327 - 11th Botany Textbook Volume 1

GOVERNMENT OF TAMIL NADU

BOTANY

HIGHER SECONDARY FIRST YEAR

VOLUME - I

Untouchability is Inhuman and a Crime

A publication under Free Textbook Programme of Government of Tamil Nadu

Department of School Education

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Government of Tamil Nadu

First Edition - 2018

NOT FOR SALE

Content Creation

The wise

possess all

State Council of Educational

Research and Training

© SCERT 2018

Printing & Publishing

Tamil NaduTextbook and Educational

Services Corporation

www.textbooksonline.tn.nic.in

II

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CONTENTS

BOTANY

UNIT I: Diversity of Living World

Chapter 1 Living World 1

Chapter 2 Plant Kingdom 47

UNIT II: Plant Morphology and Taxonomy of Angiosperm

Chapter 3 Vegetative Morphology 98

Chapter 4 Reproductive Morphology 123

Chapter 5 Taxonomy and Systematic Botany 160

UNIT III: Cell biology and Biomolecules

Chapter 6 Cell: The Unit of Life 225

Chapter 7 Cell Cycle 260

Chapter 8 Biomolecules 276

Annexure

References 305

Glossary 307

Competitive Examination Questions 311

Botanical Names and Common names 317

E-book Assessment DIGI links

Lets use the QR code in the text books ! How ?

• Download the QR code scanner from the Google PlayStore/ Apple App Store into your smartphone

• Open the QR code scanner application

• Once the scanner button in the application is clicked, camera opens and then bring it closer to the QR code in the text book.

• Once the camera detects the QR code, a url appears in the screen.Click the url and goto the content page.

III

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Learning Objectives:

Learning objectives are brief statements that describe what

students will be expected to learn by the end of school year,

course, unit, lesson or class period.

Chapter Outline

Illustrate the complete overview of chapter

Amazing facts, Rhetorical questions to lead students

to biological inquiry

List of Botanical terms

Tamil terminology for Botanical terms given for easy

understanding

Activity

Directions are provided to students to conduct activities

in order to explore, enrich the concept.

HOW TO USE

THE BOOK

Infographics

Evaluation

Visual representation of the lesson to enrich learning .

Assess students to pause, think and check their understanding

To motivate the students to further explore the content

digitally and take them in to virtual world

ICT

To enhance digital Science skills among students

Concept Map

Conceptual diagram that depicts relationships between

concepts to enable students to learn the content schematically

Career corner

List of professions related to the subject

References

List of related books for further details of the topic

Web links

List of digital resources

Glossary

Explanation of scientific terms

Competitive

Exam questions

Model questions to face various competitive exams

IV

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TNAU

B.Sc. Agriculture,

B.Sc. Horticulture

B.Sc. Forestry,

B.Sc Sericulture

B.Tech Biotechnology

B.Tech Agricultural Engineering

B.Tech Horticulture

B.Tech Food process Engineering

B.Tech Energy and

Environmental Engineering

B.Tech Bioinformatics

B.Sc Agribusiness Management

B.Tech Agricultural IT

M. Tech. Environmental Engineering

M. Sc in Agriculture

M. Sc in Agricultural Extension

M. Sc in Agronomy

M. Sc in Soil Science

M. Sc in Agricultural Biotechnology

M. Sc in Agricultural Marketing

M. Sc in Agricultural Microbiology

M. Tech in Agricultural Engineering

M. E in Agricultural Engineering

Master of Agriculture in Entomology

Master of Agriculture in Horticulture

Master of Agriculture in Animal Sciences

Master of Agriculture in Entomology

Master of Agriculture in Plant Pathology

Master of Agriculture in Agricultural

Economics and Rural Sociology

Master In Agriculture And

Rural Development

Scope of Botany

Higher Studies and Career Opportunities

TNMGRMU

AIIMS

MEDICAL Indian Medicine and

MBBS

M.D/M.S/M.D.S

M.Ch. (5 year course)

B.D.S

M.D.S

Homoeopathy Courses

B.A.M.S. - Ayurvedic Medicine

B.H.M.S. - Homoeopathic Medicine

B.N.Y.S. - Naturopathy and Yogic

B.S.M.S. - Siddha Medicine

B.U.M.S. - Unani Medicine

Undergraduate Courses (UG)

MBBS

B.Sc Nursing (post Certificate)

B.Sc. (Hons.) Nursing

Paramedical Courses (PM)

B.Sc. (Hons.) Opthalmic Techniques

B.Sc. (Hons.) Medical Technology

Allied Health Sciences

B.Sc.(N)- Bachelor of Science in Nursing

B.P.T.- Bachelor of Physiotherapy

M.P.T. - Master of Physiotherapy

B.O.T. - Bachelor of Occupational Therapy

M.O.T. - Master of Occupational Therapy

B.Sc. - Accident & Emergency Care Technology

B.Sc. - Audiology & speech Language Pathology

B.Sc. - Cardiac Technology

B.Sc. - Cardio Pulmonary Perfusion Care Technology

B.Sc. - Critical Care Technology

B.Sc. - Dialysis Technology

B.Sc. - Neuro Electrophysiology

B.Sc. - Medical Sociology

B.Sc. - Nuclear Medicine Technology

B.Sc. - Operation Theatre & Anaesthesia Technology

B.Sc. - Physician Assistant

B.Sc. - Radiology Imaging Technology

B.Sc. - Radiotherapy Technology

B.Sc. - Fitness and Lifestyle Modifications

B.Sc. - Clinical Nutrition

Diploma Course

Accident & Emergency Care Technology

Critical Care Technology

Health Care Aide (as per 245th GC)

Operation Theatre & Anaesthesia Technology

Ophthalmic Nursing Assistant

Scope Support Technology

Medical Record Science

Optometry Technology

Radiology & Imaging Technology

Medical Lab Technology

Cardiac Non Invasive Technology

Dialysis Technology

Postgraduate Courses (PG)

M.D/M.S/M.D.S

M.Ch. (5 year course)

M.Sc. / M. Biotechnology

Integrated ed courses

Mode of selection: Entrance conducted by

concern institution or NEET

M.Sc in Life sciences- 5 year Integrated

course

Indian institute of Science, Bengaluru

Website: http://www.iisc.ac.in/

National Institute of Science

Education and Research (NISER) ,

Bhubaneswar, Kolkata , Pune ,

Mohali, Bhopal ,Thiruvananthapuram ,

Tirupati and Berhampur

Website: http://www.niser.ac.in

B.Sc.,B.Ed -5 year Integrated course

Regional Institute of Education

Ajmer, Bhopal, Bhubaneswar, Mysuru

and Shilillong

Website: www.riemysore.ac.in

SCIENCE

Courses in Arts & Science Coleges

and Universities

B.Sc. Botany

B.Sc. Plant Biology & Plant Biotechnology

B.Sc Biochemisty

B.Sc Bio-computing

B.Sc. Plant Pathology

M.Sc. Botany

M.Sc Biotechnology

M.Sc. Bio-chemistry

M.Sc. Bioinformatics

M.Sc Immunology and Microbiology

M.Sc. Applied Medical Biotechnology & clinical

Research

M.Sc. Genetic Engineering & Plant Breeding

M.Sc. Applied Plant Science

M.Sc. Plant Biology & Plant Biotechnology

M.Sc. Plant molecular Biology

M.Sc. Mycology & Plant pathology

M.Sc. Plant science

ANNA UNIVERSITY

B.E. Bio Medical Engineering

B.Tech. Industrial Bio technology

B.Tech. Food technology

B.Tech. Bio technology

V

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Research Institutions in various areas of Botany

Name of the Institution Research Areas Website

International Centre for Genetic Engineering

and Biotechnology (ICGEB), New Delhi

Mammalian Biology; Plant Biology; Synthetic Biology and Biofuels. www.icgen.org

National Institute of Virology, Pune Epidemology, Basic virology; Diagnostics. www.niv.co.in

www.cdfd.org.in

Center for DNA Fingerprinting and Diagnostics,

Hyderabad

Computational Biology, Bioinformatics; Protein structure, Dynamic

and Interactions Epigenetic

Institute of Life Sciences, Bhubaneswar Infectious disease;Immune biology; Cancer biology; Nanotechnology www.ils.res.in

Centre for Cellular and Molecular Biology, Genetics & evolution, Genomics; Cell Biology & Development. www.ccmb.res.in

Hyderabad.

Central food Technological Research Institute, Mysore.

Food science and Technology www.cftri.com

www.cimap.res.in

Central Institute of medicinal and Aromatic

Plants, Lucknow.

National Botanical Research Institute,

Lucknow.

Agronomy & soil sciences; Biotechnology, Crop protection; Genetics

and plant breeding;

Genetics and molecular biology; Plant microbe interaction & Pharmacogonosy.

www.nbri.res.in

Institute of Genomics and Integrative Biology Genomics and Molecular medicine, Chemical and systems biology. www.igib.res.in

Bose Institute, Kolkatta Molecular and cellular biology www.boseinst.ernet.in

www.ncbs.res.in

National Centre for Biological Sciecnes,

Bengaluru

Birbal Sahni Institute od Palaeobotany (BSIP)

Lucknow.

School of Medical Science and Technology, Indian

Institute of Technology, Kharagpur, West Bengal.

Institute of Wood Science and Technology,

Bengaluru.

Centre for Ecological Sciences, Indian Institute

of Science. Bengaluru.

Biochemistry, Biophysics, Bioinformatics, Genetics and development;Cellular

organization & signelling neurobiology etc.

Palynology in fossil fuel exploration; Dendrochronology; Ethnobotany;

Micropaleontology; Carbon 14Dating

www.bsip.res.in

Tissue Engineering; Biomaterials; Herbal medicine & Bio-Engineering. www.smstweb.iitkgp.

ernet.in

Tree improvement and Genetics; Chemistry of Forest Products. iwst.icfre.gov.in

Behaviour Ecology; Evolution; climate change & conservation. www.ces.iisc.ernet.in

Botanical Survey of India(BSI), Kolkatta To Survey, research and conservation of plant resources, flora and

endangered species.

www.bsi.gov.in

VI

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Research Institutions in various areas of Botany

Name of the Institution Research Areas Website

Indian Agricultural Research Institute (IARI)

New Delhi

Indian Institute of Horticultural Research,

Bengaluru

Genetics & Plant Breeding; Plant Pathology; Microbiology; Post Harvest

Technology

www.iari.res.in

Horticultural Research; Biotechnology; Entomology; Pathology www.iihr.res.in

Agharkar Research Institute, Pune Biodiversity & Palaeobiology, Bioenergy, BioprospectingNanobioscicence

National Bureau of Plant Genetic Resources

(NBPGR) New Delhi

Institute of Forest Genetics and Tree Breeding,

Coimbatore.

Central Soil Salinity Research Institute, Karnal,

Haryana

Central Institute of Post Harvest Engineering &

Technology, Ludiana

Central Plantation crops Research Institute,

Kerala

Indian Institute of Crop Processing Technology,

Thanjavur.

Central Tuber Crops Research Institute,

Thiruvananthapuram.

National Centre for Integrated Pest

Management (ICAR) New Delhi

www.aripune.org

Plant genetic resources management and use. www.nbpgr.ernet.in

Tree improvement; Bio-prospecting of Forest Natural Resources www .ifgtb.icfre.gov.in

Reclamation and Management of Salt affected soils. Bio-remediation

of waste waters. Carbon Sequestration

Rapid Evaluation of Food Quality and Safety; Packaging and storage

of agricultural produce and products.

Crop improvement; Production; Protection; Plant physiology and

Biochemistry.

Agricultural Process Engineering Renewable energy for food processing

.

www .cssri.nic.in

www.ciphet.in

www.cpcri.gov.in

www.iicpt.edu.in

Development of Agro techniques for tuber crops www.ctcri.org

Pest Management www.ncipm.org.in

Indian Institute of Spices Research, Kozhikode. Collection, conservation, evaluation and cataloging of germplasm. www.spices.res.in

Central Institute for Cotton Research, Nagpur, (Regional station: Coimbatore & Sirsa)

Crop improvement, Crop Production and Crop Protection. www.cicr.org.in

www.circot.res.in

Central Institute for Research on Cotton Technology,

(CIRCOT) Mumbai

Improvement in Ginning of cotton; Improvement and quality evaluation

of fibers and production of value added products.

Directorate of Cashewnut & Cocoa, Agri, Kerala Cocoa production and processing www.dccd.gov.in

VII

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Research Institutions in various areas of Botany

Name of the Institution Research Areas Website

National Research Center on Plant Biotechnology,

New Delhi

Genetic engineering for biotic resistance. www.nrcpb.org

Indian Institute of Soil Sciences (IISS), Bhopal Study of organic and inorganic nutrient sources affect soil biological

activity.

www.iiss.nic.in

National Institute of Plant Genome Research

(NIPGR), New Delhi

Structural and Functional Genomics in Plants; Computational biology;

Genome analysis and molecular mapping.

www.nipgr.res.in

Sugarcane Breeding Institute, ICAR,

Coimbatore.

