lower lids used to cover rabbit and monkey). the eyes during feeding (Figure 3.60). The gill slits are naked (no operculum) Class Chondrichthyes and has a spiracle which is a modified All members of this class have paired fins, gill slit on top of the head that provides paired nares, jaws, and a two chambered oxygenated blood directly to the eye and heart. Additionally, they have scales brain through a separate blood vessel. and endoskeletons made of cartilage. The intestine is short but with absorptive Members of class Chondrichthyes features increased by spiral valves. include dogfish, sharks, skates, and rays. 190 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 190 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Lateral line Dorsal fin Eye Mouth Caudal fin Gills openings Anal fin Pectoral fin Clasper (males) Pelvic fin Figure 3.60 Structure of a shark Class Osteichthyes as separate gill openings covered by The class includes all bony ﬁshes, such opercula. as tuna, tilapia, rainbow fish, herring and catfish. They are all aquatic organisms f) They produce eggs and undergo found in marine and fresh water bodies. external fertilisation. Distinctive features of class g) They have swim bladder, which is Osteichthyes in the abdominal cavity next to the The following features differentiate backbone. This helps them to rise and members of the class Osteichthyes from sink (buoyancy) in water at particular other fishes. depth without using much energy. h) They have a terminal mouth. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY a) They have thin, round, and cycloid Structure of Tilapia scales (made up of bones) on their skins, which are impermeable to water, The body is laterally ﬂattened and hence reducing water loss in marine tapered at both ends. Has a streamlined environment, and restrict entry of water shape to overcome water resistance in fresh water ﬁsh. during swimming. Its body surface is covered by cycloid scales, which point b) They are bony fish, as they have bony backwards in order to reduce resistance skeletons. during swimming. The fish has a lateral line that runs along the side of its body. c) They have paired pectoral and pelvic The lateral line is a series of sensory ﬁns, supported by bony rays for organs called neuromasts that helps swimming. the ﬁsh to sense vibrations and water pressure for navigating and locating prey d) They have homocercal (symmetrical) (Figure 3.61). tail ﬁns. e) They have four pairs of visceral clefts BIOLOGY FORM 5 KIWANDANI.indd 191 191 10/10/2019 14:06

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE Dorsal fin Caudal fin An eye Lateral line Mouth Anal fin Operculum Pectoral fin Pelvic fin Figure 3.61 Structure of a tilapia Class Amphibia GOFVOERRNONMLEINNTE PURSOEPOENRLTYYamphibians are “tied” to water bodies in This class includes amphibians such order to survive and reproduce. Normally, as frogs, toads, caecilians as well as amphibians undergo metamorphosis from salamanders. Amphibians are tetrapod a juvenile as an aquatic larval form into a with the exception of caecilians, which terrestrial adult. are limbless. All amphibians lay eggs with the exception of some caecilians and Distinctive features of class Amphibia some toads. For example members of the Amphibians have the following distinctive caecelian genera Scolecomorphus and features: Schistometopum give birth to live young. a) They dwell both in water and on land, as Also the toad genus Nectophrynoides; the members of this genus also give they depend on water for reproduction, birth to live young. In the latter genus hence the name amphibian, which of Nectophrvnoides there is the Kihansi means double life. Spray Toad (Nectophrynoides asperginis); a small toad endemic to Tanzania with this b) Amphibians’ offspring begin their life unique characteristic of giving birth to cycle under water and breath by means live young toadlets. of gills. As they grow to adulthood they move to terrestrial and breathe by means of either skin or lungs. The word amphibia refers to “double life”, c) They have soft moist skin without or life in water and on land. Amphibians scale, used for gaseous exchange to are cold-blooded (ectothermic) supplement lungs and buccal cavity. vertebrates whose body temperature is not regulated by internal mechanisms. They d) Amphibian eggs have a jelly structure, inhabit a wide range of habitats, ranging which is prone to dehydration when from terrestrial to aquatic environments. exposed to air. Most amphibians spend a part of their life in aquatic environment and another e) Amphibian’s fertilization takes place part in terrestrial environment. Due to outside the female body (with the their life cycle and physiology, many exception of some caecilians and some toads including the Kihansi spray toad which give birth to live young). 192 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 192 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms f) They have two pairs of pentadactyl fore limbs, whereas in female frogs these limbs for locomotion. The forelimbs are absent. Moreover, the abdomen of the have less musculature, while the male frog is much slender than that of the hind limbs are webbed and long with female frog. powerful muscles for jumping. g) They have long and protruding eyes GOFVOERRNONMLEINNTE PURSOEPOENRLTYYStructure of Kihansi spray toad for viewing preys widely and for The Kihansi spray toad is a tiny toad of avoiding enemies. just about two centimetres in length, endemic to a two hectare area of Kihansi h) They have sticky tongue, which helps Gorge, of the Udzungwa Mountains, in them in capturing prey. the southern central of Tanzania. The toad is a highly specialized toad species, i) They undergo metamorphosis for adapted to giving birth to a fully formed development from larval to adult stage toadlet. Currently it is one of the very in their life cycle. few amphibian species known to give birth to fully formed toadlets. The overall Structure of a frog background colour of Kihansi spray toad The body of the adult frog is divisible is golden yellowish, with yellow and into the head and trunk. The neck and tail brown speckles on the dorsal surface, or parts are absent. The head is blunt, and dark lateral bands with adjacent lighter the mouth is terminal, with two ﬂexibly striping (Figure 3.62b). Ventrally, the skin movable jaws. The head bears external is translucent, whitish near the throat and nares, a pair of nostrils that lead into nasal posterior, with the liver, fat bodies, and passages. The eyes are large, bulged and intestines visible through the ventral skin. covered by a nictitating membrane that Moreover, these toads have flaps over the protects them while in water. Behind the nostrils that may be a special adaptation eye, there is a circular patch, a tympanum for living in the spray zone of waterfalls. or eardrum, which receives sound signals. On the feet, toes are partially webbed, with no external tympana. The trunk widens in the middle, but tapers towards the end; four legs help in Body systems of chordates swimming and jumping. The hind limbs Chordates have a number of body systems end in ﬁve digits and are larger and more which enable them to perform various muscular than the fore limbs that end in physiological processes. Digestive and four digits. In both, fore and hind limbs, urinogenital systems of a frog or toad and the digits are webbed for swimming rat or mouse will be emphasized in this text. purpose (Figure 3.62a). Frogs exhibit sexual dimorphism in that male frogs have sound producing vocal sacs and copulatory pads on the ﬁrst digit of the BIOLOGY FORM 5 KIWANDANI.indd 193 193 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Warts Nostril Eye Hind limb Mouth Webbed toes Tympanum Fore limb Fore finger digits (a) (b) Figure 3.62 A photo showing the structure of (a) a frog (b) Kihansi spray toad Source: UDSM, Zoology and Wildlife Conservation Digestive system of a frog GOFVOERRNONMLEINNTE PURSOEPOENRLTYYinto the stomach to support swallowing The alimentary canal of a frog consists and ensure that small food particles are not of the mouth, buccal cavity, pharynx, retained in the anterior parts. The stomach oesophagus, duodenum, ileum, and the is thick walled, folded and elongated to rectum, which open into the cloaca at the increase the surface area for secretion of anus. The mouth is wide for ingestion of gastric juice used for digestion. large pieces of food material. They have flattened buccal cavity that emerges with The duodenum lies parallel to the stomach the pharynx and it contains small, conical and receives the secretions of bile and and sharp pointed teeth which are similar pancreas via hepato-pancreatic duct. The (homodont) used for cutting and crushing internal surface of the duodenum has many the food particles. Close to the angles of folds, which increase the surface area for the jaws, there are two small openings, one secretion and absorption. The duodenum on each side, known as eustachian tubes. connects to the ileum, which has several These tubes are used for balancing pressure coils, and longitudinal internal folds, in the inner ear while the frog is swimming. where most of the digested food substances Ventrally in the midline there is a narrow are absorbed here. The alimentary canal longitudinal slit (glottis) which leads into terminates in a rectum, which is short, and the larynx. wide. Rectum is the place where feaces accumulate, and later pass periodically They have a short oesophagus that bears through the anal sphincter into the cloaca longitudinal folds, which close to prevent and eventually egested out of the body. entry of air into the stomach and allow The liver consists of two large lobes (the dilation during swallowing of food. Buccal left lobe and the median lobe). The median cavity, pharynx and oesophagus have cilia, lobe is smaller than the left lobe. The gall which constantly drive the mucus backward bladder (lies between the liver lobes) and the bile duct run into the duodenum 194 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 194 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms through the pancreas. The pancreas lies and later discharge into the duodenum. In between the stomach and the duodenum. the mesentery near the duodenum lies a The secretions are discharged into the bile spherical red structure called spleen, which duct, which become hepato-pancreatic duct has no digestive role (Figure 3.63). Oesophagus Stomach Liver Pacreas Gall bladder Mesentery Duodenum Ileum Rectum Cloaca GOFVOERRNONMLEINNTE PURSOEPOENRLTYYFigure 3.63 The digestive system of a frog Urinogenital system of a male frog fluids possibly secreted by the blood A male frog is slender, with nuptial pads vessels from its wall, which acts as a on the first finger which is one of the reserve of water during dry seasons. morphological features that distinguish Cloaca is an outlet that serves as the it from female frog, which is fat, with an only opening for digestive, reproductive expanded abdomen due to the presence and urinary tracts. Also, a frog has two of eggs in the ovisacs. A male frog has testes, each suspended by a double fold two kidneys, which are dark red, oval, of mesorchium. They lie ventrally below and somehow flattened, located near the front part of the kidneys, and from to the testes, ventrally and below the them there are several fine vasa efferentia ureter. The ureter passes along the outer that cross the mesorchium and enter the border of each kidney, and opens into the anterior kidney tubules which convey cloaca. The bladder is a thin sac arising sperms to the ureter. In both left and right as a ventral outgrowth, the cloaca, with ureter, there is a pouch-like gland situated its outlet closed by a sphincter. Since on each side of the male urinary bladder the ureter is not opening to the bladder, (vesicula seminalis) which store sperms it is not a urinary bladder, but contains until the breeding period (Figure 3.64). 195 BIOLOGY FORM 5 KIWANDANI.indd 195 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Fat body Left testis Right testes Vasa efferentia in the mesorchium Kidney Vesicula seminals Ureter Bladder Cloaca Figure 3.64 The urinogenital system of a male frog Urinogenital system of a female frog Female frog has left and right ovaries, lying in the same position as the testes, each suspended by a mesovarium and overlie the kidneys. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Right lung Right liver lobe Fat body Left ovary Mesovarium Left oviduct Right ovary Cloaca Kidney Right oviduct Ureter Ovisac Bladder Figure 3.65 The urinogenital system of a female frog 196 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 196 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms The ovaries have flattened and numerous GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 3.66 Positioning the frog or toad for half black and half white eggs which dissection can be seen through epithelium. They are connected to a long thin tube called f) Pin the frog down on the tray through oviduct. Each oviduct is dilated in its the fore and hind limbs; the pin on posterior region to form an ovisac, which each hand and foot should be at an store eggs until the laying period. The angle to the tension put on it. kidneys are connected to a tube called ureter that is used solely as a urinary duct, g) Use forceps to lift the skin of the while in male frogs it passes both, sperms abdomen and use scissors to make a and urine. The ovisac and ureter open to slit in the mid ventral line, and then the cloaca (Figure 3.65). insert one blade of the scissors into the slit (Figure 3.67). Dissection of a frog or toad Dissecting a frog or toad is a common and Figure 3.67 Opening the body cavity of an important experience in the structural and anesthetized frog or toad anatomical studies of a typical vertebrate. The inside of a frog represents the general form for a vertebrate; as the organs present in a frog and the way they are laid out are similar enough to that of other animals. General procedure for dissection of a frog or toad a) Put on a pair of gloves. b) Wet a piece of cotton wool with chloroform and put it inside an airtight container such as desiccator. c) Put a live frog or toad inside the container, containing wet cotton wool, and leave it for about four to five minutes to anaesthetize it. d) Take the frog or toad from the airtight container using forceps, place it on the dissecting tray or board and leave it for about 30 minutes to allow evaporation of chloroform. e) Lay the frog or toad on its dorsal side (back), leaving the ventral side (abdomen) facing upwards (Figure 3.66). 197 BIOLOGY FORM 5 KIWANDANI.indd 197 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Cut the skin forward to the level of j) Lift the abdominal vein by using the lower jaw; cut transversely at the forceps and cut alongside it to the level of each arm as far as the elbows. breast bone (xiphisternum). Then, Similarly cut the skin back to the level hold the loose piece of the abdominal of the pelvic girdle and cut towards wall up and cut across the centre of the side of each hind limb down to the the xiphisternum. Grip the cut piece, knee. loosen it as far as the ligatured part and cut it close to that part; be careful not h) Hold the skin with forceps and loosen to cut the vein. the skin from the underlying muscles using the surgical blade, turn the skin k) Cut through the pectoral girdle on flap back and pin it. either side of the mid-line and remove the central piece of the girdle to expose i) Ligature the ventral abdominal vein at the heart, and then cut the body wall two sides. Use scissors to make two transversely below the arms. small slits and insert a loop of thread through the slits by using forceps and l) Turn the tray in such a way that the legs grip between their points; pull the are facing away from you, cut the body thread through the slits and cut the wall on either side of the mid-line to loop, and then tie the threads apart the pelvic area, remove the portion of in order to prevent bleeding and cut the body wall and cut transversely to between the ligatured points (Figure each leg. Pin aside the body wall and 3.68). turn the tray to its original position. At this point the body cavity will be already opened up. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY m) Remove any debris and leave the dissection clean. Sting n) Cover the dissection completely with water to avoid the drying of the organs and enhance clear observation. A hole o) With the help of a hand lens, observe ligature the visceral (general) view of the dissected frog and note the position and shape of the organs (Figure 3.69). Figure 3.68 Ligaturing of the a frog 198 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 198 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Lung Heart Gall bladder Anterior part of anterior Liver abdominal vein Ileum Stomach Posterior part of anterior Duodenum abdominal vein Rectum Bladder Figure 3.69 General view (visceral) of the dissected frog or toad p) In displaying the digestive system, pinGOFVOERRNONMLEINNTE PURSOEPOENRLTYYr) In case of a female frog; pin the right out the stomach to either side of the animal. Pin out the lungs, and turn the ovary on top of the left ovary, loosen liver lobes forward and hold them in place with pins and grip the ileum to and pin out the right oviduct and pin cut the mesentery and loosen the coils, the bladder aside. but do not cut the mesentery of the duodenum and rectum. Rearrange the s) For the nervous system; remove duodenum in position to expose the the pins from the skin of the head pancreas and pin out the ileum to your and remove the floor of the mouth right hand side to make all features by cutting through angle of the jaw visible. to expose the first spinal nerve (the hypoglossal nerve) which curves q) In displaying the urinogenital system, the pharynx and proceeds forward the cloaca should be opened by ventrally around the floor of the mouth removing the ventral portion of the to supply the tongue. pelvic girdles. This should be done by inserting one blade of the scissors t) Remove the flesh from both fore limbs through the girdle, followed by cutting around the shoulders and remove the through the girdle as near to the mid pins from the lungs and the stomach. line as possible, and lastly cutting on Cut through the oesophagus and each side and removing the central remove the lungs, heart, stomach and portion of the girdle. Care should other parts of the alimentary canal. be taken to avoid cutting the blood vessels. u) Remove the reproductive and excretory parts, when removing the kidney. Take care not to cut the aorta. v) Remove any remaining membranes surrounding the abdominal lymph sacs in order to expose the second spinal nerve called the brachial nerve (which 199 BIOLOGY FORM 5 KIWANDANI.indd 199 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools receives branches from the first and GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Activity 3.15 Dissection of a frog/toad third nerve to form the brachial plexus) to display the visceral or general view and other 3rd to 10th spinal nerves. (in situ) and digestive system. w) Trace the sympathetic cords on Materials either side of the aorta, notice the Fresh male or female frog or toad, sympathetic ganglia and identify the dissecting kit, dissecting tray or board, rami communicanes between the a piece of thread, chloroform, water, a spinal nerves and the sympathetic pair of gloves, and cotton wool. ganglia. Procedure x) Cut the flesh of the pelvic girdles a) Dissect the frog or toad in a usual through both thighs and trace the sciatic plexus (formed as an interconnection way, open up the body cavity and of the seventh, eighth, ninth and tenth) pin aside the body wall to display the and the sciatic nerve (which passes visceral (general) view of the animal down the leg close to the femur, and in an undisturbed condition. composed of the mainly joined eighth and ninth nerves). b) Deflect the alimentary canal to your right hand side; which is the left hand Safety precautions side of the animal and pin it to fully and display the digestive system. 1. Care should be taken when working with live specimens such as frogs Questions or toads, also chemicals like 1. Draw a large, neat well-labelled chloroform, as well as apparatus and equipment including the dissection diagrams of the following: kit tools. a) Visceral/general view. 2. The working area, equipment and b) Digestive system. instruments used must be thoroughly c) Compare your diagrams with cleaned after use using appropriate methods. Good hygiene practices that of Figures 3.63 and Figure should be observed at all times; 3.69. keep hands away from the mouth, nose, eyes and face during and 2. Explain the significance of ligaturing after dissection; and wash hands and flooding the specimen with thoroughly using an antiseptic or water. soap immediately after conducting a dissection practical session. 3. State the role(s) of each part of the digestive system. 3. All other laboratory safety rules and regulations should be adhered to 4. Classify the frog to class level. under the supervision of a teacher or laboratory technician whenever working in the laboratory. 200 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 200 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Activity 3.16 Dissection of a frog to regulate their body temperature by display the urinogenital system behaviour, either by basking in the sun Materials to warm themselves or by hiding under Fresh male or female frog or toad, cover to cool their body. Most of them dissection kit, dissecting tray or dish, a are tetrapods, with claws on their toes. piece of thread, chloroform, water, and cotton wool. Reptiles such as snakes and some lizards are legless, although they are descendants of four-limbed ancestors. Procedure GOFVOERRNONMLEINNTE PURSOEPOENRLTYYDistinctive features of class Reptilia a) Dissect the frog or toad in a usual Reptiles possess the following unique way to open up the body cavity. features, which differentiate them from b) Deflect the alimentary canal to your other chordates: right hand side and pin it to fully, display the urinogenital system. a) They have dry scaly skin with horny scales. Questions 1. With reasons, state the sex of your b) They have two pairs of pentadactyl limbs, except some members, such as specimen. snakes, which have no limbs. 2. Draw a large well-labelled diagram c) They undergo internal fertilization and of your dissection. Compare your their fertilized yolky eggs are laid on diagram with that of Figure 3.64 and land or retained until hatching. Figure 3.65. d) They lay amniotic eggs that have a 3. Outline the role (s) of each of the leathery shell to prevent rapid water labelled parts. loss. 4. How does the urethra of a male e) Their eyes are located at the front of differ from that of a female? the head to facilitate binocular vision. Some reptiles can move each eye Class Reptilia independently, and this helps them to The class comprises a group of animals find food and escape from predators. including turtles, crocodiles, alligators, chameleons, tortoises, snakes, and lizards. Structure of a lizard Most of them have four limbs while others Lizards have dry scaly skin, and most of do not have limbs. Reptiles are found in them have clawed feet and external ear diverse habitats, such as deserts, mountains, openings. Most lizards are small, with rocks, treetops and in water. They are mostly four legs and a long tail that, in many terrestrial with few aquatic members such species, is fragile and easily broken but as turtles and terrapins. They are cold- regenerate later (Figure 3.70). The legs blooded (ectothermic) vertebrates. Their of some lizards are greatly shortened or body temperature fluctuates according to vestigial, making animals such as the the environmental temperature. Reptiles glass lizard or a slow worm have a snake- like appearance. They are distinguished from true snakes by their movable eyelids. 201 BIOLOGY FORM 5 KIWANDANI.indd 201 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Head Tail Trunk Nostril Short leg Ear Mouth Toe with claw Figure 3.70 Structure of a lizard Class Aves GOFVOERRNONMLEINNTE PURSOEPOENRLTYYhave large eye to body ratio; and large The class Aves includes all birds. It is an eyes give birds good and keen eyesight extremely distinctive and successful class. important in flight. Birds can migrate during Aves are bipedal feathered and warm- harsh conditions, since they have wings blooded (homoeothermous) animals, as that enable them to move fast. Birds are they are able to maintain a constant body widely spread all over the world; some are temperature. They have unique “one-way” found in very cold snowy environments and breathing system. They have light, yet others in dry and hot environments. strong hollow bones, forming a skeleton in which many bones are fused or lost and Structure of a pigeon have powerful flight muscles. Birds have The body is spindle shaped and the size evolved specific adaptations to enable varies from 20-25 cm. The body is divided them fly. They have fused hollow bones into the head, neck, trunk, and tail. Most making birds have light weight, have a parts of the body are covered by feathers. large keel for attaching flight muscles and The head is small and rounded (Figure have large chest muscles used for flight. 3.71). It is anteriorly pointed into a short Birds also have their fore limbs modified beak. On the lateral side of the head, there is for flight and have feathers which are used a pair of prominent eyes. The ear comprises for flying. They have also developed long of small apertures on the posterior side of flight feathers on the wings and tail to help the eyes. Each aperture remains covered by birds attain balance and steer. Birds have a special group of feathers called auricular developed air sacs connected to the lungs feathers. Each aperture leads to a canal enabling them to extract more oxygen to called external auditory meatus, which is release more energy to power flight. Also closed below by the tympanic membrane. they have four chambered heart that enable The trunk is the greatest and widest part of them get more oxygen and avoid mixing the body. It is boat-shaped and bears a pair oxygenated and deoxygenated blood. Birds of wings and a pair of legs. The entire foot is have well developed brain enabling them covered with horny epidermal scales. At the to have quick reaction during flight. They hind end of the trunk is the cloaca aperture. 202 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 202 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms Eye Neck Beak (bill) Contour feathers Wrist Greater wing coverts Flight feathers on tail Tibia Finger digit Figure 3.71 Structure of a pigeon Claw Distinctive features of the class Aves GOFVOERRNONMLEINNTE PURSOEPOENRLTYY become waterproof. Ostrich and parrot Aves are different from other chordates lack oil gland. due to possession of the following features: h) Their alimentary canal has additional a) Their bodies are covered by chambers called crop and gizzard. The crop stores and softens the food, while overlapping feathers. the gizzard helps in crushing and b) They lost teeth; instead, they have churning the food. modiﬁed mouthparts into different i) Birds are capable of flying except for a types of beaks (bills). Beaks are few species such as ostrich, penguins, adapted for many different feeding and kiwi. habits, such as seed crushing, fruit scooping, flesh tearing, nectar sipping, Class Mammalia and wood chiseling. The class Mammalia consists of all animals with mammary glands. It is an extremely c) They have cylindrical, long necks diverse and very advanced group in the connecting heads and trunks. kingdom Animalia. Members of the class Mammalia include: human, mouse, rabbit, d) They have two pairs of pentadactyl cow, lion, bat, whale, and donkey. limbs. The front limbs are modiﬁed into a pair of wings, which bear quill Distinctive features of class mammalia feathers for ﬂight, while the hind limbs Mammals are different from other chordates are covered by scales and are adapted because: for perching, walking or swimming. a) They have fur or hair that cover their e) They undergo internal fertilisation and skin. The skin is glandular, with two produce eggs with calcareous shells. types of glands, namely, sebaceous and sweat glands. f) Their sternum forms a sharp ventral keel, providing muscles attachment b) Females (mothers) have mammary for ﬂight. glands, which produce milk for their newborn. g) They have oil gland above the cloaca, which preens the feather so that they BIOLOGY FORM 5 KIWANDANI.indd 203 203 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools c) They have external ears called pinna animals like kangaroo, which bear in addition to middle and inner ears, immature young ones and duck-billed which are used for collection of sound platypus, and echidna which lay eggs. waves and leading them to ear canal. The middle ear has three small soft Structure of a mouse bones called ear ossicles namely; Structurally, an adult mouse has an average malleus, incus, and stapes. length of 7.5-10 cm. Its body is divided into head, neck, and trunk. The head bears d) They have heterotrophic mode of external ear ﬂaps called pinnae, eyes, nutrition with different types of teeth nostrils and a mouth. The latter has long, (heterodont dentition) for different hair extensions called vibrissae or tactile functions, depending on the mode of whiskers (Figure 3.72). The neck is short feeding. and wide, connecting the head to the trunk. The trunk bears four walking legs, two e) They have highly developed brains. short hind legs and two long front legs, each with ﬁve digits. The trunk also bears f) They have muscular diaphragm, which a long tail which is either hairless or has separates the thorax from abdominal sparse covering of hair. The whole body cavity. of the mammal is covered by fur (pelage). g) They are viviparous (give birth to young ones). The developing foetus is held in the uterus, and gets nourishment through placenta, except in primitive Hairless ear Eye GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Sensory whisker Hind limb Tail with fur Short legs clawed feet Figure 3.72 Structure of a mouse Digestive system of a mouse pieces. Down from the mouth, there are The alimentary canal of a mouse starts oesophagus, stomach, pancreas, and small from the mouth to the anus. The mouth intestine. The small intestine has three consists of sixteen teeth; twelve molar and segments (duodenum, jejunum and ileum), four incisors (two on the upper jaw and the followed by the large intestine, with four other two on the lower jaw). The lower segments namely: caecum, colon, rectum incisors teeth are more developed, pointed, and anus. The stomach is a hollow organ sharp and longer than the rest, and are used (pouch-shaped) lying in the ventral part of for cutting the food into small chewable the abdomen, and is partly covered by liver 204 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 204 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms lobes. It is concerned with the digestion of food and temporary storage before further digestion in the small intestine (Figure 3.73). Bile duct Oesophagus Stomach Hepatic portal vein Pancreas Pancreatic ducts Jejunum Duodenum Ileum Hepatic portal Chain of lymph nodes vein from rectum covering hepatic portal vein Tributary of hepatic portal Rectum vein in mesentery Colon Spermatic cord Caecum Appendix Figure 3.73 The digestive system of a mouse The liver has four lobes; one on the left, twoGOFVOERRNONMLEINNTE PURSOEPOENRLTYYwhich pass through the numerous small on the right, and one in the centre. The liver pancreatic ducts that enter the duodenum for has two functions in digestion: secretion digestion. The main functions of the small of bile and receiving the absorbed food intestine are digestion and absorption of from the small intestine through hepatic the products of digestion. Duodenum is the portal vein. It lacks gall-bladder, instead first part of the small intestine, connected the cystic ducts from the liver lobes join to the stomach by a pyloric sphincter; to form the bile duct which conveys bile to which receives and digests the released the duodenum. The hepatic portal vein runs food from the stomach using bile and from the liver to the intestines; covered by other digestive juices. Jejunum and ileum a chain of lymph nodes and form branches are similar in both structure and function. in the mesentery (plural mesenteries) and They are both involved in digestion of other parts of the intestine. food as well as absorption of nutrients. The overall functions of the large intestine is to The mesenteries are the continuous set of complete absorption of water mainly from support tissues, which attach the intestines to the posterior wall of the abdomen. They undigested food particles, manufacture of support efficient digestion and maximum absorption of digested food by helping in certain vitamins, formation of feaces and storage of fat and allowing lymphatics, blood expelling faeces from the body through vessels, and nerves to supply the intestines. the anus. The main role of caecum is the The pancreas secretes digestive enzymes, absorption of water and salts remained after completion of digestion in the small intestine, as well as mixing and lubricating 205 BIOLOGY FORM 5 KIWANDANI.indd 205 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools its contents using the mucus secreted from fertilization and their developing foetus its internal thick wall of mucous membrane. or embryo. Rectum connects the colon to the anus, which aids in temporary storage of feaces The kidneys are bean shaped structures before its release (when the sphincter found on the back of the abdominal cavity contracts), and aids their release through on either side of the spine and are embedded the anus (when the sphincter relaxes). in the fats. On top of each kidney are small glands called adrenal glands (Figure 3.74). Urinogenital system of a male mouse In addition, a small and delicate tube called The urinary and reproductive systems are ureter is attached to each kidney, which integrated in some ways and are usually leads the urine to the urinary bladder. The studied together as urinogenital system. urinary bladder is connected to the urethra, However, the excretory system eliminates which carries urine from the bladder to the waste product and the reproductive system urethral orifice then to the outside through produces sperms in male and eggs in female the penis. and provide conducive environment for Ureter GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Adrenal gland Kidney Spermatic cord Fat Lumber lymph node Vesicular seminalis Bladder Coagulating gland Cut Figure 3.74 The urinogenital system of a male mouse Males have two openings on the pelvic area; genital opening and the anus. The genital opening passes both urine and sperms via a penis hanging out from or between the two 206 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 206 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms scrotal sacs. The scrotal sacs protect the Urinogenital system of a female mouse testes (singular testis). The testes (which The female pelvic area has three openings; secrete sperms) are connected to a coiled urethral opening, genital (vaginal) opening tube called epididymis which collects and the anus. The kidney and ureter have the produced sperms and store them. The the same composition as in males, except epididymis is very long twice the length of that the urethra, which passes both urine the testis. It has caput, corpus, and caudal and sperms in males, in females the urethra regions and it is connected to the tubular passes only urine conveyed from the bladder vas deferens which transports sperms from and passes to the outside environment the epididymis to the urethra. The urethra through urethral opening. The vagina not only carries the urine, but also sperms terminates to the long duplex tubes one through the penis to the outside of the body. on each side called uterus, which later On the left and right of the urinary bladder accommodates multiple developing foetus. there are folded glands called the seminal At the tip of each uterus is an ovary (eggs vesicles (vesicula seminalis) bearing a producing gland) which is enclosed within coagulating gland, and below the urinary a thin-walled ovarian sac surrounded by bladder, which store urine. There are other fats. Each ovary is connected to the uterus glands known as prostate glands at each via a single small undulating coils called side of the urethra and Cowper’s glands, fallopian tube (Figure 3.75). which are small ovoid structures, found at the root of the penis. There are two preputial glands, each wrapped on one side of the ventral wall. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Kidney Adrenal gland Fat Ureter Ovary Bladder Uterus Mesovarium of oviduct Vagina Cut pelvic girdle Vagina Anus Clitoris Figure 3.75 The urinogenital system of a female mouse 207 BIOLOGY FORM 5 KIWANDANI.indd 207 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Dissection of mouse or rat Pinned limb A mouse or rat is a typical vertebrate animal whose many aspects of structural Point to organisation are similar to those of start a cut other mammals, including human being. Moreover, mice or rats are also important Figure 3.76 Positioning the mouse or rat research tool for modeling human disease for dissection progression and development in the laboratory. They have also helped to speed d) Lift the skin in the mid-ventral line up the progress of research and enabled using forceps, and cut to make a small the development of important new drugs. slit (Figure 3.77). Cut forward to the Therefore, by examining the physiology, level of the lower lip and backwards anatomy and metabolism of a mouse or rat, around the penis and between the scientists can gain a valuable insight into scrotal for a male specimen while for how human system functions. Despite the the female cut the skin backward as differences in their body size and appearance, far as the anus, passing either side of Mice/rats share a distinct genetic similarity urinary and genital apertures. to humans; and their ability to reproduce and mature quickly make them efficient and economical candidate mammals for scientific studies. The purpose of conducting rat or mouse dissection is to explore and study the internal organs and systems of the basic mammalian anatomy. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY General procedure of dissection of a Penis mouse or rat Scrotal sac a) Put on a pair of gloves. Figure 3.77 Opening the body cavity of an b) Place a live male or female mouse anesthetized mouse or rat or rat in a container with a lid and anaesthetize it using chloroform soaked e) Use fingers to pull the skin aside, in a small roll of cotton wool for five loosen it from the body wall, stretch minutes. it and pin it back. c) Lay the mouse or rat on the dissecting tray or dish, with the ventral side (abdomen) facing upwards (Figure 3.76). Pin it down on the tray through the fore and hind limbs, make sure that the pins face outwards. 208 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 208 10/10/2019 14:06

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f) Lift the abdominal wall using forceps, FOR ONLINE USE ONLY make an incision and cut up to the DO NOT DUPLICATE xiphoid cartilage and down to the left and right ribs. Stretch the body wall Comparative studies of natural groups of organisms and pin it aside (Figure 3.78). Examine the contents of the abdominal cavity i) When displaying urinogenital system, in undisturbed condition (in situ or the alimentary canal should be removed visceral/general view) and draw a well first followed by the removal of fats labelled diagram. from the kidneys using blunt forceps and clear the ureter. Mouth j) In male mouse, open the scrotal sac Eosophagus by cutting its ventral wall to expose the testes, caudal and caput epididymis Liver Spleen as well as the vas deferens. Lay the Small Stomach bladder, seminal vesicles, coagulating intestine Large glands and prostate glands on one side. Pancreas intestine k) In female mouse/rat grip the clitoris, Caecum Rectum pull it gently so that the urethra is held away from the pelvis, and cut Anus the ventral part of the girdle. Lift the oviducts and remove the mesovarium to expose ureters on both sides, remove the fat bodies from the kidneys and ureter, but leave them around the ovaries (the ovaries are enclosed within the thin walled ovarian sac and connected to a very small and much coiled fallopian tube) and observe the very long tube called fallopian tube near to the uterus. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 3.78 General view of the dissected mouse Safety precautions or rat 1. Consider issues such as allergies or g) To display the digestive system, adjust sneezing from loose rat or mouse furs. the positions of the alimentary canal by moving the bulk of the intestine to 2. Rat or mouse may bite a person the left hand side of the specimen to and cause pains, so be careful when expose the duodenum and the colon. dealing with live a rat or mouse. h) Grip the duodenum and colon, pull 3. Good hygiene practices should be them apart to expose hepatic portal observed all the time; keep hands vein and turn the bulk of the intestines away from the mouth, nose, and eyes over to untwist them, rearrange the and face during and after dissection digestive structures and draw a well and wash hands with antiseptic labelled diagram. soap immediately after a dissection practical session. BIOLOGY FORM 5 KIWANDANI.indd 209 209 10/10/2019 14:06

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Biology for Advanced Level Secondary SchoolsGOFVOERRNONMLEINNTE PURSOEPOENRLTYY FOR ONLINE USE ONLY DO NOT DUPLICATE 4. Other safety laboratory rules and precautions should be adhered to Revision questions under the supervision of a teacher or laboratory technician. 1. With example(s) categorize viruses based on the nature of their genomes Activity 3.17 Dissection of a rat or and morphology of their capsids. mouse to display the digestive and urinogenital systems 2. What are the advantages and disadvantages of viruses? Materials Fresh male or female rat or mouse, 3. Classify bacteria on the basis of the dissection kit, dissecting tray or dish, following: chloroform, and cotton wool. a) Morphology Procedure a) Collect a live male or female rat or b) Gram stain test mouse; put it in a container with lid 4. Account for the advantages and and anaesthetize it with chloroform disadvantages of members of soaked in a small roll of cotton wool kingdom Monera. for about five minutes. b) Dissect a mouse in the usual way, to 5. Explain the adaptations of fully display the digestive system and Entamoeba histolytica to its mode of urinogenital system. life. Questions 6. Explain how Plasmodium is able to 1. Draw well labelled diagrams of exist in humans and mosquitoes. the displayed systems in (b) above. 7. Describe the general and distinctive Compare your diagrams with those features of phylum Apicomplexa. of Figures 3.73, 3.74 and 3.75 respectively. 8. Euglena is an ancestor of plants and 2. Explain the role(s) of each labelled animals. Explain. part. 3. How does the urethra of a female 9. How is Phytophthora adapted to rat or mouse differ from that of a its mode of life? male? 4. Classify the organism to class level. 10. Spirogyra resembles plants. Explain. 11. Explain with examples the advantages and disadvantages of Protoctists. 12. Describe the general and distinctive features of basidiomycetes. 13. Explain the advantages and disadvantages of fungi. 14. Differentiate between coniferophytes and angiospermophytes. 210 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 210 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Comparative studies of natural groups of organisms 15. Explain the economic importance of kingdom Plantae. 16. Arthropods are the most successful animals on the earth. Justify. 17. How are Aves adapted for flight? 18. Classify the following organisms to their class level; moss plant, monkey, cactus, blood fluke, snake, mite, housefly, sugarcane, earthworm, Kihansi spray toad, shark, and bean plant. 19. Explain the distinctive features of amphibians. 20. How are the following organisms adapted to their mode of life? a) Fern plant b) Earthworm c) Kihansi spray toad. 21. Explain the adaptive features of mammals. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY BIOLOGY FORM 5 KIWANDANI.indd 211 211 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools FourChapter irritaCoobrdinialtiiontaynd Introduction In organisms the body parts work together for various roles, resulting into a coordinated body. Animals have two systems of coordination namely nervous coordination and endocrine coordination, while plants have hormonal coordination. Nervous coordination is accomplished by the nervous system composed of nerve ﬁbres, brain and spinal cord, whereas hormonal coordination is accomplished by endocrine system which is composed of the endocrine glands. In plants, responses are in the form of slow modiﬁed growth or movements called turgor movement. In this chapter you will learn about nervous coordination in mammals, hormonal coordination in mammals, coordination in plants, and phytohormones (plant hormone). GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 4.1 Nervous coordination in mammals sensory and relay neurones, while those As in other animals, nervous coordination nerves which transmit signals from the in mammals is accomplished by the brain are called motor or efferent nerves. nervous system. The mammalian nervous Nervous coordination enables a mammal system consists of a central nervous to respond rapidly to external and internal system and peripheral nervous system. stimuli. The central nervous system is made up of the brain and spinal cord, whereas the Nervous tissue peripheral nervous system is made up of The nervous tissue is a specialized tissue the nerve ﬁbres. The nerve ﬁbres branch made up of nerve cells (neurones). A from the central nervous system and extend neurone is the basic unit structure of to all parts of the body. Coordination is the nervous tissue which consists of the accomplished through a set of signals cell body, dendrites and axon. Nervous channeled into a series of nerve cells. tissues make up the Central Nervous The nerves that transmit signals from the System (CNS) and Peripheral Nervous body to the central nervous system are System (PNS). The central nervous called afferent nerves, and they include system consists of the brain and spinal 212 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 212 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability cord, while the peripheral nervous system Types of neuroglia comprises of the cranial and spinal There are six types of neuroglia, four nerves, which are packed together with of which are found in the CNS and two their motor and sensory endings. Nervous in the PNS. The neuroglia found in the tissue is the main tissue component of the CNS include astrocytes, microglial cells, nervous system and it consists of closely ependymal cells and oligodendrocytes, packed nerve cells or neurones with very while those found in PNS include satellite small intercellular spaces. Nervous tissue cells and Schwann cells (Figure 4.1 a to f). contains two types of cells, namely; The collection of glia cells residing within neurones and neuroglia. Neurones are the walls of intestinal tract, beginning in specialized nerve cells which generate the oesophagus and extending down to and conduct nerve impulses. Neuroglia the anus are known as enteric glia. The six are non-neuronal cells which assist in types of neuroglia are explained below: propagation of the nerve impulses and provision of nutrients to the neurones. a) Microglial cell Neuroglia also serve as supporting cells that provide electrical insulation and These are the smallest neuroglial cells remove debris. Cells of the neuroglia (Figure 4.1a). They are macrophage cells produce myelin sheath that increases the that make up the primary immune system speed of impulses along the axon of the for the CNS. These phagocytic cells help neuronal ﬁbres and offers protection for to remove bacteria and waste (cleaning the axon. neuronal debris). GOFVOERRNONMLEINNTE PURSOEPOENRLTYY (a) (b) (c) (d) (e) (f) Figure 4.1 Types of neuroglia (a) microglial (b) astrocytes (c) oligodendrocytes (d) ependymal (e) schwann and (f) satellite cells BIOLOGY FORM 5 KIWANDANI.indd 213 213 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools b) Astrocytes GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Examples of effectors include a muscle These are star-shaped macroglial cells with and a gland. many processes (Figure 4.1b). They are b) The cells of the nervous tissues are the most abundant glial cells in the CNS. tightly packed for effective working of Their roles are to provide metabolic and the tissue. structural support to the neurones. c) The cells of the nervous tissues have c) Oligodendrocytes large number (high concentration) of These are cells with very few processes mitochondria which help to generate (Figure 4.1c). They are found in the CNS. energy. This is important because They form myelin sheath on the axons of a nervous tissues require large amount neurone which have lipid-based insulation of energy for efﬁcient functioning. for increasing the speed at which the action potential can travel down the axons. d) They have neuroglia (glial cells) that provide protection and support to the d) Ependymal cells tissues. These are ciliated cells which line up the central cavities of the brain and spinal cord e) The cells in the PNS are capable of where they form a fairly permeable barrier regenerating themselves. This is due between cerebrospinal ﬂuid that ﬁlls these to the presence of neurolemma (also cavities (Figure 4.1d). known as neurilemma). e) Schwann cells f) The cells in the nervous tissues These are equivalent to oligodendrocytes produce neurotransmitter chemicals (Figure 4.1e). They surround nerve ﬁbres which act as conveyors that carry in the PNS. They help to maintain axons impulses from one neurone to another and form myelin sheaths in the PNS. across the synaptic gap. f) Satellite cells g) Nerve cells or neurones have nodes They line the surface of neuronal cell of Ranvier and fatty myelin sheath bodies in ganglia within the PNS (Figure which facilitate rapid transmission of 4.1f). They are analogous to astrocytes. impulses. Adaptive features of nervous tissues The Central Nervous System (CNS) The nervous tissues have the following adaptive features: The CNS, which consists of the brain and a) They have nerve cells (neurones) that the spinal cord has the grey matter and white matter. The grey matter is comprised receive information from sensory parts of cell bodies, dendrites, unmyelinated and send or transmit it to the CNS for axons, and very few myelinated axons. In interpretation and then to the effector contrast, the white matter is comprised of for a response. An effector is any part myelinated axons. The main function of of the body that produces response. the central nervous system is to integrate information from various sources. The collection, both from internal and external environment is done by receptors. They 214 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 214 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability usually form the sensory system along GOFVOERRNONMLEINNTE PURSOEPOENRLTYYform a communication network. Neurones with neurones which transmit the collected are the basic structural and functional information from different parts. The units of the nervous system. They are collected information is processed and responsible for transmission of impulses integrated in the central nervous system, from one part of the body to another. and ﬁnally the information is transmitted to effectors (muscles and glands) which The main portion of the neurone is the produce appropriate responses. cell body, which contains a nucleus. The cytoplasm of the cell bodies contains Functions of the nervous system granules called Nissl’s bodies. Extending The nervous system has the following from the cell body are one or more short functions: extensions called dendrites. These receive a) It receives stimuli from the signals from the sensory receptors and transmit electrical signals or impulses to environment using receptor cells or the cell body. The neurone also contains sensory input. long extension called axon. In some cells, axons are covered by a fatty layer of b) It converts the stimuli into electrical material known as myelin sheath. Within impulses by the process called the cell body there are ﬁne neuroﬁbrils transduction. that extend from the dendrites to the axon. An axon is a long, stem-like part of the c) It transmits nerve impulses. The cell that sends action potential signals to impulse is transmitted from the the next cell. Outside the myelin sheath sensory receptor to the CNS and then is a cellular layer called neurilemma, to the effector, which is capable of containings sheath of Schwan cells which producing an appropriate response. are essential for rapid propagation of nerve impulse as well as nourishment and d) It stores information so that behaviour insulation of the axon. The myelin sheath can be modified according to the past together with neurilemma constitute the stimuli. medullary sheath (Figure 4.2), inside the axon there is a space containing charged Neurones ions called axoplasm. Nerve cells or neurones are conducting cells of the nervous system found between the receptors and effectors. These spread throughout the body of an organism and Dendrites Schwan cell nucleus Nucleus Cell body Myelin sheath Axon terminal Node of Ranvier Nissil’s Axon bodies Figure 4.2 Structure of a typical neurone 215 BIOLOGY FORM 5 KIWANDANI.indd 215 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Neurones are supported, protected, and Sensory neurones (Afferent neurones) nourished by non-neuronal cells of the Sensory and intermediate neurones are nervous system, which are known as also known as afferent neurones. These glial cells. Together with extracellular are neurones with long dendrites and short tissue, glial cells make up the neuroglia. axon. The cell body and dendrites of the Some neuroglias are phagocytic cells sensory neurones mostly lie outside the that remove bacteria and debris from the brain and spinal cord. Sensory neurones neurones while others provides metabolic transmit nerve impulses from sensory and structural support. receptors to the CNS (Figure 4.3) for the interpretation. Types of neurones Based on their function and structure there are three types of neurones; which are sensory neurones, intermediate neurones (interneurones), and motor neurones. Synaptic end Cell body Skin receptor Node of Ranvier Myelin sheath Axon GOFVOERRNONMLEINNTE PURSOEPOENRLTYYDirection of nerve impulse Dendron Figure 4.3 Structure of a sensory neurone Interneurones (Intermediate neurones) Dendrites These are also known as connector Cell body neurones or relay neurones (Figure 4.4). Axon They are much smaller nerve cells with Synaptic ending many interconnections. Interneurones have short dendrites and short or long Figure 4.4 Structure of an intermediate neurone axons. They lie entirely within the CNS (brain and spinal cord). They transmit nerve impulses within the CNS; that is, they relay information between sensory and motor neurones. The sensory neurones and intermediate neurones both carry impulses towards the CNS. 216 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 216 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability Motor neurones (Efferent neurones) effector organs such as muscles or glands, Motor neurone have short dendrites and which eventually respond to the stimulus long axons; their dendrites and cell bodies (Figure 4.5). Axon always transmits are located in the CNS; and the axon is impulses away from the cell body while outside the CNS. Motor neurones transmit dendron carries impulses towards the cell nerve impulses from the CNS to the body. Nucleus Cell body Dendrite Axon Myelin sheath Direction of nerve impulse Node of Ranvier Figure 4.5 Structure of a motor neurone GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Classiﬁcation of neurones based on the are sensory neurones that have two number of dendrites processes coming from the cell body; one Neurones can also be classiﬁed on the dendron and one axon. Bipolar sensory basis of the number of their dendrites neurones are found in the retina of the eye, arising from the soma (cell body). In ganglia of the vestibulocochlear nerve this classiﬁcation, there are three main and the olfactory epithelium. Multipolar types of neurones. These include unipolar, neurones have three or more processes bipolar and multipolar neurones. Unipolar coming from the cell body. They possess neurones have a single short dendrite one axon and two or more dendrites. terminating onto bush-like tufts or Multipolar neurones form the major part dendrites. These are found in the granular of the CNS. They include interneurones layer of the cerebellum. Bipolar neurones and motor neurones. (Figure 4.6). BIOLOGY FORM 5 KIWANDANI.indd 217 217 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools (a) (b) (c) (d) Figure 4.6 Structural classiﬁcation of neurones (a) unipolar (b) bipolar (c) pseudo unipolar and (d) multipolar Exercise 4.1 GOFVOERRNONMLEINNTE PURSOEPOENRLTYYelectrical charge is maintained by active transport of sodium ions out of axoplasm. 1. Describe the structure of the A cell in this state is said to have a resting nervous tissue. potential and it is polarised. At this state, the potential difference existing across the 2. Explain the adaptive features of cell surface membrane inside the cell with the nervous tissue. respect to the outside part is negative, which is about -70 mV. At this time, the 3. With the help of diagrams, describe axon does not conduct any impulse. The the types of neurones. cytoplasm inside the axon has a high concentration of K+ and low concentration Nerve impulses of Na+. This is contrary to the outside A nerve impulse is an electrical signal that part which has a low concentration of travels along the axon. It is generated when K+ and high concentration of Na+. The the nerve cell is activated. Movement of resting potential is maintained by active ions in and out of the neurone causes a transport and passive diffusion of ions. sudden change in the voltage across the It is active transport of ions against the wall of the axon. This triggers a wave of electrochemical gradient of sodium/ electrical activity that passes from the cell potassium (Na+/K+) pump. These are body along the length of the axon to the carrier substances located in the cell synapse. surface membrane. They are driven by energy supplied by ATP (Figure 4.7). The Resting potential rate of diffusion is characterised by the This occurs when the neurone is at rest. permeability of the axon membrane to the In an inactive neurone, the axoplasm is ion. The K+ has membrane permeability negatively charged with respect to the of about 20 times greater than that of Na+. outside of the cell. The difference in 218 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 218 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability (K+)=20 nM Na+ / K+ pump Outside (Na+)=450 nM K+ channel ++ + + ++ + ++ Membrane potential -60mV - -- - -- - -- (K+)=400 nM ATP Inside (Na+)=50 nM ADP Figure 4.7 A membrane at resting potential (Polarised membrane) Action potential GOFVOERRNONMLEINNTE PURSOEPOENRLTYYinside the axon, which consequently An action potential is a rapid, temporary becomes more depolarized. Since sodium change in membrane potential. It may gates are sensitive to depolarization, qualify as the most important type of the greater the depolarization, the more electrical signal in cells. In a neurone, sodium gates are open, allowing more action potential is generated by special sodium ions to enter into the cell, hence types of voltage-gated ion channels greater depolarization and this is called a embedded in cell’s plasma membrane. A positive feedback loop. Positive feedback neurone displaying the nerve impulse is loop causes acceleration in the entry of said to have an action potential and the sodium to the potential difference peaks cell is depolarised. Stimulation of axon by at about +40 mV. This peak corresponds electrical impulse may result into a change to the maximum concentration of sodium in potential difference of about +40 mV inside the axon. The total depolarization across the axon membrane, from more associated with the action potential has negative inside to more positive inside. therefore been from -70 mV to +40 mV. The action potential has the following Action potential is generated by a sudden three distinct phases: opening of sodium channels. This occurs in response to stimulus which brings a) Depolarisation about a slight depolarisation or loss of charge of the axon membrane. Opening This is the decrease in voltage across of Na+ gates increases permeability the membrane. It occurs when there is a of the axon membrane to sodium ions stimulus that leads to the opening of the which enter the axon by diffusion. This sodium channel to increase inﬂow of increases the number of positive ions sodium ions. The process makes the inside of the cell less negative. 219 BIOLOGY FORM 5 KIWANDANI.indd 219 10/10/2019 14:06