Breeding of superior sugarcane varieties/ genotypes; www.sugarcane.res.in

National Centre for Agricultural Economics

and Policy Research (NCAP), New Delhi

Agricultural technology policy. www.ncap.res.in

National Institute of Abiotic Stress

Management., Pune

Basic and strategic research on management of abiotic stresses of crop

plants.

www.niam.res.in

Central Research Institute for Dryland

Agriculture, Hyderabad

Dryland, Agrometerology and Crop sciences crida.in

Central Research Institute for Jute & Allied

Fibres, Kolkata, West Bengal

Crop improvement, Crop production, Crop protection, Agricultural

research.

www.crijaf.org.in

Indian Institute of Pulses Research (IIPR),

Kanpur

Genetics & Plant Breeding and Seed Science www.iipr.res.in

National Research Centre for Groundnut(N-

RCG) Junagarh, Gujarat

Productivity and quality of groundnut; repository of groundnut germplasm

and information on groundnut researches

www.nrcg.res.in

Indian Institutes of Science Education and Research(IISER)

- Berhampur, Bhopal,

Kolkata, Mohali, Pune, Thiruvananthapuram,

and Tirupati.

Microbial Ecology; Marine Molecular Ecology; Marine Biology. www.iiserkol.ac.in

www.issertvm.ac.in

VIII

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Chapter

1

Unit I: Diversity of

Living World

Living World

Learning Objectives

The learner will be able to,

• Differentiate living and non-living

things.

• Appreciate the attributes of living

organisms.

• Compare the different classifications

proposed by biologists.

• Recognize the general characters,

structure and reproduction of

Bacteria.

• Identify the characteristic features

of Archaebacteria, Cyanobacteria,

Mycoplasma and Actinomycetes.

• Describe the characteristic features

of fungi.

• Outline the classification of fungi.

• Describe the structure and

reproduction in Rhizopus and

Agaricus.

• Discuss the structure and uses of

Mycorrhizae and Lichens.

Chapter Outline

1.1 Attributes of

Living organisms

1.2 Viruses

1.3 Classification of

Living world

1.4 Bacteria

1.5 Fungi

Earth was formed some 4.6 billion years

ago. It is the life supporting planet with

land forms like mountains, plateaus,

glaciers, etc., Life on earth exists within

a complex structure called biosphere.

There exist many mysteries and wonders

in the living world some are not visible

but the activity of some capture the

attention of all. For example the response

of sun flower to the sunlight, the twinkling

firefly in the dark forest, the rolling water

droplets on the surface of lotus leaf, the

closure of the leaf of venus fly trap on

insect touch and a squid squeezing ink to

escape from its predator. From this it is

clear that the wonder planet earth harbors

both landforms and life forms. Have you

thought of DNA molecule? It is essential

for the regulation of life and is made up

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of carbon, hydrogen, oxygen, nitrogen

and phosphorus thus nonliving and living

things exist together to make our planet

unique.

According to a survey made by

Mora et al., 2011 the number of estimated

species on earth is 8.7 million. The living

world includes microbes, plants, animals

and human beings which possess unique

and distinct characteristic feature.

1.1 Attributes of living organisms

The attributes of living organisms are given

below and is represented in Figure 1.1

Growth

Metabolism

Respiration

Nutrition

ATTRIBUTES

OF LIVING

ORGANISMS

Irritability

Movement

Reproduction

Excretion

Figure 1.1: Attributes of living organisms

Growth

Growth is an intrinsic property of all

living organisms through which they can

increase cells both in number and mass.

Unicellular and multicellular organisms

grow by cell division. In plants, growth

is indefinite and occurs throughout

their life. In animals, growth is definite

and occurs for some period. However,

cell division occurs in living organisms

to repair and heal the worn out tissues.

Growth in non-living objects is extrinsic.

Mountains, boulders and sand mounds

grow by simple aggregation of material

on the surface. Living cells grow by the

addition of new protoplasm within the

cells. Therefore, growth in living thing is

intrinsic. In unicellular organisms like

bacteria and amoeba growth occurs by cell

division and such cell division also leads

to the growth of their population. Hence,

growth and reproduction are mutually

inclusive events.

Cellular structure

All living organisms are made up of cells

which may be prokaryotic or eukaryotic.

Prokaryotes are unicellular, lack

membrane bound nuclei and organelles

like mitochondria, endoplasmic reticulum,

golgi bodies and so on (Example: Bacteria

and Blue green algae). In Eukaryotes a

definite nucleus and membrane bound

organelles are present. Eukaryotes may

be unicellular (Amoeba) or multicellular

(Oedogonium).

Reproduction

Reproduction is one of the fundamental

characteristic features of living organisms.

It is the tendency of a living organism

to perpetuate its own species. There

are two types of reproduction namely

asexual and sexual (Figure 1.2). Asexual

reproduction refers to the production

of the progeny possessing features more

or less similar to those of parents. The

sexual reproduction brings out variation

through recombination. Asexual

reproduction in living organisms occurs

by the production of conidia (Aspergillus,

Penicillium), budding (Hydra and Yeast),

binary fission (Bacteria and Amoeba)

fragmentation (Spirogyra), protonema

(Mosses) and regeneration (Planaria).

Exceptions are the sterile worker bees

and mules.

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(a)

Nucleus

(b)

to change is called Homeostasis. It

is essential for the living organism to

maintain internal condition to survive in

the environment.

Movement, Nutrition, Respiration

and Excretion are also considered as the

property of living things.

The levels of organization in living

organism begin with atoms and end

in Biosphere. Each level cannot exist

in isolation instead they form levels of

integration as given in Figure 1.3.

Metabolism

(c)

(d)

Figure 1.2: Types of Asexual

Reproduction

(a) Conidia formation-Penicillium,

(b) Budding-Yeast, (c) Fragmentation-

Spirogyra, (d) Regeneration-Planaria

Response to stimuli

All organisms are capable of sensing their

environment and respond to various

physical, chemical and biological stimuli.

Animals sense their surroundings by sense

organs. This is called Consciousness.

Plants also respond to the stimuli. Bending

of plants towards sunlight, the closure of

leaves in touch-me-not plant to touch are

some examples for response to stimuli

in plants. This type of response is called

Irritability.

Homeostasis

Property of self-regulation and tendency

to maintain a steady state within an

external environment which is liable

The sum total of all the chemical

reactions taking place in a cell of living

organism is called metabolism. It is

broadly divided into anabolism and

catabolism. The difference between

anabolism and catabolism is given in

Table 1.1

Table 1.1: Difference between

anabolism and catabolism

Anabolism

Building up

process

Smaller

molecules

combine together

to form larger

molecule

Chemical energy

is formed and

stored

Example:

Synthesis of

proteins from

amino acids

Catabolism

Breaking down

process

Larger molecule

break into smaller

units

The stored chemical

energy is released

and used

Example:

Breaking down of

glucose to CO 2 and

water

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Living

Non Living

Biosphere

Ecosystem

Community

Population

Individual organism

Organ systems

Organs

Tissues

Living cells

Organelles

Molecules &

Compounds

Atoms

Ecosystem

Individual

organism

Living cells

Colloids

Crystals

Mixture

Figure 1.3: The levels of organization

and integration in living organism

III

II

I

Did you go through the headlines of

newspapers in recent times? Have you heard

of the terms EBOLA, ZIKA, AIDS, SARS,

H1N1 etc.? There are serious entities which

are considered as “Biological Puzzle”

and cause disease in man. They are called

viruses. We have learnt about the attributes

of living world in the previous chapter.

Now we shall discuss about viruses which

connect the living and nonliving world.

The word virus is derived from

Latin meaning ‘Poison’. Viruses are

sub-microscopic, obligate intracellular

parasites. They have nucleic acid core

surrounded by protein coat. Viruses in

their native state contain only a single

type of nucleic acid which may be either

DNA or RNA. The study of viruses is

called Virology.

Activity 1.1

Collect Vallisneria leaves or Chara from

nearby aquarium and observe a leaf or

Chara thallus (internodal region)under

the microscope. You could see cells

clearly under the microscope. Could

you notice the movement of cytoplasm?

The movement of cytoplasm is called

cytoplasmic streaming or cyclosis.

1.2 Viruses

W.M. Stanley

(1904-1971)

An American Scientist obtained virus

in crystallised form from infected

tobacco juice in the year 1935. He was

jointly awarded “Nobel Prize” with

Dr. J.H. Northrop for Chemistry in

1946.

1.2.1 Milestones in Virology

1796 Edward Jenner used vaccination

for small pox

1886 Adolf Mayer demonstrated the

infectious nature of Tobacco mosaic

virus using sap of mosaic leaves

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1892 Dimitry Ivanowsky proved that

viruses are smaller than bacteria

1898 M.W. Beijierink defined the

infectious agent in tobacco leaves

as ῾Contagium vivum fluidum’

1915 F.W.Twort identified Viral infection

in Bacteria

1917 d’Herelle coined the term

‘Bacteriophage’

1984 Luc Montagnier and Robert Gallo

discovered HIV (Human Immuno

Deficiency Virus).

1.2.2 Size and shape

Viruses are ultramicroscopic particles.

They are smaller than bacteria and their

diameter range from 20 to 300 nm. (1nm =

10 -9 metres). Bacteriophage measures

about 10-100 nm in size. The size of TMV

is 300×20 nm.

Generally viruses are of three types

based on shape and symmetry (Figure 1.4).

i. Cuboid symmetry – Example:

Adenovirus, Herpes virus.

ii. Helical symmetry – Example:

Influenza virus, TMV.

iii. Complex or Atypical – Example:

Bacteriophage, Vaccinia virus.

1.2.3 Characteristic features of Viruses

Living Characters

• Presence of nucleic acid and protein.

• Capable of mutation

• Ability to multiply within living cells.

• Able to infect and cause diseases in

living beings.

• Show irritability.

• Host –specific

Non-living Characters

• Can be crystallized.

• Absence of metabolism.

• Inactive outside the host.

• Do not show functional autonomy.

• Energy producing enzyme system is

absent.

1.2.4 Classification of Viruses

Among various classifications proposed

for viruses the classification given by

David Baltimore in the year 1971 is

given below. The classification is based

on mechanism of RNA production, the

nature of the genome (single stranded –ss

Fibre

DNA

Protein

RNA

Capsid

Head

DNA

Collar

Sheath

Basal plate

(a) (b) (c)

Tail fibre

Figure 1.4: Shapes of Viruses

(a) Adenovirus, (b) Tobacco Mosaic virus, (c) T 4 Bacteriophage

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Table 1.2: Different Classes of viruses

Class

Class 1 - Viruses with dsDNA

Class 2 –Viruses with (1) sense ssDNA

Class 3 –Viruses with dsRNA

Class 4 –Viruses with (1)sense ssRNA

Class 5 – Viruses with (2)sense ssRNA

Class 6 – Viruses with (1) sense ss RNA –RT: that replicate with

DNA intermediate in life cycle

Class 7 – Viruses with ds DNA –RT: that replicate with RNA

intermediate in life cycle

Example

Adenoviruses

Parvo viruses

Reo viruses

Toga viruses

Rhabdo viruses

Retro viruses

Hepadna

viruses

or double stranded - ds ), RNA or DNA,

the use of reverse transcriptase(RT), ss

RNA may be (1) sense or (2) antisense.

Viruses are classified into seven classes

(Table 1.2).

Viral genome

Each virus possesses only one type of

nucleic acid either DNA or RNA. The

nucleic acid may be in a linear or circular

form. Generally nucleic acid is present

as a single unit but in wound tumour

virus and in influenza virus it is found

in segments. The viruses possessing

DNA are called ‘Deoxyviruses’ whereas

those possessing RNA are called

‘Riboviruses’. Majority of animal

and bacterial viruses are DNA viruses

(HIV is the animal virus which possess

RNA). Plant viruses generally contain

RNA (Cauliflower Mosaic virus possess

DNA). The nucleic acids may be single

stranded or double stranded. On the

basis of nature of nucleic acid viruses

are classified into four Categories. They

are Viruses with ssDNA (Parvoviruses),

dsDNA (Bacteriophages), ssRNA (TMV)

and dsRNA(wound tumour virus).

1.2.5 Tobacco Mosaic Virus (TMV)

Tobacco mosaic virus was discovered

in 1892 by Dimitry Ivanowsky from the

Tobacco plant. Viruses infect healthy

plants through vectors like aphids, locusts

etc. The first visible symptom of TMV

is discoloration of leaf colour along the

veins and show typical yellow and green

mottling which is the mosaic symptom.

The downward curling and distortion of

young apical leaves occurs, plant becomes

stunted and yield is affected.

Structure

Electron microscopic studies have revealed

that TMV is a rod shaped (Figure 1.4b)

helical virus measuring about 280x150µm

with a molecular weight of 39x10 6 Daltons.