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools b) Rapid repolarisation All the three phases of the action potential occur within few milliseconds (ms) for the This is the process that changes the action potential to begin in a giant axon, membrane potential back to negative the membrane potential must shift from inside and positive outside. A fraction its resting potential of -70 mV to about of a second after the sodium gates open, +40 mV. If the membrane depolarises depolarisation of the axon membrane less than that, an action potential does not causes the potassium gates to open too, occur. However, if this threshold potential and potassium diffuses out of the cell. is reached, sodium ion channels in the Since potassium is positively charged, the axon membrane open. Ions, thus rush into inside of the cell becomes less positive and the axon following their electrochemical starts the process of repolarisation, then, it gradients. The inside of the membrane returns to its original resting potential. becomes less negative and then positive with respect to the outside. When the c) Hyperpolarisation membrane potential reaches about +40 mV, a rapid change occurs and the repolarisation This occurs after the impulse has been phase begins (Figure 4.8). The change transmitted; the action potential falls down is caused by the closure of sodium ion and the sodium gates close immediately. channels and the opening of potassium ion But potassium gates delay to close, causing channels. more K+ ions to exit the axon and this makes the membrane slightly more negative than the resting potential. Hyperpolarisation of the axon overshoots into more negative potential than the original potential. Membrane Potential (mV) GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Action Refractory 50 potential period Depolarization Repolarization 0 Threshold potential Resting potential -50 Resting potential Hyperpolarization -100 01234567 Time (milliseconds) Action potential in a neurone Figure 4.8 Graph showing the propagation of nerve impulse across a membrane 220 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 220 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability In summary, an action potential occurs due to opening or closing of speciﬁc channels in the plasma membrane in response to changes in voltage. An action potential always has the same three-phase form; even though the size of the resting potential, threshold potential, and peak depolarization may vary among the species or even among different types of neurones in one species. Conduction of nerve impulse along the axon The mechanism for impulse transmission along the axon involves the following steps: a) Polarization of the neurone’s membrane Sodium is in high concentration on the outside, whereas potassium is in high concentration on the inside. Cell membranes surround neurones, like any other cell in the body which has a membrane. When a neurone is not stimulated, just sitting with no impulse to carry or transmit, its membrane is said to be polarised. Being polarized means that the electrical charge on the outside of the membrane is positive while the electrical charge on the inside of the membrane is negative (Figure 4.9). Outside of axon Plasma membrane of axon Inside of axon Figure 4.9 Polarised axon membrane b) The resting potential gives the neurone a break When the neurone is polarised, it is said to be at its resting potential. It remains in this state until when the stimulus comes along (that is, when it is stimulated). When action potential is initiated, a region of the membrane depolarises. As the result the adjacent region becomes depolarised as well (Figure 4.10). Passive depolarization spreads GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Na+ Figure 4.10 Propagation of nerve impulse across a membrane (depolarization) c) Action potential Sodium ions move inside the membrane when a stimulus reaches a resting neurone. The gated ion channels on the resting neurone’s membrane open suddenly to allow the Na+ that was on the outside of the membrane to rush into the cell. While this happens, the neurone changes from being polarised to being depolarised. After more positive ions enter inside the membrane, the inside becomes positive and polarisation is removed and the threshold is reached (Figure 4.11). 221 BIOLOGY FORM 5 KIWANDANI.indd 221 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Na+ Figure 4.11 Propagation of nerve impulse across a membrane (action potential) d) Repolarisation Localised electrical circuits are established, causing further inﬂux of sodium ions and so progression of the impulse. Behind the impulse, potassium ions begin to leave the axon along the concentration gradient, hence repolarisation beginning to occur due to the outward flow of K+ ions. The depolarisation speeds forward, triggering an action potential (Figure 4.12). Figure 4.12 Propagation of nerve impulse across a membrane (localization) During repolarisation, potassium ions move outside, while sodium ions stay inside the membrane. After repolarisation, the inside of the cell becomes ﬂooded with Na+; the gated ion channels on the inside of the membrane open to allow K+ to move to the outside of the membrane. With K+ moving to the outside, the membrane’s repolarisation restores electrical balance, although it is the opposite of the initial polarised membrane that had Na+ gates close. Otherwise, the membrane could not repolarize (Figure 4.13). Then Na+ ions are actively forced out of the axoplasm in the process called sodium pump. However, since K+ ions are also involved in this process, the process is best called cation pump. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 4.13 Propagation of nerve impulse across a membrane (repolarization) Characteristics of nerve impulses Nerve impulses have the following characteristic features: a) Transmission speed Impulses are always transmitted at a very high speed. Depending on the nature of a nerve cell, the speed of transmission varies from 0.5 to 100 metres per millisecond. The speed of impulse transmission is determined by body temperature, axon diameter, and presence of myelin sheaths. 222 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 222 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability i) Body temperature iii) Presence of myelin sheaths The speed of impulse transmission depends Axons with myelin sheaths conduct on the body temperature of the organism, impulses at higher speed than those such that, the speed of impulse transmission without sheaths. The myelin sheath in homoeothermic organsms is greater than allows impulses to leap from one node in poikilothermic organisms. of ranvier to another, thereby increasing transmission speed (Figure 4.14). This is ii) Axon diameter the saltatory conduction. The greater the axon diameter the higher the transmission speed. This is because increased axon diameter minimizes the resistance of the axoplasm. Nerve impulse propagation K+Na+ K+Na+ Axon Myelin sheath cells Nodes of ranvier Figure 4.14 Leap of impulse from one node of Ranvier to another in a myelinated axon b) Unidirectionality GOFVOERRNONMLEINNTE PURSOEPOENRLTYYis unable to propagate an action potential Impulses always ﬂow in only one direction, regardless of the strength of the stimulus. that is, from cell body to terminal dendrites The relative refractory period lasts for 5 in the neurone, or from pre-synaptic to post ms. During this period, the impulse can – synaptic neurone across a synapse. be propagated if its strength exceeds a threshold value. The significance of the c) Refractory period refractory period is to ensure unidirectional During this period, a part of an axon is unable flow of impulse and to separate one action to conduct a new impulse immediately after potential to the next. propagation of an action potential. The resting potential is restored by outward d) All-or-nothing law movement of K+ ions and prevention of According to this law, for the action inward movement of Na+ ions. potential to be propagated, the stimulus applied should exceed a threshold value. Furthermore, the refractory period is The threshold value is the minimum divided into two phases namely; absolute energy level, and when reached, the action refractory period and relative refractory potential will be generated. However, period. Absolute refractory period lasts the size of the action potential will not for 1 ms. In this period, a part of an axon decrease as it is transmitted along the 223 BIOLOGY FORM 5 KIWANDANI.indd 223 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools neurone, but it will always remain the GOFVOERRNONMLEINNTE PURSOEPOENRLTYYpresynaptic membrane is modiﬁed for the same. In other words, the action potential attachment of synaptic vesicles and the is both generated and kept the same or release of transmitter substance into the not generated if the threshold value is not synaptic cleft. The postsynaptic membrane exceeded. contains large protein molecules, which act as receptor sites for the transmitter e) Propagation (Conduction) substances and numerous channels and A nerve impulse is conducted as a wave pores for the movement of ions into the of depolarisation that moves along the postsynaptic neurone (Figure 4.15). surface of the nerve cell. This means that progressive depolarisation of the The neurotransmitter substance is either axon membrane leads into impulse produced by the cell body of the neurone transmission. or synaptic knob. These substances are synthesised by enzymes stored in Structure of a chemical synapse the cell body. The neurotransmitters The point where the axon of one neurone allow the transmission of signals joins the dendrite or cell body of another from one neurone to the next across neurone is known as a synapse. The synapses. There are many types of membrane of the ﬁrst neurone connecting neurotransmitters, and these include to the synapse is called a presynaptic acetylcholine, norepinephrine, serotonin, membrane while the other membrane of dopamine, and glutamate. The two the next neurone is called a postsynaptic common neurotransmitters in vertebrates membrane. These membranes between are acetylcholine (Ach; an ammonium the two neurones are separated by a gap of compound) and norepinephrine (also about 20 nm called the synaptic cleft. At called noradrenaline). Neurones using the end of the presynaptic neurone, there acetylcholine as a neurotransmitter is a bulge called synaptic knob. are described as cholinergic neurones, while those using norepinephrine The cytoplasm of the synaptic knob (noradrenaline) are called adrenergic contains numerous mitochondria and neurones. Norepinephrine is released in small synaptic vesicles. Transmission the sympathetic nervous system by some across a synapse is carried out by chemical nerves, while acetylcholine is released by substances called neurotransmitters; all nerves except some nerves in the brain. which are stored in synaptic vesicles. The 224 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 224 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability End of axon Synaptic knob Mitochondrion Synaptic cleft Synaptic vesicle containing Dendrite neurotransmitter substances Pre - synaptic membrane Protein receptor Post synaptic membrane Ion channel Figure 4.15 Structure of the chemical synapse Synaptic transmission of nerve GOFVOERRNONMLEINNTE PURSOEPOENRLTYYThese channels are capable of passing impulses an electrical current, causing voltage The nerve impulse passes down the changes in the pre synaptic cell to induce dendrite, through the cell body, and voltage changes in the post synaptic cell. down the axon. At the end of the axon, This synapse can be effective when the the impulse encounters a ﬂuid-ﬁlled neurones are very close together (2 nm). space separating the end of the axon The main advantage of electrical synapse from the dendrite of the next neurone or is that it facilitates the rapid transfer from a muscle cell. This space is called of signals from one cell to the next. In the synapse. The synapse located at the chemical synapses, impulse transmission junction of a neurone and muscle ﬁbre is facilitated by chemical substances is called a neuromuscular junction. Such called neurotransmitters. synapses can be classiﬁed based on their means of transmission of impulses across Mechanism for synaptic transmission their gaps. In this typology, two types are a) An action potential arrives at the end revealed, namely electrical and chemical synapses. An electrical synapse is the of the axon and induces changes in the one in which the physiological continuity cell membrane (Figure 4.16). between pre and post synaptic neurones is provided by a special channel called a gap junction between the two neurones. BIOLOGY FORM 5 KIWANDANI.indd 225 225 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Axon of presynaptic neurone Mitochondrion Synaptic knob Synaptic vesicle Synaptic cleft Postsynaptic Membrane of membrane postsynaptic neurone Postsynaptic membrane Area of receptor sites Figure 4.16 Conduction of nerve impulses at the presynaptic knob and action potential b) Depolarisation at the synaptic knob after arrival of nerve impulses create the action potential which opens voltage-gated calcium channels located near the synapse in the presynaptic membrane, thus increasing the permeability of the membrane to calcium (Ca2+) ions. The electrochemical gradient for Ca2+ results in the inﬂow of calcium ions through the open channels (Figure 4.17). GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Ca2+ Ca2+ Ca2+ Permeability of presynaptic membrane to Ca2+ increases Figure 4.17 Permeability of presynaptic membrane to the calcium ions 226 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 226 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability c) In response to the increase of calcium concentration inside the axon, synaptic vesicles fuse with the presynaptic membrane and release neurotransmitters into the gap between the cells which is called the synaptic cleft. The delivery of neurotransmitters into the cleft is an example of exocytosis (Figure 4.18). Synaptic vesicles fuse with presynaptic membrane and rapture Neurotransmitters Figure 4.18 Presynaptic membrane fused with synaptic vesicles d) The vesicles then return to the cytoplasm and are reﬁlled with transmitter substance. The neurotransmitter diffuses across the synaptic cleft, a process which takes 0.5ms per synapse. Upon reaching the postsynaptic membrane, it binds with receptor molecules which recognise the molecular structure of the acetylcholine molecule (Figure 4.19). GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Diffusion of transmitter molecules across cleft Transmitter molecules attached to receptor sites Channels open up and allow ions to enter from synaptic cleft (permeability of postsynaptic membrane increases) Figure 4.19 Transmitter molecules attached to receptor sites on postsynaptic knob BIOLOGY FORM 5 KIWANDANI.indd 227 227 10/10/2019 14:07

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE e) The arrival of acetylcholine at the postsynaptic membrane changes excitatory postsynaptic potential in the shape of the receptor site. This the post synaptic neurone. Once the initiates ion channels to open up. neurotransmitter has depolarised the The excitatory synapse which opens post synaptic neurone, it is hydrolysed ion channels on the postsynaptic to form acetyl and choline by the membrane allowing sodium ions to enzyme “acetylcholinesterase” which enter and potassium ions to leave. This is found in the postsynaptic membrane. creates a new potential known as the This prevents the successive impulse merging at the synapse (Figure 4.20). Hydrolytic enzymes such as acetylcholinesterase break down transmitter molecules Local depolarisation and propagation of an action potential Figure 4.20 Local depolarisation and propagation of an action potential in postsynaptic membrane The resulting acetyl and choline diffuses GOFVOERRNONMLEINNTE PURSOEPOENRLTYYthreshold value and so generate an action across the synaptic cleft into the synaptic potential in the postsynaptic neurone, this knob of the presynaptic neurone where is called temporal summation. All events they get stored in their vesicles for further described are for excitatory synapse, use. The process is facilitated by energy some known inhibitory synapses respond produced by numerous mitochondria to neurotransmitter by opening potassium in the knob. The overall depolarising ion channels and leaving the sodium ion effect of several Excitatory Postsynaptic channels closed. Potassium, therefore, Potential (EPSPs) is called summation. moves out causing the membrane to be When two or more EPSPs simultaneously polarised; consequently, it prevents the arising at different regions either on the threshold value to be exceeded. Thus no same or different neurones, producing action potential will be created. sufﬁcient depolarisation which can starts an action potential in the postsynaptic Functions of synapses neurone, the phenomenon is known as a) They transmit information between spatial summation. neurones. The synapses pass The excitatory postsynaptic potential impulses in one direction only. builds up as more neurotransmitter Such impulses are transmitted at the substance arrives until sufﬁcient presynaptic membrane and received depolarisation occurs to exceed the by the postsynaptic membrane, which 228 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 228 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability ensures one direction of ﬂow along a GOFVOERRNONMLEINNTE PURSOEPOENRLTYY released by synapse steadily falls off given pathway. in a response to a constant stimulation until the supply of the transmitted b) They amplify impulses by substance is exhausted. acetylcholine which is released at a f) They allow convergence, spatial neuromuscular junction which excite summation and integration of the the post synaptic membrane and stimuli. In convergence of the stimuli, ampliﬁes any weak impulse arriving. the postsynaptic nerves receive Repeated low level stimuli can be impulses from a large number of amplified as each impulse is arriving excitatory and inhibitory presynaptic at the synapse, causing the release of neurones. In a spatial summation more neurotransmitter, resulting in postsynaptic neurone is able to sum- one larger impulse in the postsynaptic up the stimuli from all presynaptic neurone. Therefore, this allows the neurones, where the synapse act as a body to respond to the stimuli more centre for the integration of stimuli effectively. from different sources; hence produces the coordinated response. c) They act as junctions that transmit electric nerve impulses between Exercise 4.2 neurones, or between neurone and effector cells. A synaptic connection 1. Explain the following concepts: between a neurone and muscle cell is known as neuromuscular junction. a) Action potential d) They ﬁlter out low level stimuli; as b) Resting potential more neurotransmitter diffuses across the synaptic cleft, the excitatory c) Polarization postsynaptic potential increases. For the impulses to be generated in the d) Depolarisation of nerve cells postsynaptic neurone, it must reach the action potential of about +40 2. Describe the formation and mV. This implies that weak impulses conduction of nerve impulses along in the presynaptic neurone do not the axon. cause enough neurotransmitter to be released for an action potential in the 3. Outline the characteristics of nerve postsynaptic neurone to be generated. cells. As a result, synapses are able to filter out low level stimuli that the body 4. Using clear illustrations, describe does not need to respond, that is a way the synaptic transmission of nerve of conserving energy. impulses. e) They allow adaptation to intense 5. State the role of synapses in the stimulation and fatigue. The amount nervous system. of transmitted substance which is BIOLOGY FORM 5 KIWANDANI.indd 229 229 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools 4.2 Sensory receptor GOFVOERRNONMLEINNTE PURSOEPOENRLTYYSingle sensory neurone receptor The receptor is a cell or a nerve ending or These receptors are simple and mostly a group of nerve endings specialised for primitive. They consist of a single sensory reception of stimuli and change speciﬁc neurone which is capable of detecting the stimuli into nerve impulse. The ability stimulus and giving rise to a nerve impulse of receptors to convert stimuli or events passing to the central nervous system. which occur in the environment into a Examples include: skin mechanoreceptors nerve impulse is known as transduction. in the pacinian corpuscles. The structures which transform stimulus energy into electrical responses which Complex receptors is the nerve impulses in axons are called These sense cells consist of modiﬁed transducers. Receptors are therefore epithelial cells. They can detect stimuli. biological transducers that convert Sensory cells, sensory neurones, and energy from both external and internal other associated or accessory structures environments into electrical impulses. are examples of complex receptors. The They may be grouped together to form cones, rods, lens and iris (in the eye) are a sense organ, such as the eye or ear, or examples of sense cells. they may be scattered, as in those of the skin and viscera. The coordinated activity b) Classification of sensory receptors of an organism relies upon a continuous based on type of stimuli input of information from internal and external environments. When the Based on the type of stimulus they information received leads to a change in detect in the environment, there are activity or behaviour of the animals, it is several types of sensory receptors, which called stimulus. The specialised region of include: mechanoreceptor, photoreceptor, the body which has the ability of detecting thermoreceptor, nociceptor, chemoreceptor, the stimulus is known as sensory receptor. osmoreceptor and electroreceptors. Types of sensory receptors Mechanoreceptors Receptors can be classiﬁed into different They detect mechanical stimuli which groups based on their structure, type, and are caused by mechanical forces such as the location of stimuli they detect. sound or vibration, touch, pressure, and gravity. Touch receptors are found all over a) Classification of sensory receptors the body. Other touch receptors include based on structure Merkel’s discs and Meissner’s corpuscles which detect light and pacinian corpuscles Based on their structure there are two which sense deep pressure and vibration. types of receptors, and these are: single Mechanoreceptors are responsible for sensory neurone receptors and complex detecting changes that are perceived receptors (sense organs). such as sound or touch. They are also responsible for maintaining equilibrium balance and proper tone in muscles and joints (Figure 4.21). 230 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 230 10/10/2019 14:07

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Meissner’s corpuscle FOR ONLINE USE ONLY Pacinian corpuscle DO NOT DUPLICATE Coordination and Irritability Merkel’s disc Free nerve ending Figure 4.21 Structure of the touch receptors Photoreceptors These are receptors which detect electromagnetic stimuli such as light. There are two types of photoreceptors namely; rods and cones. These are found in the retina of an eye for detecting dim and bright light respectively (Figure 4.22). GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Conjunctiva Vitreous humour Sclera Ganglion cell Amacrine cell Iris Choroid Bipolar cell Lens Fovea Rods Pupil Cornea Blind spot Cones Suspensory Optic nerve Horizontal cell ligament Retina Ciliary body Extrinsic muscle Figure 4.22 Structure of the photoreceptors BIOLOGY FORM 5 KIWANDANI.indd 231 231 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Thermoreceptors Examples of thermoreceptors are bulbs of Thermoreceptors are specialised nerve cells Krauze which sense coldness and organ or receptors that can detect differences of Rufﬁn which detects heat. These cells in temperature. They can detect hotness are connected to heat gain and heat loss (heat) and coldness (cold). They are thus centres of the hypothalamus. of two types, heat and cold receptors. They are found throughout the skin to Nociceptors (pain receptors) allow sensory reception throughout These are receptors that can detect pain the body. The location and number of and they are found in the skin, muscles, thermoreceptors determine the sensitivity bones, blood vessels, and some organs of the skin to temperature changes. (4.23). Heat Light Pain Cold Hair receptor touch receptor receptor Epidermis Dermis GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Nerve Connective Hair Strong tissue movement pressure Figure 4.23 Sensory receptors of the skin Chemoreceptors impulses from these receptors travel to the These are receptors which detect chemical olfactory bulb (Figure 4.24). When odour stimuli such as smell, taste, and humidity. molecules enter the nose, they stimulate They have the ability to respond to a diverse the olfactory cilia (tiny hairs) attached to range of chemical substances in food, receptor cells, causing nerve impulses to nasal passage, and blood. For example, pass to the olfactory bulb and then to the olfactory receptors in the roof of the nasal brain. cavity can be stimulated by odours. Nerve 232 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 232 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability Olfactory bulb Born Olfactory nerve fibre Olfactory cell Olfactory hair (receptors) Mucus layer Figure 4.24 Structure of the olfactory lobe Taste buds are located on the upper surface of the tongue. Each bud contains about 25 sensory receptor cells with tiny taste hairs exposed to drink and food dissolved in saliva (Figure 4.25). Such buds sense the five basic tastes: bitter, sour, salty, sweet, and umami (a savoury, meaty taste). A combination of odours and the basic tastes produce subtler tastes. Basal cells Taste cells Taste pore GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Foliate Vallate papillae papillae Gustatory Microvilli afferent axons Synapse (c) Papilla Fungiform Tongue Taste buds papillae (b) (a) Figure 4.25 Structure of the taste receptors BIOLOGY FORM 5 KIWANDANI.indd 233 233 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Osmoreceptor Proprioceptors They detect the changes in osmotic These are internal sensory receptors that pressure. The osmoreceptors are primarily monitor the degree of stretch of muscles found in the hypothalamus and kidney of and tendons around the body. This most homoeothermic organisms. They information gives an individual a sense contribute to regulate fluid balance in of balance and awareness of the position the body (osmoregulation) and modulate of various parts of the body in relation to osmolarity in the kidney. each other (Figure 4.26). Electroreceptors Motor Electroreceptors detect natural electrical neurons stimuli. They are almost found in aquatic or amphibious animals because salt water Sensory neurons is a better conductor of electricity than air. The ampullae of Lorenzini are an example Muscle of electroreceptors in sharks. Some terrestrial organisms such as arachnids, cockroaches and bees are known to have electroreceptors. c) Classification of sensory receptors Muscle spindle based on the location of the stimuli they Tendon detect Based on the location of stimulus they Figure 4.26 Structure of the proprioceptors detect in the environment, three types of receptors; interoceptors, exteroceptors proprioceptors. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Interoceptors Mammalian eye These receptors detect stimulus which The eye is a sense organ which receives originates from the inside of the body; light of various wavelengths, reﬂected especially from internal organs and the from objects at varying distances in the gut. For example, stomach pain stimulus is visual ﬁeld and converts it into electrical detected by pain receptor (nociceptor) and impulses (Figure 4.27). Optic nerves blood pressure change stimulus is detected transmit these impulses to the brain by pressure receptor (baroreceptor). where an image of remarkable precision is perceived. The principal functions of Exteroceptors the eye include: controlling the amount of These are receptors which detect external light entering it, focusing images from the stimuli such as light, temperature, external world by means of a lens system, olfactory and tactile. For example, the skin and processing the captured image into a thermoreceptors detect the temperature pattern that can be seen. changes of the external environment. Ear, eye and nose also detect stimuli that originate from external environment. 234 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 234 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability Conjunctiva Vitreous humour Sclera Iris Choroid Lens Fovea Blind spot Pupil Optic nerve Cornea Retina Suspensory Extrinsic ligament muscle Ciliary body Figure 4.27 Vertical section of the human eye Eye accommodation muscles of the iris diaphragm contract, the This is the reﬂex mechanism by which radial muscles relax, the pupil becomes light rays from an object are brought smaller, and less light enters the eye. This to focus on the retina. It involves two process prevents damaging the retina and processes namely; reﬂex adjustment of the increases the depth of focus. In dim light, pupil’s size and refraction of light rays. the circular muscles of the iris diaphragm relax, the radial muscles contract, the Reﬂex adjustment of the pupil’s size pupil become large, and more light enters This involves the control of the amount of the eye. This decreases the depth of focus light entering the eye, either bright light of the eye (Figure 4.28). or dim light. In bright light, the circular GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Dim light Circular muscle Bright light Radial muscle relax relax Radial muscle Circular muscle contract contract Pupil Pupil dilates Pupil constricts (a) (b) Figure 4.28 Reﬂex adjustment of the pupil’s size in (a) dim and (b) bright light Refraction of light rays rays from a distant object (more than 6m Refraction of light rays involves bending away), are nearly parallel to one another of light rays as they move through different towards the eye while those from a closer media in the eye. At all distance range, object tend to spread out (diverging) light rays enter to the eye and refracted as they make angle from the object. In to come into exact focus on retina. Light all these two cases, light rays must be refracted or bent to focus on the retina. 235 BIOLOGY FORM 5 KIWANDANI.indd 235 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Refraction is greater for light from near ciliary muscle contracts, the tension on objects than for distant objects. The the suspensory ligaments is reduced, and refraction is achieved at the air-cornea the lens fattens due to its elastic nature surface and at the lens when the light which increases the degree of refraction of passes from one medium to another with a light. When the ciliary muscles relax, the different refractive index. The function of suspensory ligaments are stretched, pulling the lens is to produce the ﬁnal refraction the lens outwards, making it thinner, and that brings light to a sharp focus on the decreasing the degree of light refraction. retina. The lens is elastic and changes the Changing the shape of lens in different shape by the contraction and relaxation manners causes the lens to focus light rays of the ciliary muscle which encircles it. from near and distant objects on the retina. This assists the lens in adjusting the light This process is called accommodation. from both distant and near objects, which Light rays refraction in an eye at different cannot be done by cornea. When the distances is shown in Table 4.1. Table 4.1 Refraction of light rays in human eye at different distances Light from a distant object Light from a nearby object 1. Parallel light rays reach the eye. 1. Diverging light rays reach the eye. 2. Cornea refracts (bends) light ray. 2. Cornea refracts (bends) light ray. 3. Circular ciliary muscle relaxes. 3. Circular ciliary muscle contracted. 4. Suspensory ligament stretched. 4. Suspensory ligament slacks. 5. The lens is pulled out. 5. The lens becomes more convex. 6. Light focused on the retina. 6. Light focused on the retina. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Parallel rays from a distant object Cilliary Diverging rays Cilliary muscles muscles Tight from nearby object contract Loose relaxes ligaments ligaments Image Image Object at infinity Thin Nearby Thick eye object eye lens lens The structure of the retina neurones with synapse, connecting the The retina is comprised of three layers photoreceptor layer and the inner layer. of cells. The outermost layer is the Horizontal and amacrine cells are found in photoreceptor layer containing rods the middle layer. The innermost layer is an and cones, partially embedded in the internal surface layer containing ganglion pigmented epithelial cells of the choroid cells with dendrites in contact with layer. The rods and cones convert light bipolar neurones and axons of the optic energy into the electrical energy of the nerve (Figure 4.29). It is important to note nerve impulse. The middle layer is an that cats and some nocturnal carnivorous intermediate part which contains bipolar mammals possess a reﬂective layer called 236 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 236 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability tapetum which is found behind the retina. the vision of cats and nocturnals in dim light. The bright light shown by cats’ eyes This protein layer reﬂects light back into at night is the result of the reﬂection from the eye and gives an opportunity for rod the tapetum. cells to absorb it. This character improves Rod Choroid epithelium Photoreceptor layer Vesicles Layer of pigment Cone Outer Infolding of cell segment surface membrane Constriction Pair of cilia Inner Mitochondria segment Nucleus Synaptic End bulb region (equivalent of GOFVOERRNONMLEINNTE PURSOEPOENRLTYY synaptic knob) Intermediate layer Horizontal cell Bipolar neurone Amacrine cell Ganglion cell Internal surface layer BIOLOGY FORM 5 KIWANDANI.indd 237 LIGHT RAYS Axon of optic Figure 4.29 Structure of the retina nerve 237 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Structural differences between rods GOFVOERRNONMLEINNTE PURSOEPOENRLTYYfrom macular degeneration. Individuals and cones who have lost cone function are blind, Rods and cones are generally similar whereas those who have lost rod function in structure, but they differ in size and only experience difﬁculty seeing at low shape, as well as in the arrangement of the levels of illumination (night blindness). membranous discs in their outer segments. At the lowest levels of light, only rods are Differences in the transduction activated. Such rod mediated perception mechanisms of the two receptor types is called scotopic vision; the difﬁcult of also contribute to the ability of rods and making visual discriminations under very cones to respond to different ranges of low light conditions where only the rod light intensity. For example, rods produce system is active. The problem is primarily a reliable response to a single photon of the poor resolution of the rod system and, light, whereas more than 100 photons to a lesser degree, the lack of perception are required to produce a comparable of colour in dim light since such cones are response in a cone. Another difference is not involved to a signiﬁcant degree. that, the response of an individual cone does not saturate at high levels of steady Although cones begin to contribute to illumination, as does the rod response. visual perception at about the level of Although both rods and cones adapt to starlight, spatial discrimination is still operate over a range of luminance values, very poor. As illumination increases, the adaptation mechanisms of the cones cones become increasingly dominant in are more effective. This difference in determining what is seen. In addition, they adaptation is evident in the time course are the major determinant of perception of the response of rods and cones to light under relatively bright conditions, such ﬂashes. The response of a cone, even as normal indoor lighting or sunlight. The to a bright light ﬂash that produces the contribution of rods to vision drops out maximum change in photoreceptor current nearly entirely in the so called photopic pick up is about 200 ms; which is more vision because their response to light than four times faster than rod recovery. saturates, that is, the membrane potential of individual rods no longer varies as The arrangement of the circuits that a function of illumination because all transmit rods and cones information to of the membrane channels are closed. retinal ganglion cells also contributes to Mesopic vision occurs in levels of light the different characteristics of scotopic at which both rods and cones contribute and photopic vision. In most parts of the to vision at twilight. Thus, from these retina, rods and cones signals converge considerations, it should be clear that on the same ganglion cells; that is, most of what we think of as “seeing” is individual ganglion cells respond to both mediated by the cone system. Thus, the rod and cone inputs, depending on the loss of cone function is devastating, as level of illumination. The early stages it occurs in elderly individuals suffering of the pathways that link rods and cones 238 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 238 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability to ganglion cells, however, are largely GOFVOERRNONMLEINNTE PURSOEPOENRLTYYMechanism of photoreception independent. For example, the pathway Rods contain light sensitive pigment from rods to ganglion cells involves a rhodopsin, which is attached to the distinct class of bipolar cells called rod outer surface of vesicles. Rhodopsin is a bipolar that, unlike cone bipolar cells, molecule formed by the combination of a does not contact retinal ganglion cells. protein called scotopsin with a small light- Instead, rod bipolar cells synapse with the absorbing molecule called retinene which dendritic processes of a speciﬁc class of is a carotenoid molecule derived from amacrine cells that makes gap junctions vitamin A. When the rhodopsin molecule and chemical synapses with the terminals is exposed to bright light, it breaks down of cone bipolars. These processes, in turn, into retinene and scotopsin. This process make synaptic contacts on the dendrites of is called bleaching. ganglion cells in the inner surface layer. Rhodopsin Bleaching Retinene + Scotopsin Moreover, the rod and cone systems differ dramatically in their degree of Rhodopsin is reformed immediately when convergence; a factor which contributes light stimulation decreases. Trans retinene greatly to their distinct properties. Each rod is ﬁrst converted into cis retinene and then bipolar cell is contracted by a number of recombined with scotopsin. This process rods, and many rod bipolar cells contract a is called dark adaptation. Similary, the given amacrine cell. In contrast, the cone cone system has a very high spatial system is much less convergent. Thus, resolution but it is relatively insensitive to each retinal ganglion cell that dominates light. It is therefore specialised for acuity central vision (called midget ganglion at the expense of sensitivity. This property cells) receives input from only one cone of the cone system allows us to see colour. bipolar cell, which in turn is contacted by a single cone. Convergence makes the rod Physiology of seeing system a better detector of light, because The eye works on the same principle as small signals from many rods are pooled that of the camera. Light rays from the to generate a large response in the bipolar object pass from the external part of the cell. At the same time, convergence eye to the retina through the conjunctiva, reduces the spatial resolution of the rod cornea, aqueous humour and pupil system; since the source of a signal in a (Figure 4.30). The pupil is an opening rod bipolar cell or retinal ganglion cell (an aperture) which is controlled by the could have come from anywhere within a iris (like camera shutters) depending relatively large area of the retinal surface. on the amount of light. The stronger the The one-to-one relationship of cones to amount of light, the smaller the size of the bipolar and ganglion cells is, of course, aperture. The lens is positioned between required to maximize acuity. the outer and inner chambers of the eye, and its major function is to focus images on the retina by changing its thickness BIOLOGY FORM 5 KIWANDANI.indd 239 239 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools depending on the amount of light from be seen. Thus, the role of the retina is distant or nearby objects. On the retina, to translate light into nerve signals and there are cone and rod photoreceptors, allow us to see under various conditions which are connected to the brain via a ranging from starlight to sunlight. It also bundle of ﬁbres called optic nerve. The distinguishes the wavelengths for us to information received is processed in the discriminate colors. brain, and consequently, the object can Iris Light Retina Inverted image of object Object Lens Optic nerves Figure 4.30: Structure of a mammalian eye showing physiology of seeing The mammalian ear GOFVOERRNONMLEINNTE PURSOEPOENRLTYYwindow (fenestra ovalis) and the round The mammalian ear consists of three window (fenestra rotunda). There are parts, namely the outer, middle and inner three connected bones called ear ossicles, ear. The outer ear comprises of an external which are held in position by muscles. ﬂap of skin covered by elastic cartilage These are malleus (hammer), incus (anvil), called pinna. The pinna collects sound and stapes (stirrup). The middle ear is air waves and directs them into the ear canal ﬁlled part that depends on the equalization (external auditory meatus). Across the end of pressure outside and inside the ear to of ear canal is a tympanic membrane or prevent damaging the ear drum. There is ear drum which separates the outer ear a eustachian tube (auditory tube) which from the middle ear. The opening of the connects the middle ear to the pharynx. auditory canal is lined with ﬁne hairs and Via this tube, air enters and leaves the glands which secrete earwax, which is middle ear during swallowing to equalise located in the upper wall of the auditory pressure (Figure 4.31). canal. Ear wax guards the ear against entrance of foreign materials such as dust Unlike the outer ear and middle ear which and microorganisms. is ﬁlled with air, the inner ear comprises of a complex system of ﬂuidﬁlled tubes. In the middle ear, the tympanic The cochlea, the coiled structure, is an membrane begins and ends at a bony wall organ for hearing while the semicircular containing two small openings covered by canal and the vestibule are organs for membranes. The two openings are oval body balance. 240 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 240 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability Pinna Semicircular canals Vestibular nerve Facial nerve Auditory nerve Cochlea Eustachean tube External auditory meatus (ear canal) Stapes Ear Incus ossicles Malleus Tympanic membrane Outer ear Middle ear Inner ear Figure 4.31 Structure of a mammalian ear The structure of the membranous GOFVOERRNONMLEINNTE PURSOEPOENRLTYYas the vestibular apparatus. The cochlear labyrinth of the mammalian inner ear duct is located within the bony scaffolding There are two labyrinths in the inner the cochlea. It is held in place by the spiral ear, namely the bony labyrinth and lamina. The saccule and utricle are two membranous labyrinth; one is inside membranous sacs located in the vestibule. the other. The membraneous labyrinth is comprised of the cochlea, vestibule The utricle is larger than saccule, and it and three semicircular canals. All these receives the three semicircular ducts. structures contain a ﬂuid called perilymph. The saccule is globular in shape and Membranous labyrinth lies within the receives the cochlear duct. Endolymph bony labyrinth. drains from the saccule and utricle into the endolymphatic duct. The duct extends The membranous labyrinth is a continuous through the vestibular aqueduct to the system of ducts ﬁlled with endolymph. It posterior aspect of the petrous part of the is comprised of the cochlear duct, three temporal bone. Here, the duct expands to a semicircular ducts, saccule and the utricle. sac where endolymph can be secreted and The cochlear duct is situated within the absorbed. Semicircular ducts are located cochlea and is the organ of hearing. The within the semicircular canals, and share semicircular ducts, saccule, and utricle their orientation (Figure 4.32). are the organs for balance, are also known BIOLOGY FORM 5 KIWANDANI.indd 241 241 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Semicircular canals Utricle Saccule Cochlea Endolymphatic duct Figure 4.32 Components of the membranous labyrinth Mechanism of hearing The motion of the stapes against the oval The mammalian ear functions as an organ window sets up waves in the ﬂuids of the for hearing and balance. The process cochlea, causing the basilar membrane to of hearing starts when sound waves vibrate. This stimulates the sensory hair enter the outer ear and travel through cells of the organ of corti, on the basilar the external auditory canal until they membrane, to send nerve impulses to the reach the tympanic membrane, causing brain. When they reach the auditory area the membrane and the attached chain of of the cerebral cortex, they are interpreted auditory ossicles to vibrate. The malleus as a sound. Many sensory hair cells with then takes the pressure from the inner different thresholds at which they are surface of the tympanic membrane and stimulated exist. The louder the sound, the passes it by means of the incus to the stapes. greater the number of sensory hair cells There are about 20 times multiplication of will be stimulated at any one point of the sound pressure as it moves from outside basilar membrane (Figure 4.33). to inner ear. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Vestibular canal Perilymph Reissner’s membrane Endolymph Median canal Perilymph Tectorial Organ of membrane Corti Basilar membrane Sensory hair cell Auditory neurone Tympanic canal Figure 4.33 Transverse section of cochlea showing the organ of corti 242 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 242 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability Maintaining body balance in mammals The brain then initiates motor impulses to The parts of the ear which are concerned various muscles to correct the imbalance with balance are the semicircular canals (Figure 4.34). and vestibule. The semi circular canals are three curved tubes containing endolymph, All information that aid balance and which communicates with the middle positioning of the body relative to chamber of the cochlea via the utriculus gravity, as well as changes in the position and sacculus. Each of the three canals is due to acceleration and deceleration is set in a plane at right angles to the other. provided by utriculus and sacculus. Such Any movement in any plane will cause information is provided by granules movement of canals in the direction of the known as otoliths which are embedded head. Each of the three canals possesses a in jellylike materials. Various movements swollen portion, the ampulla, within which of the head cause this otolith to displace there is a ﬂat gelatinous plate, the cupula. sensory hair cells on the regions of the The movement of endolymph displaces walls of utriculus and sacculus which the cupula in the opposite direction to respond to vertical and lateral movements the head movement. The sensory hair respectively. Then the sensory hair cells found at the base of the cupula detects send appropriate sensory impulse to the the displacement and sends impulse to brain. the brain through the vestibular nerve. Anterior semicircular GOFVOERRNONMLEINNTE PURSOEPOENRLTYYCrista ampullaris and cupula canal Lateral semicircular canal Posterior semicircular canal Ampullae (a) Crista Direction Cupula is pushed over and stimulates hair cells Cupula Endolymph ampullaris of rotation Sensory hair cells Supporting cells Endolymph Stereocilia are bent Sensory nerve fiber lags behind due to inertia (b) (c) Vestibular neurone Figure 4.34 Structure of the semicircular canals showing (a) position of ampula and cupula (b) section of ampula at stationary and (c) section of ampula during body movement 243 BIOLOGY FORM 5 KIWANDANI.indd 243 10/10/2019 14:07

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 4.1 Stand upright and rotate your body 4.3 Hormonal coordination in several rounds (about 5 times). Stop and mammals explain with reasons how you feel. Hormonal coordination in mammals is a Exercise 4.3 function of the endocrine system, which is composed of a series of glands known as 1. Name the main types of sensory endocrine glands. They are called endocrine receptors and explain their functions glands because they are ductless. The in the mammalian body. system is called “endocrine” to distinguish it from “exocrine” glands that use ducts to 2. Explain the process of convey their chemical agents to the target accommodation in mammalian eye. cells or substances e.g. glands producing digestive enzymes. These glands secrete 3. Describe the structure of retina. speciﬁc chemical ﬂuids called hormones 4. Describe the structure of the directly into the blood stream. Due to this reason, the endocrine gland is surrounded membranous labyrinth of the by numerous blood vessels. A hormone is a mammalian ear. chemical messenger produced by a ductless 5. Explain the mechanism of hearing in gland, transported by blood and shows its mammals. effects in a region away from the site of 6. Explain how semicircular canals production. Table 4.2 gives a list of some function with respect to balance and hormones, endocrine glands and where they posture in mammals. are produced (Figure 4.35), and the activity that they regulate. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Pituitary Suprarenal Ovaries Parotid (in female) Pineal Prostate Parathyroid Mammary Thyroid (in females) Red bone marrow Liver Pancreas Testes (males) Figure 4.35 Location of endocrine glands in a cow 244 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 244 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability Table 4.2 Hormones, glands where they are produced and the activity they regulate Endocrine gland Hormone(s) produced Functions Thyroid Thyroxine, Regulate vital body functions. Triiodothyronine Parathyroid Stimulates and maintains metabolism, growth Calcitonin and development. Adrenal (Cortex) Parathyroid Hormone Reduction of blood Ca2+ levels. (PTH) Aldosterone Control calcium within the blood. Adrenal Cortisol, (Medulla) Corticosterone, Increases blood Na+ levels; increase K+ Pancreas Cortisone secretion. Pineal gland Epinephrine (Adrenaline) Regulates blood pressure. Norepinephrine Increases blood glucose levels; Testes anti-inflammatory effects. Insulin Stimulates fight-or-flight response, increases Ovaries Glucagon blood glucose levels and increase metabolic activities. Melatonin Reduces blood glucose levels. Androgens Increases blood glucose levels. Oestrogen Regulates some biological rhythms and protect CNS from free radicals. Regulates, promotes, increases or maintains sperm production and male secondary sexual characteristics. Promotes uterine lining growth and female secondary sexual characteristics. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Properties of hormones in the blood triggers the pancreas to Hormones are all produced by specific release insulin to lower the level of cells of endocrine system, they are blood glucose. Another factor is the transported through the blood, they presence of another hormone in the show their effect to the site away from blood. Majority of the hormones released its source, hormones are speciﬁc for a from the anterior pituitary gland are particular target, they are soluble organic stimulating hormones, which direct other molecules and are effective even at low glands to secrete their hormones. For concentration. instance, the growth hormone releasing factor causes the release of the thyroxin Feedback mechanisms for hormonal hormone. Stimulation by neurones from coordination the autonomic nervous system can also The release of hormones by glands is cause secretion of hormones. Under the controlled by several factors, including condition of stress, fear or danger, the the presence of speciﬁc metabolites in body secretes hormones to combat the the blood. For example, excess glucose situation. 245 BIOLOGY FORM 5 KIWANDANI.indd 245 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools The timing of hormone release and the inhibits further production by inhibiting amount of hormone to be released are the production of Thyrotropin Releasing regulated by a feedback mechanism. Hormone (TRH) by the hypothalamus and Feedback mechanisms are self regulatory thyroid stimulating hormone (TSH) by mechanisms in which when there is a anterior pituitary gland. Therefore, in this disturbance or deviation in a system, case, the product of a series of reactions series of events occur to either remove the controls its own production by turning disturbance (negative feedback) or make off the pathway, when it reaches a certain the system to deviate further (positive level. feedback). Usually, it is a negative feedback mechanism which regulates Negative feedback is also observed in the release of hormones. In rare cases production and regulation of insulin in the positive feedback mechanisms may occur. body. A rise of sugar level in the blood is An example of the negative feedback detected by β cells of islets of Langerhans mechanism is the release of the thyroxine of the pancreas, which release the insulin hormone (Figure 4.36). hormone. The hormone will then convert glucose into glycogen which is stored in Hypothalamus Small effect the liver and muscles. This causes the level of sugar in the blood to decrease. The TRH Thyroxine lower level of glucose then causes the b Anterior pituitary Main effect cells to reduce production of insulin. This, inturn, triggers the release of glucagon TSH GOFVOERRNONMLEINNTE PURSOEPOENRLTYYThyroxinefrom α-cells of islets of Langerhans of Thyroid the pancreas. This hormone converts Thyroxine glycogen into glucose. Blood/tissue The interaction between hormonal and Increased BMR nervous systems Coordination process is achieved when Key: Inhibition nervous and endocrine systems act Stimulation together. Although the nervous system and the endocrine system are two different Figure 4. 36 Factors regulating thyroxine systems, both release chemical substances secretion and homeostatic control of the as a means of communication between cells. The principal role of both systems metabolic rate is to coordinate and control various physiological activities in organisms. The Thyroxine helps in regulating the major centres for linking the two systems are the pituitary gland (control centre for metabolic rate, growth and development endocrine glands) and the hypothalamus of an organism. The control of the release (the control centre for the nervous system). of thyroxine is determined by the level The hypothalamus collects information of thyroxine with four iodine atoms from the brain and blood vessels passing (T4) circulating in the blood. If there is high concentration of T4 in the blood, it 246 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 246 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability through it to the pituitary gland. The GOFVOERRNONMLEINNTE PURSOEPOENRLTYYhormones that regulate the production pituitary gland directly or indirectly of a wide variety of other hormones. All controls the secretions of other endocrine pituitary hormones stimulate the release glands. of target gland hormones. As their levels increase, they inhibit the secretion of The pituitary gland, which is located hypothalamus and pituitary hormones. at the base of the brain, is directly When their levels in the blood fall below a connected to the brain region called certain level, hypothalamus and pituitary hypothalamus. This physical link between inhibition stop and start secreting their the hypothalamus and pituitary is the basis chemicals again. This is also referred to as for the connection or link between the a negative feedback mechanism. central nervous system and the endocrine system. The pituitary has two distinct The posterior pituitary gland is an segments, namely the anterior pituitary extension of the brain. It stores and releases and the posterior pituitary. The anterior antidiuretic hormone (ADH) or vasopressin pituitary gland is connected by blood and oxytocin hormone which are produced vessels called the portal system, which by neurosecretory cell bodies, lying in the has one capillary bed in the hypothalamus hypothalamus. They pass down the nerve and another in the anterior pituitary. Also ﬁbres. Nerve impulses are relayed to the it has nerve terminals that release two cell bodies of these neurosecretory cells groups of chemical substances known as from other regions of the brain. They releasing and inhibiting factors into the are transmitted down the axons, where blood capillaries at the hypothalamus hormones are stored in vesicles (Figure end of portal system. These chemical 4.37). The whole process involves both substances pass to the pituitary end and nervous and endocrine systems. This is cause the release of six trophic hormones referred to as a neuroendocrine response, (hormones that stimulate other endocrine resulting into a pattern of behaviour hormones to release hormones) which are known as a neuroendocrine reﬂex. stored in the anterior pituitary gland. ADH is released in response to a fall in the In the year 1930, a biologist documented water content of blood plasma and leads the consequences of removing the entire to an increase in the permeability to water pituitary from laboratory rats. As a of distal convoluted tubule in the nephron result of pituitary removal, the animals of the kidney. On the other hand, oxytocin stopped growing, failed to maintain causes the contraction of the uterus during normal body temperature, and suffered birth and ejection of milk from nipples. atrophy (shrinkage) of their genitals, Oxytocin and contraction of the uterus thyroid glands, and adrenal cortex. Not is a positive feedback mechanism. The surprisingly, their life span shortened more the concentrations of oxytocin, the dramatically. These experiments stronger the contraction of the uterus suggested that, in addition to secreting becomes. growth hormones, the pituitary secretes 247 BIOLOGY FORM 5 KIWANDANI.indd 247 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Hypothalamus Superior hypophyseal Neurosecretory cells artery Primary capillary plexus of hypophyseal portal system Infundibulum Hypophyseal portal vein Posterior pituitary Secondary capillary plexus of Pituitary gland Anterior hypophyseal portal system pituitary Figure 4.37 Relationship between the hypothalamus and pituitary gland Exercise 4.4 GOFVOERRNONMLEINNTE PURSOEPOENRLTYYand response to external stimuli which results into growth movements and also 1. Explain the feedback mechanisms movement of organs. There are three types of hormonal coordination. of growth movements in plants, namely tactic movement, nastic movement, and 2. Describe the interaction between tropic movement. hormonal and nervous systems in the mammalian body. a) Tactic movement Tactic movement; also known as taxis 3. The pituitary gland is said to be a (plural taxes) is the type of movement master gland. Substantiate. which involves the entire cell or organism moving from one place to another in 4. Explain the role of hypothalamus in response to external stimuli such as light, coordination. water, and chemicals. Tactic movement occurs in plant reproductive cells and in 4.4 Coordination in plants some organisms such as Euglena, and Plants do not have a nervous system; they Chlamydomonas. Taxes may be grouped rely on chemical coordination. Therefore, as positive taxis and negative taxis. most of their responses are slower A positive taxis is when an organism compared to animals. Unlike animals, or cell moves towards the source of plants do not move from one place to stimulation, while negative taxis is when another; although the movement is shown an organism or cell moves away from by the characteristics of plants’ sensitivity 248 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 248 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability the source of stimulation. For example, of temperature (thermonasty) or light Chlamydomonas always moves towards intensity (photonasty). An example of light of low intensity and away from light nyctinasty is the opening and closing of high intensity. This type of response of petals of some ﬂowers that occur in is known as phototactic response or response to alternation in the duration of phototaxis. In this example, the movement day and night. Another example is sleep towards light of low intensity is a positive movements of leaves of some leguminous phototaxis, whereas, that away from light plants in response to the onset of darkness. of high intensity is a negative phototaxis. Types of tactic movements (taxes) Thermonasty Based on the nature or kind of a stimulus This is a movement of plant parts in involved, different types of tactic response to temperature. For example, movements (taxes) can be identiﬁed. some flowers close when the temperature Examples of taxes include phototaxis drops, or some leaves fold when the (response to light) which can be seen temperature is too high. in Euglena and blue green algae and chemotaxis (response to chemicals) as seen Chemonasty in lower plants such as Funaria where by This is the movement of plant parts male gamete move towards the chemical in response to chemicals stimuli, for substance released by egg cells. Others example, sundew plants close glandular include geotaxis (gravity), aerotaxis hairs due to chemical produced by insect (oxygen), magneotaxis (magnetic field) when land on it, this prevents escape of and rheotaxis (water current). the insect. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY b) Nastic movement Photonasty Nastic movement is a non-directional This is the movement of plant parts in movement of a part of stationary plant in response to light. For instance, some response to an external stimulus. Based on flowers or leaves fold following the sun the nature of stimuli, nastic movements shine, or the opening and closing of can be divided into the following groups: flowers depending on whether it is day or night (Figure 4.38). Nyctinasty This is a nastic movement which occurs in response to diurnal changes BIOLOGY FORM 5 KIWANDANI.indd 249 249 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools (a) (b) Figure 4.38 Nastic movement in flower (a) during the day the flower opens and (b) during the night the flower closes Seismonasty between different sides of the plant part. This is the movement of plant parts For example, changes in the water contents in response to touch. Seismonastic of the tissues at the base of the leaf of the movement is also known as thigmonastic Mimosa plant results in the shrinkage movement. An example of seismonastic and folding of its leaﬂets. Such response movement is folding of leaves of Mimosa may be due to different stimuli, such as pudica in response to touch (Figure 4.39). light, touch, heat, or electric shock. After a suitable recovery period, the leaﬂets open Generally, nastic movement can result again. Normally, they remain expanded from changes in turgor or growth rate during the day while closed at night. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 4.39 Nastic movement in the leaﬂets of the Mimosa plant 250 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 250 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability c) Tropic movement is kept in a horizontal position, the shoot This is the movement of part of a plant will bend and start growing in an upright associated with growth of plant tissue direction while the roots change their caused by a differential concentration of direction of growth downwards (Figure plant hormones, usually auxins, under a 4.41). specific stimulus. The stimuli involved include light, gravity, water/humidity, and Negative pressure or touch, among others. Some geotropic common examples of tropic movement in plants include phototropism, geotropism, and hydrotropism. Phototropism. Plant growth movement Positive associated with light. Shoots tend to geotropic grow towards light (positive phototropic movement), and if the light is coming Figure 4.41 Geotropism in plant from a single direction the plant will bend towards that source of light (Figure 4.40). Hydrotropism. Hydrotropism takes The roots show the opposite tendency place in response to moisture. Roots are (negative phototropism). generally positively hydrotropic (Figure 4.42 a and b). (a) GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Root grows Moist soil straight Water Clay pot (b) Figure 4.40 Shoot grow towards light Root grows towards water Geotropism. This is caused by the earth’s gravitational pull. Shoots show negative Dry soil Moist soil geotropic movement, that is, they grow away from the force of gravity, while roots Figure 4.42 Movement of roots towards water show positive geotropism. If a potted plant (a and b) 251 BIOLOGY FORM 5 KIWANDANI.indd 251 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Exercise 4.5 GOFVOERRNONMLEINNTE PURSOEPOENRLTYY of ions, and through vascular tissues (xylem and phloem). 1. Distinguish between plant and animal coordination. d) Each plant hormone evokes many different responses. 2. Explain the following terms: e) The effects of different plant hormones a) Tactic movement overlap and may be stimulatory or inhibitory. b) Nastic movement f) Each plant hormone performs speciﬁc 3. With examples, differentiate functions in the plant body. between seismonasty and photonasty. g) The biosynthesis of plant hormones within plant tissues is always diffuse, 4.5 Plant hormones (Phytohormones) not localized. Plant hormones or plant growth hormones are chemical substances that regulate h) The production of plant hormones plant growth. They are also known as occurs very often at sites of active phytohormones or plant growth regulators. growth within meristems, before cells Plant hormones are signal molecules have been fully differentiated.After the produced within the plants and usually production, they are sometimes moved occur in extremely low concentrations. to other parts of the plant, where they They regulate cellular processes in cause an immediate effect; or they can targeted cells within the plant. be stored in cells to be released later. Characteristics of plant hormones Types of plant hormones a) Plant hormones are chemicals that are There are ﬁve main types or groups of plant hormones. These are auxins, gibberellins, required in small amounts to promote cytokinins, ethene (ethylene), and abscisic and inﬂuence growth, development acid (ABA). These hormones can perform and differentiation of plant cells and their functions either independently or tissues. They are active and effective synergistically (working together to effect even at very low concentrations. a certain function). For example, auxins b) They are produced in certain parts are known as growth promoters, since of the plant and transported to other they inﬂuence plant growth and assist in parts of the plant where they elicit producing a phototropic response which speciﬁc biochemical, physiological or results into growth. Sometimes, auxins morphological responses. and gibberellins act together to bring about c) They are transported within the plants cell elongation. This is called synergism. by four different types of movements Alternatively, two plant hormones may namely; localised movement, work opposing one another, like auxins cytoplasmic streaming, slow diffusion which induces apical dominance while cytokinins prevent it. This is known as antagonism. 252 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 252 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability Auxins GOFVOERRNONMLEINNTE PURSOEPOENRLTYYa) Promote fruit setting Auxins are chemical compounds produced The synthetic auxins such as Indolebutyric in the root and shoot apices of the plants. acid (IBA) and Naphthalene acetic acid One of their common forms is Indoleacetic (NAA) are used to promote fruit setting. Acid (IAA). Auxins have the following role Fruit setting involves a series of changes in plants: taking place after fertilisation in the ovary, a) They inﬂuence cell enlargement, bud resulting into development of a fruit. Auxins can be used for setting some fruits formation, and root initiation. such as tomatoes and pepper, resulting into production of fruits without fertilisation. b) They facilitate production of phototropic NAA can also be used to control pre- response. harvest fruit drop and fruit thinning in various crops such as apples. c) Auxins together with cytokinins control the growth of stems, roots, and b) Promote rooting in cuttings fruits. Auxins (IBA and NAA) are very effective d) They affect cell elongation by altering in stimulating root development from stem cell wall plasticity. cuttings. This is commonly applied in crops that are propagated through stem cutting, e) They stimulate cambium of such as cassava. This form of asexual meristematic cells to develop stems, reproduction ensures that no change can leaves and flower buds, while in stems, occur in the genetic make up of the plants. they differentiate secondary xylem. c) Weed killers f) They inhibit the growth of lateral buds, Phenoxyacetic acid is used as a selective hence promote apical dominance. weed killer as it kills broad leaf plant species, especially dicotyledons; hence it is g) They promote lateral and adventitious used in removing dicotyledonous weeds in root development and growth. cereal (monocotyledonus) crops. Benzoic acids are also used as a powerful weed h) They regulate speciﬁc protein killer, thus they are used against deep- synthesis in seeds as they develop rooted weeds. within the ﬂower after pollination. i) They stimulate development of fruits without fertilisation (parthenocarpy). j) They inhibit abscission in leaves and fruits. Application of synthetic auxins in crop d) Prevent sprouting in potatoes production Phenoxyacetic acid is used to prevent Auxins can be synthesised for agricultural sprouting in potatoes. It is also used to use. It is a proven fact that synthetic auxins prevent premature falling of fruits and are more useful and cheaper than naturally leaves in crop plants. produced auxins. Synthetic auxins play the following roles in agriculture: BIOLOGY FORM 5 KIWANDANI.indd 253 253 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Gibberellins GOFVOERRNONMLEINNTE PURSOEPOENRLTYYe) They increase plants’ resistance to Gibberellins such as Gibberellic Acid pests and diseases. (GA) include a wide range of chemicals that are produced naturally within plants. Cytokinins Like auxins which can be produced in Cytokinins (CKs) are a group of chemicals industry, gibberellins are also commercially that inﬂuence cell division and shoot produced from fungal culture. They formation in plants. In the past, when the perform the following role in plants: cytokinins were ﬁrst isolated from yeast a) They stimulate stem elongation and cells they were called ‘kinins’. They are found mostly in regions of rapid cell pollen tube growth. division, particularly in seeds and fruits, where embryos develop. They perform the b) Inﬂuence cell division. following role in plants: a) They promote cell division in the c) They promote ﬂowering, seed germination and differentiation after presence of auxins. germination. b) They induce delayed senescence of d) They are important in seed germination, leaves and fruits. as they effect enzyme production that mobilises food production needed for c) They are responsible for mediating growing new cells. This is done by transportation of auxins throughout modulating chromosomal transcription the plant and affecting internodal in the growing seedling. length and growth. e) Promote bolting in rosette plants, d) They promote lateral bud growth. hence increasing inter nodal lengths. e) They counter the apical dominance f) Promote cell division and elongation induced by auxins. in the presence of auxins. f) They break seed and bud dormancy at g) Reverse the inhibition of shoot growth appropriate temperatures. and dormancy induced by Abscisic acid. Application of synthetic cytokinins in crop production h) Break seed dormancy. Synthetic cytokinins have the following application in crop production: Application of synthetic gibberellins in crop production a) They are used to prolong the shelf life The synthetic gibberellins have the of fresh crops such as cabbage and following role in plants: lettuce. a) They promote fruit setting. b) They break bud and seed dormancy. b) They enhance malting in brewing c) They keep ﬂowers fresh. industries. c) They reverse genetic dwarﬁsm. d) They break seed dormancy. 254 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 254 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Coordination and Irritability Ethene (Ethylene) GOFVOERRNONMLEINNTE PURSOEPOENRLTYYAbscisic Acid (ABA) Unlike other plant hormones, ethene is in ABA is also known as stress hormone; gaseous state. It is formed from the amino because its production is stimulated by acid methionine and released from ripening environmental stress or other adverse fruits, nodes of stems, ageing leaves, and conditions, such as drought and water ﬂowers. It is produced as a metabolic logging. In contrast to other growth byproduct of most plant organs. It plays substances such as auxins, gibberellins, the following role in plants: and cytokinins, which are plant growth a) It stimulates ripening of fruits. promoters, ABA is a growth inhibitor; hence it acts antagonistically to the b) It is involved in axillary bud inhibition. growth promoters. It is produced by This occurs when auxins are any tissue containing chloroplasts. It is transported from the apical meristem concentrated in leaves, fruits, and seeds. of the stem downward, stimulating The term abscisic acid originates from the the production of ethylene, which belief that it was a direct cause of leaf fall suppresses axillary bud development. (abscission), although this is now known to be not true. Abscisic acid has the following c) It suppresses stem and root elongation, role in plants: especially during physiological stress a) It promotes dormancy and inhibits as in drought. growth. d) It breaks bud dormancy. b) It causes abscission (fall of leaves and Application of synthetic ethylene in fruits). When fruit ripens, the level crop production of auxins which inhibits abscission Synthetic ethylene has the following falls, while that of abscisic acid which application in agriculture: promotes abscission increases. a) It promotes fruit ripening within a c) It promotes closing of stomata under relatively short period of time. water stress conditions. b) It is applied to citrus fruits to attain Application of synthetic abscisic acid attracting colours before being in crop production presented for sale. Abscisic acid can be sprayed on tree crops to regulate fruit fall at the end of the season. c) It induces ﬂowering in pineapples. This helps to ensure that fruits fall at the time; hence avoiding the need for repeating d) It stimulates the latex ﬂow in rubber picking of fruits over a long time span. trees. BIOLOGY FORM 5 KIWANDANI.indd 255 255 10/10/2019 14:07

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE Revision questions 6. Outline the differences between 1. State the functions of cell body and rods and cones. myelin sheath. 7. Describetypesoftacticmovements. 2. Describe the characteristics of a nerve impulse. 8. Explain the concept of nastic movement. 3. Explain how an impulse is transmitted across the synapse. 9. Outline the role of phytohormones in plants. 4. Draw a well labelled diagram of the mammalian ear. 10. Explain the application of natural and synthetic phytohormones in 5. What are the major differences crop production and weed control. between the nervous system and hormonal system? 11. Explain the role of synthetic phytohormones for the development of industrialised Tanzania. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 256 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 256 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE FiveChapter Nutrition Introduction Living organisms require energy in order to accomplish various metabolic activities. The main source of energy for organisms in all ecosystems is the sun. Organisms obtain their food in different ways. Autotrophs use light energy and simple inorganic substances such as water and carbon dioxide from their environment to synthesize their own food. Heterotrophs, on the other hand, obtain already made complex organic molecules such as carbohydrates, proteins and fats, break them down, assimilate and use them to maintain their life functions. In this chapter, you will learn about food manufacturing in plants and digestion in mammals. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 5.1 Concept of nutrition to synthesize food. This is the process known as photosynthesis. A second group There are different modes of nutrition of autotrophs use a process known as chemosynthesis. Sulphur bacteria, for by which living organisms obtain food example, use inorganic sulphur as the in order to obtain energy and nutrients source of energy for synthesizing their that are required for different metabolic food, and Methanobacter sp. (bacteria activities and survival. Nutrition entails living in deep oxygen-depleted oceans) a process by which living organisms take use methane as a source of energy. Other in food and use it for metabolic activities organisms that cannot make their own such as growth, and body repair. Based on food but depend on other organisms for their modes of nutrition, living organisms food and energy are called heterotrophs. These include animals, fungi and some are categorised into two main groups bacteria. namely; autotrophs and heterotrophs. All 5.2 Autotrophic nutrition In this type of nutrition, organisms acquire organisms that can make their own food energy from sunlight and utilize it to from simple inorganic substances such as water and carbon dioxide are called autotrophs. Autotrophs such as plants, green algae, and some bacteria, have the green pigment (chlorophyll) used 257 BIOLOGY FORM 5 KIWANDANI.indd 257 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools synthesize their food using carbon dioxide Acidithiobacillus thiooxidans) found in (CO2) obtained from the atmosphere. The hot springs containing hydrogen sulphide organisms that are capable of utilizing obtain energy by oxidizing inorganic sunlight or chemical energy to make sulphur. Organisms which obtain their their own food from simple inorganic energy from chemicals through oxidation materials are referred to as autotrophs, reaction are called chemoautotrophs. The which literally mean self-feeders. energy obtained by both photoautotrophs Autotrophs such as plants, cyanobacteria, and chemoautotrophs is used to build algae, purple sulphur bacteria, purple food in form of complex molecules such non-sulphur bacteria, and green sulphur as sugar, starch, protein, and lipids from bacteria use sunlight energy and chemial carbondioxide. energy to manufacture their food. These are collectively called photoautotrophs, Food manufacturing in plants which is a combination of three Greek (Photosynthesis) words: photos, auto, and trophos Photosynthesis refers to a process whereby meaning ‘light,’ ‘self,’ and ‘nourishment organisms containing chlorophyll and or feeders’ respectively. Therefore the carotenoid pigments manufacture their term photoautotroph literally refers to an own food in the form of carbohydrates organism capable of manufacturing its own from simple inorganic substances food using light energy. Photoautotrophs (carbon dioxide and water) using sunlight such as plants, cyanobacteria and energy. Examples of photosynthetic algae contain green pigments such as organisms are plants and some bacteria chlorophyll 'a', 'b' and 'carotenoid'. These (bacteriochlorophyll). pigments are important in absorbing light GOFVOERRNONMLEINNTE PURSOEPOENRLTYY energy which is vital in the synthesis However, photosynthesis in plants of food in plants by the process known differs from that of bacteria in terms of as photosynthesis. Bacteria contain the products released. Unlike bacteria, bacteriochlorophyll which performs the plants release oxygen as a by product. same function as chlorophyll. Generally, In addition, photosynthesis in plants the light absorbed by the chlorophyll in involves pigments such as chlorophyll, green plants is converted into chemical and carotenoids while bacterial energy during photosynthesis. photosynthesis uses bacteriochlorophylls in most cases. Bacteria therefore lack Besides light, inorganic chemicals are deﬁnite chloroplasts as opposed to plants the alternative sources of energy for the which contain deﬁnite chloroplasts. synthesis of food. Energy from such chemicals is normally acquired by these In green plants, photosynthesis can be organisms through oxidation reactions. For summarised by the following equation. example, Iron bacteria called Ferrobacillus obtain their energy by oxidising ferrous 6CO2 + 6H2O sunlight C6H12O6 + 6O2 to ferric ion, sulphur bacteria called chlorophyll Thiobacillus thiooxidans (also known as 258 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 258 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition Thus, the raw materials for photosynthesis sugar. However, the end product is a triose are carbon dioxide and water. Plants sugar called 3-phosphoglyceraldehyde obtain carbon dioxide from the (3-PGAL). The equation shows that the atmosphere, which diffuses into the source of oxygen is carbon dioxide. This leaf through stomata. Water is normally is not correct because experiments using absorbed from the soil into the plant the two oxygen isotopes, O18 and O16, body by the roots and transported via show that the oxygen given off during xylem tissue to the leaves which are the photosynthesis comes from water, and not photosynthetic organs of plants. The light from carbon dioxide. Thus, more water energy is trapped by chloroplasts which enters the reaction so that some of it is contain chlorophyll, the photosynthetic evolved as a byproduct as revealed in a more pigments of the leaves or stems in some accurate equation below. In this equation, plant species. One of the functions of CH2O is an empirical formula for the light energy is photolysis of water, which carbohydrate formed by photosynthesis. refers to splitting of a water molecule in presence of light to produce hydrogen, 2H2O + CO2 sunlight CH2O + O2 + H2O oxygen, and electrons. These products chlorophyll of photolysis of water are required in the ﬁrst stages of photosynthesis. The oxygen GOFVOERRNONMLEINNTE PURSOEPOENRLTYYThe site for photosynthesis released during photosynthesis comes Photosynthesis takes place in the green from water molecules. Two molecules of parts of the plant leaves’ mesophyll water produce one molecule of oxygen. and bundle sheath cells which have Light is also important in producing chloroplasts. A chloroplast is a double biochemical energy in plants. This energy membranous organelle found in the is required in ﬁxing carbondioxide cytoplasm. Its matrix is called stroma into phosphoglycerate which is rapidly which contains DNA, free ribosomes, converted into sugars and other forms membrane ribosomes, starch grains, lipid of organic molecules, such as starch and droplets and photosynthetic enzymes. The protein for storage and cellular uses. stroma also contains stacks of ﬂattened sacs or membranes called thylakoids Ultimately, carbohydrates and other which contain photosynthetic pigments forms of organic molecules synthesized called chlorophyll and other accessory by autotrophs are the major sources of pigments. Thylakoids are stacked together energy for all heterotrophs. Therefore, to form column-like structures called they are regarded as energy harvesters in grana (singular granum). all ecosystems. Structurally, chlorophyll is a long The traditional equation of photosynthesis hydrocarbon chain with a hydrophobic highlighted above does not illustrate the (water hating) tail a complex ring of real situation of photosynthesis because, hydrophilic (water loving) head in the among other reasons, it gives the end interior. Based on the structure, different product of photosynthesis as a hexose types of chlorophylls can be discerned. (Figure 5.1) 259 BIOLOGY FORM 5 KIWANDANI.indd 259 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools CH2CH3 CH3 H3C O H2C=CH NN CO2CH3 Mg HH NN CH3 H CH3CH2CH2CO2CH2CH=CC(HC3H2CH2CH2CCHH23CH)3CH3 Figure 5.1 The Chemical structure of chlorophyll There are several types of chlorophyll GOFVOERRNONMLEINNTE PURSOEPOENRLTYYMechanism of photosynthesis pigments, including chlorophyll 'a', 'b', The initial stage of photosynthesis can be 'c', and 'd'. Some organisms contain more viewed in two major phases or reactions than one type of chlorophyll pigment. and these are light reaction (light However, chlorophyll a and b are more dependent reaction) which takes place in abundant in most plants while the majority the thylakoid (grana) of the chloroplasts, of protoctists and cyanobacteria contain and dark reaction (light independent chlorophyll c and d. Chlorophyll absorbs reaction) which occurs in the stroma of red, blue and violet light but reﬂects green the chloroplasts (for the structure of the light. This makes all plants to appear chloroplast, refer to Chapter One, Figure green in color. Principally, the function of 1.12). The light reaction is vital for the chlorophyll is to convert light energy into subsequent stage of photosynthesis (dark chemical energy. Other photosynthetic reaction), because it is during this stage pigments are beta carotenes and when energy, electrons, and hydrogen are phycobilins (found in organisms such produced. as red algae and cyanobacteria), the red phycobilin is called phycoerythrobilin Light reaction (Light dependent and the blue phycobilin is known as reaction) phycocyanin. They act as light energy Light reaction stage of photosynthesis transfer to the chlorophyll to be utilized in occurs in the thylakoids of the chloroplasts. the photosynthesis process. Photosynthetic Normally, chloroplasts are aligned in bacteria contain photosynthetic pigments such a way that their thylakoids are held called bacteriochlorophyll which are not at right angle to the light source in order contained in the chloroplast. This is because to maximize light absorption. Within bacteria are single celled organisms, the thylakoids, chlorophyll pigments are and the entire cell is an equivalent of arranged in groups called photosystems, a chloroplast. Bacteriochlorophyll are which are specialised form of chlorophyll distributed in the membranes of the that commonly exists in two forms cytoplasm. namely; Photosystem I and Photosystem II. Chlorophyll photosystems are named in chronological order of their discovery, not in a way they are involved in light reaction. 260 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 260 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition Thus, photosystem I was discovered GOFVOERRNONMLEINNTE PURSOEPOENRLTYYthe electrons can move back to their original before photosysytem II. Photosystem I has position in photosystem I, in the process a specialised form of chlorophyll called called cyclic photophosphorylation. pigment 700 abbreviated as (P700) while Photosystem II has specialised form of Non-cyclic photophosphorylation chlorophyll pigment, 680 abbreviated as The mechanism of non-cyclic (P680). The numbers 700 and 680 stand for photophosphorylation involves both peak of wavelength of light which excite photosystems I and II in a non-cyclic electrons in these pigments. This implies movement of electrons to produce ATP. that the respective absorption peak for When the chlorophyll in Photosystem II P700 and P680 is at the wavelength of 700 absorbs light, releases an excited pair of nm and 680 nm. Structurally, photosystem electrons which are transferred to a series is a complex of chlorophyll, accessory of electron acceptor and carrier systems pigments, proteins, and other molecules. including cytochromes. As the electrons They are important in the absorption and pass through different carrier systems, they transfer of light energy through a series of release energy, but these electrons are not reduction oxidation (redox) reactions. returned to their original position in the photosystem II rather they are handed over Light reaction uses both photosystems I to the photosystem I. The energy released in and II, which are embedded in the thylakoid a series of electron flow system is used by membrane. Essentially, light reaction an enzyme called ATP synthase located in starts in photosystem II. Light energy the thylakoid membrane to synthesize ATP (or photons) is absorbed by photosystem by binding inorganic phosphate to ADP. II. The absorbed energy is transferred to This process is called phosphorylation, the chlorophyll centre causing electrons which literally means phosphate addition. in the chlorophyll centre to be energised. However, the energy used in phosphorylation The energised electrons are excited within emanates from the sunlight. Hence, this the chlorophyll molecule; consequently, ATP synthesis is precisely described as they move from ground to a higher photophosphorylation. It should be noted energy state. This process is known as that as the two excited electrons leave photo activation. The excited electrons the photosystem II in the ﬁrst stage after are progressively passed on from one being activated by the light of wavelength chlorophyll molecule to the subsequent 680 nm, they are replaced immediately one via a series of electron carriers to by electrons released from the splitting a nearby electron acceptor molecule of water molecules within the thylakoid. found in the electron transfer chain. The Water molecule splits into hydrogen ion movement of electrons can be in one or proton (H+), oxygen and two electrons direction because they do not move back (H2O →2H+ + ½O2 + 2e-). This process is to their original position in photosystem called photolysis, because it only occurs in II but progress to photosystem I, the the presence of light. Thus, oxygen does process which is described as non- cyclic not come from carbondioxide, but from the photophosphorylation. On the other hand, split of water molecules. 261 BIOLOGY FORM 5 KIWANDANI.indd 261 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools The chlorophyll of photosystem I is also NADP is therefore important in maintaining the ﬂow of electrons in the activated and absorb light energy of the thylakoid membrane as it is the ﬁnal electron acceptor.Therefore, the normal wavelength 700 nm. The absorbed energy ﬂow of electrons can be inhibited, if this excites the electrons, causing them to electron acceptor is limited. move from Photosystem I and transfer through a series of electron acceptor and Thus, the synthesis of ATP in this way is carrier molecules, including Ferredoxin described as a non-cyclic and ferredoxin-NADP reductase. As photophosphorylation, because the electrons these electrons move through the carrier from photosystem II move in one direction. systems, they lose their energy but they They do not move back to their original are not returned to their original position, molecule, instead they move through instead they are handed to NADP+, where different electron carriers, and they are together with hydrogen proton (H+) taken up by photosystem I to fill the gap from photolysis of water, reduce NADP+ of the lost electrons used to reduce NADP. to NADPH2, also written as NADPH+ The formed ATP and NADPH are used or NADPH + H+, as indicated by the in the Calvin cycle or dark reaction to produce carbohydrates while the oxygen following equation: gas from photolysis of water is released into the air as a byproduct. NADP+ + 2H + 2e− NADPH + H+ The light energy is now stored in the NADPH molecule which accumulates in the stroma to be used in the dark reaction (Figure 5.2). GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Primary Primary Electron Electron Acceptor Acceptor 2e- 2e- 2e- 2e- Pheophytin Light rays 2e- Light rays Ferredoxin Plastoquinone 2e- ADP + Pi 2e- NADP+ + 2H+ ADP Cytochrome NADPH 2e- Photosystem II 2e- Photosystem I H2O 1 O2 + 2H + 2 by - product Figure 5.2 Non-cyclic photophosphorylation 262 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 262 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition Cyclic photophosphorylation to ADP forming ATP with the aid of Cyclic photophosphorylation involves ATP synthase. In this cycle, only ATP is production ofATPwhich uses photosystem produced, but NADPH and oxygen are I but not photosystem II. This begins not produced. with photo activation of photosystem I through which the electrons are excited The amount of ATP required in Calvin and pass on to a chain of electron carriers. cycle is much higher than that produced in These electrons travel back along a chain the non-cyclic photophosphorylation. This of carriers to their original position in makes the cyclic photophosphorylation photosystem I (Figure 5.3). As electrons important to balance the ATP deﬁcit travel back, they release energy which without increasing NADPH. is utilised to bind inorganic phosphate Light rays Primary ADP+Pi Electron ATP Acceptor 2e- 2e- Electron carrier systems 2e- Photosystem IGOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 5.3 Cyclic photophosphorylation Table 5.1 Differences between cyclic and non-cyclic photophosphorylation Cyclic photophosphorylation Non-cyclic photophosphorylation Excited electrons always return to the original Excited electrons do not return to the position or molecule. original position or molecule. It involves only one photosystem (P700). It involves two photo systems (P700 Photolysis of water does not occur. and P680). Reduced compounds are not formed; the only Photolysis of water occurs. product is ATP. Reduced compounds especially NADPH The ﬁnal destination of electrons is photo are formed together with ATP. system I. The ﬁrst source of electrons is photosystem I. The ﬁnal destination of electrons is NADP. Oxygen is not produced. The ﬁrst source of electrons is water. Oxygen is produced. BIOLOGY FORM 5 KIWANDANI.indd 263 263 10/10/2019 14:07