The virion is made up of two constituents, a

protein coat called capsid and a core called

nucleic acid. The protein coat is made up

of approximately 2130 identical protein

subunits called capsomeres which are

present around a central single stranded

RNA molecule. The genetic information

necessary for the formation of a complete

TMV particle is contained in its RNA. The

RNA consists of 6,500 nucleotides.

6

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1.2.6 Bacteriophage

Viruses infecting bacteria are called

Bacteriophages. It literally means ‘eaters

of bacteria’ (Gr: Phagein = to eat). Phages

are abundant in soil, sewage water, fruits,

vegetables, and milk.

Structure of T 4 bacteriophage

The T 4 phage is tadpole shaped and

consists of head, collar, tail, base plate and

fibres (Figure 1.4). The head is hexagonal

which consists of about 2000 identical

protein subunits. The long helical tail

consists of an inner tubular core which is

connected to the head by a collar. There

is a base plate attached to the end of tail.

The base plate contains six spikes and tail

fibres. These fibres are used to attach the

phage on the cell wall of bacterial host

during replication. A dsDNA molecule of

about 50 µm is tightly packed inside the

head. The DNA is about 1000 times longer

than the phage itself.

1.2.7 Multiplication or Life Cycle of

Phages

Phages multiply through two different

types of life cycle. a. Lytic or Virulent cycle

b. Lysogenic or Avirulent life cycle

a. Lytic Cycle

During lytic cycle of phage, disintegration

of host bacterial cell occurs and the

progeny virions are released (Figure 1.5a).

The steps involved in the lytic cycle are as

follows:

(i) Adsorption

Phage (T 4 ) particles interact with cell

wall of host (E. coli). The phage tail

makes contact between the two, and tail

fibres recognize the specific receptor

sites present on bacterial cell surface. The

lipopolysaccharides of tail fibres act as

receptor in phages. The process involving

the recognition of phage to bacterium

is called landing. Once the contact

is established between tail fibres and

bacterial cell, tail fibres bend to anchor

the pins and base plate to the cell surface.

This step is called pinning.

(ii) Penetration

The penetration process involves mechanical

and enzymatic digestion of the cell wall

of the host. At the recognition site phage

digests certain cell wall structure by viral

enzyme (lysozyme). After pinning the tail

sheath contracts (using ATP) and appears

shorter and thicker. After contraction of

the base plate enlarges through which

DNA is injected into the cell wall without

using metabolic energy. The step involving

injection of DNA particle alone into the

bacterial cell is called Transfection. The

empty protein coat leaving outside the cell

is known as ‘ghost’.

(iii) Synthesis

This step involves the degradation of

bacterial chromosome, protein synthesis

and DNA replication. The phage nucleic

acid takes over the host biosynthetic

machinery. Host DNA gets inactivated and

breaks down. Phage DNA suppresses the

synthesis of bacterial protein and directs

the metabolism of the cell to synthesis

the proteins of the phage particles and

simultaneously replication of Phage DNA

also takes place.

(iv) Assembly and Maturation

The DNA of the phage and protein coat are

synthesized separately and are assembled

to form phage particles. The process of

7

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Adsorption

Penetration

Capsid

DNA

Bacterial

genome

Phage

DNA

assembling the phage particles is known as

maturation. After 20 minutes of infection

about 300 new phages are assembled.

(v) Release

The phage particle gets accumulated

inside the host cell and are released by the

lysis of host cell wall.

b. Lysogenic Cycle

Synthesis

Assembly and

maturation

Release

(a) Lytic cycle

Phage

Host cell

Release of

new phage

particle

Phage DNA

Bacterial

chromosome

Circular

phage DNA

Prophage

Reproducing

bacterial cell

(b) Lysogenic cycle

Figure 1.5: Multiplication cycle of phage,

In the lysogenic cycle the phage DNA

gets integrated into host DNA and gets

multiplied along with nucleic acid of the

host. No independent viral particle is

formed (Figure 1.5b).

As soon as the phage injects its linear

DNA into the host cell, it becomes

circular and integrates into the bacterial

chromosome by recombination. The

integrated phage DNA is now called

prophage. The activity of the prophage

gene is repressed by two repressor proteins

which are synthesized by phage genes.

This checks the synthesis of new phages

within the host cell. However, each time

the bacterial cell divides, the prophage

multiplies along with the bacterial

chromosome. On exposure to UV radiation

and chemicals the excision of phage DNA

may occur and results in lytic cycle.

Virion is an intact infective virus

particle which is non-replicating outside

a host cell.

Viroid is a circular molecule of ssRNA

without a capsid and was discovered by

T.O.Diener in the year 1971. The RNA of

viroid has low molecular weight. Viroids

cause citrus exocortis and potato spindle

tuber disease in plants.

Virusoids were discovered by

J.W.Randles and Co-workers in 1981.

They are the small circular RNAs which

8

---

are similar to viroids but they are always

linked with larger molecules of the viral

RNA.

Prions were discovered by Stanley

B. Prusiner in the year 1982 and are proteinaceous

infectious particles. They are

the causative agents for about a dozen

fatal degenerative disorders of the central

nervous system of humans and other

animals. For example Creutzfeldt – Jakob

Disease (CJD), Bovine Spongiform Encephalopathy

(BSE) – commonly known

as mad cow disease and scrapie disease

of sheep.

Viruses infecting blue green algae

are called Cyanophages and are first

reported by Safferman and Morris in

the year 1963(Example LPP1 - Lyngbya,

Plectonema and Phormidium). Similarly,

Hollings(1962) reported viruses

infecting cultivated Mushrooms and

causing die back disease. The viruses

attacking fungi are called Mycoviruses

or Mycophages.

1.2.8 Viral diseases

Viruses are known to cause disease

in plants, animals and Human beings

(Figure 1.6). A list of viral disease is given

in Table 1.3

(a)

(b)

Blister

like

pustules

Figure 1.6: Viral diseases (a) Mosaic

disease of tomato, (b) Symptom of

Chicken pox

Table 1.3: Viral diseases

Plant diseases Animal diseases Human diseases

1.Tobacco mosaic

2. Cauliflower mosaic

3. Sugarcane mosaic

4. Potato leaf roll

5. Bunchy top of banana

6. Leaf curl of papaya

1. Foot and mouth disease

of cattle

2. Rabies of dog

3. Encephalomyelitis of

horse

7. Vein clearing of Lady’s

finger

8. Rice tungro disease

9. Cucumber mosaic

10. Tomato mosaic disease

1. Common cold

2. Hepatitis B

3. Cancer

4. SARS(Severe Acute

Respiratory Syndrome)

5. AIDS(Acquired Immuno

Deficiency Syndrome)

6. Rabies

7. Mumps

8. Polio

9. Chikungunya

10. Small Pox

11. Chicken pox

12. Measles

9

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Streaks on Tulip flowers are due to

Tulip breaking Virus which belong to

Potyviridae group.

Viruses of Baculoviridae group are

commercially exploited as insecticides.

Cytoplasmic polyhedrosis Granulo

viruses and Entomopox viruses were

employed as potential insecticides.

1.3 Classification of Living World

From the Previous chapter we know that the

planet earth is endowed with living and non

-living things. In our daily life we see several

things in and around us. Imagine you are on

a trip to Hill station. You are enjoying the

beauty of mountains, dazzling colour of the

flowers, and melodious sound of the birds.

You may be capturing most of the things

you come across in the form of photography.

Now, from this experience can you mention

the objects you came across? Can you record

your observations and tabulate them. How

will you organize the things? Will you place

mountain and flowers together or tall trees

and trailing herbs in one category or place

it in different category? If you place it in

different category, what made you to place

them in different category? So classification

is essential and could be done only by

understanding and comparing the things

based on some characters. In this chapter

we shall learn about classification of living

world.

Many attempts have made in the

past to classify the organisms on earth.

Theophrastus, “Father of botany” used

the morphological characters to classify

plants into trees, shrubs and herbs.

Aristotle classified animal into two

groups. i.e., Enaima (with red blood)

and Anaima (without red blood). Carl

Linnaeus classified living world into

two groups namely Plants and Animals

based on morphological characters. His

classification faced major setback because

prokaryotes and Eukaryotes were grouped

together. Similarly fungi, heterotrophic

organisms were placed along with the

photosynthetic plants. In course of time,

the development of tools compelled

taxonomists to look for different areas like

cytology, anatomy, embryology, molecular

biology, phylogeny etc., for classifying

organisms on earth. Thus, new dimensions

to classifications were put forth from time

to time.

1.3.1 Need of Classification

Classification is essential to achieve

following needs

• To relate things based on common

characteristic features.

• To define organisms based on the

salient features.

• Helps in knowing the relationship

amongst different groups of organisms.

• It helps in understanding the evolutionary

relationship between organisms.

1.3.2 Classification of Living world

A comparison of classification proposed

for classification of living world is given

in Table 1.4

10

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Table 1.4: Systems of Classification

Two Kingdom Three Kingdom Four Kingdom Five Kingdom

Carl Linnaeus

(1735)

Ernst Haeckel

(1866)

Copeland

(1956)

R.H. Whittaker

(1969)

1. Plantae

1. Protista

1. Monera

1. Monera

2. Animalia

2. Plantae

2. Protista

2. Protista

3. Animalia

3. Plantae

3. Fungi

4. Animalia

4. Plantae

5. Animalia

1.3.3 Five Kingdom Classification

R.H.Whittaker, an American taxonomist

proposed five Kingdom classification

in the year 1969. The Kingdoms include

Monera, Protista, Fungi, Plantae and

Animalia (Figure 1.7). The criteria

adopted for the classification include cell

structure, thallus organization, mode of

nutrition, reproduction and phylogenetic

relationship. A comparative account of

the salient features of each Kingdom is

given in Table 1.5

Merits

• The classification is based on the

complexity of cell structure and

organization of thallus.

• It is based on the mode of nutrition

• Separation of fungi from plants

• It shows the phylogeny of the organisms

Demerits

• The Kingdom Monera and protista

accommodate both autotrophic and

heterotrophic organisms, cell wall

lacking and cell wall bearing organisms

thus making these two groups more

heterogeneous.

• Viruses were not included in the

system.

Carl Woese and co-workers in the year

1990 introduced three domains of life viz.,

Bacteria, Archaea and Eukarya based

on the difference in rRNA nucleotide

sequence, lipid structure of the cell

membrane. A revised six Kingdom

classification for living world was

proposed by Thomas Cavalier-Smith in

the year 1998 and the Kingdom Monera

is divided in to Archaebacteria and

Eubacteria. Recently Ruggerio et al., 2015

published a seven Kingdom classification

which is a practical extension of

Thomas Cavalier’s six Kingdom scheme.

According to this classification there

are two SuperKingdoms (Prokaryota

and Eukaryota) Prokaryota include

11

---

Plantae

Spe

permatophyta

Bryophyta

Charophytaa

Oomycete

Phaeophytah

Chlorophyta

Rhodophyt

hyta

Pteridophyta

Ascomycota

Bacillariophytaa

Fungi

Basidiomycotaa

Zygomycota

Myxomyce mycete

Mastigophora

ran

Anne

nelidad

Nematoda

Dictyosteliidae

Platyhelminthes

Animalia

Arthropoda

Mollusca

Vertebratee

Protochordata

Echinodermataa

Chaetognatha

Coelenterata

Porifera

Ciliophora

Cyanophyta

Bacteria

Rhizopoda

Protista

Monera

Figure Figure 1.10 Five 1.7: Five kingdom Kingdom classification

two Kingdoms namely Archaebacteria

and Eubacteria. Eukaryota include the

Protozoa, chromista, fungi, Plantae

and Animalia. A new Kingdom, the

Chromista was erected and it included

all algae whose chloroplasts contain

chlorophyll a and c, as well as various

colorless forms that are closely related

to them. Diatoms, Brown algae,

cryptomonads and Oomycetes were

placed under this Kingdom.

Red tide is caused

by toxic bloom of

Dinoflagellates like

Gymnodinium breve

and Gonyaulax

tamarensis. A major red tide incident

in west coast of Florida in the year

1982 killed Hundreds and thousands

of fishes.

Activity 1.2

Visit to a pond and record the names of

the biotic components of it with the help

of your teacher. Tabulate the data and

segregate them according to Five Kingdom

classification

12

---

Table 1.5: Comparison of Five Kingdoms

Kingdom

Criteria Monera Protista Fungi Plantae Animalia

Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic

Level of Unicellular Unicellular Multicellular

organization

and unicellular

Cell wall Present

(made up of

Peptidoglycan and

Mucopeptides)

Nutrition Autotrophic

(Phototrophic,

Chemoautotrophic)

Heterotrophic

(parasitic and

saprophytic)

Motility Motile or

non-motile

Organisms Archaebacteria,

Eubacteria,

Cyanobacteria,

Actinomycetes and

Mycoplasma

Present in some

(made up of

cellulose), absent in

others

Autotrophic-

Photosynthetic.

Heterotrophic

Motile or

non-motile

Chrysophytes,

Dinoflagellates,

Euglenoids, Slime

molds, Amoeba,

Plasmodium,

Trypanosoma,

Paramecium

Present (made up of

chitin or cellulose)

Heterotrophicparasitic

or

Saprophytic

Tissue/organ Tissue/organ/organ

system

Present (made up of

cellulose)

Autotrophic

(Photosynthetic)

absent

Heterotrophic

(Holozoic)

Non-motile Mostly Non-motile Mostly motile

Yeast, Mushrooms

and Molds

Algae, Bryophytes,

Pteridophytes,

Gymnosperms and

Angiosperms

Sponges,

Invertebrates and

Vertebrates

13

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1.4 Bacteria

Bacteria Friends or Foes?

Have you noticed the preparation of curd

in our home? A little drop of curd turns

the milk into curd after some time. What is

responsible for this change? Why it Sours?

The change is brought by Lactobacillus

lactis, a bacterium present in the curd.

The sourness is due to the formation of

Lactic acid. Have you been a victim of

Typhoid? It is a bacterial disease caused

by Salmonella typhi, a bacterium. So we

can consider this prokaryotic organism as

friend and foe, due to their beneficial and

harmful activities.

1.4.1 Milestones in Bacteriology

1829 C.G. Ehrenberg coined the term

Bacterium

1884 Christian Gram introduced

Gram staining method

1923 David H. Bergy published First

edition of Bergey’s Manual

1928 Fredrick Griffith discovered

Bacterial transformation

1952 Joshua Lederberg discovered of

Plasmid

Bacteria are prokaryotic, unicellular, ubiquitous,

microscopic organisms. The study

of Bacteria is called Bacteriology. Bacteria

were first discovered by a Dutch scientist,

Anton van Leeuwenhoek in 1676 and were

called “animalcules”.

1.4.2 General characteristic features of

Bacteria

Robert Koch (1843–1910)

Robert Heinrich Hermann Koch

was a German physician and

microbiologist. He is considered as

the founder of modern bacteriology.

He identified the causal organism for

Anthrax, Cholera and Tuberculosis.

The experimental evidence for the

concept of infection was proved by him

(Koch’s postulates). He was awarded

Nobel prize in Medicine/Physiology

in the year 1905.

• They are Prokaryotic organisms and

lack nuclear membrane and membrane

bound organelles.

• The Genetic material is called nucleoid

or genophore or incipient nucleus

• The cell wall is made up of

Polysaccharides and proteins

• Most of them lack chlorophyll, hence

they are heterotrophic (Vibrio cholerae)

but some are autotrophic and possess

Bacteriochlorophyll (Chromatium)

• They reproduce vegetatively by Binary

fission and endospore formation.

• They exhibit variations which are due to

genetic recombination and is achieved

through conjugation, transformation

and transduction.

The shape and flagellation of the bacteria

varies and is given in Figure 1.8

14

---

Coccus

Diplococcus

Staphylococcus

Tetracoccus

Monotrichous

Lophotrichous

Sarcina

Streptococcus

Amphitrichous

Bacillus

Diplobacillus

Peritrichous

Vibrio

Spirillum

Atrichous

1.4.3 Ultrastructure of a Bacterial cell

Figure 1.8: Shape and flagellation in bacteria

The bacterial cell reveals three layers (i) Capsule/Glycocalyx (ii) Cell wall and

(iii) Cytoplasm (Figure 1.9)

Capsule

Cell wall

Plasma membrane

Figure 1.9: Ultrastructure of a bacterial cell

15

Mesosome

Cytoplasm

Nucleoid (DNA)

Flagellum

Plasmid

Inclusion

Polyribosome

Pilus

---

Duodenal and Gastric

ulcers are caused by

Helicobacter pylori,

a Gram negative

bacterium

• Bt toxin from Bacillus thuringiensis

finds application in raising insect

resistant crops (Bt Crops).

Capsule/Glycocalyx

Some bacteria are surrounded by a

gelatinous substance which is composed

of polysaccharides or polypeptide or both.

A thick layer of glycocalyx bound tightly

to the cell wall is called capsule. It protects

cell from desiccation and antibiotics.

The sticky nature helps them to attach to

substrates like plant root surfaces, Human

teeth and tissues. It helps to retain the

nutrients in bacterial cell.

Cell wall

The bacterial cell wall is granular and is

rigid. It provide protection and gives shape

to the cell. The chemical composition of

cell wall is rather complex and is made up of

Peptidoglycan or mucopeptide ( N-acetyl

glucosamine, N-acetyl muramic acid

and peptide chain of 4 or 5 aminoacids).

One of the most abundant polypeptide

called porin is present and it helps in the

diffusion of solutes.

Plasma membrane

The plasma membrane is made up of

lipoprotein. It controls the entry and exit

of small molecules and ions. The enzymes

involved in the oxidation of metabolites

(i.e., the respiratory chain) as well as the

photosystems used in photosynthesis are

present in the plasma membrane.

Cytoplasm

Cytoplasm is thick and semitransparent.

It contains ribosomes and other cell

inclusions. Cytoplasmic inclusions

like glycogen, poly-β-hydroxybutyrate

granules, sulphur granules and gas vesicles

are present.

Bacterial chromosome

The bacterial chromosome is a single

circular DNA molecule, tightly coiled

and is not enclosed in a membrane as in

Eukaryotes. This genetic material is called

Nucleoid or Genophore. It is amazing

to note that the DNA of E.coli which

measures about 1mm long when uncoiled,

contains all the genetic information of

the organism. The DNA is not bound to

histone proteins. The single chromosome

or the DNA molecule is circular and at

one point it is attached to the plasma

membrane and it is believed that this

attachment may help in the separation of

two chromosomes after DNA replication.

Plasmid

Plasmids are extra chromosomal double

stranded, circular, self-replicating,

autonomous elements. They contain genes

for fertility, antibiotic resistant and heavy

metals. It also help in the production of

bacteriocins and toxins which are not

found in bacterial chromosome. The size

of a plasmid varies from 1 to 500 kb usually

plasmids contribute to about 0.5 to 5.0%

of the total DNA of bacteria. The number

of plasmids per cell varies. Plasmids are

classified into different types based on the

function. Some of them are F (Fertility)

factor, R (Resistance) plasmids, Col (Colicin)

plasmids, Ri (Root inducing) plasmids and

Ti (Tumour inducing) plasmids.

16

---

Mesosomes

These are localized infoldings of plasma

membrane produced into the cell in the

form of vesicles, tubules and lamellae.

They are clumped and folded together to

maximize their surface area and helps in

respiration and in binary fission.

Polysomes / Polyribosomes

The ribosomes are the site of protein

synthesis. The number of ribosome per

cell varies from 10,000 to 15,000. The

ribosomes are 70S type and consists of two

subunits (50S and 30S). The ribosomes

are held together by mRNA and form

polyribosomes or polysomes.

Flagella

Certain motile bacteria have numerous

thin hair like processes of variable length

emerge from the cell wall called flagella.

It is 20–30 μm in diameter and 15 μm in

length. The flagella of Eukaryotic cells

contain 9+2 microtubles but each flagellum

in bacteria is made up of a single fibril.

Flagella are used for locomotion. Based on

the number and position of flagella there

are different types of bacteria (Figure 1.8)

Fimbriae or Pili

Pili or fimbriae are hair like appendages

found on surface of cell wall of

gram-negative bacteria (Example:

Enterobacterium). The pili are 0.2 to 20 µm

long with a diameter of about 0.025µm. In

addition to normal pili there are special

type of pili which help in conjugation

called sex pili are also found.

1.4.4 Gram staining procedure

The Gram staining method to

differentiate bacteria was developed by

Danish Physician Christian Gram in

the year1884. It is a differential staining

procedure and it classifies bacteria into

two classes - Gram positive and Gram

negative. The steps involved in Gram

staining procedure is given in Figure

1.10. The Gram positive bacteria retain

crystal violet and appear dark violet

whereas Gram negative type loose the

crystal violet and when counterstained

by safranin appear red under a

microscope.

Prepare a smear of bacterial culture

Stain with Crystal violet for 30 seconds

Rinse in distilled water for 2 seconds

Grams Iodine for 1 minute

Rinse in distilled water

Wash in 95% ethanol or acetone

for 10 to 30 seconds

Rinse in distilled water

Safranin for 30–60 seconds

Rinse in distilled water and blot

Observe under microscope

Figure 1.10: Steps involved in Gram

Staining

17

---

Most of the gram positive cell wall

contain considerable amount of teichoic

acid and teichuronic acid. In addition,

they may contain polysaccharide

molecules. The gram negative cell wall

contains three components that lie outside

the peptidoglycan layer. 1. Lipoprotein

GRAM POSITIVE

2. Outer membrane 3.Lipopolysaccharide.

Thus the different results in the gram stain

are due to differences in the structure and

composition of the cell wall (Figure 1.11).

The difference between Gram Positive

and Gram negative bacteria is given in

Table 1.6.

GRAM NEGATIVE

Outer membrane

Lipoproteins

Peptidoglycan

Periplasmic space

Cytoplasmic membrane

Lipopolysaccharides

Porin

Protein

Figure 1.11: Difference between Gram positive and Gram negative bacteria

Table 1.6: Difference between Gram Positive and Gram Negative Bacteria

S.No Characteristics Gram positive Bacteria Gram negative Bacteria

1. Cell wall Single layered with

0.015µm-0.02µm

2. Rigidity of cell wall Rigid due to presence of

Peptidoglycans

Triple layered with

0.0075µm–0.012µm thick

Elastic due to presence of

lipoprotein-polysaccharide

mixture

3. Chemical composition Peptidoglycans-80%

Polysaccharide-20%

Teichoic acid present

4. Outer membrane Absent Present

5. Periplasmic space Absent Present

6. Susceptibility to

penicillin

Highly susceptible

Peptidoglycans-3 to 12%

rest is polysaccharides and

lipoproteins. Teichoic acid

absent

Low susceptible

7. Nutritional requirements Relatively complex Relatively simple

8. Flagella Contain 2 basal body rings Contain 4 basal body rings

9. Lipid and lipoproteins Low High

10. Lipopolysaccharides Absent Present

18

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What are Magnetosomes ?

Intracellular chains of 40-50

magnetite (Fe 3 O 4 ) particles are

found in bacterium Aquaspirillum

magnetotacticum. and it help the

bacterium to locate nutrient rich

sediments.

1.4.5 Life processes in Bacteria

Respiration

Two types of respiration is found in

Bacteria. They are 1. Aerobic respiration

2. Anaerobic respiration.

1. Aerobic respiration

These bacteria require oxygen as

terminal acceptor and will not grow under

anaerobic conditions (i.e. in the absence of

O 2 ) Example: Streptococcus.

Obligate aerobes

Some Micrococcus species are obligate

aerobes (i.e. they must have oxygen to

survive).

2. Anaerobic respiration

These bacteria do not use oxygen for

growth and metabolism but obtain their

energy from fermentation reactions.

Example: Clostridium.

Facultative anaerobes

There are bacteria that can grow

either using oxygen as a terminal

electron acceptor or anaerobically using

fermentation reaction to obtain energy.

When a facultative anaerobe such as E. coli

is present at a site of infection like an

abdominal abscess, it can rapidly consume

all available O 2 and change to anaerobic

metabolism producing an anaerobic

environment and thus allow the anaerobic

bacteria that are present to grow and cause

disease.

Example: Escherichia coli and Salmonella.

Capnophilic Bacteria

Bacteria which require CO 2 for their

growth are called as capnophilic bacteria.

Example: Campylobacter.

Nutrition

On the basis of their mode of nutrition

bacteria are classified into two types

namely Autotrophs and Heterotrophs.

I Autotrophic Bacteria

Bacteria which can synthesis their own

food are called autotrophic bacteria. They

may be further subdivided as

A. Photoautotrophic bacteria

Bacteria use sunlight as their source of

energy to synthesize food. They may be

1. Photolithotrophs

In Photolithotrophs the hydrogen donor

is an inorganic substance.

a. Green sulphur bacteria: In this type of

bacteria the hydrogen donor is H 2 S and

possess pigment called Bacterioviridin.

Example: Chlorobium.

b. Purple sulphur bacteria: For bacteria

belong to this group the hydrogen donor

is Thiosulphate, Bacteriochlorophyll

is present. Chlorophyll containing

chlorosomes are present Example:

Chromatium.

2. Photoorganotrophs

They utilize organic acid or alcohol as

hydrogen donor. Example: Purple non

sulphur bacteria – Rhodospirillum.

B. Chemoautotrophic bacteria

They do not have photosynthetic pigment

hence they cannot use sunlight energy.

This type of bacteria obtain energy from

organic or inorganic substance.

19

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1.Chemolithotrophs

This type of bacteria oxidize inorganic

compound to release energy.