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 5.1 Experiment to prove the importance of light during upper sides of the leaf to prevent the photosynthesis entry of light. c) Place the plant in sunlight for 3-4 Materials hours. A healthy potted plant, petri dish or d) Detach the selected covered leaf and white tile, a beaker containing water, remove the black paper covering it. forceps, hot water bath, a piece of wire e) Place the detached leaf in the beaker gauze, tripod stand, burner, match box, containing water. Boil it for about 10 alcohol (90% ethanol), strip of black minutes. paper (carbon paper), Iodine solution, f) Take out the leaf and boil it in boiling and clips (Figure 5.4). 90% ethanol in the hot water bath for 10 minutes. Procedure g) Take out the leaf and wash it under a) Take a potted plant and keep it in a running water to remove traces of ethanol and softening the tissues. dark place for 2-3 days so that the h) Spread the leaf on a petri dish or leaves get destarched. white tile and put a few drops of b) Cover part of one of its leaves with a Iodine solution on it. Observe the strip of black paper. Make sure that changes in colour. you cover both the lower and the Black paper GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Green leaf Alcohol Beaker Leaf boiling in water Bunsen burner Decolorised Decolorised Petri dish leaf in water leaf Iodine solution Figure 5.4 Experiment to show the importance of light during photosynthesis 264 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 264 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition Questions GOFVOERRNONMLEINNTE PURSOEPOENRLTYYimply that the reactions cannot take place in the presence of light. It simply means 1. Why was it important to destarch the that light energy is not a vital factor in leaf before starting the experiment? this phase of photosynthesis. The vital factor here is atmospheric carbondioxide, 2. What was the reason for covering and the products of light reaction are ATP the leaf with a black paper? and NADPH. Dark reaction is therefore a synthetic stage of photosynthesis. 3. What was the reason of boiling the However, such reactions, as cited earlier leaf in alcohol? are energetically dependent on light reactions. The dark reactions involve 4. Which colour was observed after a chain of enzyme controlled reactions adding Iodine solution on a boiled described by Melvin Calvin, Andrew leaf? Benson and James Bassham in 1946- 1953. These reactions involve a full 5. What does the observed colour cycle of reactions also called the Calvin indicate? cycle or Calvin-Benson cycle; named after Calvin and Benson. The Calvin Exercise 5.1 cycle (Figure 5.5) has three major phases which are carbondioxide (CO2) ﬁxation, 1. Explain how plants obtain reduction of glycerate phosphate (GP), light energy and convert it to also called phosphoglyceric acid (PGA), biochemical energy. and regeneration of ribulose biphosphate (RuBP). 2. Brieﬂy explain the importance of cyclic photophosphorylation in Carbon dioxide ﬁxation photosynthesis. Carbondioxide (CO2) used in dark reaction comes from the atmosphere. It 3. Differentiate cyclic from non- diffuses into the plant tissue via stomata cyclic photophosphorylation. pores located in the leaves or stems in some plants such as cactus. The absorbed Dark reaction (Light independent CO2 is attached to a 5-carbon compound reactions) called RuBP to form unstable 6-carbon Dark reaction does not require light energy, and it takes place in the stroma of compound by carboxylation reaction. The the chloroplasts. The overall purpose of dark reaction is to convert carbon dioxide 6-carbon molecule quickly splits into two from the atmosphere into carbohydrates or sugars which are used to power 3-carbon energy rich molecules called primary activities in plants and build their structures. The process of converting glycerate phosphate which, in principle carbon dioxide into carbohydrates requires energy produced by ATP and the are carboxylic acid, 3-phosphoglyceric reducing power obtained from NADPH both produced from the light reaction. acid (3-PGA or PGA). The fact that these chains of reactions are described as dark reactions does not RuBP is therefore called the carbon dioxide acceptor due to its ability to accept or combine with carbondioxide. The reaction is catalysed by Ribulose 1,5-biphosphate carboxylase (Ribulose 265 BIOLOGY FORM 5 KIWANDANI.indd 265 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools biphosphate carboxylase) enzyme, which Carboxylation is followed by a chain of is abundant in the stroma of the chloroplast, reactions which involve reduction of PGA and it is usually abbreviated as RuBP carboxylase, or RuBisCo, or Rubisco, or Reduction of phosphoglyceric acid RuBPCase, or RuBPco. The PGA are the (PGA) ﬁrst stable product of photosynthesis and The reduction reaction begins when energy their formation marks the ﬁrst major step supplied by ATP and the reducing power of in the ﬁxing of carbon dioxide in green NADPH are used to remove oxygen from plants and photoautotrophic bacteria into the PGA. This reduction reaction produces energy rich molecules. a 3-phosphoglyceraldehyde (3-PGAL or PGAL) also called glyceraldehyde RuBP + CO2 + H2O RuBP Carboxylase 2PGA phosphate (GP), which is a triose sugar (5C) (3C) (3-Carbon sugar) containing phosphate group. ATP ADP + Pi PGA PGAL Phosphoglyceric acid Phosphoglyceraldehyde (3 carbon acid) (3 carbon sugar) NADPH+H+ NADP + + H2O The difference between the PGA and the GOFVOERRNONMLEINNTE PURSOEPOENRLTYYphase of the Calvin cycle to regenerate PGAL is that, the former is a 3-carbon RuBP consumed in the first reaction of acid (-COOH) while the latter is 3-carbon carbon dioxide fixation. aldehyde (-CHO), therefore, PGAL is the first carbohydrate in photosynthesis which Regeneration of RuBP is a sugar with more chemical energy than RuBP is an important molecule utilised PGA. It should be noted that the ATP and in the synthesis of sugars, therefore, it is NADPH utilised in this phase of Calvin necessary for plants to produce enough of cycle are obtained from the light dependent it for synthesis of more sugars and other reactions. The ADP and NADP+ return to vital molecules. RuBP is regenerated the thylakoids to be converted back to ATP from PGAL, which combines with and NADPH, respectively, by the light Ribulose phosphate (RuP) molecules reactions. One of the PGAL molecules is as summarized in the equation below. set aside to be used as a building block This process involves a complex series of glucose and other molecules such as of rearrangement of carbon atoms sucrose, starch, cellulose, amino acids, between sugar phosphates to generate fatty acids and glycerol. These products 5-carbon sugar from 3 carbon-sugar. The are used for various biological roles formed 5-carbon sugar (RuP) is then including respiration, building plant cell phosphorylated by the remaining ATP wall, building the body, and component of from light reaction to generate ribulose cell membranes. The majority of PGAL bisphosphate (RuBP). The produced molecules will be forwarded to the third RuBP can combine with the additional carbon dioxide molecules and continue to the Calvin cycle reaction. 266 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 266 10/10/2019 14:07

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FOR ONLINE USE ONLY Nutrition DO NOT DUPLICATE ATP ADP PGAL Rearrangement of carbon atoms RuP RuBP Phosphoglyceraldehyde Ribulose phosphate Ribulose bishosphate (5C) (3C) (5C) Note that in order to form a glucose consumed to synthesize twelve molecules molecule, the cycle has to run six times of PGAL, where by only two molecules because each turn of the cycle adds only of PGAL are used to make carbohydrate one carbon from the incoming carbon (glucose) while ten molecules are used dioxide to form two molecules of PGAL, to regenerate 6 molecules of RuBP in the that is, six molecules of carbon are regeneration phase (Figure 5.5). 6 molecules CO2 Stage 1 Carbon fixation 6 molecules 12 molecules of RuBP 3-PGA 6ADP Calvin Cycle 12ATP 6ATP 12ADP + 12Pi 6 molecules RuP Stage 2 Stage 3 Reduction Regeneration of RuBP 12NADPH+12H+ 12NADP+ 10 molecules 3-PGALGOFVOERRNONMLEINNTE PURSOEPOENRLTYY 12 molecules 2 molecules 3-PGAL 3-PGAL Sugars example Glucose (C2H12O6) and other products Figure 5.5 The Calvin cycle Exercises 5.2 C3 and C4 plants Different plants use different pathways 1. Explain how light and dark reactions to fix carbon during the process of of photosynthesis are interdependent. photosynthesis. Fixing carbon is the way plants remove carbon from atmospheric 2. Describe the steps involved in the carbon dioxide and turn it into organic conversion of phosphoglyceric acid molecules like carbohydrates. Basing on into sugar. the first product of photosynthesis just after carboxylation, plants are grouped 3. What is the fate of PGAL formed in into C3 and C4 plants. photosynthesis? 4. Naming Calvin cycle as a dark reaction is sometimes misleading. Substantiate. 267 BIOLOGY FORM 5 KIWANDANI.indd 267 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools C3 plants GOFVOERRNONMLEINNTE PURSOEPOENRLTYYalso known as RuBP oxygenase. There is In some plants, the ﬁrst product of no energy-rich compound produced, since photosynthesis immediately after 2-phosphoglycolate produced cannot carboxylation is a 3-phosphogylceric enter the Calvin cycle; rather it enters in acid (3-PGA). These plants ﬁx carbon the conversion pathways and use NADPH dioxide, following the Calvin cycle as and ATP to generate PGA, hence decrease explained in the preceding section. Plants in yield. Decreased concentration of which yield a 3-PGA, as the ﬁrst product carbon dioxide occurs during dry or hot after carboxylation, are described as C3 conditions because the stomata pores plants. Fixation of carbon dioxide occurs through which carbon dioxide diffuses in the chloroplasts of the bundle sheath into the plant normally close to minimise cells. C3 plants account for approximately water loss through transpiration under 85% of all plants including Bryophytes, such conditions. The global increase in ferns, most grasses, and trees. They also temperatures and drought conditions in include crops such as cotton, tobacco, some places emanating from climatic spinach, soybean, and cereal grains (rice, changes is likely to impact C3 plants more wheat). This implies that most food that than C4 plants, which are more efﬁcient we eat comes from C3 plants. C3 plants photosynthetically. Photorespiration involves perform well in temperate conditions, but a complex network of enzyme reactions they suffer photorespiration which is also which exchange the cellular metabolites called oxidative photosynthetic carbon between three organelles, namely cycle or C2 photosynthesis in hot and dry chloroplasts, leaf peroxisomes and conditions. mitochondria (Figure 5.6). The formed 2-phosphoglycolate is dephosphorylated Photorespiration by removing of phosphate group (Pi) This is a condition which occurs when to form glycolate which leaves the carbon dioxide concentration in the chloroplast to the peroxisome. In the chloroplast drops below 50 ppm while the peroxisomes, Glycolate is oxygenated level of oxygen is relatively higher. Under to give glyoxylate and in this process this condition, oxygen and carbon dioxide hydrogen peroxide gas is evolved. The compete for the same active site on RuBP formed glyoxylate is converted into carboxylase enzyme. This in turn triggers glycine, then this product enters the the enzyme to utilize oxygen to oxidise mitochondrion in which it is converted RuBP to form one molecule of 3-PGA into serine through the series of reactions. (three carbon) and 2-phosphoglycolate The produced serine is transported to (two carbon compound) instead of the peroxisome and it is converted into acting on carbon dioxide to produce two hydroxypyruvate then to Glycerate molecules of PGA (three carbon). (Glyceric acid). The glycerate formed is transported to the chloroplasts, and with O2 + RuBP RuBP carboxylase Phosphoglycolate + PGA the help of ATP it is converted into 3-PGA 5C 2C 3C by adding Pi in its carbon number 3. Since the reaction is an oxygenation reaction, the enzyme RuBP carboxylase is 268 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 268 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition regeneration of carbon dioxide acceptor, and re-ﬁxation of carbon dioxide in the bundle sheaths. Figure 5.6 Photorespiration pathway a) Fixation of carbon dioxide in the mesophyll cell C4 plants Photosynthesis in most tropical and Carbon dioxide ﬁxation occurs in the subtropical plant species, such as maize mesophyll cells and involves and sugar cane yields a 4-carbon compound carbondioxide acceptor known as called oxaloacetate (oxaloacetic acid) phosphoenolpyruvate (PEP). The carbon after carboxylation, and they are thus dioxide is attached to PEP to form a referred to as C4 plants. C4 plants have 2 4-carbon molecule called oxaloacetate. major biochemical pathways (Figure 5.7). This carboxylation reaction is catalysed by The ﬁrst pathway involves transporting phosphoenolpyruvate carboxylase (PEP carbon dioxide from the mesophyll to carboxylase) enzyme. In this reaction, the chloroplast of the bundle sheath, a therefore, hydrogen and carbon dioxide pathway which was described in 1966 are added to PEP to form oxaloacetate. by Hatch and Slack. This pathway is The PEP carboxylase has relatively higher therefore called Hatch-Slack pathway in carbon dioxide afﬁnity compared to RuBP honor of these two Australian scientists. carboxylase which is used in carboxylation The second pathway in C4 plants is the in C3 plants. normal C3 pathway (Calvin cycle) which commences once the carbon dioxide is GOFVOERRNONMLEINNTE PURSOEPOENRLTYYPEP + CO2 PE P carboxylase Oxaloacetate released in the bundle sheath cells. C4 pathway is characterised by four major The oxaloacetate formed is further events: fixation of carbon dioxide in converted into another 4-carbon the mesophyll cell, shunting of malate, compound called malate NADPH + H+ NADP+ Oxaloacetate Malate (4c) (4c) b) Shunting of malate The shunting commences as malate gets streamed to chloroplasts of the bundle sheath cells through small pores called plasmodesmata, found in the cell wall. In the chloroplasts, malate dissociates, yielding hydrogen, carbon dioxide and a 3-carbon acid called pyruvate (pyruvic acid). 269 BIOLOGY FORM 5 KIWANDANI.indd 269 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Malate CO2 should be noted that shunting of malate is (4C) necessary to ensure movement of carbon Pyruvate dioxide and hydrogen from the mesophyll NADPH + H+ (3C) to the bundle sheath cells. The hydrogen liberated reduces NADP into NADPH NADP+ which will be used in carbon dioxide re- ﬁxation. The stages (a) and (b) accomplish This ultimately leads to high accumulation the Hatch-Slack pathway. of carbon dioxide in the bundle sheaths. It Jhvjhkjkjkj Epidermal cells (Non photosynthetic) Chloroplasts of mesophyll cells GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Chloroplasts of Bundles shealth cells Figure 5.7 The Hatch-Slack pathway c) Regeneration of carbon dioxide d) Re-ﬁxation of carbon dioxide in acceptor bundle sheaths Pyruvate generated in the shunting of The released carbon dioxide from the malate as explained in (b) is converted dissociation of malate (refer to the back into PEP by the addition of organic shunting of malate above) enters the C3 phosphate supplied by ATP. pathway (Calvin cycle). At this stage, the carbon dioxide is accepted by RuBP to Pyruvate Phosphoenol produce 3-PGA, a reaction is catalysed by (3C) pyruvate (PEP) RuBP carboxylase enzyme. The NADPH (3C) will reduce 3-PGA to sugar (3-PGAL) in ATP ADP the same way as C3 plants. Generally, the C4 pathway consumes more energy (ATP), and it is more efﬁcient in 270 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 270 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition yielding carbon dioxide compared to the factor in photosynthesis, C4 plants can C3 pathway. However, ATP consumption photosynthesize, even if the stomata are is not a problem, considering that much closed due to the presence of high levels of it is produced during light reactions. of carbon dioxide in the bundle sheath The fact that the C4 pathway produces cells, just about 20 to 120 times higher high yields under high concentration of than normal. carbon dioxide makes photosynthesis in C4 plants more efﬁcient in carboxylation Differences between C3 and C4 plants compared to C3 plants which under certain The major differences between these conditions such as hot, dry conditions two types of plants are evident in the undergo photorespiration. The PEP photosynthesis process. Generally, the carboxylase in the mesophyll of C4 plants basic metabolism of the C3 and C4 plants has a high afﬁnity to carbon dioxide, and is similar, but the latter is more complex. it does not get competitively inhibited The C4 plants are therefore evolutionarily by oxygen to cause photorespiration. more advanced than C3 plants (Table 5.2). Although carbon dioxide is a limiting Table 5.2 Differences between C3 and C4 plants GOFVOERRNONMLEINNTE PURSOEPOENRLTYY C4 plants The ﬁrst product in carbon dioxide C3 plants ﬁxation is a 4-carbon compound called The ﬁrst product in carbon dioxide ﬁxation is oxaloacetic acid. a 3-carbon compound called phosphoglyceric Photosynthesis is not limited by low levels acid. of atmospheric carbon dioxide, hence photorespiration does not occur. Photosynthesis is limited by low levels of atmospheric carbon dioxide, hence Carboxylation reaction is accomplished by photorespiration may occur in a limited the enzymes RuBP carboxylase and PEP supply of carbon dioxide. carboxylase to ﬁx carbon dioxide. Carboxylation reaction is accomplished by The carbondioxide acceptors are the the enzyme RuBP carboxylase to ﬁx carbon 3-carbon compound (PEP) and the 5-carbon dioxide. compound (RuBP). Carbondioxide ﬁxation occurs in both, The carbondioxide acceptor is a 5-carbon mesophyll cells and bundle sheath cells. compound called RuBP. They are more efﬁcient in ﬁxing carbon Carbondioxide ﬁxation occurs in bundle dioxide. sheath cells only. They have two types of cells, each with its own type of chloroplast. (Kranz aatomy). They are less efﬁcient in ﬁxing carbon diox- ide. They tolerate both hot and dry conditions. They have only one type of chloroplast in their leaf bundle sheath cell. Example of C4 plants: millet, sorghum and sugar cane. They do not tolerate hot and dry conditions. They are adapted to cool and wet environment. Example of C3 plants: soybeans spinach, rice and grasses. BIOLOGY FORM 5 KIWANDANI.indd 271 271 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Exercise 5.3 GOFVOERRNONMLEINNTE PURSOEPOENRLTYYInhibitors An inhibitor is a substance or factor which 1. Describe how C4 plants are adapted may slow down the rate of reaction. to synthesize sugars in the tropical For example, many herbicides such as and subtropical climates. Dichlorophenyl Dimethyl Urea (DCMU) interfere with the electron ﬂow in the 2. Using your knowledge of C3 and chloroplast; thus, inhibit the light reaction, C4 plants, explain which plants are and hence no photophosphorylation. In more vulnerable to climate changes. addition, a relatively higher concentration of oxygen (above 21%) in the atmosphere 3. Differentiate C3 plants from C4 tends to inhibit the rate of photosynthesis, plants. because it lowers the amount of carbondioxide available to the plant. Factors affecting the rate of photosynthesis Leaf structure and position For photosynthesis to take place efﬁciently, Leaf is a photosynthetic organ of a plant. It certain conditions must be met, and raw contains chloroplasts, which are organelles materials must be present. The process for food synthesis. Leaves have special of photosynthesis is influenced by both adaptation to enhance carbon dioxide and internal and external factors. light absorption for photosynthesis. For example, they have a broad surface area a) Internal factors exposed to light illumination and thin The internal factors which are also called leaves with large surface area absorb more plant factors are chlorophyll concentration, light than small and thick leaves. Carbon enzymes, inhibitors, and leaf structure and dioxide penetrates more quickly in thin position. leaves than in thick leaves. Additionally, leaves with thin and transparent epidermis Chlorophyll concentration allow more light to reach the chloroplasts. Chlorophyll is a green photosynthetic Furthermore, leaves, particularly of most pigment located in the chloroplast, tropical plant tree species, are positioned especially in the grana. Chlorophyll is at a certain angle which is normally more responsible for trapping light energy or less vertical. This reduces excessive during light reaction. When chlorophyll light interception and temperature on the concentration in the leaves is very low, leaf. Reducing this natural angle of leaf the rate of light reaction will be reduced, may be detrimental to the chloroplast because only a little amount of light will because it increases light interception and be trapped for the reaction, resulting in excessive temperature. Thus, maintaining reduction in the rate of photosynthesis. high leaf angle orientation in tropical Low concentrations of chlorophyll in plant trees is necessary in reducing excessive leaves can be caused by several factors, light interception and leaf temperature to such as mineral deﬁciency, ageing, lack of protect chlorophyll from photo damage light and diseases such as fungal diseases due to excessive light. This in turn or infections. 272 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 272 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition enhances photosynthetic activity and GOFVOERRNONMLEINNTE PURSOEPOENRLTYY d) Take out the leaf and place it in helps to sustain high plant productivity. boiling ethanol in a water bath for about 10 minutes. Enzymes Photosynthesis is an enzyme controlled e) Remove the leaf from ethanol and process. For example, the enzyme PEP wash it with running water. carboxylase is crucial in the ﬁxation of carbon dioxide in the mesophyll cells. f) Place the leaf on a white tile and add Similarly, RuBP carboxylase is an a few drops of Iodine solution. important enzyme necessary for carbon dioxide ﬁxation in bundle sheath cells g) Record any observable changes. during dark reaction. Another enzyme is ATP synthase found in the thylakoid h) Draw a diagram of the leaf showing membrane. This enzyme is vital for ATP the colour pattern after being stained synthesis during photophosphorylation with iodine solution. process. These enzymes perform their role actively under optimal condition below i) Compare the colour pattern of the which they become inactive or above patches with that of the original leaf which they are denatured. If the enzymes in b). are inactive, the rate of photosynthesis proceeds very slowly. In contrast, when Safety precaution the enzymes are very active, the rate of Avoid direct ﬂame near ethanol because photosynthesis becomes very high. it is highly inﬂammable. Activity 5.2 Investigating the role of Questions chlorophyll in photosynthesis 1. Why was the variegated leaf used in Materials the above experiment? Variegated plant, Iodine solution, bea- 2. Explain your observations. ker, ethanol, water, and white tile. 3. What was the reason for boiling the Procedure leaf in ethanol? 4. From the observations made in the a) Take a potted plant with variegated leaves which has been exposed to experiment, what is the role of chlo- sunlight for three to four hours. rophyll in the leaf? b) Take one leaf and draw its diagram b) External factors indicating the pattern of the colour The external factors which are also of the patches. termed as environmental factors include; atmospheric carbon dioxide concentration, c) Place the leaf in the beaker containing water availability, wind, temperature, hot water and boil it for about 10 mineral and nutrients supply as well as minutes. light. BIOLOGY FORM 5 KIWANDANI.indd 273 273 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Atmospheric carbon dioxide GOFVOERRNONMLEINNTE PURSOEPOENRLTYYWater availability concentration Water is one of the essential raw materials The average concentration of carbon for photosynthesis. It also plays other roles dioxiode in the atmosphere is about in the plant body such as translocation of 0.03%. As the concentration of carbon minerals and gases as well as products of dioxide increases from the average photosynthesis. Shortage of water leads to value, it also increases the rate of wilting of plant leaves which in turn causes photosynthesis. Carbon dioxide is closing of the stomata. This results into a required in light independent reactions, reduced diffusion rate of carbon dioxide but the concentration above 0.1% can into the chloroplast, and hence a decreased damage plant leaves. On the other hand, rate of photosynthesis. Additionally, water low levels of carbon dioxide tend to limit shortage causes cells to become ﬂaccid; the rate of photosynthesis. It should be thus they cannot function well and this noted that, C3 plants are affected by low affects the translocation of synthesised concentration of carbon dioxide in the products. atmosphere, while C4 plants are efﬁcient in utilising carbon dioxide even when the Light concentration in the atmosphere is low. The effect of light on the rate of photosynthesis can be described on the Temperature basis of its quality (light wavelength) and Within the optimum range of temperature, quantity (light intensity). the rate of photosynthesis tends to double for every 10 oC rise of temperature. For Light quality (wavelength of colours). example, the optimum temperature for Photosynthesis usually occurs when green plants that survive in temperate climates plants absorb light within a limit of visible is 25 oC. The temperature above 35 oC light spectrum. The most effective range usually causes denaturation of enzymes is within a red-orange band (600- 700 nm) catalyzing photosynthesis in both, dark and a blue-violet band (400-500 nm). The and light reactions, leading to slowing central band is also effective, but less than down, or stopping of photosynthesis. others because the chlorophyll molecules In low temperature such as below 10 oC, show very little absorption of light in enzymes catalysing photosynthesis this region. Maximum light absorption become inactive, hence lower its rate. corresponds to the maximum rate of photosynthesis. Nutrients supply Minerals such as magnesium and Light intensity. The rate of photosynthesis nitrogen are components of chlorophyll. varies proportionally to light intensity. Deﬁciency of these minerals reduces the However, at a certain point called light rate of photosynthesis because the plant saturation point, the rate of photosynthesis lacks enough chlorophyll molecules for reaches its maximum and therefore trapping enough light energy. attains constancy. Any further increase in light intensity brings no effect on the 274 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 274 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition rate of photosynthesis, if other factors Wind velocity are limiting. However, unless the plant Wind moving at high speed reduces the is adapted to high light intensity, the rate of photosynthesis because strong wind chlorophyll might undergo bleaching. usually facilitates transpiration and hence Leaf adaptation to very high light intensity affects the availability of water. Therefore, includes presence of thick cuticle and speedy wind reduces the amount of hairs. Light intensity varies with location water available as the raw material for and seasons of the year. In the tropical and photosynthesis, and consequently reduces subtropical areas, light intensity is higher the rate of photosynthesis. than in the temperate areas. Light intensity also decreases during rainy seasons due to Exercise 5.4 cloud cover. During photosynthesis, the plant consumes 1. Describe photosystem I and carbon dioxide via respiration as it photosystem II in green plants and eliminates oxygen, which is important for show how they are involved in respiration. A point is reached when light producing NADPH and ATPduring intensity causes the rate of photosynthesis light reaction of photosynthesis. to balance with that of respiration. This means that the rate of carbon dioxide 2. Explain how plants such as sugarcane production from respiration is equals and sorghum are adapted to to that of carbon dioxide consumption overcome photorespiration. in photosynthesis. This is called a 3. Explain how light quality and intensity affect the rate of compensation point of a plant, at which photosynthesis. net gain of atmospheric air is zero (Figure 5.8). Rate of photosynthesis Light saturation Higher CO2 5.3 Heterotrophic nutrition GOFVOERRNONMLEINNTE PURSOEPOENRLTYYconcentrationHeterotrophic nutrition is the mode of nutrition in which an organism feeds by Low CO2 taking in organic substances made by other concentration organisms. Organisms that obtain organic food substances from other organisms Carbondioxide are termed as heterotrophs. Examples: taken up animals, fungi, some protoctists and most monerans. Carbondioxide Net gas exchange zero given out0 Food materials synthesized by autotrophs are in the form of complex molecules, Light intensity which contain chemical energy locked Compasation point CO2 released in their bonds. Heterotrophs ingest large during respiration equals that taken molecules and they require a digestive up during photosynthesis Figure 5.8 The light intensity and compensation point BIOLOGY FORM 5 KIWANDANI.indd 275 275 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools system to break down large food GOFVOERRNONMLEINNTE PURSOEPOENRLTYYfrom dead or decaying bodies of other molecules into simpler forms which can organisms, mainly plants and animals. be absorbed for utilization in their bodies. Digestion is accomplished by producing Furthermore, they require energy to carry extracellular digestive enzymes which out life processes like cellular metabolism. reduce the tissues of the dead or decaying Some bacteria form a special group of organisms into solution form which can heterotrophs called photoheterotrophs. be readily taken up. Most bacteria and These bacteria can utilize organic raw fungi, such as Mucor, Rhizopus, and yeast materials to synthesize their food in are saprotrophs. the presence of light energy. Animals, including human beings utilize six b) Symbiotic nutrition (Symbiosis) different types of nutrients for proper The term symbiosis literally means ‘living body functioning. These nutrients can together.’ Symbiosis is therefore a natural be categorized into two major groups: association between two or more different organic and inorganic nutrients. Organic species. There are three common types nutrients include carbohydrate which of symbiotic relationships which are supply energy for body functions, fats or mutualism, commensalism and parasitism. lipids which constitute the major part of cell membrane and stored form of body Mutualism. This refers to the association energy, proteins for growth and repair between two living organisms of different of body tissues, and vitamins for body species in which both benefit. Therefore, defence. Inorganic nutrients include water the association or relationship is beneﬁcial which is a vital ﬂuid required for chemical to both partners. The cellulose digesting reactions to take place and transport of bacteria living in the ruminant herbivores materials and minerals which are essential is an example of organisms which show for proper body functioning. a mutualistic relationship. These bacteria can only survive in anaerobic conditions Types of heterotrophic nutrition found in a ruminant’s alimentary canal, Heterotrophs obtain their food by and they feed on cellulose contained various ways. There are three forms in the host’s diet. On the other hand, of heterotrophic nutrition, namely ruminants cannot digest cellulose directly saprophytic, symbiotic, and holozoic but, as the cellulose digesting bacteria nutrition. feed on the cellulose, they convert it into simple compounds which can be digested, a) Saprotrophic nutrition absorbed and assimilated by the ruminants. This type of nutrition is also referred to as Mutualistic form of symbiotic nutrition is saprophytic nutrition. The term saprotroph also evident between leguminous plants comes from two Greek words; sapros and nitrogen ﬁxing bacteria, where by and trophos where sapros means ‘rotten’ the bacteria accommodated within the and trophos means ‘feeder.’ This type root nodules of these plants fix nitrogen of nutrition involves organisms feeding from the air by converting it into nitrogen on soluble organic compounds obtained useful compounds such as nitrates. These 276 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 276 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition nutrients are required by plants for their GOFVOERRNONMLEINNTE PURSOEPOENRLTYYthe internal organs or tissues of the host growth and development, while on body. These types of parasites are called the other hand, the bacteria benefit by endoparasites. On the other hand, some getting shelter and synthesised nutrients parasites such as ticks and bed bugs attach from the plants. Algae and fungi form a themselves on the surface of the body mutualistic association called lichen. In of their living host and suck ﬂuids from this relationship algae synthesise food them; and these are called ectoparasites. and supply some to the fungi while Both endoparasites and ectoparasites are the fungi cover the algae and protect it highly adapted to their mode of nutrition. from desiccation. Also, fungi and roots For example, most parasites have hooks of vascular plants form a mutualistic and haustoria for attachment and sucking association called mycorrhizae. The role of nutrients from the host. fungi in this relationship is to increase the surface area for the plant roots absorption c) Holozoic nutrition of nutrients. The plant supplies some of Holozoic nutrition is a form of the manufactured food to the fungi which heterotrophic nutrition exhibited mainly normally cannot photosynthesise its food. by free living animals which have a specialized digestive tract, also called Commensalism. Commensalism is a close alimentary canal. The nutrition of this association between two living organisms form involves several steps such as of different species in which one organism taking in solid or liquid food, followed benefits and the other organism neither by mechanical and chemical digestion in benefits nor is harmed. For example, cattle the alimentary canal. The digested food egrets follow herds of cattle or buffalo and materials are reduced into simple forms, feed on insects disturbed by the animals. which can be absorbed and assimilated by The cattle and buffalo are not harmed by body cells. Holozoic organisms include the feeding activities of the cattle egret. animals such as herbivores which feed on Therefore, in this association one member plants, carnivores which feed on living (the cattle egret) benefits while the other animals; omnivores which feed on both (cattle or buffalo) neither benefits nor is plants and ﬂesh, and decomposers feeding harmed. on remains of dead animals and plants, or on dung and faeces. The undigested Parasitism. Parasitism is a close food is eliminated from the body while association between two organisms of the digested soluble food molecules get different species, whereby one organism absorbed and later assimilated to generate called a parasite beneﬁts by obtaining its energy and some are incorporated into the nutrients and shelter from another living body cells. organism called a host. Normally, the parasite may ultimately cause harm to Holozoic nutrition in mammals the host but, in some cases, it can exist The food taken in by mammals in most without killing the host. Some parasites cases is in solid form; therefore, it must be such as tape worms and liver ﬂuke live in converted into simpler form, for it to be 277 BIOLOGY FORM 5 KIWANDANI.indd 277 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools absorbed and assimilated in their bodies. enzymes on smaller pieces to yield The holozoic nutrition involves ingestion, digestion, absorption, assimilation, and simpler molecules with suitable size egestion. for absorption by the epithelia cells. Chemical digestion is a complex process a) Ingestion that involves a diversity of digestive This process involves taking in solid or enzymes secreted by the alimentary canal, liquid food into the gut or alimentary canal which convert various food substances or gastrointestinal tract of an organism. into simpler and absorbable form. For It is aided by structures such as teeth, example, polysaccharides are broken tentacles and claws through which food down into monosaccharides; proteins are substance is taken into the mouth through eating or drinking. broken down into amino acids; and fats or lipids are broken down into fatty acids and glycerol. b) Digestion GOFVOERRNONMLEINNTE PURSOEPOENRLTYYc) Absorption Digestion is the process of breaking This is the uptake of the digested soluble down large biochemical compounds products and other substances across the contained in food into smaller and soluble linings of the gut into the blood stream and molecules that can easily be absorbed lymphatic system. The soluble substances into the body. It involves mechanical and include vitamins and minerals. The small chemical digestion. Mechanical digestion intestine is the site where digested foods involves the physical break down of the are absorbed through diffusion or active food into smaller pieces; and this begins transport. The inner wall of the small in the mouth where the food is chewed intestine; also called the mucosa is lined and rolled by the tongue, while lubricated with microscopic ﬁnger-like projections by the saliva before it is swallowed. The called villi. The epithelial cells of the tongue, teeth and saliva are thus important small intestine have microvilli. Both villi in preparing the food from large particles and microvilli have a role of increasing into bolus which can easily be swallowed surface area for nutrients absorption. for subsequent digestion stages. The The villi are equipped with a network of mastication of food from larger particles blood capillaries and lymphatic vessels. to small ones is necessary for reducing Normally, the absorbed nutrients enter the the food into ﬁne particles which makes it blood vessels and are supplied to different easy to be swallowed as well as harnessing body organs. nutrients from the food during digestion. Additionally, mechanical digestion d) Assimilation involves mechanical contraction of the This is the process of incorporating and gut, which pounds up and mixes the semi- using the absorbed food molecules into solid foods. the body. The digested materials, which are absorbed into the blood, are carried Similarly, digestion process is done by the blood stream to the body cells and chemically by the action of digestive tissues for use in life processes such as 278 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 278 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition respiration, growth, repairing body tissues The process of digestion and maintaining good health. In addition, Digestion in mammals such as human excess of such food materials may be beings occurs throughout the alimentary stored for future use in the liver, muscles canal. The alimentary canal in humans and adipose tissues. comprises of mouth, oesophagus, stomach, small intestine, large intestine e) Egestion (colon), caecum, rectum and anus Egestion is the process of eliminating (Figure 5.9). The alimentary canal is also undigested food materials from the gut associated with the accessory organs such through the anus. This is the ﬁnal stage as the liver, salivary glands, and pancreas, in holozoic nutrition in mammals during which assist in digestion. The wall of the which the undigested food materials or alimentary canal has almost the same faeces are removed from the alimentary basic structure throughout its length. The canal. wall is lined by the simple epithelium or glandular epithelium tissue and all parts of the gut contain circular and longitudinal muscles. Mouth GOFVOERRNONMLEINNTE PURSOEPOENRLTYYParotid gland Tongue Submandibular gland Sublingual gland Pharynx Eusophagus Liver Stomach Gallbladder Spleen Pancreas Duodenum Transverse colon Ascending colon Jejunum Ileum Descending colon Appendix Cecum Anus Sigmoid colon Rectum Anal canal Figure 5.9 The human alimentary canal BIOLOGY FORM 5 KIWANDANI.indd 279 279 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Epithelial tissue GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Cilia (microvilli) Epithelial tissue is a living tissue of Mucus in goblet cell various parts of the body. It consists of a single cell layer which usually occurs on Nucleus the surface and covers the organs, cavities, Absorptive cell and tubes. For instance, it lines the Basement membrane heart, blood vessels, lymphatic vessels, Connective tissue and the intestine within the organism. There are two major types of epithelial Figure 5.10 Simple columnar epithelium tissue; one is the simple epithelial tissue which has a single layer of tissue and is Glandular epithelium further subdivided into ﬁve sub types This epithelium tissue contains secretory namely; squamous, cuboidal, columnar cells that are closely packed (Figure 5.11). pseudostratiﬁed, ciliated, and glandular Secretory cells secrete materials such as epithelial tissues. The second group of mucus into the cavity or a space lined by it. epithelial tissue comprises of epithelia For example, in the stomach and the small tissues which have more than one cell intestine the mucus protects and lubricates thick. This group includes transitional and the lumen of the intestine and stomach. In stratiﬁed epithelial tissues. some parts, glandular epithelium is folded in various ways to form glands such as Columnar epithelium gastric glands whose major function is This tissue consists of thin columns of to secrete enzymes and ﬂuids. Glandular elongated cells arranged at right angle epithelium can be individual cells, such to the basement membrane. The cells as goblet cells or aggregates of glandular possess nuclei at their bases, and they are cells, such as multicellular glands like mostly associated with regions such as the exocrine and endocrine glands. Examples walls of the intestines and stomach, where of glandular epithelial tissues found in the secretion and absorption are the major digestive system include simple tubular functions. Columnar epithelium tissues glands such as crypts of Lieberkuhn found are adapted to withstand wear and tear. in the intestines, simple branched tubular Epithelial tissue cells are interspaced by glands such as gastric glands found in the goblet cells that are responsible for the stomach walls (gastric mucosa), and secreting mucus which helps to protect compound saccular and compound tubular the stomach from digestive enzymes and glands of the salivary glands. acidic content of the gastric glands. Some epithelial tissues are ciliated while others Secreted materials have microvilli that increase the surface area for absorption. Part of the surface Duct of gland that is occupied by the microvilli is called brush boarder (Figure 5.10). Secreted cells of gland Figure 5.11 Glandular epithelium 280 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 280 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition Cuboidal epithelium buccal cavity rolls the food into a ball-like This tissue is made up of cells which are structure called bolus and forces it against cube-like in shape with a central nucleus. the soft palate during swallowing, thereby They usually form a lining of the salivary closing the nasal cavity. The opening in glands where they perform secretory the larynx (voice box) called glottis, is functions (Figure 5.12). In some cases also closed by a flap like structure called the cell surface of this tissue is ciliated or epiglottis. Then, the bolus enters the ﬂagellated. oesophagus. Cells The oesophagus In the oesophagus the bolus is moved by Nucleus a series of wave-like movement caused by involuntary contraction and relaxation Basement of its circular and longitudinal smooth membrane muscles. This process is described as peristalsis. The contraction of circular Figure 5.12 Cuboidal epithelium muscles (inner muscles) causes the oesophagus to become narrow and long. Digestion in the mouth The contraction of longitudinal muscles Mechanical and chemical digestion of food (outer muscles) causes the oesophagus starts in the mouth. Mechanical digestion to become wide and short. These is achieved by teeth through mastication contractions and relaxations of circular (chewing). During mastication, the food and longitudinal muscles push the bolus is mixed with saliva, a watery mixture of down the alimentary canal. Additionally, mucus and amylase secreted by the salivary the peristalsis waves of contractions assist glands in response to thought, smell, taste in mechanical digestion (Figure 5.13). or sight of food. Saliva is a neutral or very GOFVOERRNONMLEINNTE PURSOEPOENRLTYY weak alkali with the pH ranging between Relaxed muscles Oesophagial sphincter 6.5 and 7.5. Saliva has the following Relaxed muscles contracted functions with regard to digestion: it lubricates food so that it can move through Contracted muscles the oesophagus easily; it catalyses the hydrolysis of starch into maltose using Sphincter relaxed the enzyme called salivary α-amylase; It maintains pH of the mouth between 6.5 Stomach and 7.5. This level is optimum for the action of salivary amylase to function which is accomplished by its constituent mineral salts (example NaHCO3). Chemically, the digestion of food in the Figure 5.13 Wave of peristalsis in the oesophagus mouth involves converting starch into maltose by salivary α-amylase. The tongue which is located at the back of the 281 BIOLOGY FORM 5 KIWANDANI.indd 281 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools The stomach positioned between the small intestine and The stomach is a highly elastic muscular the stomach. The stomach wall consists organ. It has two valve-like rings of of a layer of mucous membrane called smooth muscles called sphincters that can gastric mucosa, it is highly folded and open and close. One sphincter is called is equipped with small pits (gastric pits) cardiac sphincter. It is located between the leading to gastric glands (Figure 5.14), in oesophagus and the stomach. The second which gastric juice is secreted. sphincter is called pyloric sphincter. It is Gastric pits Surface Pepsinogen Pepsin epithelium Gastric gland Gastric gland HCl Mucous cell neck Parietal cells Gastric glands Chief cells GOFVOERRNONMLEINNTE PURSOEPOENRLTYYFigure 5.14 Structure of the gastric mucosa Gastric juice has the following Pepsinogen. It is produced by the chief components: cells of the stomach wall. It is a precursor Water. This is a solvent involved in or inactive form of pepsin. Pepsinogen hydrolysis by which food substances are is activated by hydrochloric acid in the broken down. stomach to form pepsin; an enzyme responsible for the breaking down of Hydrochloric acid (HCl). This is an acid polypeptides into peptides. produced by parietal cells of the gastric mucosa. Hydrochloric acid activates Prorennin: This is a precursor of rennin, prorennin and pepsinogen into rennin and the enzyme that catalyses the conversion pepsin respectively, also kills any bacteria of soluble milk protein into an insoluble that might have entered the stomach milk protein. In other words, rennin is through food. an important enzyme in coagulation or curdling of milk in the stomach. The Mucus. This protects the stomach from its coagulated milk is semi solid and it can own digestive enzymes and lubricates the be retained in the stomach for a relatively wall for easy passage of food to the small long time for proper digestion. This is very intestine. important in lactating young mammals. 282 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 282 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition In the stomach, mechanical digestion also GOFVOERRNONMLEINNTE PURSOEPOENRLTYYthe living body which makes it slightly occurs due to continuous contractions of shorter, unlike in a dead person where it the stomach wall which enhance breaking becomes somewhat longer (about twice as down of food mechanically. The combined much longer as its normal size in a living action of mechanical and chemical person). This is because death makes the digestion produces a creamy paste, an small intestine to lose its muscle tone acid chyme. The formation of this chyme and stretches as it become loose. Unlike stimulates the receptors on the stomach the large intestine, the small intestine has wall, which in turn stimulates the pyloric numerous folds and projections called sphincter muscles to relax and allow food villi on its lining which are important in to pass into the duodenum. Digestion of increasing the surface area for digestion food in the stomach may take about 4 to and absorption of food to take place. 6 hours. The surface area of the small intestine of a human is about 200 m2 which is The intestines surprisingly closer to 100 times the surface The intestines are contained within the area of our body skin. Schematically, the abdominal part of the body and they small intestine is normally surrounded by constitute the longest and the massive part the large intestine in three sides. of the alimentary canal. The word intestine comes from a Latin word meaning “gut or The small intestine is not straight but rather internal”. The intestines are of two types a coiled tube which literally has three namely; the small intestine which forms a major distinct regions namely duodenum, vital part in the digestion and absorption jejunum, and ileum. The sectioning of of foods. The second type is the large the small intestine is based on its internal intestine which among other functions structure and function in digestion and is mainly important in re-absorption of absorption of foods. water from the food residues before they are egested. Duodenum. This is the initial part of the small intestine immediately bordering The small intestine with the pyloric sphincter of the stomach This part of the intestine has smaller on the fore or proximal side and with the diameter compared to that of the large jejunum on the distal end. This part of the intestine and for this reason it is called a intestine is curved and it assumes a C- small intestine. The diameter of the small shape. The mid region of duodenum is an intestine of human being is approximately important part in which secretions from 2.5 cm while the large intestine has a the pancreas and gall bladder together diameter of about 7.6 cm, which is about with intestinal wall secretions meet. The three times wider than the small intestine. acidic chyme that enters the duodenum The small intestine is the longest of all is subjected to chemical digestion by the parts of the alimentary canal. It has the secretions coming from the pancreas, length of about 9 metres in a living person. intestinal wall, and the liver. The small intestine muscles are tight in 283 BIOLOGY FORM 5 KIWANDANI.indd 283 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools The liver produces a secretion called GOFVOERRNONMLEINNTE PURSOEPOENRLTYYabsorbed materials are in form of mineral bile which is released into duodenum via electrolytes, proteins, carbohydrates, and the bile duct from the gall bladder. The fats. These materials are utilized by the bile contains bile salts such as sodium body. taurocholate and glycocholate which are responsible for emulsiﬁcation of fats. Ileum. This is the final section of the Sodium bicarbonate has no digestive role, small intestine in most of high vertebrates, but rather it neutralises the acidic chyme including mammals, reptiles and birds. It from the stomach. The bile and pancreatic is the longest region of the small intestine juice which ﬂow into the duodenum are stretching from the distal portion of regulated by hepatopancreatic sphincter. the jejunum through proximal portion The pancreas is linked to the duodenum of caecum of the large intestine at the by a pancreatic duct. This exocrine gland ileocecal sphincter which is also known as produces various secretions which are a valve. In human being, it range between 2 collectively termed as pancreatic juice and 4 metres long and pH ranging between which contains the following components 7 and 8 (neutral to slightly alkaline). In and their function in brackets: amylase comparison to the other two parts of the (converts starch into maltose), small intestine ileum, is characteristically trypsinogen (inactive form of trypsin thicker; more vascularised and has more which is converted into active form mucosal folds. Parasympathetic and called trypsin by enterokinase). Others sympathetic nerve ﬁbres provide extrinsic are trypsin (converts protein into smaller innervations to the small intestine. The peptides), lipase (converts fats into fatty wall of ileum secretes intestinal juices acids and glycerols), peptidase (converts (saccus entericus) which contain mucus, peptides into amino acids), nucleases sodium hydrogen carbonate (NaHCO3) (convert nucleic acids into nucleotides), and digestive enzymes. Mucus and chymotrypsin (converts protein into small sodium hydrogen carbonate are secreted polypeptides), and sodium hydrogen by Brunner’s glands, which are found in carbonate (neutralizes the acid from the the interstitial wall. The role of mucus stomach). is to lubricate the interstitial wall and prevent corrosion, whereas sodium Jejunum. This is the second region hydrogen carbonate helps to neutralise of the intestine and middle portion of acidic chyme. small intestine measuring approximately between 2 and 3 meters long. This The digestive enzymes produced by region stretches from the duodenum and the epithelial cells of interstitial wall connects it with the ileum. However include carbohydrase and proteases. there is no clear demarcation between Carbohydrase enzymes such as amylase jejunum and the ileum. It is responsible converts remained starch into maltose, for nutrients absorption from the digested lactase converts lactose to galactose and food to the blood stream with the aid of glucose, and sucrase converts sucrose into finger like structures known as villi. The fructose and glucose. Protease (erepsin) enzymes convert peptide into amino 284 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 284 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition acids. Additionally the ileum performs GOFVOERRNONMLEINNTE PURSOEPOENRLTYYlymphatic capillaries. Moreover, there absorptive role as it absorbs vitamin B12, are lacteal vessels in the villi which bile salts and any other nutrients which are important for the transportation of are not absorbed in the jejunum. fat soluble substances (fatty acids and glycerol) into lymph vessels. The ileum as a site for absorption Ileum is a site for digestion and absorption The mucosa between the folds contains of digested food in the alimentary canal. deep tissues lined by cells that lead to a The absorption is done through diffusion or tubular intestinal gland called crypt of active transport aided by various adaptive Lieberkühn. This gland secretes slightly features including presence of circular alkaline juice which is triggered by folds, villi, and microvilli. These features irritation on the mucosa caused by acidic increase the surface area for absorption of chyme. nutrients. Villi are ﬁnger-like projections on the intestinal wall which are equipped Microvilli are cylindrical extensions of with smaller folds called microvilli on the epithelial mucosa cells. They are their surface. The surface occupied by much smaller than the villi, measuring microvilli is called a brush boarder. Folds about 1µm. Due to their small size, a are deep ridge like structures found on the mass of microvilli appears as ﬁne bristle mucosa and submucosa wall. These folds brush called brush borders. The surface are important in disrupting the straight of microvilli contains enzymes which movement of food into meander-like accomplish digestion of proteins and movement which ultimately delays food carbohydrates. The brush borders increase movement in the ileum, thus availing the surface area of the membrane plasma more time for digestion and absorption to to increase absorption. Microvilli increase take place. the surface area for absorption (Figure 5.15). The surface of the villus is lined with The villi are numerous hair-like the epithelial cells having large number of projections found on the surface of the mitochondria to provide energy for active folds. The function of the villi is to transport of nutrients, such as amino acids increase the surface area of the intestinal and glucose which are taken against their epithelium for an effective absorption. concentration gradient. Normally in 1 mm2 there can be as many as 40 villi. Mucosal epithelium composed These nutrient-rich blood from the of absorptive cells which covers the small intestine are carried to the liver villi. The villi are equipped with a large via the hepatic portal vein. Presence of number of blood vessels that carry sugars, longitudinal and circular muscles in the minerals, vitamins, and amino acids to the villus enhances contraction and relaxation liver for processing. Each villus is supplied which brings villus into contact with the with venules, arterioles, capillaries and food. BIOLOGY FORM 5 KIWANDANI.indd 285 285 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Figure 5.15 Transverse section of a small intestine The large intestine GOFVOERRNONMLEINNTE PURSOEPOENRLTYYrelatively more in number than they are in This is the last part of the alimentary canal the small intestine. The mucus in the large that extends from a blind pouch called intestine is important in lubricating the caecum through anus. It surrounds the food residues moving out as faeces while small intestine in three sides. This type also protecting the intestine from effects of the intestine is involved in the ﬁnal of acids and gases produced by enteric stage of water absorption, synthesis of bacteria. The large intestine therefore, certain vitamins, formation and expulsion had four major regions, namely: caecum, of faeces to outside the body. The region colon, rectum and anus. between the ileum and caecum has a sphincter known as ileocaecal sphincter Caecum. This is a sac-like structure and it is responsible for the movement of of about 6 cm suspended interior to undigested food materials from the ileum the ileocecal valve. Undigested food to the large intestine. materials from the ileum are ﬁrst received by this region of the large intestine where The large intestine differs in many ways absorption of water and salts is continued. from the small intestine as explained In this region a winding tube called earlier. Besides its diameter, which appendix is attached and its function is is relatively larger than that of small not clearly known hence it is considered intestine; it has a few enzymes secreting as a vestigial organ. However, appendix is cells in its walls. The villi which are reported to have immunological function numerous in the small intestine are missing because it contains a group of white blood in the large intestine. The wall of the large cells. Recent studies have also shown intestine is thus simple in structure and appendix to have bacteria reservoir which has simple columnar epithelium. The are important in repopulating the enteric intestinal mucus secreting glands are bacteria in the early stages of individuals 286 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 286 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition suffering diarrheal illness. As the faeces GOFVOERRNONMLEINNTE PURSOEPOENRLTYYthe rectum. The walls of the rectum have pass along the large intestine, some water curved contours and lateral bends which is absorbed into the blood stream. create internal transverse folds called rectal valves. The function of these valves Colon. This region of the intestine borders is to separate faeces from gas in order to with caecum and it is made up of four sub prevent simultaneous passage of faeces regions namely the ascending, transverse, and gas. descending and sigmoid regions. Food residues from caecum enter the ascending Anus. This region is also called anal canal region of the colon ﬁrst which is on the and constitutes the ﬁnal part of the large right side of abdomen and travel up intestine. The length of the anal canal is through the ﬁrst bend of the colon to the between 3.8 to 5 cm and it opens to the transverse region of the colon. The residue exterior of the body at the anus. It has continues through the second bend to the two types of muscles; the internal anal descending colon which is on the left side sphincter and external anal sphincter. The of the posterior abdominal wall and enters former ﬁrst type of muscle is made up the sigmoid colon. of smooth muscles, and its contractions are involuntary, while the later is made Generally, colon is very important in the up of skeletal muscles and they are water balance of the body. Every day, under voluntary control. Under normal about seven litres of water from drinks conditions, these two types of muscles and watery secretions produced internally, make the sphincter remain closed except enter the gut. If most of these were not when defaecating. reabsorbed, it could lead to dehydration of the body. Thus, re-absorption of water in Nervous and hormonal control of the the large intestine is necessary to prevent gastric juice secretion water loss. Digestion is vital for the functions of all systems of a human body. It is under the Rectum. After food residues have passed nervous and hormonal control systems. through the sigmoid colon, the remaining Until 19th century, biologists regarded intestinal content is stored as faeces in the digestive system as being entirely the rectum which measures about 20 under nervous control. However, in 1902 cm long. Rectum is located interior to a British physiologist Sir William M. the pelvis and it produces some mucus Baylyss discovered secretin hormone materialwhich are added to the faeces in as vital in the control of gastrointestinal order to lubricate it for easy passage to the functions. Three types of hormones outside by the process called defecation. involved in digestion are secretin, gastrin The desire for defecation is caused by the and cholecystokinin. Secretion and presence of a large quantity of faeces in release of these hormones is stimulated by presence of certain food molecules in the stomach and small intestine. BIOLOGY FORM 5 KIWANDANI.indd 287 287 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Digestion process is controlled by This in turn causes the secretions of two types of nervous system namely; histamine and increases hydrochloric acid the somatic nervous system and the and gastrin secretion in the stomach. In autonomic nervous system. The somatic comparison to other phases, the cephalic nervous system enables the body to adapt phase contributes about 20% of the gastric to stimuli such as touch and smell from secretions while eating. the external environment and is the system that controls the gastrointestinal tract. This Gastric phase. This is the second phase somatic nervous system is further divided and it is so called because it triggers into sympathetic and parasympathetic gastric activity. It occurs once the food is nervous systems. Stimulation of chewed and has arrived in the stomach. sympathetic system brings about shunting The partially digested food substances of blood from gastrointestinal tract. This such as proteins in the stomach stimulate reduces digestive activity and causes dry the endocrine cells in the stomach walls to mouth and cessation of salivation. secrete gastrin from gastric glands which increase the secretion of the gastric juice. The parasympathetic nervous system, on GOFVOERRNONMLEINNTE PURSOEPOENRLTYYNormally, the ingested food stimulates the contrary, is responsible for the secretion gastric activity by stretching the stomach of saliva, production of digestive enzymes, and raising pH of its contents. Stretching activation of digestion process and activates the short and long reﬂexes that increased peristalsis. The parasympathetic lead into the production of acetylcholine system dilates blood vessels to increase secreted by the parasympathetic nerve blood ﬂow to the gastrointestinal tract fibres. The acetylcholine and histamine after the consumption of food, due to from the gastric glands together with great or high metabolic demand placed gastrin stimulate parietal cells to secrete on the body by the gut. The control of hydrochloric acid. The chief cells gastric juice secretion occurs in three secrete pepsinogen in response to gastrin phases, namely, nervous, gastric, and secretion. Digestion of protein into intestinal phases. The mechanisms of the peptides and amino acids, stimulate gastrin nervous and hormonal control of digestion cells directly to secrete more gastrin phasewise is as detailed here under. to accelerate further protein digestion. Normally, peptides buffer the stomach The nervous or cephalic phase. This is acidity; therefore, as they leave the the initial stage which is initiated by sight, stomach acidity increases and as pH gets thought, taste, or smell of food, which below 2, a negative feedback is triggered later triggers a reﬂex in which nerve impulses relayed from the brain cause to inhibit the parietal and gastrin cells. gastric glands to release their secretions. Generally, the nervous signals that trigger This process winds up the gastric phase this phase emanate from cerebral cortex appetite centres and are transmitted to as the need for pepsin and HCl declines. the stomach through the vagus nerve. Furthermore, when fat-containing food enters the stomach, the hormone called enterogastrone or gastric inhibitory peptide is released from the wall of the stomach. This hormone decreases the ﬂow 288 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 288 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Nutrition of gastric juice and reduces movement Exercise 5.5 of the muscles of the stomach (churning motions) or gastric peristalsis. 1. Describe the structure of epithelial tissue of the digestive system. Intestinal phase. This phase occurs when chyme arrives in the ﬁrst region 2. Explain how glandular tissues of the of the small intestine called duodenum alimentary canal are adapted to the and triggers gastric activity and nervous functions they perform. reﬂexes. Food material in the duodenum stimulates both the alkaline and enzyme- 3. a) Describe the functions of the rich components of pancreatic juice. The mammalian stomach. alkaline component of pancreatic juice is secreted in response to the presence of acid b) Explain why surgical removal in the duodenum. The acidiﬁed chyme in of the stomach in human is not the duodenum triggers the secretion of necessarily fatal. secretin and cholecystokinin (CCK) or pancreozymin (PZ) from the duodenal 4. Describe the role of the liver in walls. Secretin causes the production of digestion. bile and mineral salts from gall bladder and pancreas respectively. CCK stimulates the GOFVOERRNONMLEINNTE PURSOEPOENRLTYY secretion of enzymes from pancreas and contraction of gall bladder to release bile. Moreover, secretin and CCK suppress gastric secretion and motility in which a decline in gastrin secretion and contraction of pyloric sphincter will limit admission of more chyme into the duodenum. This gives the duodenum ample time to work on the chyme it has received before receiving more. The enteroendocrine cells also secrete gastric-inhibitory peptide, also called gastrointestinal inhibitory peptide (GIP) which inhibits the secretion of gastric acid in the stomach. Also GIP stimulates insulin secretion in preparation for processing nutrients that are about to be absorbed by the small intestine. Trypsin in the duodenum inhibits the release of enzymes via the inhibition of CCK.This is a feedback control mechanism which limits the quantity of enzymes in the small intestine and may have a protective function. 289 BIOLOGY FORM 5 KIWANDANI.indd 289 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Revision questions 6. Using vivid examples, explain types of heterotrophic nutrition. 1. Distinguish between autotrophic and heterotrophic modes of nutrition. 7. Explain the role of the pancreas in digestion. 2. Photosynthesis is not possible without photolysis of water. Explain. 8. Explain the process of digestion in human alimentary canal. 3. Explain the role of RuBP and NADPH in photosynthesis. 9. Bile does not contain enzyme, yet it is important for digestion. Explain. 4. Differentiate between cyclic and non-cyclic photophosphorylation. 10. Give an account on the nervous and hormonal control of the gastric juice 5. Describe the mechanism of Hatch- secretion. Slack in C4 plants. 11. Explain the factors that affect the rate of photosynthesis. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 290 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 290 10/10/2019 14:07