Examples:

1. Sulphur bacteria

Thiobacillus thiooxidans

2. Iron bacteria

Ferrobacillus ferrooxidans

3. Hydrogen bacteria

Hydrogenomonas

4. Nitrifying bacteria

Nitrosomonas and Nitrobacter

Cell wall

Nucleoid

Daughter

cells

(a)

Endospore

Thick wall

(b)

2. Chemoorganotrophs

This type of bacteria oxidize organic

compounds to release energy.

Examples:

1. Methane bacteria – Methanococcus

2. Acetic acid bacteria – Acetobacter

3. Lactic acid bacteria – Lactobacillus

II. Heterotrophic Bacteria

They are Parasites (Clostridium,

Mycobacterium) Saprophytes (Bacillus

mycoides) or Symbiotic (Rhizobium in

root nodules of leguminous crops).

1.4.6 Reproduction in Bacteria

Bacteria reproduces asexually by Binary

fission, conidia and endospore formation

(Figure 1.12). Among these Binary fission

is the most common one.

Binary fission

Under favourable conditions the cell

divides into two daughter cells. The

nuclear material divides first and it is

followed by the formation of a simple

median constriction which finally results

in the separation of two cells.

Figure 1.12: Asexual Reproduction in

Bacteria (a) Binary fission,

(b) Endospore

Endospores

During unfavourable condition bacteria

produce endospores. Endospores are

produced in Bacillus megaterium, Bacillus

sphaericus and Clostridium tetani.

Endospores are thick walled resting

spores. During favourable condition, they

germinate and form bacteria.

Sexual Reproduction

Typical sexual reproduction involving the

formation and fusion of gametes is absent

in bacteria. However gene recombination

can occur in bacteria by three different

methods they are

1. Conjugation

2. Transformation

3. Transduction

1. Conjugation

J. Lederberg and Edward L. Tatum demonstrated

conjugation in E. coli. in the year

1946. In this method of gene transfer the

donor cell gets attached to the recipient cell

20

---

with the help of pili. The pilus grows in size

and forms the conjugation tube. The plasmid

of donor cell which has the F+ (fertility

factor) undergoes replication. Only

one strand of DNA is transferred to the recipient

cell through conjugation tube. The

recipient completes the structure of double

stranded DNA by synthesizing the strand

that complements the strand acquired from

the donor (Figure 1.13).

(a)

R-Strain

S-Strain

Heat-Killed

S-Strain

R-Strain and Heatkilled

S- Strain

Mouse lives Mouse dies Mouse lives Mouse dies

Conjugation pilus

F + cell

F - cell

Chromosome

F plasmid

F + cell

F + cell

Figure 1.13: Conjugation

2. Transformation

Transfer of DNA from one bacterium

to another is called transformation

(Figure 1.14). In 1928 the bacteriologist

Frederick Griffith demonstrated

transformation in Mice using

Diplococcus pneumoniae. Two strains of

this bacterium are present. One strain

produces smooth colonies and are

virulent in nature (S-type). In addition

another strain produce rough colonies

and are avirulent (R-type). When S-type

of cells were injected into the mouse,

the mouse died. When R-type of cells

were injected, the mouse survived.

He injected heat killed S-type cells

into the mouse the mouse did not die.

When the mixture of heat killed S-type

(b)

Figure 1.14: Transformation in Bacteria

(a) Griffith’s experiment on Transformation

(b) Mechanism of Transformation

cells and R-type cells were injected

into the mouse. The mouse died. The

avirulent rough strain of Diplococcus

had been transformed into S-type cells.

The hereditary material of heat killed

S-type cells had transformed R-type cell

into virulent smooth strains. Thus the

phenomenon of changing the character

of one strain by transferring the DNA of

another strain into the former is called

Transformation.

21

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3. Transduction

Zinder and Lederberg (1952) discovered

Transduction in Salmonella typhimurum.

Phage mediated DNA transfer is called

Transduction (Figure 1.15).

Transduction is of two types

(i) Generalized Transduction (ii) Specialized

or Restricted Transduction

(i) Generalized Transduction

The ability of a bacteriophage to carry

genetic material of any region of

bacterial DNA is called Generalised

transduction.

(ii) Specialized or Restricted Transduction

The ability of the bacteriophage to carry

only a specific region of the bacterial

DNA is called specialized or restricted

transduction.

1.4.7 Economic importance of Bacteria

Bacteria are both beneficial and Harmful.

The beneficial activities of bacteria are

given in Table 1.7.

Phage

Phage DNA

Bacterial chromosome

Virulent

phage

Defective

particle

Defective

particle

Recipient

Cell

Generalised Transduction

Specialised Transduction

Figure 1.15: Transduction in Bacteria

22

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Table 1.7: Economic importance of Bacteria

Beneficial aspects Bacteria Role

1. Soil fertility

Ammonification

Nitrification

Nitrogen fixation

2. Antibiotics

1. Bacillus ramosus

2. Bacillus mycoides

1. Nitrobacter

2. Nitrosomonas

1. Azotobacter

2. Clostridium

3. Rhizobium

23

Convert complex proteins in the dead

bodies of plants and animals into

ammonia which is later converted into

ammonium salt

Convert ammonium salts into nitrites and

nitrates

(i) Converting atmospheric nitrogen into

organic nitrogen

(ii) The nitrogenous compounds are also

oxidized to nitrogen

(iii) All these activities of bacteria increase

soil fertility

1. Streptomycin Streptomyces griseus It cures urinary infections, tuberculosis,

meningitis and pneumonia

2. Aureomycin Streptomyces aureofaciens It is used as a medicine to treat whooping

cough and eye infections

3. Chloromycetin Streptomyces venezuelae It cure typhoid fever

4. Bacitracin Bacillus licheniformis It is used to treat syphilis

5. Polymyxin Bacillus polymyxa It cure some bacterial diseases

3. Industrial Uses

1. Lactic acid Streptococcus lactis and

Lactobacillus bulgaricus

2. Butter Streptococcus lactis,

Leuconostoc citrovorum

3. cheese Lactobacillus acidophobus,

Lactobacillus lactis

4. Curd Lactobacillus lactis

5. Yoghurt Lactobacillus bulgaricus

6. Vinegar

(Acetic acid)

Acetobacter aceti

Convert milk sugar lactose into lactic acid

Convert milk into butter, cheese, curd and

yoghurt

This bacteria oxidizes ethyl alcohol

obtained from molasses by fermentation

to vinegar(acetic acid)

(Continued)

---

7. Alcohol and

Acetone

(i) Butyl alcohol

(ii) Methyl alcohol

Clostridium acetobutylicum

Alcohols and acetones are prepared from

molasses by fermentation activity of the

anaerobic bacterium.

8. Retting of fibres Clostridium tertium The fibres from the fibre yielding plants

are separated by the action of Clostridium

is called retting of fibres.

9. Vitamins Escherichia coli Living in the intestine of human beings

produce large quantities of vitamin K and

vitamin B complex.

10. Curing of Tea

and Tobacco

Clostridium acetobutylicum

Mycococcus candisans,

Bacillus megatherium

Vitamins B 2 is prepared by the

fermentation of sugar.

The special flavor and aroma of the tea

and tobacco are due to fermentation.

Bacteria are known to cause disease in plants, animals and Human beings. The List is

given in Table 1.8, 1.9, 1.10 and Figure 1.16.

S.No.

Name of the

Host

Table 1.8: Plant diseases caused by Bacteria

Name of the

disease

Name of the pathogen

1 Rice Bacterial blight Xanthomonas oryzae

2 Apple Fire blight Erwinia amylovora

3 Carrot Soft rot Erwinia caratovora

4 Citrus Citrus canker Xanthomonas citri

5 Cotton Angular leaf spot Xanthomonas malvacearum

6 Potato Ring rot Clavibacter michiganensis subsp.

sepedonicus

7 Potato Scab Streptomyces scabies

Table 1.9: Animal diseases caused by Bacteria

S. No Name of the Animal Name of the disease Name of the pathogen

1. Sheep Anthrax Bacillus anthracis

2. Cattle Brucellosis Brucella abortus

3. Cattle Bovine tuberculosis Mycobacterium bovis

4. Cattle Black leg Clostridium chanvei

24

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Table 1.10: Human diseases caused by Bacteria

S.No Name of the disease Name of the pathogen

1. Cholera Vibrio cholerae

2. Typhoid Salmonella typhi

3. Tuberculosis Mycobacterium tuberculosis

4. Leprosy Mycobacterium leprae

5. Pneumonia Diplococcus pneumoniae

6. Plague Yersinia pestis

7. Diphtheria Corynebacterium diptheriae

8. Tetanus Clostridium tetani

9. Food poisoning Clostridium botulinum

10. Syphilis Treponema pallidum

and prepare a smear by squeezing the

content into a clean slide. Follow Gram

staining method and identify the bacteria.

(a)

(b)

Figure 1.16: Plant diseases caused by

bacteria (a) Citrus canker (b) Potato scab

Have you heard about the word

“Probiotics”

Bacteria forms

Biofilms and leads

to dental caries

and Urinary tract

infection (UTI)

Ralstonia synthesize PHB (Poly-βhydroxyl

butyrate) a microbial plastic

which is biodegradable.

Probiotic milk products, tooth paste are

available in the Market. Lactobacillus,

Bifidobacterium are used to prepare

probiotic yoghurt and tooth paste

Activity 1.3

Collect some root nodules of leguminous

crops. Draw diagram. Wash it in tap water

1.4.8 Archaebacteria

Archaebacteria are primitive prokaryotes

and are adapted to thrive in extreme

environments like hot springs, high

salinity, low pH and so on. They are mostly

chemoautotrophs. The unique feature of

this group is the presence of lipids like

glycerol & isopropyl ethers in their cell

membrane. Due to the unique chemical

composition the cell membrane show

resistance against cell wall antibiotics and

lytic agents. Example: Methanobacterium,

Halobacterium, Thermoplasma.

25

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• Pseudomonas

putida is a superbug

genetically engineered

which breakdown

hydrocarbons.

• “Pruteen” is a single cell protein

derived from Methylophilus and

Methylotropus.

• Agrobacterium tumefaciens cause

crown gall disease in plants but its

inherent tumour inducing principle

helps to carry the desired gene

into the plant through Genetic

engineering.

• Thermus aquaticus is a thermophilic

gram negative bacteria which

produces Taq Polymerase a key

enzyme for Polymerase Chain

Reaction (PCR).

• Methanobacterium is employed in

biogas production. Halobacterium,

an extremophilic bacterium grows

in high salinity. It is exploited for

the production β carotene.

1.4.9 Cyanobacteria (Blue Green Algae)

How old are Cyanobacteria ?

Stromatolites reveals the truth.

Stromatolites are deposits formed

when colonies of cyanobacteria bind

with calcium carbonate. They have a

geological age of 2.7 billion years. Their

abundance in the fossil record indicates

that cyanobacteria helped in raising the

level of free oxygen in the atmosphere.

Cyanobacteria are popularly called

as 'Blue green algae' or 'Cyanophyceae'.

They are photosynthetic, prokaryotic

organisms. According to evolutionary

record Cyanobacteria are primitive

forms and are found in different

habitats. Most of them are fresh water

and few are marine (Trichodesmium and

Dermacarpa) Trichodesmium erythraeum

a cyanobacterium imparts red colour to

sea (Red sea). Species of Nostoc, Anabaena

lead an endophytic life in the coralloid

root of Cycas, leaves of aquatic fern Azolla

and thallus of hornworts like Anthoceros

by establishing a symbiotic association

and fix atmospheric nitrogen. Members

like Gloeocapsa, Nostoc, Scytonema are

found as phycobionts in lichen thalli.

Salient features

• The members of this group are

prokaryotes and lack motile

reproductive structures.

• The thallus is unicellular in

Chroococcus, Colonial in Gloeocapsa

and filamentous trichome in Nostoc.

• Gliding movement is noticed in some

species(Oscillatoria).

• The protoplasm is differentiated into

central region called centroplasm

and peripheral region bearing

chromatophore called chromoplasm.

• The photosynthetic pigments include

c-phyocyanin and c-phycoerythrin

along with myxoxanthin and

myxoxanthophyll.

26

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• The reserve food material is

Cyanophycean starch.

• In some forms a large colourless cell

is found in the terminal or intercalary

position called Heterocysts. They are

involved in nitrogen fixation.

• They reproduce only through vegetative

methods and produce Akinetes

(thick wall dormant cell formed

from vegetative cell), Hormogonia (a

portion of filament get detached and

reproduce by cell division), fission,

Endospores.

• The presence of mucilage around the

thallus is characteristic feature of this

group. Therefore, this group is also

called Myxophyceae

• Sexual reproduction is absent.

• Microcystis aeruginosa, Anabaena

flos-aquae cause water blooms

and release toxins and affect the

aquatic organism. Most of them fix

atmospheric nitrogen and are used

as biofertilizers (Example: Nostoc,

Anabaena). Spirulina is rich in

protein hence it is used as single cell

protein. The thallus organisation and

methods of reproduction is given in

Figure 1.17

A prokaryote takes a joy ride on

polar bear (Aphanocapsa montana -

a cynobacterium grow on the fur of a

polar bear).