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Chapter FOR ONLINE USE ONLY DO NOT DUPLICATE Six respirationGaseous exchange and Introduction All living organisms exchange gases between their respiratory surfaces and the surrounding environment. Respiration is an energy yielding process that liberates energy, which is used by living organisms to perform various body activities. It is a vital process to all living organisms as it provides energy for all metabolic processes. In this chapter, you will learn about the mechanisms of gaseous exchange in mammals and plants and the process of respiration. 6.1 Gaseous exchange in mammals GOFVOERRNONMLEINNTE PURSOEPOENRLTYYcavity together with the heart. The cavity Gaseous exchange entails a process of has a protective bony cage called the rib exchanging respiratory gases between the cage. The rib cage has ribs and intercostal cell of an organism and its environment. muscles that allow its movements during Oxygen is required for aerobic exhalation and inhalation of air. It is respiration. All organisms that undergo surrounded by a double pleural membrane aerobic respiration obtain oxygen from between which pleural fluid is found. their environment and carbon dioxide, a The fluid aids as a lubricant, preventing waste product of respiration is returned abrasion of the lungs during breathing. to the environment. The area for gaseous It is also associated with the muscular exchange within the organism’s body is sheath known as the diaphragm. The called respiratory surface. The process diaphragm separates the thorax from the of gaseous exchange takes place by abdomen. During inhalation the volume diffusion. In mammals and other animals, of the thoracic cavity increases, thus the principal organ for gaseous exchange lowering pressure. This is caused by the is the lung(s). downward movement of the diaphragm and the outward movement of the ribs. The internal structure of the During exhalation, the volume of the mammalian lung thoracic cavity decreases, thus raising the A pair of lungs is situated in the thoracic pressure. This is caused by the upward 291 BIOLOGY FORM 5 KIWANDANI.indd 291 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools movement of the diaphragm and inward It also moistens the air that passes down movement of the ribs. to the alveoli. The trachea branches at its lower end into two bronchi. Like the The lungs consist of the trachea, bronchi, trachea, each bronchus has cartilage and bronchioles, alveolar ducts, alveolar sacs ciliated epithelium with goblet cells which and alveoli (Figure 6.1). The alveoli are play a role of trapping dust and bacteria. the main functional units of the lungs. Each bronchus subdivides into many Trachea is the windpipe that connects the smaller tubes known as bronchioles. They larynx and the bronchi. It receives air from have cartilage, cilia, and the goblet cells the nostrils through the nasal cavity. In the that work similarly as in the trachea and latter, the air is warmed and cleared from bronchi; they trap foreign substances. The dust and germs that may have entered the bronchioles branch into very ﬁne tubes, cavity with it. The nasal cavity possesses alveolar ducts, ending into alveolar sacs hairs which help to trap dusts and other and each alveolar sac opens into a group of tiny particles. The trachea has cartilages alveoli. The alveolar ducts, alveolar sacs, in its walls that keep it ﬁrm and intact. It and alveoli do not possess cartilage, cilia is associated with ciliated epithelium and and goblet cells. The alveolus possesses goblet cells. The cilia beating moves the features that allow it to function in a trapped dusts and bacteria back to the cavity special way compared to other structural where they get swallowed. The goblet parts of the lungs. cells are essential for mucus production that traps dusts and bacteria altogether. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Trachea (wind pipe) Larynx Ring of cartilage Clavicle (collar bone) Right lung External intercostal muscles Bronchus Internal intercostal Bronchioles muscles Sternum Alveoli Left lung Intercostal muscle Left rib Right rib Pleural cavity Pleural membrane Diaphragm Figure 6.1 Structure of the mammalian lungs 292 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 292 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration Alveolus for efﬁcient gaseous exchange. In the The alveolus is a tiny air-ﬁlled sac of process of gaseous exchange, oxygen gas the mammalian lung. Gaseous exchange from the alveoli diffuse quickly across the takes place in the alveolus and actually, alveolar wall through the air-blood barrier it is a functional unit of the lungs. The into the blood capillaries and carried to estimated total amount of the alveoli in the the heart through pulmonary vein. On average human is about 700 million that the other hand, the carbon dioxide from has a total surface area of over 80 square the body tissues enters the heart and metres which facilitate the rate of gaseous carried from the heart to the lungs by the exchange. The alveoli are thin, moist and pulmonary artery. It diffuses through the are well supplied with a dense capillary blood capillary to the alveoli and is then networks, hence they are highly adapted exhaled (Figure 6.2). Trachea with rings Alveoli of cartilage Bronchioles Aorta Alveoli Right pulmonary Blood capillary arteries networks Superior Carbondioxide venacava leave blood Right capillaries and pulmonary enter to the vein alveolus GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Right lung Oxygen leave the alveolus and enter to Pulmonary the blood capillaries artery Left lung Pulmonary vein Figure 6.2 Structure of the mammalian lungs showing the association between alveoli and blood vessels during gaseous exchange Structurally, the alveoli possess the energy required to breathe in and connective tissues with elastic collagen inﬂate the lungs. It also kills bacteria ﬁbres that allow them to expand and trapped in the incoming air through the recoil during breathing. Alveoli have nostrils. In addition, it increases the rate of special epithelia cells in their walls that gaseous exchange in mammals. They also secrete a detergent-like chemical known have macrophages which are protective as surfactant into the alveolar space. The cells that remove debris and microbes by surfactant lowers the surface tension of phagocytosis (Figure 6.3). the ﬂuid inside the alveoli, hence reducing BIOLOGY FORM 5 KIWANDANI.indd 293 293 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Connective tissue cell Epithelial cell produce surfactant Macrophage Alveolar air space Epithelial cell Alveolar barriers Blood plasma White blood cell Blood capillary Red blood cells Figure 6.3 Structure of the alveolus Surface tension of the lungs GOFVOERRNONMLEINNTE PURSOEPOENRLTYYActivity 6.1 Observation of the The surface tension provided by surfactant structure of the mammalian lungs stabilizes the alveoli during inflation and dilation resulting from inhalation Materials and exhalation of gases. The surfactant Mouse or rat, dissection kit, dissecting is a phospholipid and a protein chemical tray, chloroform, and cotton wool. produced in early development stage of foetus. This chemical helps to lower Procedure the surface tension and promote lungs’ a) Use your dissection knowledge to expansion during inspiration (inhalation) and preventing alveolar collapse. It is open up the body cavity of a mouse also believed to protect the lungs from in the usual way to display the infections. lungs. b) Use a hand lens to observe the The proteins and lipids that make up the thoracic and abdominal cavities as surfactant have both hydrophobic and well as the diaphragm. hydrophilic region that are important in lowering the surface tension by adsorbing Questions to the air–water surface interface, with 1. Draw a well labelled diagram of hydrophobic head groups in water and hydrophobic tail facing towards the air. your dissection. 2. Explain the functions of each part of 294 the mammalian lungs. Safety precautions 1. Laboratory rules and regulations should be adhered to. 2. Rat or mouse may bite and also their fur may cause allergy to a human being. Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 294 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration Factors governing gaseous exchange at GOFVOERRNONMLEINNTE PURSOEPOENRLTYYc) Availability of high supply of blood respiratory surface capillaries Gaseous exchange occurs on the respiratory surface; a boundary between The mammalian respiratory surfaces the external environment and the interior are well supplied with blood by blood of the body of an organism. Mammalian capillaries. This enables high uptake of respiratory surface consists of many air oxygen in the alveoli, which increases the sacs called alveoli which are found inside rate of gaseous exchange. In the red blood a pair of lungs. An efﬁcient gaseous cells, there is haemoglobin that helps to exchange occurs when the respiratory transport oxygen by combining with it surface has large surface area and can to form oxyhaemoglobin which helps in quickly distribute and collect gases transportation of oxygen to different parts throughout the body. Moreover, an of the body where it is required. efﬁcient gaseous exchange can occur when the respiratory surface has ability d) Thickness of the membrane to speed up or slow down the exchange The rate of gaseous exchange is affected rate to meet the body demand. In general, by the thickness of the membrane across for an efﬁcient gaseous exchange in which the gases have to diffuse. A thick mammals, the respiratory surface must membrane reduces the rate at which gases have the following features: diffuse from areas of high concentration to those of low concentration. This is due a) Large surface area of the membrane to long distance of travel as the result There is a direct relationship between of membrane thickness. Generally, the the surface area and the rate of gaseous thickness of the membrane is inversely exchange. Generally, the larger the surface proportional to the rate of diffusion. area of the membrane, the higher the rate of gaseous exchange. This is because e) Diffusion distance when the surface area is large, more blood The distance across which air, blood, or and air can circulate, hence increasing the plasma ﬂuid has to diffuse also determines rate of gaseous exchange. the rate of gaseous exchange. In single- celled organisms, gaseous exchange b) Concentration gradient tends to be faster because the gases Concentration gradient is created when have to diffuse through only one cell the two sides separated by a membrane surface membrane while in multi-cellular have different concentrations of gases. organisms, gaseous exchange requires a This difference in concentration is complex transportation and respiratory actually what facilitates the process of system as the gases are transported gaseous exchange because gases can through a longer distance. move from areas of high concentration to those of low concentration. Therefore, for f) Moist surface gaseous exchange to occur there must be Since respiratory gases are transported a concentration gradient. in solution form, they must dissolve in liquid before they are carried away from 295 BIOLOGY FORM 5 KIWANDANI.indd 295 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools the respiratory surfaces. Thus, an efﬁcient from gills in ﬁsh and tadpoles to lungs in respiratory surface must be moist for rapid adult amphibians, reptiles and mammals. exchange and transportation of respiratory gases. Oxygen transport in vertebrates In vertebrates oxygen is transported in g) Permeability two ways: as dissolved oxygen in blood Since the membrane form the boundary plasma and by means of red blood cells. between organism and its extracellular The oxygen transported in solution form in environment, its permeability affects the the blood plasma accounts for only about rate of gaseous exchange. Therefore, a two percent (2%), and the remaining ninty respiratory surface must be permeable to eight percent (98%) is transported by the allow gases to pass through. red blood cells. The red blood cells have a red pigment called haemoglobin which Oxygen and carbon dioxide transport is responsible for transport of oxygen and in vertebrates carbon dioxide in the blood. Structurally, Oxygen and carbon dioxide are the the haemoglobin molecule consists of respiratory gases that have to be transported four Iron-containing parts and four protein from one part of the body to another. chains. Each haemoglobin molecule binds Oxygen is transported from the respiratory to four oxygen molecules, forming the surfaces to the respiring body tissues and oxyhaemoglobin molecule. This is carried carbon dioxide has to be transported from to individual cells in the body tissue where the respiring body tissues to the respiratory it is released. The binding or combination surfaces. Vertebrates such as mammals, of oxygen and haemoglobin is a reversible birds, reptiles, amphibians and ﬁsh, have process as shown in the equation below: a variety of respiratory surfaces, ranging GOFVOERRNONMLEINNTE PURSOEPOENRLTYY According to the above equation, at high the haemoglobin becomes. Usually the oxygen concentration, oxyhaemoglobin graph is S-shaped or sigmoid. is formed, whereas at low oxygen concentration, oxyhaemoglobin dissociates The curve shows the following: into haemoglobin and oxygen. This a) At relatively low oxygen concentration, dissociation releases oxygen from haemoglobin. The balance can be shown there is uncombined haemoglobin in the by an oxygen dissociation curve of blood and little or no oxyhaemoglobin oxyhaemoglobin (Figure 6.4). In the exists. This is most likely to occur oxygen dissociation curve, the greater in the body tissues, where oxygen the concentration or partial pressure of concentration is likely be low. oxygen, the more saturated with oxygen b) At relatively high oxygen concentration, haemoglobin combines with oxygen 296 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 296 10/10/2019 14:07

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in the blood to form oxyhaemoglobin. FOR ONLINE USE ONLY Therefore, most haemoglobin molecules DO NOT DUPLICATE are saturated with oxygen. This situation Gaseous exchange and respiration is likely to occur in the lungs, where oxygen concentration is high. % saturation of haemoglobin with oxygen 100 80 60 40 20 00 5 10 15 Partial pressure of oxygen/ KPa Figure 6.4 The oxygen dissociation curve of haemoglobin The effect of carbon dioxide in the GOFVOERRNONMLEINNTE PURSOEPOENRLTYYdissociation curves when less carbon transport of oxygen in blood dioxide is present and when more carbon Increased concentration of carbon dioxide dioxide is present in the blood. can affect oxygen transport in the blood. This is because haemoglobin can combine The Bohr Effect with carbon dioxide (although to a lesser The Bohr Effect is an increase in carbon extent) to form carbaminohaemoglobin. dioxide partial pressure of the blood or The presence of carbon dioxide lowers decrease in blood pH resulting into a the afﬁnity of haemoglobin to oxygen lower afﬁnity of haemoglobin to oxygen. and causes the release of oxygen from It is manifested by right-ward shifting haemoglobin. Therefore, an increase in of oxygen dissociation curve, resulting carbon dioxide in the tissues causes faster from enhanced unloading of oxygen by release of oxygen from haemoglobin and haemoglobin. The relationship between this is known as the Bohr Effect which is carbon dioxide partial pressure and blood the result of shifting of dissociation curves pH is mediated by carbonic anhydrase to the right in areas with increased partial which catalyses conversion of gaseous pressure of carbon dioxide (Figure 6.5). carbon dioxide to carbonic acid, that in The effect of carbon dioxide concentration turn releases a free hydrogen ion, hence on oxygen transport by haemoglobin can reducing the local pH of blood. be revealed by comparing the oxygen 297 BIOLOGY FORM 5 KIWANDANI.indd 297 10/10/2019 14:07

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Biology for Advanced Level Secondary Schools% saturation of haemoglobin with oxygenFOR ONLINE USE ONLY 100 Without CO2 in the blood DO NOT DUPLICATE 80 With CO2 in the blood 60 40 20 0 0 5 10 15 Partial pressure of oxygen/ kPa Figure 6.5 Oxygen dissociation curves of haemoglobin at different partial pressures of carbon dioxide Transport of carbon dioxide GOFVOERRNONMLEINNTE PURSOEPOENRLTYY solution form and a small amount as Carbon dioxide diffuses out of the tissues carbonic acid. into the blood for transportation. The body does not allow accumulation of carbon b) It can be transported in combination dioxide because it forms an acid with with proteins: carbon dioxide water that could lead to fatal changes of combines reversibly with haemoglobin blood pH. Carbon dioxide is transported to form a compound known as both, in plasma and in red blood cells by carbaminohaemoglobin. It does not bind three different ways. to iron as oxygen does but to amine group a) It can be transported either as physical (NH2) at the end of each polypeptide chain of haemoglobin and plasma proteins. solution (as dissolved carbon dioxide) About 10 – 20% of carbon dioxide is or as carbonic acid (H2CO3). However transported in this way. it is only about ﬁve percent (5%) of carbon dioxide that is transported in c) It can be transported as hydrogen carbonic acid (H2CO3). This reaction bicarbonate ions (HCO3-). Most of is catalysed by the enzyme carbonic the carbon dioxide (about 85%) in anhydrase which is found in red the body is transported as hydrogen blood cells. Then, the carbonic acid carbonate. Carbon dioxide enters red dissociates to form bicarbonate ions blood cells in the tissue’s capillaries (HCO3-) and hydrogen ions (H+). where it combines with water to form Student’s Book Form Five 298 BIOLOGY FORM 5 KIWANDANI.indd 298 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration Most of the hydrogen carbonate ions reaction occurs and carbon dioxide is formed in the red blood cells diffuse released (Figure 6.6). from the cytoplasm to the plasma and combine with sodium to form sodium The dissociation of carbonic acid increases hydrogen carbonate. The negatively the acidity of the blood. Hydrogen ions charged hydrogen carbonate ions are lost (H+) then react with oxyhaemoglobin from the blood cells, leaving them with to release bound oxygen and reduce the a more positive charge. This is balanced acidity of the blood. This buffering action by diffusion of chloride ions (Cl-) in the allows large quantities of carbonic acid opposite direction, maintaining the balance to be carried in the blood without major of negative and positive ions in either changes in blood pH. side of the plasma and red blood cells. This is called the chloride shift which This reversible reaction accounts for the is also known as the Hamburger shift or Bohr Effect. Carbon dioxide is a waste Hamburger phenomenon. It is named after product of respiration. Its concentration is the founder, Hartog Jakob Hamburger. high in the respiring cells; it is here where The chloride shift reaction occurs in the the haemoglobin releases oxygen. respiring cell. When the red blood cells reach the lungs the reverse process or GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Tissue CO2 + H2O H2CO3 H++ HCO3- fluid CO2 + HHbNH2 CO2 (Haemoglobin) HHbNHCOOH NaHCO3 (carbamino-haemoglobin) Plasma HHb Na+ + O2 Tissue O2 + Hb Erythrocyte Cl- fluid (oxyhaHembOog2 lobin) Chloride shift Mitochondrion Red blood cell Figure 6.6 Carbon dioxide transport by plasma and red blood cells BIOLOGY FORM 5 KIWANDANI.indd 299 299 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Haemoglobin is strongly attracted to altitudes, but the atmospheric pressure carbon dioxide molecules. Carbon dioxide falls with increasing altitudes. The is removed to reduce its concentration in oxygen tension (partial pressure of the cell and is transported to the lungs oxygen molecules dissolved in blood where its concentration is low. This process plasma) varies with altitudes (Table 6.1). is continuous since oxygen concentration Organisms living in a particular altitude in the lungs, is always higher than that of have to develop adaptive features that carbon dioxide, while in the respiring cells can enable them to sustain their lives in carbon dioxide concentration is always their particular environment. Among the higher than that of oxygen. organisms that live in the environments that need them to develop some adaptive Adaptation of organisms to oxygen features aimed at facilitating oxygen uptake uptake include mountain dwellers, divers, The percentage of oxygen in the air and mammalian foetus. does not change signiﬁcantly at different Table 6.1 The effects of altitude on the atmospheric pressure and oxygen tension Altitude(m)above Atmospheric Oxygen Oxygen tension(kPa) sea level pressure(kPa) content(%) 21.2 0 101.3 20.9 15.7 2500 74.7 20.9 11.3 5000 54.0 20.9 8.1 7000 38.5 20.9 5.5 10000 26.4 20.9 GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Adaptations to oxygen uptake for a) Their bone marrow produce more red mountain climbers and dwellers blood cells in order to raise the oxygen- In mountain climbers and high altitude carrying capacity of the blood. dwelling mammals, the rate of metabolism is high in order to ensure constant b) They possess a form of haemoglobin generation of enough energy to cope with with higher afﬁnity to oxygen. climbing activities, hence the supply of This allows loading of oxygen by oxygen should be assured. However, the haemoglobin even at low oxygen partial pressure of oxygen in high altitude tension. is low which makes the climbers difficult to pick up oxygen. For these reasons, c) They secrete more alkaline urine mountain climbers and mammals living that normalises blood pH. The in high altitudes develop the following chemoreceptors become sensitive adaptive features: to carbon dioxide concentration and normal ventilation rates are maintained. 300 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 300 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration d) Their tissues are tolerant to high levelsGOFVOERRNONMLEINNTE PURSOEPOENRLTYYb) They have a high blood volume with of lactic acid due to oxygen deficiency. plenty of haemoglobin and myoglobin. This allows long oxygen retention time. e) They have larger lungs, hence increased lung volumes and total lung c) They have a high tolerance to lactic capacity, therefore large amount of acid and carbon dioxide, that is, their haemoglobin loaded with oxygen. muscles can work anaerobically while holding their breath. f) They have deep and slow breathing rate that improves ventilation efficiency d) They can tolerate tremendous for oxygen, since blood oxygenation atmospheric pressure at great depths. increases, and it reduces systemic and Their lungs and ribs are collapsible; pulmonary blood pressures. air spaces are minimised; and nitrogen absorption is limited. Adaptations to oxygen uptake for divers e) Diving mammals slow their heart rate, Divers in the deep water do not depend stop their breathing, and shunt blood on lungs as a source of oxygen; instead, flow from their extremities to the brain, they rely on enhanced oxygen stored in heart, and muscles when starting a dive. their blood and muscles. Collapse of the lungs forces air away from the alveoli, f) Seals can hold their breath for about where gaseous exchange between the two hours. They rely on internal oxygen lungs and blood occurs. This blunting of stores when they are down there. gaseous exchange is important in the deep diver because it prevents the absorption of g) Myoglobin of the seals and dolphins is nitrogen into the blood and the subsequent more concentrated than that of humans, development of high blood nitrogen almost ten times, this gives them a levels. High blood nitrogen pressure can chance of storing oxygen for a long time exert a narcotic effect (so-called nitrogen when under water. narcosis) on the diver. It may also lead to nitrogen bubble formation during ascent, Adaptations of the mammalian foetus a phenomenon known as decompression to oxygen uptake sickness or “the bends”. Collapse of the The foetus lives and develops inside lungs in deep divers helps to avoid these the maternal womb (uterus). It obtains two problems. Thus, diving mammals, nutrients, exchange gases and waste besides the collapse of their lungs, have products with the maternal blood via the the following adaptive mechanisms to placenta. For the foetus to obtain oxygen oxygen uptake: from maternal blood, the oxygen has to diffuse from maternal blood to foetus a) They use oxygen more efﬁciently, that blood. There are some adaptations to this, is, they ﬁll their lungs and exchange which are; 90% of their air in each breath. Thus, a) Foetal haemoglobin has higher afﬁnity before a dive is taken, they take a deep breath to accumulate oxygen in their to oxygen; hence it can readily combine lungs. with oxygen to form oxyhaemoglobin 301 BIOLOGY FORM 5 KIWANDANI.indd 301 10/10/2019 14:07

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY DO NOT DUPLICATE (Figure.6.7). This allows the foetus to extract oxygen from the maternal leads to a change in function when blood supply. In adult hemoglobin, compared to adult hemoglobin. It has the protein subunits are identical been shown that the structural changes beta-chain subunits, while in foetal in foetal hemoglobin caused by the hemoglobin, the two subunits are substitution of gamma subunits for identical gamma subunits. This change beta-chains, allows foetal hemoglobin in structure of foetal hemoglobin also to have a higher affinity to oxygen. 100% oxygen Foetal haemoglobin with Adult haemoglobin haemoglobin 50% of saturation % PURSOEPOENRLTYY 5 10 Partial pressure of Oxygen (kPa) Figure 6.7 Oxygen dissociation curve for foetal and adult haemoglobin b) There is increased intake of oxygen GOFVOERRNONMLEINNTEExercise 6.1 by maternal blood due to increased haemoglobin so as to ensure a large 1. Explain why babies can stay alive in supply of oxygen to the foetus blood. the wombs of their mothers despite the fact that they are not in direct contact c) The uterine wall is highly vascularised with the atmospheric air. (provided with blood vessels) to ensure continuous supply of oxygen 2. Describe the ways by which oxygen to the foetus, as a result, the foetus and carbon dioxide are transported in loads its haemoglobin with oxygen vertebrates. efficiently. 3. Draw the oxygen-haemoglobin dissociation curve and comment on its shape. 4. What is chloride shift? Explain how it occurs. 302 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 302 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration 6.2 Gaseous exchange in plants Stomatal opening and closing Plants obtain oxygen and carbondioxide The opening and closing of stomata mainly through their leaves. They also depends on changes in the turgor pressure use lenticels (raised pores found on stems of the guard cells. When water ﬂows of woody plants) for exchanging minute into the guard cells by osmosis, their amounts of gases. They require oxygen turgor increases and they expand. Due for respiration and carbon dioxide for to the relatively inelastic inner wall, the photosynthesis. These gases diffuse into guard cells bend and draw away from the intercellular spaces of the leaf through each other, allowing the opening of the stomatal pores which are normally found pore, hence the air passes into the leaf. on the underside of the leaf and the gases If the guard cells lose water, the opposite diffuse into the cells that require them happens and the pore closes. The guard (Figure 6.8). The lenticel is a porous tissue cells lower their water potential to draw consisting of cells with large intercellular in water from the surrounding epidermal spaces in the periderm of secondarily cells by actively accumulating potassium thickened organs; the bark of woody stems, ions. This process requires energy in the and roots of dicotyledonous ﬂowering form of ATP. The energy is supplied by plants. Like the stomata, it functions as the mitochondria that are found in the a pore that provides a pathway for the guard cells. direct exchange of gases between internal tissues and the atmosphere. GOFVOERRNONMLEINNTE PURSOEPOENRLTYYWaxy cuticle Upper epidermis Palisade Air space mesophyll Spongy O2 Vascular bundle mesophyll containing xylem and Stoma phloem Guard cell with chloroplasts CO2 Lower epidermis Figure 6.8 Internal structure of a leaf showing the position of stomata for gaseous exchange BIOLOGY FORM 5 KIWANDANI.indd 303 303 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools The process of respiration in plants GOFVOERRNONMLEINNTE PURSOEPOENRLTYY e) Using forceps and a needle, take occurs throughout the day and night, out the layer of the leaf and place providing energy to the plants. The light it on a slide. dependent phase of photosynthesis can only occur during the day time and stops f) Add a drop of glycerin over the leaf at night or during darkness. One product layer to prevent the leaf layer from of respiration is carbon dioxide gas. getting dry, then place a slide cover This can be used by the plant directly over it. for photosynthesis. However, during the day, the rate of photosynthesis can be 10 g) Use a blotting paper to remove the or even 20 times faster than respiration excess stain and glycerin. (depending on light intensity). Therefore, the stomata must stay open for longer h) Observe the leaf layer on a slide periods to allow adequate diffusion of under the microscope. carbon dioxide from the atmosphere into the plant cells. Questions Activity 6.2 Observation of stomata 1. Draw and label what you have on a plant leaf observed. Materials 2. What conclusion can you make from A potted Tradescantia plant, water, for- your observation? ceps, needle, surgical or razor blade, watch glasses, light microscope, slide, Safety precaution slide cover, blotting paper, safranin, and Be careful when working with sharp glycerin. objects such as needle, surgical or razor blade. Procedure a) Remove a healthy leaf from the Exercise 6.2 potted plant. 1. Explain the factors that govern b) Use a surgical or razor blade and efﬁcient gaseous exchange at the respiratory surfaces. forceps to remove a thin outer layer from the lower surface of the leaf. 2. Describe the adaptations of mountain (Alternatively, you can do this by climbers or dwellers to oxygen folding the leaf, and gently pulling uptake. the thin layer apart using forceps). 3. Explain the mechanisms of gaseous c) Place the leaf layer in a watch glass exchange in plants. containing water. 4. Discuss why it is not advisable d) Add a few drops of safranin stain to sleep in a room with air-tight in a watch glass containing a thin windows while the burning charcoal layer of the leaf, then leave it for 2-3 or potted plants are inside. minutes. 5. Explain how partial pressures of CO2 and O2 may inﬂuence the process of gaseous exchange in plants and animals. 304 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 304 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration 6.3 Respiration they respire. So, the more the hydrogen Respiration is a process by which food bonds are broken, the larger the amount substances are oxidised to release of energy released. Lipids’ energy density energy in the form of ATP, which is is more than twice that of carbohydrates needed for metabolic activities in the because of their long fatty acid tails with body. Respiration takes place within the large number of hydrogen atoms. mitochondria of a cell. Since respiration takes place in a living cell, it is commonly Table 6.2 Respiratory substrates and their energy referred to as cellular respiration. There are values two types of respiration, namely aerobic respiration and anaerobic respiration. S/N Respiratory Energy value Aerobic respiration occurs in the presence of oxygen, while anaerobic respiration substrate (KJ/g) occurs in the absence of oxygen (due to that, it is sometimes referred to as 1 Carbohydrates 15.8 fermentation). Aerobic respiration involves three main stages or processes, 2 Lipids 39.4 namely glycolysis, Kreb’s cycle, and oxidative phosphorylation. Respiration is 3 Protein 17.0 an important process as it yields chemical energy in the form of ATP, which enables GOFVOERRNONMLEINNTE PURSOEPOENRLTYYa) Carbohydrates organisms to perform life activities These are the main respiratory such as movement, growth, excretion substrates used by most respiring cells. and reproduction. Respiration process Carbohydrates include polysaccharides, involves oxidation of organic compounds disaccharides, and monosaccharides. known as respiratory substrates. These are Polysaccharides such glycogen, cellulose, carbohydrates, fats, or proteins. and starch must be hydrolysed into simple monosaccharides such as glucose; in Respiratory substrates and their contrast, disaccharides have to undergo energy value hydrolysis into three monosaccharides, Different respiratory substrates release namely glucose, galactose, and different amounts of energy (Table fructose, depending on the type of the 6.2). The difference in energy values disaccharide that has been hydrolysed. of respiratory substrates is due to the Monosaccharides are usually in the form amount of hydrogen atoms present in each of hexose sugars. After their production, substrate. The more hydrogen atom in the they are then utilized in the respiratory molecule of a respiratory substrate, the pathways to release energy. more energy (ATP) is generated during respiration. Mitochondria synthesize b) Lipids (fats and oils) water using the hydrogen atoms removed Lipids can be used as a respiratory from organic molecules, such as glucose, substrate when the carbohydrates are and the oxygen atoms they take in as exhausted. When hydrolysed, each molecule releases three fatty acids and one glycerol molecule. Fatty acid are energy- rich compounds that enter the respiratory pathways in order to release energy. 305 BIOLOGY FORM 5 KIWANDANI.indd 305 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools c) Protein GOFVOERRNONMLEINNTE PURSOEPOENRLTYYand it does not require the presence Generally, protein is not used as an energy of oxygen. Physiologically, glycolysis source unless the body has no other option. produces energy at a high rate, but for a When all carbohydrate and lipid reserves short duration. In anaerobic condition, are fully utilised, proteins come into use. pyruvate can be reduced to lactate Proteins are not used in the ﬁrst place by lactate dehydrogenase. Anaerobic because of the variety of vital roles they glycolysis is also an effective means of play in the body. Proteins are hydrolysed energy production during short intense into amino acids and then deaminated. exercise. Under aerobic condition Deamination involves the removal of the pyruvate is converted to Acetyl CoA and amino group. The remaining acid may continues to the citric acid cycle (Kreb’s enter the Kreb’s cycle directly or may cycle) in the mitochondria. Pyruvate can be converted into fatty acids before they also be converted to ethanol and CO2 enter the Kreb’s cycle. The amount of (fermentation) in anaerobic conditions ATP produced from protein metabolism is and allows cells to make small amounts slightly less than glucose metabolism for of ATP. equivalent weights. Some cells such as yeast are unable Respiratory reactions to carry out aerobic respiration and There are two fundamental types of will automatically move into a type of reactions in cellular respiration, and these anaerobic respiration called alcoholic are oxidation or decarboxylation. fermentation. This occurs with the help of the enzyme pyruvate decarboxylase which Oxidation. During respiration, oxidation removes a carbon dioxide molecule from can take place in three ways; through the pyruvate to yield an acetaldehyde. addition of oxygen, removal of hydrogen The acetaldehyde is then reduced by the (dehydrogenation) removal of electrons. enzyme alcohol dehydrogenase, which transfers the hydrogen from NADH to the Decarboxylation. Decarboxylation is acetaldehyde to yield NAD and ethanol. the removal of carbon from a compound to form carbon dioxide. For a glucose Glycolysis process molecule which contains carbon, hydrogen Normally, glycolysis is a determined and oxygen, it is the hydrogen which is sequence of ten enzyme-catalyzed required for respiration. Thus, carbon has reactions and each step is facilitated by to be removed by decarboxylation. a different enzyme. The intermediates provide entry points to glycolysis, although, Glycolysis usually starts with glucose or glycogen Cellular respiration occurs in all living to produce glucose-6-phosphate. The organisms. Glycolysis is the ﬁrst stage starting points for other monosaccharides of cellular respiration whereby glucose such as galactose and fructose can be is oxidised into pyruvate. This process converted into one of these intermediates. takes place in the cytoplasm of the cell 306 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 306 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration All the reaction steps for the glycolysis the phosphate group (Pi) in an organic take place in the cytoplasm. Glycolysis molecule. In this stage of phosphorylation, yields an overall of two molecules of two phosphate groups attach to the ATP which are free energy-containing glucose in order to make it more reactive. molecules, two molecules of pyruvic acid In the first step of glycolysis, a phosphate and two “high energy” electron carrying group from ATP is transferred to glucose molecules of Nicotinamide Adenine producing glucose-6-phosphate, a more Dinucleotide (NADH). Glucose can also reactive form of glucose. The enzyme be synthesized from non-carbohydrate hexokinase, with broad specificity precursors by reactions referred to as catalyzes the phosphorylation of six- gluconeogenesis. The pentose phosphate carbon sugars by addition of a phosphate pathway enables cells to convert glucose- group to glucose in the cell’s cytoplasm. 6-phosphate, a derivative of glucose, The enzyme hexokinase splits ATP into to ribose-5-phosphate and other types ADP and the Pi is added on to the glucose. of monosaccharides. The NADH is an Phosphorylation prevents transport of important cellular reducing agent, which is glucose out of the cell and increases the also produced by this pathway. Generally, reactivity of the oxygen in the resulting glycolysis involves three main stages, phosphate ester. The negative charge of the namely phosphorylation of glucose, lysis phosphate prevents passage of the sugar and oxidation by dehydrogenation. phosphate through the plasma membrane, trapping glucose inside the cell. a) Phosphorylation of glucose Phosphorylation refers to the addition of GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Glucose (C6H12O6) + ATP ⎯H⎯exMo⎯kgina⎯se→ Glucose 6-phosphate (C6H11O6P) + ADP + H H H HC OH O H HC O P OHH HOH H OH H + ATP Hexokinase OHHOHH O OH + ADP +H Mg H H OH H OH Glucose Glucose -6- phosphate The first product of phosphorylation of glucose is glucose-6-phosphate, which is isomerized to fructose-6-phosphate by phosphoglucose isomerase enzyme. BIOLOGY FORM 5 KIWANDANI.indd 307 307 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools H H H P O C6H O HC 1 OH HC 6 O P 5 H 5 OH phosphoglucose isomerase 2 H 4 H H 1 H OH OH OH OH OH 43 3 2 H OH H OH Glucose -6-phosphate Fructose -6- phosphate Fructose-6-phosphate is further purpose for phosphorylation is to prevent phosphorylated to fructose-1,6-biphosphate, any later product from diffusing out of the under the enzyme phosphofructokinase cell because charged molecules cannot (PFK) and another ATP molecule is easily cross membranes. The entry of used to transfer a phosphate group to sugars into glycolysis is controlled at this fructose-6-phosphate to form fructose 1, step, through regulation of the enzyme 6-biphosphate. The new hydroxyl group on phosphofructokinase. C-1 is phosphorylated by ATP. Another Fructose-6-phosphate (C6H11O6P) + ATP ⎯p⎯hosp⎯hofr⎯ucto⎯kinas⎯e→ ADP + Fructose-1,6- bisphosphate (C6H10O6P2). HH GOFVOERRNONMLEINNTE PURSOEPOENRLTYYHH P O CH O HC OH PFK O C6H O HC1 O P H H OH OH + ATP 5 2 + ADP + H OH H Mg H H OH OH Fructose -6-phosphate 43 OH H Fructose 1-6-bisphosphate The phosphofructokinase catalysed reaction that are isomers of each other. These two is irreversible under cellular conditions, sugars are dihydroxyacetone phosphate and therefore, is the first committed step in and glyceraldehyde phosphate also glycolysis. known as glyceraldehyde-3-phosphate or 3-phosphoglyceraldehyde (3-PGAL). b) Lysis Only the glyceraldehyde 3-phosphate In this stage the phosphorylated 6-carbon can proceed immediately through sugar is broken down with the help glycolysis. Dihydroxyacetone phosphate of enzymes into two 3-carbon sugar must be isomerised to glyceraldehyde-3- phosphate. The enzyme aldolase splits phosphate by the enzyme phosphotriose fructose 1, 6-biphosphate into two sugars isomerase to continue with the next steps of the glycolytic pathway. 308 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 308 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration Fructose 1, 6-biphosphate (C6H10O6P2) + aldolase ↔ Dihydroxyacetone phosphate (C3H5O3P) + Glyceraldehyde phosphate (C3H5O3P) oo OO o P o 6 O C1H2 o P o o1 CH2 O P 4C H CH2 Aldolase o5 OH 2 o 2C O o + H 5C OH O o6 CH2 O P OH 3 CH2 OH o 43 OH Fructose-1-6-bisphosphate Dihydroxyacetone Glyceraldehyde-3-phosphate phosphate c) Oxidation by dehydrogenation GOFVOERRNONMLEINNTE PURSOEPOENRLTYYis composed of three carbon-based rings In this step, an enzyme removes one and a tail of two phosphate groups. The hydrogen atom and two electrons from each addition of the third phosphate group to three-carbon molecules. Both hydrogen the tail forms ATP. In this step, two new atoms are modiﬁed to hydrogen ions, ATP molecules are produced; this is the positively charged particles. The hydrogen substrate-level phosphorylation. When ion and two electrons from each three- cells require energy, another enzyme carbon molecule are transferred as a unit breaks off the third phosphate group, to a large molecule called Nicotinamide releasing energy that powers the cell. The Adenine Dinucleotide (NAD) to form removal of the third phosphate from ATP two molecules of reduced NADH. The converts ATP back to ADP, which is used hydrogen ions and electrons stored in again in cellular respiration to make more each molecule of NADH are used to make ATP. ATP in later stages of cellular respiration during oxidative phosphorylation of the When the two 3 carbon compounds electron transport chain. are separated from the phosphate groups, the three-carbon compounds are In the ﬁnal steps of glycolysis, two converted to two molecules of pyruvate, hydrogen atoms are removed from each each composed of three carbons, three three-carbon compound. These hydrogen oxygen, and three hydrogen atoms. atoms bond to free-ﬂoating oxygen When glycolysis is complete, important atoms in the cytoplasm to form water. products are produced; two molecules This step prepares the two three-carbon of NADH, two molecules of pyruvate compounds for action by the next enzyme (pyruvic acid) and two molecules of ATP. in the pathway. This enzyme removes the NADH and pyruvate are used in the next phosphate group from each of the three- steps of cellular respiration and the ATP carbon compounds. Each phosphate molecules are used for reactions in the cell group then bonds to a single molecule that require energy. of adenosine diphosphate (ADP). ADP 309 BIOLOGY FORM 5 KIWANDANI.indd 309 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools The process can be detailed as follows: GOFVOERRNONMLEINNTE PURSOEPOENRLTYYmolecule. Again two molecules of ATP Glyceraldehyde -3- phosphate or and two pyruvate are formed; as explained 3-phospho-glyceraldehyde (3-PGAL) is earlier, because the triose phosphate has converted to 1, 3-biphosphoglycerate or 1, to enter twice in the glycolysis process 3-diphosphoglyceric acid (1,3-diPGA) by that is; when 3-PGAL is used, the glyceraldehyde-3-phosphate dehydrogenase dihydroxyacetone phosphate is converted enzyme where NAD is reduced to to 3-PGAL and enters the cycle. The NADH2. Then 1,3-diPGA is converted to formation of pyruvate ends the glycolysis 3-phophoglycerate or 3-phosphoglyceric process. (Figure 6.9). acid (3-PGA) by phosphoglycerate kinase enzyme, this process involve the loss of Exercise 6.3 phosphate group (Pi) from 1,3-diPGA to form (3-PGA), and the Pi is transferred to 1. Discuss the role of enzymes in a a molecule of ADP to form the first ATP glycolytic pathway. molecules. Actually, two molecules of ATP are formed because there were two 2. What would happen if the ﬁrst enzyme triose phosphate produced in the lysis of in glycolysis is irreversibly inhibited Fructose-1,6-biphosphate. But the two by a toxic substance? ATP formed are used to pay back the initial ATP used during the first process 3. Starting with glucose, write the overall of glycolysis (phosphorylation of glucose reaction for aerobic respiration. stage). 4. What are the main stages of aerobic The formed 3-PGA is converted to respiration? List down the important 2-phosphoglycerate or 2-phosphoglyceric materials that are involved in each acid (2-PGA) by phosphoglyceromutase stage. (phosphoglycerate mutase) enzyme. This enzyme rearranges the phosphate 5. The initial stages of glycolysis group from the third carbon of 3-PGA involve the use of ATP. Explain. to the second carbon, hence forming 2-PGA. The 2-phosphoglycerate is then The fate of pyruvic acid converted to phosphoenol pyruvate The pyruvate produced during glycolysis (PEP) under the influence of enolase has two possible fates, depending on the enzyme, in this reaction water molecule is availability of oxygen in the cell. In the removed from 2-phosphoglycerate. Then presence of oxygen, the pyruvate will the phosphoenol pyruvate is converted enter Kreb’s cycle in which they will be into pyruvate (pyruvic acid) by pyruvate completely oxidised into carbon dioxide kinase enzyme, where by the phosphate and water. Alternatively, in the absence group (Pi) from PEP is transferred to of oxygen (in anaerobic condition) the ADP molecule and combine to form ATP pyruvate will undergo fermentation. 310 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 310 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration Glucose ATP Hexokinase ADP Glucose-6-phosphate Phosphoglucose isomerase Fructose -6-phosphate Phosphofructokinase Fructose 1.6-biphosphate Aldolase Triosephosphate isomerase Glyceraldehyde -3- phosphate Dihydroxyacetone phosphate NADP+ + Pi Glyceraldehyde 3-phosphate dehydrogenase NADH + H+ GOFVOERRNONMLEINNTE PURSOEPOENRLTYY1,3-biphosphoglycerate ADP Phosphoglyceratekinase ATP 3-Phosphoglycerate Phosphoglyceromutase 2-Phosphoglycerate Enolase H2O Phosphoenolypyruvate Pyruvate ATP kinase ADP Pyruvate Figure 6.9 The glycolysis process 311 BIOLOGY FORM 5 KIWANDANI.indd 311 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools The fate of pyruvic acid under aerobic (CoA) resulting into formation of respiration acetyl Coenzyme A (acetyl CoA). In aerobic respiration, the pyruvate from b) Oxidation by dehydrogenation, in the glycolysis is completely oxidised to presence of dehydrogenase enzyme carbon dioxide and water using oxygen. and NAD. In the ﬁrst stage, pyruvic acid is broken down to carbon dioxide and hydrogen. The Kreb’s cycle This occurs in the matrix of mitochondria Kreb’s cycle is also known as citric acid and involves the Kreb’s cycle. In the cycle. When oxygen is available the second stage, hydrogen is oxidised by pyruvate produced during glycolysis oxygen to water in a series of reactions enters Kreb’s cycle, named after Sir Hans that constitute the respiratory chain or Adolf Krebs (1900-1981), who worked electron transport system. This occurs on out the details of the cycle in 1930. Kreb’s the cristae of the mitochondria. cycle takes place in the matrix of the mitochondrion. The transition between glycolysis and Steps involved in the Kreb’s cycle Kreb’s cycle The Kreb’s cycle consists of a series of There is a transitional stage between enzyme-catalysed reactions. It involves glycolysis and Kreb’s cycle or tricarboxylic the following steps: acid (TCA) cycle. During this stage, each pyruvic acid molecules enters the matrix The ﬁrst step is the reaction of acetyl- of the mitochondrion where it undergoes CoA with oxaloacetate to form citrate, two types of reactions: in which the acetyl CoA (2C) is joined a) Decarboxylation, by losing a carbon to oxaloacetate (4C) to form citrate (6C). This process requires the input of water, atom as carbon dioxide: The products and it is catalysed by citrate synthetase of this oxidative decarboxylation enzyme. (acetyl) are carried by coenzyme A GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Acetyl - CoA + Oxaloacetate + H2O Citrate synthetase Citrate + Coa-SH The second step is the formation of isocitrate. In the presence of aconitase enzyme, citrate is The seccoonndverstteedpinitos itshoceitrfaoter.mTahtisiopnrocoefssiissoacccitormatpeli.shIend bthyedephryedsraetniocneanodfreahcyodnraittiaosnetoeyniezlydme, citrate iasncisoonmveerrctaeldledinistoocitirsaotec.itrate. This process is accomplished by dehydration and rehydration to yield an isomer called isocitrate. The third step of reaction is oxidation of Isocitrate. In this reaction thSetuIdsoencitt’sraBteooiskoFxoirdmatiFvievley 312 decarboxylated to form α- ketoglutarate. The enzymes involved are isocitrate dehydrogenase and oxalosuccinate decarboxylase together with NAD, and the products are NADH2 and CO2. BIOLOGY FORM 5 KIWANDANI.indd 312 10/10/2019 14:07

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GOFVOERRNONMLEINNTE PURSOEPOENRLTYY FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration ToxhiedathtTdiievhrceedaltrhybsiotrexddypseltaecotpeafdorbfrtoeoreaxfaoccyrttmliioaontαne-idsikosexttooiodgxalutifidtooaanrratmoiteof .InsTαoho-ceiftrekaInetszetoy.omIcgnietltsruhaitinstaevrr.oeaaltIvcenet.idotnTahrtihehseeisrIoesecoainctcrizattriytaoemtnedeeishtshyoedxirinodIvgasteooinvclaevislteyerdatearies isocitraantdeodxaelhosyudcrcoingaetendaescearbaonxdylaosxeatologestuhcercwinitahteNAdDe,caanrdbtohxeyplraodsuecttsoagreetNhAeDr Hw2itahndNCOA2D. , and the products are NADH2 and CO2. The foTuhretfhousrtthepsteips isththee ooxxiiddaatitoinoonf αo-fKαe-toKgluettaoragtelutotafroartme Stuoccfionyrml – CSouAc.cIinntyhel p–reCsenocAe .ofIn the presenαc-ekeotofglαut-arkateetdoeghlyudtraograenteasedeenhzyymdreo, αg-ekneatosgeluetanraztyemis eox, idαa-tivkeelytodgelcuartbaorxaytelateisd tooxfoidrmatively decarbsuocxcyinlyalteCdoAto(4foCr).mDsuuricngcinthyisl rCeaocAtion(4NCA).DD+ iusrirendguctehdistoreNaAcDtiHon2. NThAe Dpr+odisucrtsedaureced to NADHN2A.DTHh2eapnrdoCdOu2c.ts are NADH2 and CO2. TCrtcweTgaCArennuahoDhiohematpeAePrenaAenghﬁ..oolnzyCAagTeyofsﬁvTynnftuihoDssihynmrefheateAepioetPrendseehngddhﬁ..tmoledzydCosfasapTyiiutbisptnonhynnmhcestiyhAgieascedeseueoittl(pmtnscaededhCsGipaypiscniusoeponhtliciTlithAgarcseanCsceaeotocPieypmonctsupnthi)lpAlyhlzhsvhao(e.ehlGeycele–oarcGsereCadmDeytsocsdnepoincuTCnpPodleAttlvoba(n)hhoePoiG,ecynseasorAeattDyivsugtdfunhapsien.sePscdoeuShteerbnr)achogauT.edi,synseiscnbroIihnpttcttoyofuahoophieyeissuennShsanefneglryoptiuov.CedeeenlsrcCoboInmprtCcotetlygeoogfvhoiAioirnreannyafAdogAAysStovgtueeileroiytpunpDimhsCsglnAgeihcveyuteoirPrwTeocrnoaaonAlr.sePghtnideussetnpiomtpuphiicwhgnysAnlchheouiathcwlngTovtaaciereainPhanentsesCmslaieomutwcdteistorocehthooii.hr(c.pnAedvbGliehleTiInnoaenosyotlahnDcstsitriiasotriuenptesphitPnr.pmeholdethrvehsl)oTfaneoooo,otaohnCaesvascsriasltseopestpnpvht(iudAmehohoGdrheescfaeonoTasratfacsCaeivenricPtpsioseotdebtpnh)(himdA.chuoGayaeaagotnGstTaetstfsretaefnuriTPrpaogolos.ddcecyh)Prmucr.hcmsaoTimatpaeetunGioetstddshopytauiTawgllivbnacgcyttPsrno–cyohagseohieelunniriddspycgeeolhbaaurttron–yoacailttnsoeioosAtnsshiTneoiPnesf BIOLOGY FOtTirTfimtgTaynshuemRuhhhaopomMeateecoreiener5aestutseiorsnoryionKrTfgtmaTireuasxfnyzeueantImpuiteWhhtsaposnremaayhasteeeeFtAcoreeoninrrmriNaesttAsuifisneteiohotsorDtcmwionrrevAuDasaxetAffieatntpeitoaepotNtsTwssnreadhailslhIheFti,.seonvPf.irsninotaotAsoifienfitrI,dhtvtcsmstiwresnrdoevAsDhaptmsmefidupeoatopurerhopT3udceailslhehaaa1isortvPfchm.s3ottarhhoomlxeeiierI,tvsanstiofriesndiitshgpscsme(dsvdsiutuGwerhhuptsahhauceaosesaloatsolTeehchnmaittrhouFoafxeiieruoPeteacnio,fridnAiefmg)tpcnsth(dvp.htGwhuDotzahahh,barioGtlyneftoynlTeheheHnadimdtdTFoasrieruoPee2eecuw,rrnyAPsfmoei)nhto.npcpnk.,fDozahghacbirzeeGtcsynsafroiyeheHliynneyanmdentdTcsereelanm2atdurnylfhPsaoeitatbo.eocneekihl,fndoegacunritemetcdsasgrileh,nlogsniieyaneneuescdiecilanatsftosnslf.uaityaoaptbeoceceephlOcnrdplaolnuarrmmealaetdtglnliznooehst.iimlreayeuscydiwindTfesftolsms.auiyopfehacecprOmocsrqaeyelinarmeareltsusnlizaymhsdt.,faulm,iayeryewoTvfnafusslmcbauoyiaftuehusaeodsryemolrseqecyeinen.erlfsshusstnaydlmsTods,dh,uiaGretuakvhifafu.sccbrstsooniaTtueescoogsyelrOrdescilPlen.cmienAtfshevstn.doeTioanhuntGeTtpnouatahifaecre,stvsPfonTte.mcoliedrd;tdsilTsPfhcmirnAetmsehovo.shoeeiapuhonieTpinurotoeeeuyswre,mvPfnsntnn.dsfieded;tdzTsrottchorvehsoiyeshrshefnlipuehagmmoiesigroseeteyseow,.uensnnndupuffficedzaitTrotsroopcvsshoiysoerAfnoiueheafgmmdungnlors.tTeneusaa,ueuneIutprcutdiPcennghaitesrspicss,dsoeeessieotiienfudhnsncnlo.tsuiaauouoseItrctnenctghneiideeshsisdtnhstiauofsosershmte3ha11oa03r/ftt10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools the enzyme is found in tissues that have a high number of anabolic pathways, such as liver. This form produces guanosine triphosphate (GTP). GTP is energetically equivalent to ATP; however, its use is more restricted. In particular, protein synthesis primarily uses GTP. The sixth step is the oxidation of succinate to form fumarate. The conversion of succinate into fumarate involves removal of hydrogen and is catalysed by succinate dehydrogenase. In this reaction FAD is reduced to FADH2. Succinate dehydrogenase The seventh step is the hydration of fumarate to malate. This reversible reaction is catalysed The sbeyvefunmthasrtaespe,iswthhiechhyisdaralstoioknnoofwfnumasafruamteatroatmeahlyadter.aTtahsies .reversible reaction is catalysed The sbeyvfeunmtahrasstee, pwhiischtihsealshoykdnroawtinoans foumf afruamteahryadtreatatose.malate. This reversible reaction is catalTyhseesdevbeyntfhusmteapraissteh,ewhhydicrahtiiosnaolfsfoumknaroawtentoasmfaulamtea.rTahties rheyvderrsaibtalesere.action is catalysed by fumarase, which is also known as fumarate hydratase. Fumarase GOFVOERRNONMLEINNTE PURSOEPOENRLTYY bEyigmhtadEheliaghshtyteetddEthhpreiodesghtgiheyKesetdhphrnretyaioshbssdtg’eeeteshrpanoeconaiygsoxdscxeetilhridneaede.nsaaaouIdttsnixlieotroistendhnsiaaionustnfilototpdhmsfnreoiamonrcplefaerttaoshmsesudle,aatuloplNttcaresfttoAoieodrtDitnumonocioftsoftoifooxhrroenamrexdlmooauoplafcoxcrooeaaeoxdcxltoaadeialattnuoealct.oateocecTtataNewihcttoeiAahes.ntiDterTcaehwHohtaeiicfh2sst.i.irctooTehhnxaehicaisstsilitstoaochrnaerattieiacnsslategyacctsracattetoiiadtnomelgybnpsycwoeoimdusmhnabidcplycaoaohtmuetfanaidllsyaotsetfhede startinthge cKoremb’psocuycnlde. oInftthhisepKrorceesbs’,sNcAyDclies .reIdnuctehdisinptoroNcAeDssH,2N. AD is reduced into NADH2. Eighth step is the oxidation of malate to form oxaloacetate. This reaction is catalysed by malate dehydrogenase and results in the production of oxaloacetate which is the starting compound of the Kreb’s cycle. In this process, NAD is Mreadlauteced into NADH2. dehydrogenase It is important to note that glycolysis yields two pyruvate molecules, each of which enters the It is imItpisoirKmtarpenobtr’tstaoncytnctooletnesoettpehaatrhatategtllgyyl.ycTcoholulyyss,sifisosyryiaeilmedlsodlteswcoulpemyorufulgvtlaiutpceloimseeod,ltehbceuyrleestm,wueosatc.bhTeothfwuwoshK,icrthehbee’nstpecryrscoltdehseu, cantsd,of etwntoerspKtoyrtraehuvbeo’tovosifadKcattyhrvereceoepliebKemdts’riresoteeipbpolace’nrsytc,aictetucieyaolllcceeynhl.,seTse,caaeohrcempuehasap6,ccroNfohanomAterenpaDoltoyfmHon.feo2wntTl,het2hcheoFuiufccAlyetshDc,oelHfecgm2yt4l,chuuCl4cseoCtOmsbOKe2eu,2,rsmt,eth22ubebAArle’teTsiTmpmPPluciu,,elystdaaitcnpbnbldyieedeottdwwxaobarooxyle.oaKTtalw6rchoeeoNuabt.sa’c,ATsteethchDtuymeascHtpo,leerlt2oehs,m,cdeuau2ponlcerFdtlosse,A.dcuTDuchtlHeses2,. for aItomifstoihmleterpaKconurrsetliabeton’rstoytcfosytcgenlpole,utaetchrtoeahts6aietNs,gfArltyoDhcmeHor2lpey,ysr2imusFvAuyaistDeetlHdtob2se,atwc4eCotaOTpte2hy,,reyu2ivAetralTdatesPn,2msNaiotnAolderDcoyuHxlas2eltsoae,anpecdae,ct2athChteOoafmt2woimslheoicflcuerhcoleuemsln.etsTepr(hsFyeirtghuuevreate two KKtrrreaebnb’s’si6tso.c1cyr0ycyl(sceatle)sepeas,pn,tdahara(anbttd)ei)sl,.yft.rooTmahvupsoy,irfduovrraeatepmetootilaetciceoutnalet,eo, fytgieolludcsoa2scNee,AttahDteeHr,e2maynuidsetl2bdCesOtw22omNKoAlreecDbu’lHsesc2y(Fcaliegnsud,rean2dC, O2 eachto6c.a1ov0mo(idap)oraenpdent(ibtti)o).no,featchhecocmypcolneenmt oufstht e bcyeclemmuosltebceumleuslt(iFpliigedurbey 6tw.1o0. T(hau)sa, nthde p(bro)d).ucts of the Kreb’s cycle are 6NADH2, 2FADH2, 4CO2, 2ATP, and oxaloacetate molecules. The transitory step, that is from pyruvate to acetate, yields 2NADH2 and S2tCudOe2ntm’s oBloeockulFeosr(mFiFgiuvree 3146.10 (a) and (b)). BIOLOGY FORM 5 KIWANDANI.indd 314 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration Pyruvic acid NAD+ Pyruvate NADH + H+ dehydrogenase complex CO2 CoA Acetyl CoA (2C) CoA Citrate Oxaloacetate (4C) H2O synthetase Citrate (6C) NADH + H+ Malate Agunitase H2O dehydrogenase Fe2+ NAD+ Cis-aconitate Malate (4C) H2O Aconitase Fumarase Fe2+ H2O Isocitrate (6C) Fumarate (4C) Isocitrate NAD+ FADH2 Succinate dehydrogenase NADH + H+ dehydrogenase Mn2- FAD+ Succinate (4C) Oxalo-succinate (6C) Oxalosuccinate ATP/GTR Succinly CoA decarboxylase CO2 ADP/GDP CoA synthetase α-Ketoglutarate (5C) Succinly CoA (4C) GOFVOERRNONMLEINNTE PURSOEPOENRLTYY CoA α-Ketoglutarate NAD+ dehydrogenase NADH + H+ CO2 complex (a) Acetyl CoA CoA CoA NADH Oxaloacetate Citrate NAD+ Malate (4C) NAD+ Fumarate (4C) NADH + CO2 FADH2 Succinate Alpha ketoglutarate NAD+ (4c) NADH + CO2 FAD+ ATP ADP++Pi (b) Figure 6.10 Kreb’s cycle (a) detailed diagram and (b) simplified diagram BIOLOGY FORM 5 KIWANDANI.indd 315 315 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Importance of the Kreb’s cycle devoid of oxygen. Many anaerobic Kreb’s cycle is an economical way of organisms are obligate anaerobes as they turning food components in the cell into can only respire anaerobically and they usable energy. Only the acetyl groups are die in the presence of oxygen. Muscles destroyed in the cycle. The seven enzymes do also respire anaerobically whenever that carry out the various reactions and the there is deﬁciency or lack of oxygen at intermediate compounds on which these a particular tissue point. This creates enzymes act can be used again and again. the basis for categorising anaerobic respiration into alcoholic fermentation Moreover, many of the intermediate and lactic acid fermentation. compounds produced in the Kreb’s cycle are of value as starting materials for the Alcoholic fermentation synthesis of amino acids, carbohydrates, Alcoholic fermentation is also called and other cellular products. Pyruvates are ethanol fermentation which occurs in broken down to carbon dioxide. Thus, the cells, such as plant and yeast cells (Figure Kreb’s cycle degrades macromolecules 6.11). This biological process converts into simpler molecules. The Kreb’s cycle two pyruvates into two acetaldehydes releases ATP and NADH and FADH. The producing two carbondioxide molecules ATP is directly utilised by the cellular as a waste product. The two acetaldehydes activities while the NADH and FADH are are then converted to two ethanol metabolites for oxidative phosphorylation molecules by using hydrogen ions from of the electron transport system in which NADH; converting NADH back into ATP are produced. NAD+. Ethanol fermentation has many uses. These include producing alcoholic The fate of pyruvic acid under beverages, ethanol fuel, as well as raising anaerobic condition reagent in baking bread. In the absence of oxygen; the principle product of glycolysis (pyruvate) enters 2 CO2 a fermentation process. The organisms GOFVOERRNONMLEINNTE PURSOEPOENRLTYY that do not use oxygen as the ﬁnal 2 Pyruvic Acid 2 NADH 2 NAD+ 2 Ethanol proton and electron acceptor are known as anaerobes. In anaerobes, other less- Figure 6.11 Alcoholic fermentation pathway oxidising substances such as sulphate ion (SO42-), nitrate ion (NO3-), sulphur, Lactic acid fermentation and fumarate are used. These terminal This is also referred to as lactate electron acceptors have smaller reduction fermentation, which is a biological potentials than oxygen. This means process by which pyruvate is converted that less energy is released per oxidised into the metabolite lactate. In lactic acid molecule. Generally, anaerobic respiration fermentation, the pyruvic acid from is less efﬁcient in energy production than glycolysis is reduced to lactic acid by aerobic respiration. It is mainly used by NADH, which is oxidised to NAD+. prokaryotes that live in environment Lactic acid fermentation allows glycolysis to continue by ensuring that NADH is 316 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 316 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration returned to its oxidised state (NAD+). This Events of electron transport chain in anaerobic fermentation reaction occurs in some bacteria and animal cells such as in the formation of ATP muscle cells (Figure 6.12). The electron transport chain is the ﬁnal and most important step of cellular Lactate dehydrogenase Lactic acid respiration. The electron transport chain Pyruvate (electron transport system or cytochrome system) is a process by which the energy NADH NAD+ carrier molecules (NADH2 and FADH2) produced during glycolysis, Kreb’s cycle Figure 6.12 Lactic acid fermentation pathway and other catabolic processes are oxidized to release energy in the form of ATP. If oxygen is present in the cell, many The electron transport chain is a series organisms will bypass fermentation and of electron transporters embedded in the undergo aerobic respiration. However, inner mitochondrial membrane that shuttles facultative anaerobes will undergo both electrons from NADH2 and FADH2. In fermentation and aerobic respiration the process, protons are pumped from the in the presence of oxygen. Sometimes, mitochondrial matrix to the intermembrane even when oxygen is present and space, and oxygen is reduced to form water. aerobic metabolism is taking place in the mitochondria, if pyruvate is building The hydrogen atoms carried by reduced up faster than it can be metabolised, the NAD and FAD are transferred to a chain fermentation process will occur. The of other carriers at progressively lower enzyme responsible for catalysing the energy levels. As the hydrogen passes interconversion of pyruvate to lactate is from one carrier to the next, the energy known as lactate dehydrogenase. released is used to combine ADP and GOFVOERRNONMLEINNTE PURSOEPOENRLTYYinorganic phosphate (Pi) to form ATP. A Exercise 6.4 series of carriers is termed the respiratory chain. The latter has four electron carriers, 1. What is the Kreb’s cycle pathway? namely NAD, FAD, coenzyme Q and How is it related to glycolysis? cytochromes. The hydrogen atoms carried by NAD are shunted into the chain at 2. Illustrate the steps involved in the carrier one, NAD (a step ahead FAD), and Kreb’s cycle. produce a total of 3 ATP molecules as they pass through the carriers (Figure 6.13). 3. What is the importance of Meanwhile, the hydrogen atoms carried regeneration of oxaloacetate in the by FAD are introduced in the chain at ﬁnal step of Kreb’s cycle? carrier two, FAD. Therefore, a pair of hydrogen atoms carried by FAD makes 4. Carry out library search to find a total of 2 ATP molecules as it passes out if the bacteria and yeast form through the carriers. Initially, hydrogen alcohols in the absence of oxygen atoms pass along the chain. However, after or they possess a metabolic pathway the FAD stage, they split into protons (H+) that does not involve oxygen. Write and electrons. The former takes another down your findings. route out of the chain as the electrons pass through the cytochrome system. 5. Explain the fate of pyruvic acid during respiration. 317 BIOLOGY FORM 5 KIWANDANI.indd 317 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Accordingly, the pathway can be called to form water, this reaction is catalysed the electron transport system. Oxygen is by the enzyme cytochrome oxidase. The the ﬁnal electron acceptor in the electron formation of ATP through the oxidation transport system. Finally, protons and of hydrogen atoms is called oxidative electrons recombine to form hydrogen phosphorylation (Figure 6.13). atoms which create a link with oxygen 2H+ 4H+ 2H+ 3H+ CoQ Cyt Complex Space C V Complex Complex Inner I III Complex Mitochondrial IV Membrane Complex Matrix II NADH NAD+ ½ O2 H2O H+ Succinate Fumarate 2H+ 2H+ ADP + Pi 3H+ ATP + H2O Figure 6.13 Electron transport chain Generally, in the electron transport chain and uses 10 oxygen atoms (5 molecules each reduced NAD molecule results in of oxygen). Moreover, each reduced FAD production of 3 ATP and the release of molecule (from Kreb’s cycle) results in hydrogen which combines with oxygen the production of 2 ATP, hence 2 FAD to form water. Therefore, the 10 reduced molecules produce 4 ATP. Overall, the NAD molecules (2 from glycolysis, 2 electron transport chain produces a total from conversion of pyruvate to Acetyl of 34 ATP molecules from one molecule CoA and 6 from Kreb’s cycle) results in the of glucose (Figure 6.14). production of 30 ATP, 10 water molecules GOFVOERRNONMLEINNTE PURSOEPOENRLTYY ATP ATP NAD+ FADH + H+ Fe3+ Cu+ ½O2 oxidized reduced oxidised reduced H2O NADH+ H+ FAD+ Cytochrome Cytochrome reduced oxidised oxidase Fe2+ reduced Cu2+ oxidised ATP Figure 6.14 ATP produced by NADH and FADH 318 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 318 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration ATP yield in aerobic and anaerobic Thus, the energy released by complete respiration of glucose oxidation of one molecule of glucose is 2880 kJ, the negative ΔG shows that the a) In aerobic respiration reaction can occur spontaneously. A total of 38 ATP molecules are produced for every one molecule of glucose oxidized The amount of energy contained in one completely (Table 6.3). The balanced mole of ATP is 30.6 kJ. The amount of equation for aerobic respiration is: energy contained in 38 moles of ATP is 38 x 30.6 = 1162.8 kJ. The efﬁciency of C6H12O6 + 6O2 ⎯⎯→ 6CO2 + 6H2O + 38ATP energy transfer in aerobic respiration is ΔG = −2880 kJ per mol of C6H12O6 1162.8/2880 x 100% = 40.4 %. Table 6.3 Amount of ATP produced from glucose respired aerobically Respiratory process Number Number ATP Total number of NADH of FADH direct of ATP (x3ATPs) (x2ATPs) formed Molecules Glycolysis: glucose to pyruvate 2 -2 8 Link reaction: pyruvate to Acetyl 2 -- 6 CoA The Kreb’s (TCA) Cycle 6 22 24 10 24 38 Total count GOFVOERRNONMLEINNTE PURSOEPOENRLTYY b) In anaerobic respiration The amount of energy contained in 2 ATP molecules is 2 x 30.6 = 61.2 kJ. During alcoholic fermentation 2 molecules of ATP are produced for every molecule The total energy released during the of glucose used (Table 6.4). Conversion conversion of glucose to lactate is 150 kJ of glucose to ethanol produces 210 kJ per per mole. Thus, the efﬁciency of energy mole, thus the energy contained in the 2 transfer during lactate fermentation is molecules of ATP is 2 x 30.6 = 61.2 kJ. 61.2/150 x 100% = 40.8%. The efﬁciency of energy transfer during alcoholic fermentation is 61.2/210 x 100% The total energy released when glucose = 29.1% molecule is respired aerobically is 38 ATP, but the total energy released in anaerobic Alternatively, in the lactate fermentation, respiration of glucose is only 2ATP. 2 ATP molecules are produced for every Therefore, aerobic respiration is more molecule of glucose used. efficient than anaerobic respiration. Glucose 2Lactate + 2ATP BIOLOGY FORM 5 KIWANDANI.indd 319 319 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Table 6.4 Amount of ATP produced from glucose respired anaerobically Respiratory Number of Number ATP direct Total number of process NADH of FADH formed ATP molecules Glycolysis: glucose to pyruvate 2- 2 2 Respiratory pathway using lipids and GOFVOERRNONMLEINNTE PURSOEPOENRLTYYshould be hydrolysed into amino acids protein which are deaminated to remove the Lipids and proteins are respiratory amino groups. The remaining portions substrates in addition to carbohydrates, enter the respiratory pathway depending which are used by most cells. The on the number of carbons each has. The respiratory pathways for both aerobic portions with 3 carbons are converted and anaerobic process involve the stages into pyruvate; those with 4 carbons form of respiration such as glycolysis, the oxaloacetate while those with 5 carbons are Kreb’s cycle, and electron transport chain. converted into α-ketoglutarate. Example Aerobes use them all, whereas anaerobes aspartate and glutamate enter directly use only glycolysis. Lipids and proteins into the Kreb’s cycle at oxalaoacetate and are not directly accommodated in these α-ketoglutarate respectively. pathways, they are converted in a form to suit the types of the metabolites required Respiratory quotient (RQ) by such pathways (Figure 6.15). Respiratory quotient (RQ) is a measure of the ratio of carbon dioxide evolved by Lipids are polymers of fatty acids and an organism to that of oxygen consumed glycerol. They have to be hydrolysed over a given period of time. into glycerol and fatty acids. Glycerol RQ = Volume of CO2 evolved can be converted into glucose and follow the patterns in glycolysis to the electron Volume of O2 consumed transport chain. The fatty acids join the Kreb’s cycle as fatty acid fragments, each For example, the equation for a complete with 2 carbons that are joined with Acetyl aerobic oxidation of hexose sugar is CoA. The fatty acid will make several represented below: Kreb’s cycles depending on the number of fragments formed. The products of Kreb’s C6H12O6 + 6O2 ⎯⎯→ 6CO2 + 6H2O cycles will add up in generating a huge account of ATP from lipids. RQ = 6CO2 = 1 6O2 Proteins are polymers of amino acids. Amino acids have amino and carboxylic However, it is difﬁcult to have this groups. They also have a varied number of theoretically calculated value, because a carbon atoms. Being polymers, proteins substrate is rarely completely oxidised. 320 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 320 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Gaseous exchange and respiration Glucose Glycogen Fats (Triglycerides) Glycogenesis Lipogenesis Lipolysis Glyconenolysis Glycerol + Free Fatty acids Glucose -6-phosphate Gluconeogenesis Fatty acid Fatty acid synthesis oxidation Glycolysis Phoshpoenolpyruvate Alamine Glycinic Thrconine Cysteine Serine Trptophan Pyruvate Fatty acid fragments Acetyl CoA Acetoacetate Leucine Lysine Oxaloacetate Isoleucine Phenylalanine Citrate Tyrosine Tryptophan Asparagine Asparate Malate Isocitrate Arginine Proline Histidine Thrconine Kreb’s cycle Fumarate α-Ketoglutarate Glutamate Tyrocine Succinate Succinyl CoA Isoleucine Valine Phenylalanine Methionine Threonine GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 6.15 Glucose, lipids and proteins metabolism Signiﬁcance of RQ ii) The carbondioxide produced is a) It helps to indicate the type of substrate used by another process in the same organism, for instance oxidised; for example, the RQ value photosynthesis in plants or of 1.0 implies complete oxidation of formation of calcareous shells in glucose; RQ of 0.7 means oxidation some animals. of fats (fatty acids); and, for proteins, the RQ value varies, but it is around On the other hand, high RQ values imply 0.9. The RQ values of less than one kinds of anaerobic respiration. Therefore, means that oxidation of a mixture of the volume of carbondioxide evolved is substrates. greater than that of oxygen consumed (Table 6.5). b) It helps to indicate the type of metabolism taking place. For example, Examples if RQ values are less than one, the following are possible; a) The equation for respiration of the fat tripalmitin is as follows: i) Aerobic oxidation, as the volume of carbon dioxide evolved is less than that of oxygen taken in. 321 BIOLOGY FORM 5 KIWANDANI.indd 321 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools 2C51H98O6 + 145O2 ⎯⎯→ 102CO2 + 98H2O b) What is the RQ when glucose is What is the RQ for tripalmitin? respired anaerobically to ethanol and Solution: carbondioxide? RQ = Volume of CO2 evolved Solution: Volume of O2 consumed RQ = Volume of CO2 evolved Volume of O2 consumed RQ = 102O2 = 0.7 Since the process is anaerobic, the volume 145O2 of oxygen evolved is zero. So, the RQ value for tripalmitin is 0.7 Thus: RQ = 2CO2 = ∞ (Infinity) 0O2 Table 6.5 RQ values for carbohydrates, lipids and proteins Respiratory substrate Respiratory quotient Type of metabolism Aerobic respiration Carbohydrates 1 Aerobic respiration Aerobic respiration Lipids 0.7 - 0.72 Anaerobic respiration Proteins GOFVOERRNONMLEINNTE PURSOEPOENRLTYY0.8 - 0.9 Carbohydrates or lipids or pro- ∞ teins The basal metabolic rate (BMR) Factors which cause variation of the The basal metabolic rate of an organism BMR of an individual is the minimum rate of energy conversion The following factors inﬂuence the required just to stay alive during rest or variation of basal metabolic rates among sleep. It is actually the amount of energy individuals: needed to maintain body functioning while at rest, to keep the heart beating, blood Body size ﬂowing, food digested and body breathe. Small organisms have larger surface area It also referred to as resting metabolic rate to volume ratio, hence larger BMR than (RMR). In humans, BMR is measured large organisms. after an individual has undergone a standardised rest period of between 12 to Body composition 18 hours of physical and mental relaxation Fat tissue has a lower metabolic activity without taking a meal during that period. than muscle tissue. As lean muscle mass increases, the metabolic rate increases. 322 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 322 10/10/2019 14:07