Chroococcus Gloeocapsa Nostoc

Spirulina

Fission Akinete

(Synechocystis) (Anabaena)

Endospore

(Dermacarpa)

Figure 1.17: Structure and reproduction

in cyanophyceae

1.4.10 Mycoplasma or Mollicutes

The Mycoplasma are very small

(0.1–0.5µm), pleomorphic gram negative

microorganisms. They are first isolated

by Nocard and co-workers in the year

1898 from pleural fluid of cattle affected

with bovine pleuropneumonia. They lack

cell wall and appears like “Fried Egg” in

culture. The DNA contains low Guanine

and Cytosine content than true bacteria.

They cause disease in animals and plants.

Little leaf of brinjal, witches broom

of legumes phyllody of cloves, sandal

spike are some plant diseases caused

by mycoplasma. Pleuropneumonia is

caused by Mycoplasma mycoides. The

structure of Mycoplasma is given in

Figure 1.18.

27

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1.5 Fungi

Cell membrane

World War II and Penicillin

History speaks on fungi

Ribosome

DNA Strand

Figure 1.18: Structure of Mycoplasma

1.4.11 Actinomycetes (Actinobacteria)

Actinomycetes are also called ‘Ray

fungi’ due to their mycelia like growth

They are anaerobic or facultative

anaerobic microorganisms and are Gram

positive. They do not produce an aerial

mycelium. Their DNA contain high

guanine and cytosine content (Example:

Streptomyces).

Frankia is a symbiotic actinobacterium

which produces root nodules and fixes

nitrogen in non – leguminous plants such

as Alnus and Casuarina. They produce

multicellular sporangium. Actinomyces

bovis grows in oral cavities and cause

lumpy jaw.

Streptomyces is a mycelial forming

Actinobacteria which lives in soil,

they impart “earthy odor” to soil after

rain which is due to the presence of

geosmin (volatile organic compound).

Some important antibiotics namely,

Streptomycin, Chloramphenicol, and

Tetracycline are produced from this

genus.

Alexander Fleming

Discovery of Penicillin in the year 1928

is a serendipity in the world of medicine.

The History of World War II recorded

the use of Penicillin in the form of yellow

powder to save lives of soldiers. For this

discovery - The wonderful antibiotic he

was awarded Nobel Prize in Medicine in

the year 1945.

1.5.1 Milestones in Mycology

1729 P.A.Micheli conducted spore

culture experiments

1767 Fontana proved that Fungi could

cause disease in plants

1873 C.H. Blackley proved fungi could

cause allergy in Human beings

1906 A.F.Blakeslee reported

heterothallism in fungi

1952 Pontecarvo and Raper reported

Parasexual cycle

The word ‘fungus’ is derived from Latin

meaning ‘mushroom’. Fungi are ubiquitous,

eukaryotic, achlorophyllous heterotrophic

organisms. They exist in unicellular or

multicellular forms. The study of fungi is

called mycology. (Gr. mykes – mushroom:

28

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logos – study). P.A. Micheli is considered

as founder of Mycology. Few renowned

mycologists include Arthur H.R.

Buller, John Webster, D.L.Hawksworth,

G.C.Ainsworth, B.B.Mundkur, K.C.Mehta,

C.V. Subramanian and T.S. Sadasivan.

Septate mycelium

Coenocytic mycelium

Figure 1.19: Types of mycelium

E.J. Butler (1874-1943)

Father of Indian Mycology. He

established Imperial Agricultural

Research Institute at Pusa, Bihar. It

was later shifted to New Delhi and at

present known as Indian Agricultural

Research Insitute (IARI) He published

a book, ‘Fungi and Disease in Plants’ on

Indian plant diseases in the year 1918.

1.5.2 General characteristic features

• Majority of fungi are made up of

thin, filamentous branched structures

called hyphae. A number of hyphae

get interwoven to form mycelium.

The cell wall of fungi is made up of a

polysaccharide called chitin (polymer

of N-acetyl glucosamine).

• The fungal mycelium is categorised

into two types based on the presence or

absence of septa (Figure 1.19). In lower

fungi the hypha is aseptate, multinucleate

and is known as coenocytic mycelium

(Example: Albugo). In higher fungi a

septum is present between the cells of the

hyphae. Example: Fusarium.

• The mycelium is organised into loosely

or compactly interwoven fungal tissues

called plectenchyma. It is further

divided into two types prosenchyma

and pseudoparenchyma. In the former

type the hyphae are arranged loosely

but parallel to one another In the latter

hyphae are compactly arranged and

loose their identity.

• In holocarpic forms the entire thallus

is converted into reproductive

structure whereas in Eucarpic some

regions of the thallus are involved in

the reproduction other regions remain

vegetative. Fungi reproduce both by

asexual and sexual methods. The

asexual phase is called Anamorph and

the sexual phase is called Teleomorph.

Fungi having both phases are called

Holomorph.

In general sexual reproduction in fungi

includes three steps 1. Fusion of two

protoplasts (plasmogamy) 2. Fusion of

nuclei (karyogamy) and 3. Production of

haploid spores through meiosis. Methods

of reproduction in fungi is given in

Figure 1.20.

29

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1.5.3 Methods of Reproduction in

Fungi

Asexual Reproduction

1. Zoospores: They are flagellate structures

produced in zoosporangia (Example:

Chytrids)

2. Conidia: The spores produced on

condiophores (Example: Aspergillus)

3. Oidia/Thallospores/Arthrospores: The

hypha divide and develop in to spores

called oidia (Example: Erysiphe).

4. Fission: The vegetative cell divide

into 2 daughter cells. (Example:

Schizosaccharomyces-yeast).

5. Budding: A small outgrowth is

developed on parent cell, which gets

detached and become independent.

(Example: Saccharomyces-yeast)

6. Chlamydospore: Thick walled resting

spores are called chlamydospores

(Example: Fusarium).

Sexual Reproduction

1. Planogametic copulation: Fusion of motile

gamete is called planogametic copulation. a.

Isogamy – Fusion of morphologically and

physiologicall similar gametes. (Example:

Synchytrium). b. Anisogamy – Fusion

of morphologically or physiologically

dissimilar gametes (Example: Allomyces).

c. Oogamy – Fusion of both morphologically

and physiologically dissimilar gametes.

(Example: Monoblepharis)

2. Gametangial contact: During sexual

reproduction a contact is established

between antheridium and Oogonium

(Example: Albugo)

3. Gametangial copulation: Fusion of

gametangia to form zygospore (Example:

Mucor, Rhizopus).

30

4. Spermatization: In this method a uninucleate

pycniospore/microconidium

is transferred to receptive hyphal cell

(Example: Puccinia/Neurospora)

5. Somatogamy: Fusion of two somatic

cells of the hyphae (Example: Agaricus)

Nucleus

(a) Budding - Yeast

(b) Fission - Yeast

Conidium

Sterigma

Metula

Ramus

Conidiophore

(c) Conidia formation - Penicillium

(d) Thallospore -

Erysiphe

Oidium

Chlamydospore

(e) Chlamydospore -

Fusarium

---

Trichogyne

Microconidia

(f) Sporangia - Mucor

‘+’ Strain ‘ _ ’ Strain

Archicarp

Progametangium

(i) Spermatisation - Neurospora

Figure 1.20: Reproduction in Fungi

Zygospore

Zygosporangium

(g) Gametangial copulation - Rhizopus

Antheridium

Fertilization tube

Oogonium

(h) Gametangial contact - Albugo

1.5.4 Classification of Fungi

Many mycologists have attempted to

classify fungi based on vegetative and

reproductive characters. Traditional

classifications categorise fungi into

4 classes – Phycomycetes, Ascomycetes,

Basidiomycetes and Deuteromycetes.

Among these ‘Phycomycetes’ include

fungal species of Oomycetes,

Chytridiomycetes and Zygomycetes

which are considered as lower fungi

indicating algal origin of fungi.

Constantine J. Alexopoulos and Charles

W. Mims in the year 1979 proposed

the classification of fungi in the book

entitled ‘Introductory Mycology’. They

classified fungi into three divisions

namely Gymnomycota, Mastigomycota

and Amastigomycota. There are 8

subdivisions, 11 classes, 1 form class and

3 form subclasses in the classification

proposed by them.

31

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The outline of the classification is given below:

KINGDOM - MYCETEAE

DIVISION –

GYMNOMYCOTA

SUBDIVISION – 1

ACRASIOGYMNOMYCOTINA

CLASS – Acrasiomycetes

SUBDIVISION – 2

PLASMODIOGYMNOMY-

COTINA

CLASS – Protosteliomycetes

CLASS- Myxomycetes

DIVISION -

MASTIGOMYCOTA

SUBDIVISION – 1

HAPLOMASTIGOMYCOTINA

CLASS – Chytridiomycetes

CLASS – Hyphochytridiomycetes

CLASS – Plasmodiophoromycetes

SUBDIVISION – 2

DIPLOMASTIGOMYCOTINA

CLASS - Oomycetes

DIVISION –

AMASTIGOMYCOTA

SUBDIVISION -1

ZYGOMYCOTINA

Class – Zygomycetes

Class- Trichomycetes

SUBDIVISION -2

ASCOMYCOTINA

CLASS – Ascomycetes

SUBDIVISION -3

BASIDIOMYCOTINA

CLASS – Basidiomycetes

SUBDIVISION -4

DEUTEROMYCOTINA

CLASS - Deuteromycetes

1.5.5 Kingdom : Myceteae (Fungi)

Include achlorophyllous, saprophytic

or parasitic organisms with Unicellular

or multicellular (Mycelium) thallus

surrounded by chitinous cell wall.

Nutrition is absorptive except slime

molds.Reproduction is through asexual

and Sexual methods.

Division : I Gymnomycota

Nutrition Phagotrophic, members of this

group lack cell wall. Example. Dictyostelium

Division :II Mastigomycota

Flagellate cells are present(Gamete/

Zoospore). Nutrition absorptive,

mycelium coenocytic. Example : Albugo

Division : III Amastigomycota

Unicellular to multicellular forms are

included. The mycelium is septate.

Asexual reproduction occurs by budding,

fragmentation, sporangiospores, conidia

etc., Meiosis is zygotic. Example : Peziza

Recently, with the advent of

molecular methods myxomycetes and

oomycetes were reclassified and treated

under chromista.

The salient features of some of the

classes – Oomycetes, Zygomycetes,

Ascomycetes, Basidiomycetes and Form

class Deuteromycetes are discussed below.

Oomycetes

Coenocytic mycelium is present. The cell

wall is made up of Glucan and Cellulose.

Zoospore with one whiplash and one

tinsel flagellum is present. Sexual

reproduction is Oogamous. Example:

Albugo.

32

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Zygomycetes

• Most of the species are saprophytic

and live on decaying plant and animal

matter in the soil. Some lead parasitic

life (Example: Entomophthora on

housefly)

• Bread mold fungi (Example: Mucor,

Rhizopus) and Coprophilous fungi

(Fungi growing on dung Example:

Pilobolus) belong to this group

(Figure 1.21).

Sporangium

Columella

Sporangiospore

• Asexual reproduction by means of

spores produced in sporangia.

• Sexual reproduction is by the fusion of

the gametangia which results in thick

walled zygospore. It remains dormant

for long periods. The zygospore

undergoes meiosis and produce spores.

Ascomycetes

• Ascomycetes include a wide range

of fungi such as yeasts, powdery

mildews, cup fungi, morels and so on

(Figure 1.22).

Sporangiophore

Rhizoids

(a) Morchella

(a)

(b) Peziza

(b)

Figure 1.21: Zygomycetes (a) Rhizopus

(b) Pilobolus

• The mycelium is branched and

coenocytic.

(c) Cleistothecium

33

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Ostiole

Ascus

Ascospore

Paraphysis

(d) V.S. of Perithecium

(e) V.S. of Apothecium

Ascus

Paraphysis

Ascospore

Ascospore

(f) Steps involved in the development of Ascus

Figure 1.22: Structure and reproduction

in Ascomycetes

• Although majority of the species live

in terrestrial environment, some live

in aquatic environments both fresh

water and marine.

• The mycelium is well developed,

branched with simple septum.

• Majority of them are saprophytes but

few parasites are also known (Powdery

mildew – Erysiphe).

• Asexual reproduction takes place

by fission, budding, oidia, conidia,

chlamydospore.

• Sexual reproduction takes place by the

fusion of two compatible nuclei.

• Plasmogamy is not immediately

followed by karyogamy, instead a

dikaryotic condition is prolonged for

several generations.

• A special hyphae called ascogenous

hyphae is formed.

• A crozier is formed when the tip of the

ascogenous hyphae recurves forming

a hooked cell. The two nuclei in the

penultimate cell of the hypha fuse to

form a diploid nucleus. This cell form

young ascus.