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Sex GOFVOERRNONMLEINNTE PURSOEPOENRLTYY FOR ONLINE USE ONLY The basal metabolic rate (BMR) of females DO NOT DUPLICATE is lower than that of males. In average the BMR of females is 5 to 10 percent lower Gaseous exchange and respiration than that of males. The difference is that; generally, women possess more body fat Exercise 6.5 and less muscle mass than men of similar size. 1. Write short notes on Respiratory Quotient (RQ). Age The BMR decreases with age (aging). 2. What is Basal Metabolic Rate A decrease in lean muscle mass during (BMR)? adulthood results in a slow, steady decline in BMR. 3. Explain the factors that affect the BMR of an organism. Climate and body temperature The BMR of people in tropical climates is Revision questions generally up to 20 percent higher than their counterparts in more temperate climates 1. How are the lungs adapted to their because it takes energy to keep the body functions? cool. Exercise performed in hot weather also imposes an additional metabolic 2. What is the role of the mucus load. Body fat content and effectiveness secreted by the epithelium lining of clothing determine the magnitude of of the nasal passage? energy metabolism in cold environments; it takes energy to keep the body warm if 3. Describe the internal structure of you work or exercise in very cold weather. the mammalian lungs. Hormonal levels 4. Explain the mechanism of carbon Thyroxine (T4) is the key hormone dioxide transport in the mammalian released by the thyroid glands which blood. has a signiﬁcant effect upon metabolic rate. Hypothyroidism is relatively 5. Describe the respiratory substrates common, especially in women near and their energy value. or after menopause. Everyone with a weight problem should have their thyroid 6. Describe the stages involved in function checked by their doctor and glycolysis. treated appropriately if it turns out to be low. 7. Describe the fate of pyruvic acid under aerobic and anaerobic Healthy status respiration. Fever, illness, or injury may increase resting metabolic rate. Therefore, a sick 8. Explain the events in the electron person has higher rate of metabolism than transport chain during the a healthy person. formation of ATP. 9. Explain why NADH gives more ATP than FADH in the electron transport chain. 323 BIOLOGY FORM 5 KIWANDANI.indd 323 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools 10. Outline the respiratory pathways when using lipids and proteins as substrates. 11. Why does aerobic respiration produce more energy than anaerobic respiration? 12. Explain the factors that affect the rate of respiration in humans. 13. What is the role of oxygen in respiration? 14. Explain why athletes normally face the problem of muscle fatigue. 15. Making bread, beer, wine and cheese are the processes which involve fermentation. Choose one of these products and describe the involvement of fermentation in the process. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 324 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 324 10/10/2019 14:07

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FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Seven Regulation (Homeostasis) Introduction The internal environment of multi-cellular organisms is made up of tissue ﬂuids whose conditions, such as pH, temperature, pressure, glucose concentration and salt contents are always kept at a relatively constant level regardless of the fluctuations of the external environments. The ability to maintain a constant internal body environment enables an organism to survive in a variety of habitats. Keeping a stable internal environment of an organism requires constant adjustments as conditions change inside and outside the cells. Since the internal and external environments of a cell are constantly changing, adjustments must be made continuously to stay at or near the normal level. This regulatory mechanism is called homeostasis. In this chapter, you will learn about the concept of body regulation, temperature regulation, excretion and osmoregulation. You will also learn about the processes through which water content in the body is controlled. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 7.1 The concept of regulation have a control mechanism that keeps their The importance of regulation (homeostasis) internal environment constant, despite the in animals was ﬁrst pointed out by the French changes in external environment. This physiologist Claude Bernard in 1857. In one tendency enables them to exploit a wide of his researches, he used dogs to study the variety of habitats. For example, in human importance of constant internal environment beings, the internal mechanism maintains in mammals. He described variations in constant body temperature of about 37 0C glucose concentration in the blood. His despite the wide range of variation in the study revealed that the concentration environmental temperatures. This constancy of glucose in the blood of mammals enables human beings to be active in remained relatively constant regardless of different environments, while other animals variations in diet. For example, dogs that such as amphibians and reptiles have non- were well fed with food rich in meat or constant body temperature and they cannot sugar had similar glucose concentration be active in a wide range of environmental in the blood as starving dogs. From these temperatures. results, he concluded that mammals must 325 BIOLOGY FORM 5 KIWANDANI.indd 325 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Homeostatic control mechanism GOFVOERRNONMLEINNTE PURSOEPOENRLTYYa set point, stimulus, variables, receptors, The homeostatic control mechanism effectors, inputs, outputs, control centre and involves a regulator which compares compensatory response. These components the actual output with a set point. Then, are integrated to bring about homeostatic it produces some sort of error signal, control (Figure 7.1). A set point is the which sends information to the corrective desired or optimal physiological state for mechanism or effector regarding the the output. It is also known as the norm or difference between the set point and the reference point. This is usually determined actual output. The error signal is usually in genetically in the physiological process. the form of nerve impulses or hormones in In the homeostatic control mechanism the body. The corrective mechanism may variables are factors that are being regulated. include one or more effectors that set the Such factors include body temperature, controlled system and restore the output pH, blood pressure, and plasma potassium to its set point. In some physiological concentration. Anything that produces processes, such as temperature regulation, change on a variable is called a stimulus. separate but coordinated mechanisms Therefore, a stimulus can trigger changes in control deviations in different directions various body parameters such as temperature, from the set point such as the rise or fall pH, blood pressure, and plasma potassium in body temperature, and lead to a greater concentration, resulting into deviation from degree of control. a set point. The detectors or receptors tend to detect a change in variables. The corrective mechanism explained above is said to be the key component of Different types of sensory receptors exist, homeostatic control mechanism. It varies including thermoreceptors which detect the output so that it can be brought back change in body temperature. Input to the set point. Homeostasis is a dynamic communicates the information from the process which works by making continual receptor to the control centre. An example of adjustments to compensate for ﬂuctuations inputs in the homeostatic control mechanism of output. Thus, it is more accurate to is afferent nervous system. Effectors in the describe the homeostatic system as being homeostatic control mechanism are organs in a steady state or in a dynamic equilibrium or glands that carry out the response from rather than being constant. In addition, the control centre. Examples of effectors homeostatic controls can be either extrinsic include: the sweat glands, blood vessels, or intrinsic. Extrinsic control is one which and muscles. The control centre of the originates from outside of the body organ homeostatic control is the brain, particularly or tissue while the intrinsic control is the the hypothalamus. The control centre one which originates from within the body, analyses the information from the receptor organ or tissue. and determines the appropriate response to the change or stimulus. Components of homeostatic mechanism The homeostatic control mechanism The output sends the response instructions consists of different components, including, from the control centre to the effector. 326 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 326 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Regulation (Homeostasis) For example, if the temperature needs to action of the effector which will counteract be lowered, the hypothalamus will send the stimulus and bring the variable back to the information to the effector for the its normal range. response. Compensatory response is the Input - Stimulus Detector Regulator Effector Output - Response Figure 7.1 Components of the homeostatic control mechanism Feedback mechanism for homeostatic GOFVOERRNONMLEINNTE PURSOEPOENRLTYYA change in the state of an internal factor control in the body causes effectors to restore the Any change from the set point activates internal environment to its original state. the control system to initiate a sequence For instance, an increase in the level of of events so as to either restore conditions glucose in the body triggers a sequence towards their normal state, or to make the of events that tend to remove excess system deviate further. Feedback requires glucose from the blood by converting it the action of the system to be related to into glycogen. In contrast, a decrease in a reference point or set-point (optimum the level of glucose in the body causes level) of the variable being controlled. the liver to break the stored glycogen to Two forms of feedback, namely negative glucose in order to supply more glucose and positive feedback are recognised. to the cells of the body. This corrective measure allows blood glucose level to Negative feedback remain constant. This type of system in A negative feedback occurs in a situation which change in the level of an internal where the disturbance in a system sets factor causes a corrective mechanism is in motion a sequence of events which referred to as a self-adjusting system. The tends to restore the system to its original science of a self-regulating control system state. A negative feedback in homeostatic which operates via feedback mechanisms control mechanism keeps a variable, in organisms is known as cybernetics. such as the blood glucose level close to a particular value or set point (Figure 7.2). BIOLOGY FORM 5 KIWANDANI.indd 327 327 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Low blood sugar High blood sugar Pancreas Low level of sugar in the blood High level of sugar in the promote glucagon release from the pancreatic alpha cells blood stimulate beta cells of Glucagon pancreases to secrete insulin Insulin Tissue cells Glucagon stimulates glycogen Insulin stimulate breakdown into glucose in the tissue cells to take liver cells up glucose from the blood Liver Glycogen Glucose Raises blood sugar level Lowers blood sugar level Figure 7.2 Glucose and insulin negative feedback loop Positive feedback GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Further excess Positive feedback is the self-regulatory mechanism which operates when the Positive feedback system is deviated from a set point which Excess initiates a sequence of events that tends to deviate further the system. The positive Set point feedback mechanism makes the system to be unstable; that is why it is not common in Deficiency Positive feedback living organisms. An example of positive Further deficiency feedback occurs during labour, when the hormone oxytocin stimulates muscular Figure 7.3 A positive feedback mechanism contraction of the uterus; which in turn stimulates the release of more oxytocin. Another example of positive feedback Positive feedback mechanism may also mechanism is the release of volatile occur in the nerves where a small stimulus plant hormone (ethylene) by the ripening can bring about a large response to the fruits that accelerates the ripening of effectors (Figure 7.3). unripe fruits in its vicinity. The fruit ripening process involves changing the fruit texture, softening, and colour. As more fruits get ripe they produce more hormones that further continue to ripen more the surrounding fruits. 328 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 328 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Regulation (Homeostasis) Activity 7.1 Investigating the effect of positive feedback mechanism in ripening fruit Materials One bunch of ten unripe green bananas, six containers, and dry banana leaves. Procedure a) Label the six containers from A to F. b) Isolate five bananas from the bunch and put one banana in each of the five containers labelled B to F. c) Put the remaining five undetached bananas in the container labelled A. d) Cover all the containers with dry banana leaves and arrange them in series; starting with the one with five bananas. The distance from one container to another should be not less than one meter (Figure 7.4). e) Note the number of days it will take for all bananas in all containers to get ripe. A B GOFVOERRNONMLEINNTE PURSOEPOENRLTYYC D E F Figure 7.4 Experimental set up for ripening of fruits Questions 1. Compare the time taken for the bunch and individual bananas to ripen. 2. What might be the cause of the differences in ripening time? 3. Explain the significance of the phenomenon in our everyday life. Exercise 7.1 1. Brieﬂy explain the concept of regulation (Homeostasis). 2. Describe the components of the homeostatic control mechanism. 3. Explain the feedback mechanisms for homeostatic control. 4. Give a physiological example of a negative feedback control system and clearly describe how it works. 329 BIOLOGY FORM 5 KIWANDANI.indd 329 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools 7.2 Temperature regulation GOFVOERRNONMLEINNTE PURSOEPOENRLTYYphysiological control mechanisms as well Most organisms can survive in a narrow as behavioural mechanisms. range of temperature from 10 °C to 30 °C. In order to survive, most animals have Adaptation of endotherms to cold and to regulate their body temperature. The hot climatic conditions tendency of animals to adjust their body In order to survive in a variety of habitual temperature to suit the living conditions of environment, species of mammals varying temperatures in the environment have developed various physiological is termed as temperature regulation adaptive features or mechanisms. This (thermoregulation). Animals with a diversity of living environment include varying body temperature according to the the hot arid environment of the desert, changes in the environmental temperature the colder and glacial environment of are called poikilotherms (poikilos means the Arctic and Antarctic poles, the salty ‘various’ and thermo means ‘heat’). These environment of the oceans, low oxygen animals obtain most of their body heat environment of mountain peaks and the from the sources outside their bodies; dark environments of the deep sea and hence they are sometimes referred to as oceans. Animals in the cold environment ectotherms. Examples of poikilothermic such as arctic fox have insulating layers organisms include reptiles, amphibians with a thick coat of fur or thick layer of and most fish. With exception of birds and fat that help to reduce the rate of heat mammals, most animals are ectotherms. transfer thereby retaining body heat and keeping the animal’s body temperature Animals that maintain a stable body at constant level. Another strategy of temperature regardless of ﬂuctuations cold weather used by some animals is a in the environmental temperature are temporary decrease of metabolic rate and called homoiotherms or homoeotherms body temperature. This helps to decrease or homeotherms. Their heat is generated the temperature difference between the internally by metabolic activities; hence, animal body and the environment thereby they are also known as endotherms; and minimizing heat loss. they include mammals and birds. The body temperature of endotherms ranges Other adaptations for survival of animals between 37 °C and 44 °C. The higher such as bears in the extreme cold climate the body temperature, the greater the include: hibernation during the cold metabolic rate in the animal’s body. For period. The body temperature falls to a example, birds have higher metabolic rate few degrees and an animal falls into a deep to cater for the energy needed for ﬂight. sleep. This tendency enables the animal to Their body temperature ranges between conserve energy. 38.5 °C and 44 °C. Homoeotherms can regulate their body temperature through In the hot and dry environment, endotherms negative feedback control. They control develop cooling mechanism by means their body temperature independently of evaporation of water across their of the environment; they use internal respiratory surfaces or across the skin 330 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 330 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Regulation (Homeostasis) through sweat glands. Animals with fur GOFVOERRNONMLEINNTE PURSOEPOENRLTYYfour major components: the set point, such as cattle, dogs, and birds have limited detector, comparator or regulator, and ability to sweat; therefore, they rely on corrective mechanism. First, the set point panting to increase evaporation of water is the favourable skin temperature or across the moist surface of their tongue the temperature at which an individual and mouths. feels comfortable and relaxed. Second, the detectors are the thermo-receptors Another adaptation to the hot environment in the skin containing heat and cold is the possession of long loops of Henle of receptors, which are responsible for the kidney. This enables animals to produce detecting increase and decrease in the super-concentrated urine that helps to skin temperatures respectively. Third, conserve water. This tendency is common the comparator is the cortex of the brain for the desert dwellers such as kangaroo which is responsible for controlling rats, and camels. Most small animals with conscious thoughts and feelings. Thus, high surface area to volume ratio usually if the affected individual feels too cold face major difﬁculties in overcoming high or too hot can decide to take appropriate temperatures. Therefore, they remain in action, either to move to a cooler or burrows during the day when it is hot and warmer place, remove or add more come out at night when it is cool. This clothes or take other appropriate voluntary nocturnal tendency enables small animals actions that may help to bring the skin like rodents to survive in extremely hot temperature back to favourable state. The climates. Some mammals that live in error signals are sent to voluntary skeletal deserts have special adaptations in their muscles through nerve impulses. Fourth, kidneys and sweat glands that allow them corrective mechanisms are initiated to survive when only very small amounts through behavioural responses. of water are available to them. In regulating the body’s core temperature, Regulation of body temperature in actions are involuntary, controlled by endotherms internal physiological responses. The Endotherms have developed a variety of set point of the homeostatic control adaptive mechanisms for maintaining mechanism is the mean body temperature a constant or stable body temperature. (36.7 °C or 37 °C) which is genetically The adaptation for balancing heat determined. In this system, the sensor and gain and heat loss may be anatomical, control centre for body temperature are behavioural, or physiological. The located in a small part of the brain called process of controlling body temperature the hypothalamus which is sensitive to in endotherms falls under two homeostatic temperature ﬂuctuations. It possesses two systems, namely regulation of skin thermoreceptors, namely the heat loss and temperature and regulation of the body heat gain centres. The heat loss centre core temperature, which includes vital is located in the anterior hypothalamus organs of the body and the brain. The and is activated by increase in blood regulation of skin temperature involves temperature; where as heat gain centre 331 BIOLOGY FORM 5 KIWANDANI.indd 331 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools is located in the posterior hypothalamus GOFVOERRNONMLEINNTE PURSOEPOENRLTYYsurface. In cold environments, the blood and is activated by decrease in blood flow in the body escapes the skin through temperature. the shunt vessels, resulting into reduction in heat loss. Just a small amount of blood On the other hand, if the body core passes into the skin to keep the tissue temperature rises to above 40 °C, the alive. homeostatic control mechanism breaks down and positive feedback takes place. b) Sweating This causes a person to go into a state called Human beings have the ability to control hyperthermia. The patient experiences a body temperature through sweating very weak pulse rate, becomes excessively because their skins are not covered by irrational, and sluggish. If the situation is fur or feathers. They have sweat glands not controlled, the patient may go into a over the whole body that enable them coma and death may occur. to be more efﬁcient at cooling through sweating. The human being can produce Maintenance of a constant body about 1000 ml of sweat per hour. Animals temperature in warm environments with fur have limited sweat glands which When the environment is overheated, are conﬁned to areas that do not have fur, the animals use the following adaptive for example pads of the feet in dogs and mechanisms to overcome the effects of cats. Animals with feathers such as birds overheating. lack sweat glands. Their skins are covered by feathers which prevent evaporation a) Vasodilation through the skin (evaporation occurs from This is an increase in the diameter of the surface of their lungs and air sacs). superﬁcial blood vessels near the body surface caused by nerve signals, resulting c) Panting and licking into the relaxation of the vessel’s walls. In animals with few or no sweat glands The blood in the capillaries in the skin such as dogs and birds, cooling by may take three alternative routes; through evaporation takes place through the mouth capillaries close to the skin surface, in and the nose. Dogs hang out their tongues; the dermis, and beneath the layer of this may result in an increase of breathing subcutaneous fat. In warm climates, rate and excessive removal of carbon superﬁcial arterioles dilate in order to dioxide from the blood thereby reducing allow blood flow close to the skin surface. heat from the body. Some animals lick Heat from the blood is rapidly conducted their bodies to deposit saliva onto their through the epidermis to the skin surface body surfaces, which provide similar from where it is radiated away from the means of evaporative cooling. Licking body. Rise in blood pressure within the is common to some animals that do not capillaries cause them to dilate, that sweat, instead they make use of saliva to facilitate heat loss due to radiation, cool their bodies. For example; rabbits convection and conduction resulting into lick their front legs and chests, cats lick an increase of blood flow near to the skin inside of their front paws and spread the 332 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 332 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Regulation (Homeostasis) saliva across their ears and face, rats lick usually takes place during winter season, their testicle, and kangaroos lick their fore which sometimes is referred to as winter arms and wrists. dormancy. d) Use of body extremities GOFVOERRNONMLEINNTE PURSOEPOENRLTYYWinter dormancy is associated with When compared to related species from reduced body metabolic rate, low body cold climates, animals in warm climates temperatures, slow breathing and low usually have large extremities such as heartbeat rate. The animal appears to be ears and large bushy tail. They are well in a deep sleep for several days, weeks supplied with blood vessels and covered or months depending on the species. by relatively short hairs, making them This helps to conserve energy, especially good radiators of heat. during winter when food is scarce. Before entering hibernation, most animals eat e) Large surface area to volume ratio a large amount of food and store energy Animals with a large surface area to in fat deposits to survive the winter. volume ratio (relatively small animals) Hibernation can also take place during lose energy (temperature) faster than those the hottest period or summer. This state is with smaller surface to volume ratio. To called aestivation or summer dormancy. compensate for this, small animals such Some animal species that aestivate as mice feed more frequently compared include reptiles. The arousal of an animal to large animals such as lions. The former from hibernation state usually occurs animals also tend to utilize an energy - spontaneously. It is driven by some internal rich diet such as nuts rich in lipids. mechanisms. External stimuli often fail to wake the hibernating or aestivating f) Behavioural mechanisms animal, making it subject to predation if it Many desert animals regulate their is discovered by its enemies. body temperature by using different behavioural mechanisms. For example, g) Insulation some animals such as mice and hedgehogs This is provided by a layer of fur or fat that avoid heat by sheltering under the rocks protects or blubs the body against changes or by burrowing in the soil during drought in the environmental temperature. The season. Others, like bat avoid hottest thick coat of fur is called insulator while periods by being nocturnal, a tendency of the thick layer of fat is called blubber. being active during the night and inactive The insulator or blubber layer helps during the day. This minimises the rate retain body heat and keeps the animal’s of body metabolic activities during the body temperature constant. Animals day and increases at night. Some animals in the warm climates usually have fur like rodent, ground squirrels and bears with light colours to enhance sun rays’ hibernate during cold temperatures. reﬂection and thereby minimising heat Hibernation is the behavioural state where gain and accelerating heat loss from the by an animal becomes inactive, both body. During this process, the hair erector during the day and at night. This tendency muscles in the skin are relaxed and the fur 333 BIOLOGY FORM 5 KIWANDANI.indd 333 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools lies close to the skin surface. This causes GOFVOERRNONMLEINNTE PURSOEPOENRLTYYmetabolic rate; hence, additional heat the thickness of insulating warm hair to is produced in the body. The increased be reduced, and therefore, the body heat is metabolic rate of the body requires readily dispersed. increased food consumption; that is why animals feed on large amount of food in Maintenance of a constant body cold climates. temperature in cold climates Endotherms living in cold environment Temperature regulation by ectotherms and those in hot climates experiencing cold Ectotherms regulate their body weather have the following adaptations temperature mainly by behavioural means, which enable them to maintain constant depending on external heat sources; since body temperatures: these organisms do not have temperature control center like endotherms. The a) Vasoconstriction exchange is controlled by three factors When the animal is subjected to cold which are; radiation, conduction and conditions, the superﬁcial arterioles are flow. Their body temperature rises and constricted. This reduces the quantity of falls along with the temperature of the blood reaching the skin surface. Much surrounding environment. Although they blood passes beneath the insulating layer generate metabolic heat like endotherms, of subcutaneous fat; therefore, little heat they cannot increase heat production to is lost to the outside. maintain an internal body temperature. Most of the adjustment mechanisms are b) Shivering by behavioural means such as: huddling, In cold conditions, the skeletal muscles hibernation, burrowing, aestivation, of the body may undergo rhythmic clustering, migration, and exposing involuntary contractions which increase themselves to the sun in hot environment. the amount of heat produced in the body. a) Huddling c) Insulation In cold regions, animals are usually active It is achieved by an external covering of during the day. Huddling of individuals fur or feathers and or an internal layer is also another common way of reducing of subcutaneous fat. Their thickness is heat loss. Some animals are able to crowd related to the intensity of coldness to that together in a tightly packed group to keep environment. It is an effective means of them warm and reduce much heat loss reducing heat loss from the body. when an individual animal is exposed to cold open air.Therefore, this is also a d) Increased metabolic rate means of conserving heat. During cold conditions, the liver increases its metabolic rate. There is also increased b) Hibernation activity of the adrenal, thyroid, and Some animals in cold climates undergo pituitary glands resulting into secretion of a period of long sleep. During this time, hormones that help to increase the body the metabolic rate is reduced 20-100 334 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 334 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Regulation (Homeostasis) times below normal which consequently GOFVOERRNONMLEINNTE PURSOEPOENRLTYYSome ectotherms have developed some reduces food and oxygen utilisation. chemical processes to survive the cold. These animals, such as chorus frogs, c) Sun basking and gray tree frogs endure the cold by Ectothermic animals may use radiant heat undergoing chemical changes to prevent provided by the environment to warm their tissues from freezing. Other animals their bodies. Solar radiation is the most such as wood frog can tolerate and regulate common way, as many ectotherms use a frozen state by changing the chemical the sun’s rays to warm up their bodies. composition of their blood to a sugary state Reptiles and some amphibians bask in the that helps them avoid freezing. sun with their bodies spread out to increase the surface area for heat absorption. When Exercise 7.2 it is too hot, they hide in the shade or near water bodies; allowing their bodies to 1. Explain the mechanisms of cool. temperature regulation in endothermic organism. d) Clustering Some animals exhibit group behavioral 2. Show the role of the hypothalamus in mechanisms to regulate their body temperature regulation. temperatures. A good example is how honey bees cuddle together in large 3. Describe the adaptations of mammal groups to retain and generate heat. A to cold and hot climatic conditions. similar example is how some gregarious caterpillars bask in the sun in large groups 7.3 Excretion to gather heat. The maintenance of homeostasis in animals involves osmoregulation or e) Burrowing balancing the levels of water and salt in Some ectotherms burrow themselves and the body. It also involves the removal of hide deep in the ground. This helps them metabolic wastes from the body through to survive in cold environments. excretion; the process by which metabolic waste is eliminated from an organism’s f) Aestivation body. In vertebrates, this is primarily Some ectothermic animals like earthworms, carried out by the lungs, kidneys and skin. snails, frogs, crocodiles, lizards, and tortoise maintain their body temperature by Signiﬁcance of excretion reducing body metabolic activities and It is important that living organisms must protecting themselves from very high get rid of excretory wastes from their temperature. During summer time, some bodies, because the removal of wastes animals usually tend to rest in shady or prevents unbalanced body’s chemical cool places. Normally, they take a sleep equilibria. Moreover, it is a means for during the hot hours of daytime as a means removal of toxic wastes which, if allowed of avoiding environmental stress. 335 BIOLOGY FORM 5 KIWANDANI.indd 335 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools to accumulate, inhibit action of many GOFVOERRNONMLEINNTE PURSOEPOENRLTYYanimals whose gills or body surface are in enzymes involved in metabolic pathways. direct contact with water. These animals Consequently, this will lead to failure in are called ammonotelic. many physiological processes. Excretion also helps to regulate water content of the Urea. Animals like sharks, adult body ﬂuids. Excretory nitrogenous wastes amphibians, and mammals usually are removed from the bodies of living excrete urea as their nitrogenous waste. organisms in a form which is determined Urea is a much less toxic, and less soluble by the availability of water. The pH of than ammonia. It can be excreted in a blood is regulated by excretion. For moderately concentrated solution. This example, organisms tend to excrete ions elimination strategy allows body water such as hydrogen ions (H+) and hydrogen to be conserved, an important advantage carbonate ions (HCO3-) which have major for terrestrial animals with limited access inﬂuence on pH. to water. The animals in this group are termed as ureotelic. Major excretory products in animals The major excretory products in animals Uric acid. Uric acid is not toxic and it is are nitrogenous compounds such as urea, insoluble in water. Poor solubility is an ammonia, and uric acid from breakdown advantage if water conservation is needed. of proteins and nucleic acids, carbon Uric acid can be concentrated even more dioxide from cellular respiration and bile readily than urea can. Uric acid is usually pigments from breaking down of worn out excreted by insects, reptiles, and birds, red blood cells in the liver. these are collectively termed as uricotelic animals. Nitrogenous waste products Breakdown of nitrogen containing Kidney position, structure and molecules such as amino acids results in functions in human body excess nitrogen that must be removed from Kidneys are paired bean-shaped organs the body. When amino acids are broken found on each side of the back of the lower down by the body to generate energy or portion of the abdominal cavity (Figure converted into fats or carbohydrates, the 7.5). The larger left kidney is located a bit amino (NH2) group must be removed higher than the right kidney. Unlike other because they are not needed, and they organs found in the abdomen, kidneys are may be toxic. This excess nitrogen may located behind the lining (peritoneum) be excreted in the form of ammonia, urea, of the abdominal cavity. Thus, they are or uric acid. considered retroperitoneal organs. These bean-shaped organs are protected by the Ammonia. Ammonia is quite toxic back muscles and the ribs as well as the fat and highly soluble; hence it can be a (adipose tissue) that surrounds them like nitrogenous excretory product if sufﬁcient a protective padding. Located above each water is available to wash it from the body. kidney is an adrenal gland which secretes It is excreted by most ﬁsh and other aquatic adrenaline hormone. For each kidney, the 336 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 336 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Regulation (Homeostasis) renal artery supplies blood which a renal through the urethra. The exit from the vein returns to the vena cava. The ureter bladder is controlled by a sphincter (a ring removes urine produced by the kidney, of muscles). transfering it to the urinary bladder for temporary storage, before being released Right adrenal gland Aorta Right kidney Left renal artery Left renal vein Vena cava Left ureter Urinary bladder Sphinter Urethra Figure 7.5 Human urinary systemGOFVOERRNONMLEINNTE PURSOEPOENRLTYY The bean-shaped kidneys have an outer contains parts of the nephrons, glomeruli convex side and an inner concave side and capsule, while the medulla contains called the renal hilus. A transverse section tubular part of the nephrons and blood (T.S) of the kidney reveals an outer part vessels, forming the renal pyramids called cortex and an inner part called which project into the pelvis, leading to medulla. A thin connective tissue called the ureter. Kidneys are well supplied by fibrous capsule surrounds each kidney. blood vessels, forming a network of blood This capsule maintains the kidneys’ shape capillaries (Figure 7.6). and protects the inner tissues. The cortex BIOLOGY FORM 5 KIWANDANI.indd 337 337 10/10/2019 14:08

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Biology for Advanced Level Secondary Schools FOR ONLINE USE ONLY Nephron DO NOT DUPLICATE Renal cortex Collecting duct Capsule Minor calyx Renal medulla Major calyx Renal pyramid Renal pelvis Renal papilla Renal artery Renal vein Blood capillaries Venule Arteriole Ureter GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Figure 7.6 Transverse section through the mammalian kidney General functions of the kidneys c) Blood pressure regulation Kidneys are multifunctional organs, some The kidneys need constant pressure to core functions of the kidneys include: ﬁlter the blood. When it drops too low, the kidneys increase the pressure. One way is a) Excretion by producing a blood vessel constricting Kidneys ﬁlter out toxins, excess salts, protein, angiotensin, which also signals and nitrogenous wastes created by cell the body to retain sodium and water. Both metabolisms. Urea is synthesised in the constriction and retention help restore liver and transported through the blood to normal blood pressure. the kidneys for removal in urine. b) Water balance d) Red blood cell regulation As kidneys are key in the chemical When the kidneys do not get enough breakdown of urine, they react to changes oxygen, they send out a distress call in in the body’s water level every minute. As the form of erythropoietin; a hormone that water intake decreases, the kidneys adjust stimulates the bone marrow to produce accordingly and leave water in the body more red blood cells. This process is instead of helping to excrete it. called erythropoiesis. 338 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 338 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Regulation (Homeostasis) Table 7.1 Summary of parts of the kidney and their functions Parts of the kidney Description Renal hilus An indentation near the centre of the concavity of the kidney where the Renal capsule renal vein and ureter leave the kidney and the renal artery enters the kidney. A tough, fibrous membrane, surrounding the kidney. It consists of dense, irregular connective tissues which protect and help to maintain the kidney’s shape. It is also surrounded by fatty tissue which helps to protect the kidney from damage. Renal cortex The outer reddish part of the kidney that has a smooth texture; it is where the Bowman’s capsule, glomeruli, proximal and distal convoluted tubules and blood vessels are found. Renal medulla The inner striated red-brown part of the kidney. Renal pyramids Stripped, and triangular in structure within the medulla, which are made Renal pelvis of straight tubules and corresponding blood vessels. Renal artery The funnel-shaped cavity that receives urine drained from the nephrons through the collecting ducts and papillary ducts. The blood vessel that delivers oxygen- rich blood to the kidney; it enters the kidney through the hilus and divides into smaller arteries, which separate into afferent arterioles that serve each of the nephrons. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Renal vein The blood vessel that receives deoxygenated blood from the kidney and returns it to the systemic circulation. Afferent arteriole The blood vessel that delivers oxygen-rich blood to the glomerulus Efferent arteriole under high pressure. Kidney nephrons Collecting duct The blood vessel that receives oxygenated blood from the glomerulus. The functional units where the kidney’s main functions are performed: There are about a million nephrons in each kidney. This part of the kidney nephron collects urine and drains into papillary ducts, minor calyx, and major calyx, and ﬁnally into the ureter and urinary bladder. Ureter The tubular structure which conveys urine from the pelvis of the kidney to the urinary bladder. BIOLOGY FORM 5 KIWANDANI.indd 339 339 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools e) Regulation of pH of the blood needed molecules to the blood. The most Kidneys excrete hydrogen ions into primitive nephrons (pronephros) are found urine. At the same time, they conserve in the kidneys of primitive fish, amphibian bicarbonate ions which are an important larvae, and embryos of more advanced buffer of hydrogen ions. vertebrates. The nephrons found in the kidneys of amphibians and most fish, f) Regulation of the ionic composition and in the late embryonic development of blood of more advanced vertebrates, are only slightly more advanced in structure Kidneys regulate the quantities of ions (mesonephros). The most advanced in the blood. Important examples of nephrons occur in the adult kidneys, or ions whose quantities are regulated by metanephros of land vertebrates, such as the kidneys include sodium, potassium, reptiles, birds, and mammals. calcium, chloride and phosphate ions. g) Synthesis of vitamin D GOFVOERRNONMLEINNTE PURSOEPOENRLTYYThere are two types of nephrons, namely Kidneys are involved in the synthesis cortical nephrons, (which are found deep of calciferol, which is an active form of in the renal cortex) and the juxtamedullary vitamin D. nephrons, which make up about 15 percent of total nephrons and lie close to The nephron the medulla. The nephrons consist of a The nephron is the kidney’s functional unit renal corpuscle, a tubule, and a capillary that is involved in production of urine in network. These originate from the small the process of removing waste and excess cortical arteries. Each renal corpuscle is substances from the blood. Generally composed of a glomerulus (a network of nephron is responsible for the filtration, capillaries) and a Bowman’s capsule (the excretion and re-absorption of most of the cup- shaped chamber that surrounds it). water and other materials. Each kidney The Bowman’s capsule connects to a long has more than a million nephrons in the convoluted renal tubule which is divided renal cortex, which gives it a granular into three functional parts. These consist appearance on sagittal section (Figure of the proximal convoluted tubule, the 7.7). Nephrons are used to separate water, loop of Henle (nephritic loop) with its ions and small molecules from the blood descending and ascending limbs, and the molecule, and filter out wastes and toxic distal convoluted tubule, which empties materials, then it selectively returns the into the collecting ducts. 340 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 340 10/10/2019 14:08