• The diploid nucleus undergo meiotic

division to produce four haploid

nuclei, which further divide mitotically

to form eight nuclei. The nucleus gets

organised into 8 ascospores.

• The ascospores are found inside a

bag like structure called ascus. Due

to the presence of ascus, this group is

popularly called "Sac fungi".

• Asci gets surrounded by sterile hyphae

forming fruit body called ascocarp.

• There are 4 types of ascocarps namely

Cleistothecium (Completely closed),

Perithecium (Flask shaped with

ostiole), Apothecium (Cup shaped,

open type) and Pseudothecium.

Basidiomycetes

• Basidiomycetes include puff balls,

toad stools, Bird’s nest fungi, Bracket

34

---

fungi, stink horns, rusts and smuts

(Figure 1.23).

• Asexual reproduction is by means of

conidia, oidia or budding.

(a) Agaricus

(b) Geaster

• Sexual reproduction is present but

sex organs are absent. Somatogamy or

spermatisation results in plasmogamy.

Karyogamy is delayed and dikaryotic

phase is prolonged. Karyogamy takes

place in basidium and it is immediately

followed by meiotic division.

(c) Dolipore septum

• The four nuclei thus formed are

transformed into basidiospores which

are borne on sterigmata outside the

basidium (Exogenous ). The basidium

is club shaped with four basidiospores,

thus this group of fungi is popularly

called “Club fungi”. The fruit body

formed is called Basidiocarp.

Deuteromycetes or Fungi Imperfecti

(d) Clamp connection

Nucleus

Figure 1.23: Structure and

Reproduction in Basidiomycetes

• The members are terrestrial and lead a

saprophytic and parasitic mode of life.

• The mycelium is well developed,

septate with dolipore septum(bracket

like). Three types of mycelium namely

Primary (Monokaryotic), Secondary

(Dikaryotic) and tertiary are found.

• Clamp connections are formed to

maintain dikaryotic condition.

The fungi belonging to this group lack

sexual reproduction and are called

imperfect fungi. A large number of species

live as saprophytes in soil and many are

plant and animal parasites. Asexual

reproduction takes place by the production

of conidia, chlamydospores, budding,

oidia etc., Conidia are also produced

in special structures called pycnidium,

Acervulus, sporodochium and Synnema

(a) Pycnidium - Phoma

Pycniospore

35

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(b) Acervulus - Colletotrichum

Conidium

Seta

Conidiophore

Conidia

Beneficial activities

Food

Mushrooms like Lentinus edodes, Agaricus

bisporus, Volvariella volvaceae are

consumed for their high nutritive value.

Yeasts provide vitamin B and Eremothecium

ashbyii is a rich source of Vitamin B 12.

Medicine

Fungi produce antibiotics which arrest

the growth or destroy the bacteria.

Some of the antibiotics produced by

fungi include Penicillin (Penicillium

notatum) Cephalosporins (Acremonium

chrysogenum) Griseofulvin (Penicillium

griseofulvum). Ergot alkaloids (Ergotamine)

produced by Claviceps purpurea is

used as vasoconstrictors.

Industries

(c) Synnema - Graphium

Figure 1.24: Reproduction in

Deuteromycetes

(Figure 1.24). Parasexual cycle operates

in this group of fungi. This brings genetic

variation among the species.

1.5.6. Economic importance

Fungi provide delicious and nutritious

food called mushrooms. They recycle the

minerals by decomposing the litter thus

adding fertility to the soil. Dairy industry

is based on a single celled fungus called

yeast. They deteriorate the timber. Fungi

cause food poisoning due the production

of toxins. The Beneficial and harmful

activities of fungi are discussed below:

Production of Organic acid: For the

commercial production of organic acids

fungi are employed in the Industries. Some

of the organic acids and fungi which help

in the production of organic acids are:

Citric acid and Gluconic acid – Aspergillus

niger, Itaconic acid – Aspergillus terreus,

Kojic acid – Aspergillus oryzae

Bakery and Brewery

Yeast(Saccharomyces cerevisiae) is used for

fermentation of sugars to yield alcohol.

Bakeries utilize yeast for the production

of Bakery products like Bread, buns,

rolls etc., Penicillium roquefortii and

Penicillium camemberti were employed in

cheese production.

Production of enzymes

Aspergillus oryzae, Aspergillus niger were

employed in the production of enzymes

36

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like Amylase, Protease, Lactase etc.,’

Rennet’ which helps in the coagulation of

milk in cheese manufacturing is derived

from Mucor spp.

Agriculture

Mycorrhiza forming fungi like

Rhizoctonia, Phallus, Scleroderma helps in

absorption of water and minerals.

Fungi like Beauveria bassiana,

Metarhizium anisopliae are used as

Biopesticides to eradicate the pests of crops.

Gibberellin, produced by a fungus

Gibberella fujikuroi induce the plant

growth and is used as growth promoter.

Harmful activities

Fungi like Amanita phalloides, Amanita

verna, Boletus satanus are highly poisonous

due to the production of Toxins. These fungi

are commonly referred as “Toad stools”.

Aspergillus, Rhizopus, Mucor and

Penicilium are involved in spoilage of food

materials. Aspergillus flavus infest dried

foods and produce carcinogenic toxin

called aflatoxin.

Patulin, ochratoxin A are some of the

toxins produced by fungi.

Fungi cause diseases in Human beings

and Plants (Table 1.11 and Figure 1.25)

(a) Rust of wheat

(b) Anthracnose of beans

Figure 1.25: Fungal disease in plants.

Name of the disease

Plant diseases

Blast of Paddy

Red rot of sugarcane

Anthracnose of Beans

White rust of crucifers

Peach leaf curl

Rust of wheat

Human diseases

Athlete’s foot

Candidiasis

Coccidioidomycosis

Aspergillosis

Table 1.11: Diseases caused by fungi

Causal organism

Magnaporthe grisea

Colletotrichum falcatum

Colletotrichum lindemuthianum

Albugo candida

Taphrina deformans

Puccinia graminis tritici

Epidermophyton floccosum

Candida albicans

Coccidioides immitis

Aspergillus fumigatus

37

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Activity 1.4

Get a button mushroom. Draw diagram

of the fruit body. Take a thin longitudinal

section passing through the gill and

observe the section under a microscope.

Record your observations.

Dermatophytes are

fungi which cause infection

in skin. Example:

Trichophyton, Tinea,

Microsporum and Epidermophyton

The late blight disease of Potato by

Phytophthora infestans caused a million

deaths, and drove more to emigrate

from Ireland (1843-1845). In India

Helminthosporium oryzae, Blight of

Paddy is also a factor for Bengal famine

in 1942-1943

Activity 1.5

Keep a slice of bread in a clean plastic tray

or plate. Wet the surface with little water.

Leave the setup for 3 or 4 days. Observe the

mouldy growth on the surface of the bread.

Using a needle remove some mycelium and

place it on a slide and stain the mycelium

using lactophenol cotton blue. Observe

the mycelium and sporangium under the

microscope and Record your observation

and identify the fungi and its group based

on characteristic features.

1.5.7 Rhizopus

Class - Zygomycetes

Order - Mucorales

Family - Mucoraceae

Genus - Rhizopus

Rhizopus is a saprophytic fungus and

grows on substrates like bread, jelly,

leather, decaying vegetables and fruits. It

is commonly called ‘Bread mold’. Rhizopus

stolonifer causes leak and soft rot of

vegetables

Vegetative structure

The mycelium consists of aseptate,

multinucleate (coenocyte) and profusely

branched hyphae. There are horizontally

growing aerial hyphae called stolons.

The stolons produce rhizoids which are

branched and penetrate the substratum

and help in absorbing water and nutrients.

Sporangiophores are borne exactly

opposite to the rhizoids. The cell wall is

made up of chitin and chitosan. The cell

wall is followed by plasma membrane. The

protoplast is granular containing many

nuclei. Cell organelles like mitochondria,

ribosomes and endoplasmic reticulum are

present. The cell inclusions like glycogen

and oil droplets are also found.

Reproduction

Sporangium

Columella

Sporangiospore

Sporangiophore

Rhizoids

Figure 1.26: Rhizopus

Rhizopus reproduces by asexual and sexual

methods.

Asexual reproduction

During favorable conditions, erect

sporangiophores are produced exactly

opposite to the region of formation

of rhizoids of the mycelium. The

sporangiophores are unicellular, unbranched

38

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and multinucleate structures which bear

bag like structure called sporangia. Each

sporangiophore bears a single sporangium.

Sporangium possesses a sterile region

in the centre called Columella. Spores are

produced around the columella. When the

sporangial wall breaks, the columella collapses

and the spores are dispersed. When the spores

fall on a suitable substratum they germinate

and produce new mycelia (Figure 1.26).

Sexual reproduction

Sexual reproduction is present and takes

place through gametangial copulation.

Most of the species are heterothallic

but Rhizopus sexualis is homothallic.

There is no morphological distinction

between the two sexual hyphae although

physiologically they are dissimilar. Since

physiologically dissimilar thalli (hyphae)

are involved in sexual reproduction, this

phenomenon is called heterothallism.

Mycelia which produce gametangia are

of opposite strains (+) or (-). The first

step is the formation of special hyphae

called zygophores. The tips of the two

zygophores swell to form progametangia.

Further, a septum is formed near the tip

of each progametangium and results in the

formation of a terminal gametangium and

a suspensor cell. The two gametangia fuse,

and this is followed by plasmogamy and

karyogamy. The fusion of nuclei results in

the formation of a diploid zygospore. Many

nuclei belonging to opposite strains (+ or –)

pair and fuse to form many diploid nuclei.

The zygospore enlarges and develops an

outer thick dark and warty layer called

exine and inner thin layer called intine.

After the resting period the nuclei of

zygospore undergo meiosis. The zygospore

germinates to form sporangiophores and

the zygosporangium contain mixture of

(+) and (–) spores. When the spores fall on

a suitable substratum, they germinate to

produce mycelium (Figure 1.20). The life

cycle of Rhizopus is given in figure 1.27.

Spores

(+)

Sporangium

(+ or –)

Spores

(–)

Sporangium

(–)

Sporangium

(+)

Meiosis

A sexual

reproduction

Mycelium (–)

Sexual

reproduction

Zygospore

(2n)

Spores

(+ or –)

RHIZOPUS

(n)

Mycelium (+)

Progametangium

(+)

Progametangium

(–)

Gametangium

(–)

Gametangium

(+)

Figure 1.27: Life cycle of Rhizopus

1.5.8 Agaricus

Class - Basidiomycetes

Order - Agaricales

Family - Agaricaceae

Genus - Agaricus

It is a saprophytic fungus found on wood

logs, manure piles, fresh litter, pastures

etc., The fruit bodies are the visible part

of the fungi. They are found in rings

in some species like Agaricus arvensis,

Agaricus tabularis and hence popularly

called ‘Fairy rings”. Agaricus campestris is

the most common ‘field mushroom’.

Vegetative structure

The thallus is made up of branched

structures called hyphae. A large number

of hyphae constitute the mycelium.

39

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Three types of mycelia are seen

namely primary mycelium, secondary

mycelium and tertiary mycelium, The

primary mycelium develops from the

germination of basidiospore. It is septate,

uninucleate and haploid. It is also called

monokaryotic mycelium. Fusion of two

primary mycelium of opposite strains give

rise to secondary mycelium or dikaryotic

mycelium. The dikaryotic mycelium

develops into hyphal cords called

Rhizomorphs,. and perennates the soil

for a long period. The tertiary mycelium is

found in the fruit body called basidiocarp.

Each cell of the hyphae posssess a cell wall

made up of chitin and cell organelles like

mitochondria, golgibodies, Endoplasmic

reticulum etc., are also present.

Pileus

Gill

Annulus

Stipe

Figure 1.28: Agaricus-Basidiocarp

Asexual reproduction.

Agaricus produces chlamydospores during

asexual reproduction. During favourable

condition the chlamydospores germinate

and produce mycelium.

Sexual reproduction

Agaricus reproduces by sexual method

but sex organs are absent.Majority of the

species are heterothallic. Agaricus bisporus

is a homothallic species. The opposite

strains of mycelium fuse(somatogamy)

and results in the formation of dikaryotic

or secondary mycelium. Karyogamy takes

place in basidium and it is immediately

followed by meiosis giving rise to four

haploid basidiospores. The basidiospores

are borne on sterigmata. The subterranean

mycelial strands called rhizomorphs

posssess dense knots of dikaryotic hyphae.

These knots develop into Basidiocarps.

Basidiocarp

The mature basidiocarp is umbrella shaped

and is divided into 3 parts namely stipe,

pileus and gill. The stipe is thick, fleshy

and cylindrical in structure. The upper

part of the stipe possess a membranous

structure called annulus. The upper

convex surface is called Pileus which is

white or cream in colour (Figure 1.28).

The inner surface of pileus shows radially

arranged gills or lamellae. The gills vary

in length. On both the sides of the gills a

fertile layer called hymenium is present.