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Efferent arteriole FOR ONLINE USE ONLY DO NOT DUPLICATE Afferent arteriole Regulation (Homeostasis) Glomerular Distal convoluted capillary Bowman’s capsule tubule Collecting duct Branch of renal artery Proximal Branch of renal vein convoluted tubule Loop of Henle Descending limb Ascending limb GOFVOERRNONMLEINNTE PURSOEPOENRLTYYFigure 7.7 Structure of the mammalian nephron The collecting ducts fuse together and vessels) from the small ones (which pass enter the papillae of the renal medulla. into the renal tubule). Therefore, it is a site for ultra-ﬁltration; that is pressure Urine passes through the renal medulla filtration. This pressure is known as as a ﬂuid with high sodium content and hydrostatic pressure, and it stems from leaves through the renal papillae, into the blood pressure. Thus, the blood brought renal calyces, the renal pelvis, and the into the glomerular capillaries by the bladder through the ureter. afferent arteriole is pumped by the heart at high pressure; which rises as the blood The outer layer of the Bowman’s capsule leaves the wide arteriole and enters the is composed of squamous epithelial cells. narrow capillaries. The inner layer is composed of specialised cells that allow easy passage of molecules, The structures of the glomerulus and and the glomerulus consists of endothelial Bowman’s capsule is adapted for ﬁltration cells with fenestrae (pores). The renal in that, endothelial layers of glomerulus corpuscle acts as an ultra-ﬁltration unit, are very thin and have many pores to ﬁltering the blood and separating the allow the passage of a glomerular ﬁltrate. larger particles (which stay in the blood A network of ﬁbres such as collagen 341 BIOLOGY FORM 5 KIWANDANI.indd 341 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools ﬁbres, with spaces between them, allows b) They have numerous mitochondria the passage of small solute molecules in to supply energy which is constantly the ﬁltrate. They restrict the passage of needed for active uptake of substances blood cells that are larger than the pores. from the ﬁltrate. Large molecules such as proteins are also restricted from passing through and are c) Their basement membranes are very repelled by the negatively charged ﬁbres. close to the endothelial lining of Moreover, the epithelial layer of the blood capillaries to ensure fast uptake Bowman’s capsule contains podocytes, and efﬁcient transportation of the the highly modiﬁed ﬁltration cells. These reabsorbed substances back into the have extensions which interact to form body. ﬁltration slits or pores to allow the passage of the glomerular ﬁltrate. d) Channel proteins are present for transportation of substances like The proximal convoluted tubule are mainly amino acids and ions from the cells concerned with selective reabsorption so of the proximal convoluted tubule, to that valuable substances such as glucose the spaces between these cells and the are taken back to the blood but not lost basal channels. in the urine. The cells of the proximal convoluted tubule are adapted for re- e) At the base of the microvilli, small absorption as follows: proteins from the renal ﬂuid are removed by the process of pinocytosis. a) They have numerous microvilli and The proteins are then enclosed in basal channels which increase the pinocytic vesicles and are ﬁnally surface area for the absorption process. broken down by hydrolytic enzymes from the lysosomes (Figure 7.8). Afferent arteriole Efferent arteriole GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Capillary showing pore Capillaries of the glomerulus Podocyte Squamous epithelial cells of Filtration silts Bowman’s capsule Basement membrane Glomerular filtrate Microvilli Basement membrane Cells of proximal convoluted tubule Endothelium of blood capillary Space between epithelial cells Tight junction BLOOD Microvilli GLOMERULAR FILTRATE Infolding of cell surface Epithelial cell of proximal membrane forming base convoluted tubule channels Reabsorption Figure 7.8 Structure and function of renal corpuscle and proximal convoluted tubule 342 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 342 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Regulation (Homeostasis) The loop of Henle acts as a counter current GOFVOERRNONMLEINNTE PURSOEPOENRLTYYcompounds combine with carbon dioxide exchange mechanism creating a low water (CO2) gas from respiration in a solution potential (high solute content) in the form (ammonium ions and bicarbonate medulla of the kidney so that water can be ions respectively) resulting into the reabsorbed by osmosis. The descending formation of carbamoyl phosphate, by the limb has a thin membrane which is freely help of the enzyme carbamoyl phosphate permeable to water and impermeable synthetase-I. The reaction occurs in to salts and urea. The thick ascending the mitochondria of the liver cells, and limb has numerous mitochondria which requires 2 ATP molecules. provide energy for active uptake of sodium chloride and other ions from the renal b) Synthesis of citrulline ﬂuids back into the interstitial regions of The carbamoyl phosphate formed in the medulla. the ﬁrst step enters the ornithine cycle and combine with ornithine resulting in The distal convoluted tubule and collecting the synthesis of citrulline, aided by an ducts are concerned with osmoregulation; enzyme citrulline synthase or ornithine varying the amount of water reabsorbed transcarbamoylase. In the reaction the into the blood. The cells of the distal phosphate group is released. Citrulline convoluted tubule have a similar structure can easily pass through the mitochondrial to those of the proximal convoluted tubule, membrane, thus it diffuses from the with microvilli lining the inner surfaces to mitochondrion into cytosol (cytoplasm) increase the surface area for absorption, of liver cells. and numerous mitochondria to supply energy for active transport. c) Synthesis of argininosuccinate In the cytosol, citrulline combines with Formation of urea in mammals the amino group of aspartate under Urea is the nitrogenous waste product of condensation reaction catalyzed by humans and other land living mammals. enzyme argininosuccinate synthetase The body is unable to store excess to form argininosuccinate. It requires amino acids taken in the diet. Those not ATP which is hydrolysed to adenosine immediately needed for protein synthesis monophosphate (AMP) resulting in the or making sugar must be removed by utilization of two high energy bonds. the process called deamination, which is Magnesium ions (Mg2+) act as cofactors. followed by urea formation in the liver This reaction incorporates the second cells. The process of urea formation nitrogen from aspartate. occurs in the urea cycle which is also called ornithine cycle (Figure 7.9) and d) Cleavage of argininosuccinate involves the following stages: The cleavage of arginisuccinate involves the enzyme argininosuccinase, an a) Formation of carbamoyl phosphate intermediate enzyme in the urea synthesis Before the cycle, ammonia (NH3) from pathway whose function is imperative metabolism of nitrogen containing to the continuation of the cycle. It acts 343 BIOLOGY FORM 5 KIWANDANI.indd 343 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools reversibly to cleave argininosuccinate into semi-essential amino acid. Though it is a free arginine and fumarate. The arginine synthesised in the body, it is not available continues with the cycle in the other stage, for protein synthesis. Ornithine is whereas fumarate enters the Tricarboxylic regenerated in this step and the urea cycle Acid (TCA) cycle, which is also known completes by the formation of urea. The as Kreb’s cycle. The linkage between ornithine produced is transported back to TCA cycle and urea cycle is known as the the mitochondria to start the cycle again Kreb’s bi- cycle. while urea is transported to the kidney through blood vessels to be excreted. e) Cleavage of arginine Thus the urea cycle brings two amino Arginine is hydrolysed into ornithine and groups (NH2) and hydrogen carbonate ions urea under the inﬂuence of the enzyme (HCO3-) together to form urea. arginase; hence, arginine is known as a Co2+NH3 Citrulline Aspartate 2ATP Pi + AMP Pi H2O ATP AMP + Pi Carbamoyl phosphate Argininosuccinate Ornithine UreaGOFVOERRNONMLEINNTE PURSOEPOENRLTYY H2O Arginine Fumarate Figure 7.9 The Ornithine cycle Urinary disorders in human in the blood resulting into kidneys’ failure The urinary tract consists of the kidneys, to expel it via urine. The end products ureters, bladder and urethra. Urinary of protein metabolism accumulate in disorders include any infections or the blood but are normally ﬁltered out conditions that affect any of these parts when the blood passes through the of the urinary system or their functions. kidneys. However, urea accumulation The following are some of the common in the blood is comparatively high in urinary disorders in human beings: uremia victims. In such patients, urea can be removed by the process called a) Uremia haemodialysis. However, there are still This condition results from toxic effects some complications that affect people on of abnormally high concentrations of urea 344 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 344 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Regulation (Homeostasis) dialysis such as cardiovascular problems the thigh or the testicle or vulva on that and severe itching from the imbalance of side. The best way to prevent most kidney minerals in the body. stones is to drink enough fluids every day. b) Renal failure (RF) or kidney failure d) Urinary tract infections (UTI) Renal failure is a decrease or cessation In humans, UTI is caused by the invasion of glomerular ﬁltration in humans (it of microorganisms, usually bacteria, is a partial or complete loss of kidney into the urethra and bladder. The most function). Kidney failure can be either common UTI cases that affect the bladder acute or chronic. In acute renal failure and urethra are: (ARF), both kidneys abruptly stop working. The main feature of ARF is Infection of the bladder (cystitis). This either oligouria (scanty urine production) type of UTI is usually caused by bacteria, in which the daily urine output is less normally Escherichia coli (E. coli); a than 250 ml or anuria in which daily urine type of bacteria commonly found in the output is less than 50 ml. The causes of gastrointestinal tract (GIT). All women renal failure may be low blood volume are at risk of cystitis because of their (atherosclerosis), decreased cardiac anatomy, specifically the short distance output, damaged renal tubules, kidney from the urethra to the anus and the stones, nephritis, and some excessive use urethral opening to the bladder. of antibiotics. The effect of renal failure includes oedema, that is accumulation Infection of the urethra (urethritis). This of excess ﬂuids in various parts of the type of UTI can occur when GIT bacteria body which results into swelling of legs. spread from the anus to the urethra. Also, Also, the potassium level rises, leading to because the female urethra is close to the failure to produce enough erythropoietin vagina, sexually transmitted infections for adequate red blood cells production, such as herpes, gonorrhea, chlamydia and hence anaemia. mycoplasma can cause urethritis. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY c) Kidney stones (renal calculi) The infection of the urinary tract can Concentration of mineral and organic result into either minor or major illnesses. matter that forms in the kidneys results For example, an attack of cystitis- into small particles called stones. These inﬂammation of the bladder may cause may become too large, hence impairing only minor illness. The attack of the renal the normal renal function. Urine contains system is characterised by frequent and many salts in solution. If the concentration painful urination. Other complications of these mineral salts becomes excessive, involve: recurrent infections; especially the excess salts precipitate as crystals in women who experience twice or more that may enlarge to become visible solid UTI cases in a six-month period within a particles called stones. Such stones give year and permanent kidney damage from rise to severe colic pain starting in the twice acute or chronic kidney infection back and radiating down to the front of (pyelonephritis) due to an untreated UTI. 345 BIOLOGY FORM 5 KIWANDANI.indd 345 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Likewise, pregnant women get a risk of GOFVOERRNONMLEINNTE PURSOEPOENRLTYYby deﬁciency of vasopressin hormone delivering low birth weight or premature which is released by the posterior lobe infants, whereas men experience urethral of the pituitary gland. The vasopressin or narrowing (stricture). antidiuretic hormone (ADH) facilitates reabsorption of water by the distal The preventive measures include: drinking convoluted tubule and the collecting duct plenty of liquids especially water so as to of the nephrons. Therefore, lack of this dilute urine and ensure frequent urination hormone implies that much water remains hence, allowing bacteria to be flushed from in renal ﬂuid; therefore, it is lost through the urinary tract. Also, women are advised urine. The symptoms of diabetes insipidus to wipe from front to back after urinating include excessive dilute urine, intense and after defecating so as to prevent the thirst, and tiredness. Regular physical spread of bacteria from anal region to exercises and healthy eating may prevent the vagina and urethra. Furthermore, a an individual from getting diabetes. patient should seek medical advice from a Diabetic patients are advised to go to recognised health centre or hospital. the health centre or hospital for medical advice and proper treatment. e) Urinary tract obstruction This is due to blockage or constriction at Exercise 7.3 any point in the urinary tract. This impedes the normal ﬂow of urine and causes urine 1. Analyse the major excretory to be retained in the bladder or kidneys. products in vertebrates. Obstruction causes urine to become blocked up into the kidneys, the condition 2. Describe the structure of the is known as hydronephrosis. Obstructions mammalian nephron. in the urinary tract causes distension of the walls of the bladder, ureter, urethra, and 3. Explain three common disorders of kidneys. This condition may stem from the urinary system in human. Sexually Transmitted Diseases (STDs) such as syphilis and gonorrhoea. Its 4. How does the type of nitrogenous preventive measures include prevention wastes excreted by an animal relate against STDs and seeking for medical to water availability in its body? assistance whenever sensing signs of STDs. 5. Describe the mechanism of urine formation. f) Diabetes insipidus (DI) The term diabetes insipidus is made up of two words; diabetes, which means ‘overﬂow’, and insipidus which means ‘tasteless’. From this basic implication, diabetes insipidus means excessive production of very dilute urine. It is caused 346 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 346 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Regulation (Homeostasis) 7.4 Osmoregulation GOFVOERRNONMLEINNTE PURSOEPOENRLTYYa) They have rectal glands which secrete In most vertebrates, kidneys are the salts to increase their osmotic pressure. most important organs involved in This mechanism aims at balancing the osmoregulation. The kidneys perform internal osmotic pressure to that of the several functions critical to homeostasis. surrounding sea water. Such functions include maintaining the balance between water and various types b) They retain nitrogenous waste of salts. This is important because ions chemicals, such as urea, and such as Na+, Ca2+, and K+ greatly affect trimethylamine oxide (TMAO) in the functioning of the body systems such their body cells. These chemicals are as the skeletal, nervous and muscular kept in high concentrations, and they systems. The kidneys produce urine; a change the diffusion gradient enabling liquid that contains a number of different a ﬁsh to absorb water instead of metabolic wastes. The concentration ingesting it. Despite the fact that these of urine produced by an animal varies are waste products and may be harmful depending on the environment as well to the animals at high concentrations, as on the factors, such as water and the marine elasmobranches have salt intake. The process of maintaining been able to produce and retain urea constant body’s osmotic condition is because their gills are impermeable to called osmoregulation. It is concerned it. Their renal tubules in the kidneys with the regulation of water and solute are capable of reabsorbing urea from concentration of the body ﬂuids. the renal ﬂuid back to body cells. In addition, their cells are immune to the Osmoregulation in marine effects of high concentrations of urea. elasmobranches Marine elasmobranches are cartilaginous Osmoregulation in mammals ﬁsh such as sharks, rays, and skates. They An important evolutionary adaptation live in sea water whose salt concentrations that allowed animals to survive on land are higher than those of their body ﬂuids. was the development of a kidney that Due to this difference in concentrations, would produce concentrated (hypertonic) the ﬁshes tend to lose water from their urine. The need for water conservation bodies into the sea. To overcome this is particularly well illustrated in desert problem, the marine elasmobranches have mammals such as the kangaroo rat. A developed mechanisms of making their major adaptation that allows the kangaroo body ﬂuids less hypotonic to sea water. rat to conserve water is the ability to form Because of this, the animals face another very hypertonic urine twenty times more problem of a natural and continuous concentrated than its blood plasma. The diffusion of water into their bodies from kidneys of the Kangaroo rat are able to their surrounding sea water. To overcome accomplish this because the loop of Henle these problems and to make their body of their nephrons is much longer and more ﬂuids isotonic to sea water, such ﬁshes efﬁcient than that of most other mammals. have developed the following adaptations: 347 BIOLOGY FORM 5 KIWANDANI.indd 347 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Terrestrial mammals need to drink water GOFVOERRNONMLEINNTE PURSOEPOENRLTYYﬁne looped blood vessels called the Vasa at least occasionally to compensate for the recta. These vessels carry blood from the water lost from the skin and respiratory glomerulus to the renal vein. passages and through urination. Salts like sodium and chloride ions, Counter current multiplier diffuse passively out of the thin ascending In the loop of Henle, a counter current limb and pumped actively out of the exchange mechanism is combined with thick ascending limb into the surrounding the active secretion of solutes. A system tissue ﬂuids. This pumping of salts out that uses this combined type of exchange of the limb creates an osmotic gradient is called counter current multiplier which draws water out of the descending system. The loop of Henle functions as a limb into the medulla. This is because the counter current multiplier due to its close ascending limb is impermeable to water; proximity of ascending and descending therefore, water moves out of the limb limbs, permeability of the descending only to the descending limb. When water limb to water, impermeability of the in the descending limb is pumped out, it descending limb to solute, permeability causes the ﬂuid in the descending limb to of the ascending limb to solute, passive have a slightly higher salt concentration transport of solute in thin ascending compared to the ascending limb. The limb, and active transport mechanism for process continues down the length of the the thick ascending limb (Figure 7.10). loop so that this concentration effect is These features enable the loop of Henle to multiplied. The counter current multiplier create a very high concentration gradient means that the ﬂuid in and around the loop between the tissue ﬂuid and blood in the of Henle becomes saltier as it goes down medulla of the kidney and the urine in the loop, and it is saltiest at the bottom the collecting ducts. The loop of Henle end of the loop. In contrast, it becomes is connected at one end to the proximal less salty as it goes up the ascending limb convoluted tubule and at the other end Therefore, the ﬁnal salt concentration to the distal convoluted tubule. It ﬁrst depends on the length of the loop, the descends deep into the medulla and then longer the loop; the higher the ﬁnal salt bends and ascends into the cortex again. concentration in the tissues. Throughout its length, it is surrounded by 348 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 348 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Regulation (Homeostasis) Descending limb Ascending limb C O 300 300 100 300 R T H2O E X H2O M NaCl E D H2O H2O U L H2O NaCl 400 Decrease L H2O solute A 600 600 potential NaCl NaCl H2O NaCl Interstitial region Interstitial region Interstitial region H2O NaCl Cl- 1200 1000 Na+ 1,200 H2O 1,200 Active transport of NaCl Passive transport of NaCl Movement of water Figure 7.10 Counter-current multiplier system of the loop of Henle Hormonal control of osmoregulation GOFVOERRNONMLEINNTE PURSOEPOENRLTYYand pressure rises) and the urine produced As water moves in the loop of Henle, it is more concentrated. leaves the loop of Henle with the water potential greater than that of blood plasma. The regulation of salt and blood pressure This creates a concentration gradient are closely connected. If the sodium ion between ﬂuid in the distal convoluted concentration in the blood is low, the tubule and the surrounding tissue ﬂuid. blood water potential increases and water The concentration gradient is enhanced moves by osmosis into the tissue, slightly when salts are actively pumped out of the lowering the blood pressure. When blood distal convoluted tubule. Reabsorption of pressure is not sufﬁcient (below the set water in the distal convoluted tubule and point), secretory cells near the glomerulus, the collecting duct will depend on their juxtaglomerular apparatus secrete, renin. permeability, which is controlled by the The later is an enzyme that changes hormone called Antidiuretic hormone angiotensinogen (angiotensinogen is a (ADH). This hormone is released by the large plasma protein produced by the liver) posterior lobe of the pituitary gland in into Angiotensin I. Later Angiotensin response to an increased concentration of I is converted to Angiotensin II. When salts in the blood. When ADH is present, Angiotensin II reaches the adrenal cortex, more water is reabsorbed (blood volume it stimulates the secretion of aldosterone. BIOLOGY FORM 5 KIWANDANI.indd 349 349 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools This hormone promotes the excretion GOFVOERRNONMLEINNTE PURSOEPOENRLTYYa) Water and food consumption of potassium ions and the reabsorption Human beings obtain about 60% of the of sodium ions at the distal convoluted water they need from the ingested liquids, tubules. The reabsorption of sodium ions 30% from ingested food, and 10% from is followed by the reabsorption of water. metabolism. Rodents and camels adapted Therefore, blood volume and blood to arid conditions obtain approximately pressure increase. 90% of water from metabolism and 10% from ingested food. Adaptations of mammals to arid and semi-arid conditions b) Excretory adaptations High temperature and low rainfall The ability to excrete concentrated urine characterise some areas of this world. It and dry feaces is an important adaptation becomes hard to believe that animals can to arid conditions. Mammals that are survive in arid and semi-arid conditions. adapted to the desert have very long However, these animals survive because loop of Henle compared to animals that they have adaptations that allow them live in less arid regions and in aquatic to live in the hot, dry conditions. environments. A longer loop of Henle These adaptations help to balance allows urine to become very concentrated thermoregulation with water gain and due to osmotic gradients in the kidneys. loss. For instance, many mammals that Desert rodents produce concentrated urine live in the desert obtain much or all of about ﬁve times as that of humans. Longer their water from the food they consume. loop of Henle increases the efﬁciency of The reduced water intake is partially water reabsorption and hence a means for balanced through concentrated urine and conserving water. dry faeces. Evaporative cooling helps to regulate temperature. c) Behavioural adaptations Behavioural adaptations are used to To limit the water loss through evaporative reduce the amount of heat gained by cooling, some mammals are nocturnal; animals. Therefore, they reduce the have light coloration and other body need for evaporative cooling. One basic features to help them dissipate heat and behavioural adaptation is the timing of use micro-environments to reduce heat activity rhythms. Nocturnal animals gain. This is only a short list of the many are able to regulate their heat load by amazing adaptations. Characteristically, resting during the day, since night-time arid regions receive 100-250 mm of rain temperatures can be 15-20 °C lower than a year and semi-arid regions receive 250- the daytime. Examples of nocturnal 500 mm of rain per year. The following animals include the quoll, bilby, and the are some of adaptations of mammals to spinifex hopping mouse. the life in arid or semi-arid conditions: 350 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 350 10/10/2019 14:08

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Burrows are another type of GOFVOERRNONMLEINNTE PURSOEPOENRLTYY FOR ONLINE USE ONLY microenvironment that is used by smaller DO NOT DUPLICATE mammals. In Arizona burrow temperature of a round-tailed ground squirrel was Regulation (Homeostasis) recorded. The air temperature was 40 °C and the soil surface was 70 °C but the burrow Revision questions temperature did not exceed 29 °C. Many burrows are at a depth where evaporative 1. Explain the concept of regulation cooling is not needed; it does not get hot (homeostasis). enough in the burrows to require this technique. 2. With a speciﬁc example of a homeostatic mechanism, draw d) Torpor and metabolic rate a diagrammatic representation Many mammals such as rodents and showing how a body can balance its squirrels enter a period of torpor in contents through negative feedback response to severe heat. This is a period mechanism. when metabolism decreases, the heart beat and respiratory system slows down 3. How do endotherms keep their based on a circadian rhythm. Torpor body temperatures constant? can be considered as a water conserving mechanism because the animal’s body 4. Outline various ways by which temperature is lowered and it does not mammals are adapted to arid and have to rely heavily on evaporation. If semi- arid conditions. the period of torpor becomes longer, it is called aestivation or summer dormancy. 5. Briefly describe the ornithine cycle. Aestivation allows an animal to survive 6. Brieﬂy describe how the mammalian when there are high temperatures and renal tubule is adapted to its a scarcity of water and or food. An functions. aestivating animal can live longer with its energy reserves due to lowered 7. Explain the causes, effects and metabolism. Moreover, there is a reduced prevention of the following water loss through lowered breath rates. disorders in human: Metabolic rates are lower during torpor and aestivation. Mammals adapted to a) Kidney failure desert climates have lower metabolic rates in general than similar mammals that b) Kidney stones live in extreme climates. This reduces the internal heat load as well as the water used c) Diabetes insipidus for evaporation. 8. Explain the mechanism of osmoregulation in marine elasmobranches. 9. Describe the counter current multiplier system in the mammalian loop of Henle. 10. Describe the mechanism of osmoregulation in mammals. 11. Explain the mechanism of hormonal control of osmoregulation in mammals. BIOLOGY FORM 5 KIWANDANI.indd 351 351 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Glossary Acoelomate An animal that does not possess a body cavity Adenosine Triphosphate (ATP) is a complex organic chemical that provides energy to drive many processes in living cells Akaryotes/Acaryotes A cell without nucleus like viruses. Red blood cells are also classified as akaryotes because they lack nucleus after they have developed Alternation of generation Type of life cycle found in terrestrial plants and some algae in which subsequent generations of individuals alternate between haploid and diploid organisms or refers to the occurrence in the plant life cycle of both a multicellular diploid organism and a multicellular haploid organism, each giving rise to the other. Ammonotelic organisms Describes an animal that excretes ammonia as the primary waste material. Examples of ammonotelic organisms include protozoans, crustaceans, platyhelminths, cnidarians, fishes, and tadpoles of amphibians. Anaesthetize Administering a chemical or drug to an animal so as to make an animal unconscious for operation or dissection purposes GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Antheridia Male sex organ of algae, fungi, bryophytes, and spore- bearing vascular plants, such as ferns, which produces antherozoids Archegonia The egg-producing organ occurring in bryophytes (such as mosses and liverworts), ferns, and most gymnosperms. The archegonium is a multicellular, often flask-shaped structure that contains a single egg. Bacteriochlorophyll Modified chlorophyll that serves as the primary light- trapping pigment in purple and green sulphur bacteria Bisexual flower A ﬂower with both male and female reproductive structures Bronchus Passage of airway in the respiratory system that conducts air into the lungs Browsing A type of herbivory in which an animal feeds on leaves, soft shoots or fruits; generally woody plants such as 352 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 352 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Glossary shrubs. Such animals are known as browsers. Examples include; giraffe and goat. Bundle sheath cells A layer of cells in plant leaves and stems that forms a Caecilians sheath surrounding the vascular bundle. In C4 plants it Carboxylation contains chloroplasts and are the site for Calvin cycles. Carotenoid Group of limbless tropical amphibians that look like large Cladistic /Phylogenetics worms or silk snakes. It becomes difficult to differentiate Coenzyme Q between the head and the tail. Cytochromes Chemical reaction in which a carboxylic acid group is produced by treating a substrate with carbondioxide Dendrites Dissection Plant pigment responsible for bright red, yellow and Ectotherm orange hues in many fruits and vegetables. They Endemic also help chlorophyll from the photo damage during photosynthesis. An approach to biological classfication in which organisms are categorised in groups based on the most recent common ancestry shared traits A crucial component of the oxidative phosphorylation process in mitochondria which converts the energy in carbohydrates and fatty acids into ATP to drive cellular machinery GOFVOERRNONMLEINNTE PURSOEPOENRLTYY These are electron carrier agents and essential component of the electron transport chain. They can undergo reduction and oxidation (losing or gaining electron) but does not react with oxygen. Branched protoplasmic extensions of a nerve cell that propagate the electrochemical stimulation received from other neural cells to the cell body The process of cutting open the body part of anaesthetised or deceased animal or plant to investigate its anatomical structure and body systems An organism whose regulation of body temperature depends on external sources, such as sunlight or a heated rock surface A native species of animal or plant which are only found BIOLOGY FORM 5 KIWANDANI.indd 353 353 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools in a restricted area and not other places or an area in which a particular disease is regularly found, or a regular condition or disease found among particular people. Endotherm Organisms that use internally generated heat to maintain body temperature. Their body temperature tends to stay steady regardless of the environmental temperatures. The endotherms primarily include birds and mammals. Epiglottis Elastic cartilage covered with a mucosa membrane, found in the throat that prevent the food from entering the windpipe (trachea) and the lungs Facultative parasites Organisms that can live either as parasites when the host is available or as a free living organism when the host is not available Foetus Developing offspring inside the maternal uterus (womb) in a prenatal stage between embryonic stage and birth Fossorial Animals that live underground, digging tunnels and burrows. Some of them are completely subterranean, while others come up to the surface for some hours of the day. GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Glycogenolysis A process whereby glycogen which is the primary carbohydrate stored in the liver and muscle cells of animals, is broken down to glucose in order to provide immediate energy and maintain blood glucose levels during fasting. This process occurs primarily in the liver and is stimulated by two hormones, glucagon and epinephrine (adrenaline). Grazing A type of herbivory in which an animal eats grass or forbs. Such animals are called grazers, and include cows and sheep Guard cells Specialized epidermal cells of the leaves and stems. They contain chloroplasts used in photosynthesis. They occur in pairs that form a pore between them called stomata, that regulate the gaseous exchange by opening and closing of the stomatal pore. Haemoglobin (hemoglobin) An iron containing protein molecule of the red blood cell used to transport oxygen in the blood of almost all 354 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 354 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Glossary vertebrates as well as the tissues of some invertebrates. It is abbreviated as Hb or Hgb. Hepatopancreatic sphincter Muscular valve which regulates the flow of bile and pancreatic juices Hibernation Adaptation that helps many animals conserve energy by remaining inactive, greatly slowing their metabolism and reducing their body temperature for days, weeks, or months. Animals hibernate in order to survive long periods. Homoeothermic animals Animals that maintain a stable body temperature by regulating metabolic processes. Examples are birds and mammals. Hyperthermia Elevated body temperature due to failed thermoregulation that occurs when a body produces or absorbs more heat than it dissipates. Hypertonic A condition where the external environment has higher concentration of solutes than the internal environment Hypotonic A condition where the external environment has lower concentrations of solutes than that of the internal environment GOFVOERRNONMLEINNTE PURSOEPOENRLTYY In situ Item being in its natural, normal, or original place or position Intercostal muscles Several groups of muscles which make and move the chest wall. They run between one rib and another, and they are involved in the mechanical aspect of breathing. Lean muscle mass Lean mass is the total weight of the body minus all the weight due to your fat mass Lean mass = total weight – fat mass Mesophyll cells Photosynthetic cells in plant leaves which are loosely packed and lie between the bundle sheath cells and the leaf surface Metameric segmentation A series of alike segments running along the length of the body Nissl’s bodies Granular bodies of variable size found in nerve cell bodies and dendrites BIOLOGY FORM 5 KIWANDANI.indd 355 355 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Phosphorylation The process of adding a phosphate group to a molecule or an organic compound Photoheterotrophs Organisms that depend on light for energy and complex organic matter for carbon to synthesise their organic requirements Photolysis A chemical process by which water molecules are broken down into smaller units through absorption of light during photosynthesis Photorespiration A metabolic pathway that occurs in plants in the presence of light; in which ribulose biphoshate carboxylase oxygenase (RuBisCo) fix oxygen instead of carbondioxide to form phosphoglyceric acid and 2-phosphoglycolate; a product which cannot be used in the Calvin cycle. Phycobilins Light capturing bilins which are water soluble and contain chromophore that make them coloured, mainly orange, red, and blue pigments found in red algae and cyanobacteria. Phycoerythrobilin The red phycobilin, found in some organisms such as cyanobacteria and the chloroplast of red algae which act as the terminal acceptor of energy GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Phytopathogenic Organisms which are pathogenic to plants Pili Hair like filaments (tiny hollow projections) that extend from the cell membrane into the external environment. Bacteria possessing pili include Neisseria gonorrhoeae and some strains of Escherichia coli, and Salmonella. Plasmalemma Membrane which separates the interior parts of the cell from the outside environment (the extracellular space) that protects the cell from its environment, usually consisting of a lipid bilayer with embedded protein. Pleural membrane Thin, slippery and moist membrane surrounding the lungs, it has two layers; the outer layer called parietal pleura and inner layer visceral pleura with a space between them called pleural cavity filled with pleural fluid secreted by the membrane. 356 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 356 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Poikilothermic animals Animals whose body temperature fluctuates with that of the environment. Examples include amphibians and reptiles. Pseudocoelomates Animals with a primitive (false) cavity (pseudocoelum) Repugnatorial fluid Defensive secretions (odorous fluid) produced by animals, such as certain insects for defence against predators Ribulose biphosphate (RuBP) An organic substance (a 5 carbon compound) involved in Calvin cycle which is part of the light independent reactions of photosynthesis Schwan cells Cells in the peripheral nervous system that form the myelin sheath around a neuron’s axon. Schwan cells is also called neurilemmocytes. Svedberg value (s or sv) A measure of a particle’s size based on its sedimentation rate, i.e. how fast a particle of given size and shape ‘settles’ to the bottom of a solution. The units of a ribosome are often described by their Svedberg (s) values, which are based upon their rate of sedimentation in a centrifuge. Tegument The outer covering of platyhelminths, made up by an epidermal layer and sometimes provided with cilia, spines and glandular tissue GOFVOERRNONMLEINNTE PURSOEPOENRLTYY Uniramia A group of arthropods characterised by having appendages (antennae and legs) with only a single ramus (branch). They also have a single pair of antennae and an exoskeleton that is strengthened by tanning process and made water proof by a wax layer. The group has three main classes: the Chilopoda (centipedes), Diplopoda (millipedes) and Hexapoda or Insecta (insects and their relatives). Ureotelic organisms Animals that excrete urea as the primary nitrogenous waste material. Examples include cartilagenous fish, adult amphibians, and mammals including humans. Uricotelic organisms Organisms that excrete uric acid, example birds and reptiles Vaccine A biological preparartion that provides active acquired immunity against a particular disease Student’s Book Form Five 357 BIOLOGY FORM 5 KIWANDANI.indd 357 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools Bibliography Allison, L.A., Freeman, S., & Quillin, K. (2008). Biological science (5th Ed.). New York: Pearson Education. Campbell, N.A., Reece, J.B., Taylor, M.R., & Simon, E.J. (2005). Biology concepts and connections (5th Ed.). New York: Benjamin Cummings 1301 Sansome St. San Fransisco, CA 94111. Chand, S., Verma, P.S., & Pandey, B.P. (2010). Biology for class XI (2nd Ed.). New Delhi: S. Chand & Company Ltd. Clegg, C.J. & Mackean D.G. (1994). Advanced biology, principles and applications (1st Ed.). London: John Murray (Publishers) Ltd. Toole, G. & Toole, S. (1999). New understanding biology for advanced level (4th Ed.). London: Stanley Thornes (Publishers) Ltd. Green, N.P.O., Stout, G.W., & Taylor, D.J. (1997). Biological science (3rd Ed.). Cambridge: Cambridge University Press. Mackean, D.G. (2005). IGCSE biology. London: Hodder Murray, an imprint of HodderGOFVOERRNONMLEINNTE PURSOEPOENRLTYY Education. Marshall, P.T. & Hughes, G.M. (1980). Physiology of mammals and other vertebrates (2nd Ed.). New York: Cambridge University Press. Roberts, M.B.V. (1986). Biology, a functional approach (4th Ed). London: Thomas Nelson and sons Ltd. Rowett. H.G.Q. (1982). Guide to dissection. London: John Murray Publishers Ltd. Stern, K.R. (1997). Introductory plant biology. California: WCB/McGraw-Hill. TIE (2013). Diploma in secondary education, biology: Pedagogy module. Dar es Salaam: Tanzania Institute of Education. URT (2010). Biology syllabus for advanced secondary education, Form V-VI. Dar-es salaam: Tanzania Institute of Education. URT (2009). In-service training for secondary school teachers. Biology manual. Dar- es-salaam: Ministry of Education, Science and Technology. Vines A.E. & Rees, N. (1972). Plant and animal biology (Vol 1).London: Longman Group Ltd. Windelspecht, M. (2013). Biology (11th Ed.). New York: McGraw-Hill companies. 358 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 358 10/10/2019 14:08

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FOR ONLINE USE ONLY Index DO NOT DUPLICATE Index A GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 109, 110, 111, 258, 356 classification 58, 77, 82, 95, Basidiomycota 128, 133, 134 106, 175, 230, 234 abscisic acid 360 biological control 111, 136, absorption 22 coccus 105 absorption 278, 357 170, 189 cochlea 240, 241, 242, 243 acoelomate 360 biotechnology 99 cochlea 241, 242 actin 29, 58, 61 bowman’s capsule 339, 340, coelom 167, 171, 172, 175, 358 actin 29 coelomate 171, 172, 175, 190, aerobic respiration 20, 126, 341, 342 bronchus 292 358 291, 305, 306, 310, 312, bryophytes 75, 137, 138, 139, coenzyme Q 317 316, 317, 319, 324, 358 commensalism 277 Agaricus 360 268 cones 146, 147, 148, 149, 230, algal bloom 126 alternation of generation 352 C 231, 238, 239, 256, 358 alveolus 292, 293, 294 conidia 130, 131, 358 Annelida 166, 171, 172 C3 plants 268, 269, 270, 271, Coniferophyta 78, 83, 138, anthers 154 272, 274 antidiuretic hormone 247, 346, 145, 146 349 C4 plants 267, 268, 269, 271, corolla 159, 162 Archaebacteria 93, 101, 102 272, 274, 290, 353 counter current multiplier 348, archegonium 138, 140, 142, 148, 352 Calvin cycle 262, 263, 265, 351 Arthropoda 166, 175, 177, 178 266, 267, 268, 269, 270, counter current multiplier 348 artificial system of 80, 90 356, 357 crustacea 175, 176 Ascaris 169, 170, 171 cuticle 41, 138, 139, 145, 147, ascocarp 130, 131 calyx 159, 162 ascomycetes 133 capsid 94, 95, 96 149, 164, 168, 170, 171, Ascomycota 128, 130, 131 carbohydrates 33, 34, 42, 45, 178, 181, 188, 275, 303 assimilation 278 cutin 16 ATP 9, 17, 20, 22, 45, 46, 72, 305, 322 cyanobacteria 100, 101, 102, 73, 74, 76, 218, 219, carpel 155 103, 110, 112 261, 262, 263, 265, 266, cell 5, 7, 8, 10, 11, 15, 16, 31, cytokinins 254 267, 268, 270, 271, 273, cytoplasm 5, 8, 10, 17, 31, 32, 275, 303, 305, 306, 307, 32, 34, 55, 104, 108, 108, 116, 125, 132 308, 309, 310, 311, 313, 125, 132, 215, 216, 217, cytoskeleton 12, 14, 28, 30, 314, 315, 316, 317, 318, 221 358 319, 320, 323, 343, 344, cell membrane 7, 55, 125, 132 353 cellulose 31, 34, 40, 41, 46 D autolysis 25 centrioles 358 autophagy 25, 26 Chilopoda 358 Daniel-Davson’s model 358 auxins 253 chitin 34, 41, 42, 132 dark reaction 45, 260, 262, 265, chlorophyll 260, 272 B chlorophytes 123, 124 267, 273, 358 chloroplast 8, 22, 76, 120, 125 deamination 343 bacillus 105 chloroplasts 7, 21, 22, 270 deamination 306 bacteria 93, 103, 105, 106, 107, Chondrichthyes 190 dendrite 217, 224, 225, 358 Chordata 83, 166, 189, 190 diabetes insipidus 346 chromoplasts 21 diabetes insipidus 346, 351 cilia 4, 6, 31, 233, 280 dichotomous keys 358 cladistics 79 dicotyledoneae 151, 152 classification iii, v, 47, 77, 80, digestion 26, 276, 278, 279, 81, 82, 83, 84, 90, 92, 94, 95, 103, 151 281, 283, 287, 288 BIOLOGY FORM 5 KIWANDANI.indd 359 359 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools diploblastic 166, 358 GOFVOERRNONMLEINNTE PURSOEPOENRLTYY 319, 324, 358 gram-negative bacterium 4, Diplopoda 175, 177, 179, 357, fibers 358 34, 71 fibres 12, 111, 136, 288 358 fibrinogen 358, 360 gram–positive bacterium 4, disaccharides 34, 37 filaments 29, 30, 58, 124, 356, 34, 71 DNA 2, 3, 4, 5, 6, 7, 9, 18, 20, 358 grana 34, 71 21, 22, 31, 46, 55, 59, Filicinophyta 78, 83, 138, 142, growth 34, 71, 118 70, 73, 80, 92, 93, 94, gynoecium 34, 71 95, 96, 97, 98, 99, 101, 358 gynosperms 358 102, 103, 108, 110, 113, flagella 9, 30, 58, 116, 120, 259 H dormancy 128, 254, 255, 333, 121, 358 351 floral diagram 159, 162, 358 haemoglobin 57, 58, 59, 61, dryopteris 82, 88, 89, 143, 144, floral formula 161, 358 173, 295, 296, 297, 298, 145 Fluid Mosaic Model 358 299, 300, 301, 302, 358 duodenum 195, 199, 205, 279, foetus 75, 204, 206, 207, 294, 283 haustorium 121, 127 300, 301, 302 heptoses 358 E food vacuole 23, 113, 114 heterophagy 25 fragmentation 124, 138, 139 heterotrophic nutrition 276, ectotherms 330, 334, 335 fungi 9, 27, 39, 40, 41, 81, 84, ectotherms 334 277, 290, 358 effector 214, 215, 217, 229, 101, 103, 110, 111, 112, hexoses 35, 45, 358 121, 126, 127, 128, 130, hormone 246 326, 327 133, 135, 136, 137, 147, hydrophilic 13 egestion 114, 183, 278, 358 173, 210, 257, 275, 276, hydrophobic 13, 53, 57 electron transport system 73, 277, 352 hyperthermia 332 hyphae 34, 121, 122, 127, 128, 312, 316, 317, 318 G endoplasmic reticulum 118 129, 130, 131, 133, 134, endotherms 330, 331, 334, 351, galactose 34, 71 135 gametophyte 124, 137, 139, hypogynous 155 354 hypothalamus 232, 234, 246, endotherms 331, 334 140, 141, 142, 144, 145, 247, 248, 326, 327, 331, Entamoeba histolytica 111, 146, 148, 150, 154, 155, 332, 335 163 hypothalamus 246, 248 114, 115, 126, 210, 358 genetic material 6, 34, 71 enzyme inhibitors 68, 358 gibberellins 34, 71, 254 I enzymes 58, 62, 67, 68, 69, 70, glands 34, 71 glomerulus 339, 340, 341, 342, ICBN 84, 358 71, 273 348, 349 ICZN 84, 358 epigynous 156 glucagon 61, 246, 328, 354 ileum 183, 186, 195, 199, 205, ethylene 252, 255, 328 glycogen 17, 19, 39, 40, 127, Eubacteria 82, 93, 100, 101, 128, 132, 135, 166, 246, 279, 284, 285 305, 306, 327, 328, 354, ingestion 120, 194, 278, 358 102, 112, 358 358 Insecta 175, 177, 180, 181, Euglena 113, 120, 121, 210, glycogenolysis 40 glycolipids 34, 48, 71 357, 358 248 glycolysis 34, 71, 306, 307, insulin 54, 58, 61, 245, 246, Euglenophyta 113, 120, 358 319, 320, 321 exocytosis 10, 25, 358 glycosomes 26, 358 289, 328 golgi apparatus 6, 8, 9, 10, 12, Iodine solution 42, 44, 264, F 15, 17, 23, 24, 26, 27, 28, 34, 71, 76, 118, 132 265, 273, 358 FADH 316, 318, 319, 320, 323 Fehling’s reagents 358 K fermentation 109, 131, 136, kidney 26, 33, 195, 199, 206, 305, 306, 310, 316, 317, 207, 234, 247, 331, 336, 360 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 360 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Index 337, 338, 339, 340, 343, GOFVOERRNONMLEINNTE PURSOEPOENRLTYYmonosaccharides 35, 37, 39, oxyhaemoglobin 295, 296, 297, 344, 345, 347, 348 43, 45, 46, 73, 111, 132, 299, 301 Kihansi spray toad 192, 193, 278, 305, 306, 307 194, 211 oxytocin 247, 328 Kreb’s cycle 21, 305, 306, 310, monosaccharides 34, 35, 45, 312, 314, 315, 316, 317, 305 P 318, 320, 321, 344 Mucor 128, 137, 276 parasitism 277 l mycelium 122, 127, 128, 131, pellicle 116, 117, 120, 121 pentoses 35, 358 lactose 34, 37, 39, 71 133, 134 pepsinogen 282 lenticel 303 mycorrhizae 133, 147, 164, peripheral nervous system 212, light dependent reaction 358 light independent reaction 358 277, 358 213, 357, 358 lignin 15 myelin sheath 32, 48, 213, 214, peroxisomes 26 lipids 14, 47, 49, 50, 305, 320, petals 154 215, 223, 256, 357, 358 phenetics 79 322 myoglobin 61, 301 phospholipids 12, 48 loop of henle 340, 343, 347, photolysis 259, 261, 262, 290 N photoreceptors 231, 240, 358 348, 349, 350, 351 photosynthesis 258, 259, 269, lungs 24, 58, 71, 75, 177, 192, NADH 71, 306, 307, 309, 311, 315, 316, 317, 318, 319, 271, 273, 274, 290 199, 202, 291, 292, 293, 320, 323 photosystem I 260, 261, 262, 294, 295, 296, 297, 299, 300, 301, 323, 332, 335, nastic 249, 250, 251, 252 263 352, 354, 356, 358 natural system of classification phospholipids 12, 48 lysogenic cycle 98 photosystem II 260, 261, 262 lysosomes 9, 24, 25, 26, 76 80, 81, 90 phyletic 79 lytic cycle 97, 98 Nematoda 84, 166, 169, 358 Phytophthora infestans 121, nephron 247, 339, 340, 341, M 122, 123 346 pigments 21, 22, 23, 107, 120, maltose 34, 37, 38 nephron 338 Mammalia 83, 190, 203, 358 nerve impulse 14, 215, 216, 123, 136, 139, 258, 259, mammalian ear 240, 241, 242, 260, 261, 336, 356 217, 218, 219, 220, 221, pili 5, 356 244, 256, 358 222, 224, 225, 230, 256, Pinus 82, 88, 89, 145, 147, mammalian eye 240, 244, 358 358 148, 149 mechanoreceptors 230, 358 neurones 213, 215, 216, 217, plasma membrane 5, 12, 26, methanobacter 358 224 104, 221 microbodies 26, 27 node of Ranvier 223, 358 plasmid 5 microfilaments 9, 358 nomenclature v, 84, 86 Plasmodium 117, 118, 119, microglia 358 nucleus 8, 10, 31, 32, 115, 116, 126, 189, 210 microtubules 29, 118 118, 120, 125, 132, 215, Platyhelminthes 166, 167, 169 microvilli 15, 32, 278, 280, 217, 237, 280, 281 poikilothermic 190, 223, 330 nutrition iii, vi, 257 pollination 148 285, 342, 343 prokaryotes 92 millipede 179, 180, 358 O protein 12, 13, 14, 62, 96, 104, mitochondria 9, 20, 237, 305 225, 305, 306 Monera v, 77, 82, 92, 93, 100, oesophagus 183, 186, 195, 205 proteins 22, 51, 58, 59, 61, 62, oligochaeta 172 306, 320, 322 101, 102, 112, 115, 210 Oomycota 113, 121, 358 Protoctista v, 31, 77, 92, 93, monocotyledoneae 151, 152 ornithine cycle 343, 351 112, 113, 115, 123, 126 ossicles 204, 240, 242 pseudocoelomate 358 Osteichthyes 190, 191 ovary 151, 155, 156, 158, 162, 207 361 BIOLOGY FORM 5 KIWANDANI.indd 361 10/10/2019 14:08

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FOR ONLINE USE ONLY DO NOT DUPLICATE Biology for Advanced Level Secondary Schools pseudopodia 113, 114, 115 GOFVOERRNONMLEINNTE PURSOEPOENRLTYYsepals 154 337, 339, 348, 349, 357 pyrenoid 123, 124 sorus 145 tripoblastic 358 pyruvate 270, 306, 311, 315, spermatozoa 32 tropic movement 248, 251, 358 Spirogyra 112, 113, 123, 124, Trypanosoma 27, 115, 116, 317, 321 125, 210 117, 127, 189 R sporangium 122, 129, 130 tympanic membrane 202, 240, sporophyte 140, 141, 148 rachis 143 stamens 159, 162, 163 242 radial symmetry 157, 160, 161, starch 22, 34, 39, 44, 110 stigma 151, 155, 162 U 166, 358 stimulus 327 receptacle 154, 155, 186 stomata 144, 147, 149, 164, Uniramia 177, 178, 357, 358 receptors 14, 214, 215, 216, unirogenital 358 255, 259, 265, 268, 271, urea 59, 336, 343, 344, 347, 230, 231, 232, 233, 234, 274, 303, 304, 354 244, 283, 326, 331, 358 stroma 22 357, 358 receptors 230 style 151, 155, 158 uremia 113, 120, 121, 210, 248, rectum 183, 186, 194, 195, suberin 15 199, 205, 206, 209, 279, Sudan III test 50, 358 344 287 sulphur bacteria 101, 258, 352, urethritis 113, 120, 121, 210, Reptilia 190, 201, 358 358 respiration vi, 291, 305 symmetry 95, 155, 157, 158, 248 respiratory 73, 305, 306, 319, 160, 161, 162, 166, 167, uric acid 336, 357 320, 322, 323 171, 358 urinary tract infections 113, retina 217, 231, 235, 236, 237, synapse 218, 223, 224, 225, 238, 239, 240, 244, 358 226, 227, 228, 229, 239, 120, 121, 210, 248, 345 retrovirus 99, 358 256, 358 UTI 110, 111, 345 Rhizopoda 113, 114 rhizopus 92, 128, 129, 130, T V 136, 137, 276 rhodopsin 239, 358 tactic 113, 120, 121, 210, 248, vacuole 8, 32, 113, 120, 121, rhoptries 118 252 125, 132, 210, 248 ribosomes 4, 5, 7, 9, 18, 19, 23, 24, 31 taxa 113, 120, 121, 210, 248 vibrio 101, 105, 106, 111 RNA 2, 7, 18, 24, 46, 93, 94, taxonomic keys v, 86, 87 villi 113, 120, 121, 210, 248, 95, 96, 99 thermoreceptor 230, 358 rods 106, 184, 230, 231, 238, thylakoid 22, 260, 261, 262, 285 239, 256, 358 virions 94 rough endoplasmic reticulum 8, 273 viruses v, 92, 93, 94, 95, 96, 10, 18, 26 thyroxine 246, 323 tissue 32, 47, 58, 113, 138, 139, 99, 113, 120, 121, 210, S 248 151, 164, 166, 212, 213, Saccharomyces 130, 131, 132, 214, 216, 218, 232, 246, X 133 251, 255, 259, 265, 279, 280, 281, 289, 294, 296, xylem 113, 120, 121, 210, 248 saprophytic nutrition 276, 358 298, 303, 313, 316, 322, saprotrophic nutrition 358 325, 326, 328, 332, 336, Z Zoomastigina 113, 115, 116, 117, 120, 121, 210, 248 Zygomycota 113, 120, 121, 128, 129, 210, 248 362 Student’s Book Form Five BIOLOGY FORM 5 KIWANDANI.indd 362 10/10/2019 14:08