The stipe is hollow from the centre and the

central part is made up of loosely arranged

hyphae whereas the periphery is made up

of compactly arranged hyphae forming

pseudoparenchymatous tissue. The gill

region is divided into 3 regions. The

central part of gill between two hymenial

layers is called Trama (Figure 1.29). The

subhymenial layers have closely compact

tissue . The hymenium is the fertile

layer and possess club shaped basidia.

The basidium is interspersed with sterile

hyphae called paraphysis. Each basidium

bears 4 basidiospores , of these two

basidiospore belong to (+) strain and

other two of them will be (–) strain.

The basidiospores are borne on stalk

like structures called Sterigmata. The

basidiospore on germination produces

40

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Figure 1.29: V.S. of Agaricus gill

basidiospores monokaryotic

(+) mycelium (+)

basidiospores monokaryotic

(-) mycelium (-)

meiosis

somatogamy

Plasmogamy

basidia with

diploid nucleus

( Karyogamy)

basidiocarp

(2n)

rhizomorph

AGARICUS

secondary

mycelium

dikaryotic cell

Dikaryotisation

Figure Figure 1.36 1.30: Life Life Cycle Cycle of of Agaricus

the haploid primary mycelium.

Thus the life cycle of Agaricus shows

a very short diploid phase, haploid

phase and a prolonged dikaryotic phase

(Figure 1.30).

1.5.9 Mycorrhizae

The symbiotic association between fungal

mycelium and roots of plants is called as

mycorrhizae. In this relationship fungi

absorbs nutrition from the root and in

turn the hyphal network of mycorrhizae

forming fungi helps the plant to absorb

water and mineral nutrients from the soil

(Figure 1.31) Mycorrhizae are classified

into three types

Importance of Mycorrhizae

• Helps to derive nutrition in Monotropa,

a saprophytic angiosperm,

• Improves the availability of minerals

41

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Mycorrhizae

Ectomycorrhizae Endomycorrhizae Ectendomycorrhizae

The fungal mycelium

The hyphae grows mainly inside the roots, The fungi form both

forms a dense penetrate the outer cortical cells of the plant mantle and also pen-

sheath around the root. A small portion of the mycelium is etrates the cortical

root called mantle. found outside the root. This form is also called cells.

The hyphal network

Vesicular Arbuscular Mycorrhizal fungi (VAM

penetrate the Fungi) due to the presence of Vesicle or arbuscle

intercellular spaces

like haustoria

of the epidermis 1. Arbuscular mycorrhizae(VAM)

and cortex to form Example: Gigaspora

Hartignet. Example:

Pisolithus tinc-

2. Ericoid mycorrhizae -Example: Oidiodendron

3. Orchid mycorrhizae -Example: Rhizoctonia

torius

and water to the plants.

• Provides drought resistance to the

plants

• Protects roots of higher plants from

the attack of plant pathogens

Vesicle

Epiblema

Arbuscle

Endomycorrhizae

Ectomycorrhizae

Figure 1.31: T.S. of root showing

mycorrhizae

1.5.10 Lichens

Fungal

sheath

Cortex

Mycelium

The symbiotic association between

algae and fungi is called lichens. The

algal partner is called Phycobiont or

Photobiont., and the fungal partner

is called Mycobiont. Algae provide

nutrition for fungal partner in turn fungi

provide protection and also help to fix

the thallus to the substratum through

rhizinae. Asexual reproduction takes

place through fragmentation, Soredia

and Isidia. Phycobionts reproduce by

akinetes, hormogonia, aplanospore etc.,

Mycobionts undergo sexual reproduction

and produce ascocarps.

Classification

• Based on the habitat lichens are

classified into following types:

Corticolous( on Bark) Lignicolous(on

Wood) Saxicolous(on rocks)

Terricolous(on ground) Marine(on

siliceous rocks of sea) Fresh water(on

siliceous rock of fresh water).

• On the basis of morphology of the

thallus they are divided into Leprose

(a distinct fungal layer is absent)

Crustose-crust like; Foliose-leaf like;

Fruticose- branched pendulous shrub

like (Figure 1.32).

• The distribution of algal cells

distinguishes lichens into two forms

namely Homoiomerous (Algal cells

42

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evenly distributed in the thallus) and

Heteromerous (a distinct layer of

algae and fungi present).

• If the fungal partner of lichen belongs

to ascomycetes, it is called Ascolichen

and if it is basidiomycetes it is called

Basidiolichen.

(a) Crustose lichen

(b) Foliose Lichen

(c) Fruticose Lichen

Figure 1.32: Types of Lichens

Lichens secrete organic acids like Oxalic

acids which corrodes the rock surface and

helps in weathering of rocks, thus acting as

pioneers in Xerosere. Usnic acid produced

from lichens show antibiotic properties.

Lichens are sensitive to air pollutants

especially to sulphur-di-oxide. Therefore,

they are considered as pollution indicators.

The dye present in litmus paper used as

acid base indicator in the laboratories is

obtained from Roccella montagnei. Cladonia

rangiferina (Reindeer moss) is used as food

for animals living in Tundra regions.

Summary

Earth is endowed with living and

nonliving things. The attributes of living

things include growth, metabolism,

Reproduction, Irritability and so on.

Viruses are considered as Biological

puzzle and exhibit both living and non

living characteristic features. They are

ultramicroscopic, obligate parasites and

cause disease in plants and animals. They

multiply by lytic and lysogenic cycle.

Five Kingdom classification was

proposed by Whittaker, which include

Monera, Protista, Fungi, Plantae and

Animalia. Carl woese divided the living

world into 3 domains- Bacteria, Archaeae

and Eukarya. The domain Eukarya include

Plantae, Animalia and Fungi. A new

Kingdom called Chromista was erected

to include Diatoms, Cryptomonads and

Oomycetes. Bacteria are microscopic,

prokaryotic organisms and possess

peptidoglycan in their cell wall. Based on

Gram Staining method they are classified

into Gram positive and Gram negative

type. They reproduce asexually by Binary

fission. Sexual reproduction occurs

through Conjugation, Transformation

and Transduction. Archaebacteria are

prokaryotic and are adapted to thrive in

extreme environments.

Cyanobacteria are prokaryotic organisms

and are also called Blue Green Algae. The

43

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members of this group are ensheathed by

mucilage cover. They reproduce by vegetative

and asexual methods.

Fungi are Eukaryotic, heterotrophic,

unicellular or multicellular organisms.

The cell wall is made up of chitin.

They reproduce asexually by

producing sporangiospores, conidia,

Thallospores, chlamydospores etc.,

The sexual reproduction is isogamous,

ansiogamous and oogamous. In addition,

gametic copulation, gametic fusion,

spermatisation are also found. They are

beneficial to mankind. Some are known

to cause disease in plants and human

beings.

Rhizopus is commonly called’ Bread

mold fungi’. It belongs to the class

Zygomycetes. Asexual reproduction occurs

by the production of sporangiospores.

During sexual reproduction gametangial

copulation occurs and zygospore is

formed. Agaricus belongs to the class

Basidiomycetes.It is a saprophytic fungus.

Three types of mycelium , primary,

secondary and tertiary mycelium are

produced. Sexual reproduction is present

.Basidiocarps are produced after the

sexual reproduction. It bears basidia on

which four basidiospores are produced.

The symbiotic association between

the roots of higher plants and fungal

mycelium is called mycorrhizae. Lichen

thallus includes both phycobiont and

mycobiont. It is an example for symbiotic

association.

Evaluation

1. Which one of the

following statement

about virus is correct

a. Possess their own

metabolic system

b. They are facultative

parasites

c. They contain DNA or RNA

d. Enzymes are present

2. Identify the incorrect statement about

the Gram positive bacteria

a. Teichoic acid absent

b. High percentage of peptidoglycan

is found in cell wall

c. Cell wall is single layered

d. Lipopolysaccharide is present in

cell wall

3. Identify the Archaebacterium

a. Acetobacter

b. Erwinia

c. Treponema

d. Methanobacterium

4. The correct statement regarding Blue

green algae is

a. lack of motile structures

b. presence of cellulose in cell wall

c. absence of mucilage around the

thallus

d. presence of floridean starch

5. Identify the correctly matched pair

a. Actinomycete – a) Late blight

b. Mycoplasma – b) lumpy jaw

c. Bacteria – c) Crown gall

d. Fungi – d) sandal spike

44

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6. Differentiate Homoiomerous and

Heteromerous lichens.

7. Write the distinguishing features of

Monera.

8. Why do farmers plant leguminous

crops in crop rotations/mixed

cropping?

9. Briefly discuss on five Kingdom

classification. Add a note on merits

and demerits.

10. Give a general account on lichens.

11. Explain the asexual reproduction in

Rhizopus.

12. Mention the steps involved in the

sexual reproduction of Rhizopus.

13. Write outline the life cycle of Agaricus.

14. What is Sterigma?

15. Name the types of mycelium found in

Agaricus.

16. Differentiate oidium and

Chlamydospore.

17. Name the fungal group which possess

dolipore septum.

18. Mention the diseases caused by fungi

in plants.

19. Give two examples for mycorrhizae

forming fungi.

20. Differentiate Gram positive and

Gram negative bacteria.

45

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ICT Corner

Bacteria

Let’s explore the structure

and shapes of Bacteria.

Steps

• Scan the QR code or go to google play store and type bacteria interactive

educational VR 3D

• Download the app and install it

• Follow the above steps and explore the interactives of each part and its functions.

Activity

• Select structure tap and note the internal structure of bacteria

• Click cell wall and note the difference between different shapes

Step 2 Step 3

Step 1 Step 4

Step 5

URL:

https://play.google.com/store/apps/details?id=com.rendernet.bacteria&hl=en

* Pictures are indicative only

46

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Chapter

2

Plant Kingdom

Learning Objectives

The learner will be able to,

• Outline the classification of plants

• Illustrate the life cycles in plants

• Recognize the general characteristic

features and reproduction of Algae

• Describe the structure, reproduction

of Oedogonium and Chara

• Recognize the general characteristic

features of Bryophytes

• Describe the structure, reproduction

of Marchantia and Funaria

• Recognize the general characteristic

features of Pteridophytes

• Describe the structure, reproduction

of Selaginella and Adiantum

• Describe the general characteristic

features of Gymnosperms

• Explain the structure, reproduction

of Cycas and Pinus

• Recognize the salient features of

Angiosperms

Chapter Outline

2.1 Classification of Plants

2.2 Life Cycle patterns in Plants

2.3 Algae

2.4 Bryophytes

2.5 Pteridophytes

2.6 Gymnosperms

2.7 Angiosperms

Traditionally organisms existing on the

earth were classified into plants and animals

based on nutrition, locomotion and

presence or absence of cell wall. Bacteria,

Fungi, Algae, Bryophytes, Pteridophytes,

Gymnosperms and

Angiosperms were

included under

plant group.

Recently, with the

aid of molecular

characteristics the

Bacteria and Fungi

were segregated

and placed under separate kingdoms.

Botany is one of the oldest science in the

world because its origin was from time

immemorial as early men explored and

identified plants for the needs of food,

clothing, medicine, shelter etc., Plants are

unique living entities as they are endowed

with the power to harvest the light energy

from the sun and to convert it to chemical

energy in the form of food through the

astounding reaction, photosynthesis. They

not only supply nutrients to all living things

on earth but sequester carbon-di-oxide

during photosynthesis thus minimizing the

effect of one of the major green house gases

that increase the global temperature. Plants

are diverse in nature, ranging from

microscopic algae to macroscopic highly

developed angiosperms. There are mysteries

and wonders in the plant world in terms of

47

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size, shape, habit, habitat, reproduction etc., Although plants are all made up of cells there

exists high diversity in form and structure (Table 2.1).

Table 2.1: Total Number of Plant groups in the World and India

Plant group

Number of known species

World#

India*

Algae 40,000 7,357

Bryophytes 16,236 2,748

Pteridophytes 12,000 1,289

Gymnosperms 1,012 79

Angiosperms 2,68,600 18,386

* Singh, P. and Dash, S.S. 2017-Plants discoveries 2016-New Genera, species and new records, BSI, India.

# Chapman, A.D. 2009. Number of living species in Australia and the world 2 nd edition. Australian government,

Department of environment, water Heritage and Arts.

2.1 Classification of Plants

Classification widely accepted for plants

now include Embryophyta which is divided

into Bryophyta and Tracheophyta. The

KINGDOM - PLANTAE

KINGDOM - PLANTAE

Sub Kingdom - Cryptogamae

(Non-flowering/ Sub Kingdom Non seed - Cryptogamae

producing plants)

(Non-flowering/ Non seed producing plants)

Algae

Algae

latter is further divided into Pteridophyta

and Spermatophyta (Gymnospermae and

Angiospermae). An outline Classification

of Plant Kingdom is given in Figure 2.1

Sub Kingdom - Phanerogamae

( Sub Flowering/ Kingdom Seed - producing Phanerogamae plants)

( Flowering/ Seed producing plants)

Bryophyta Pteridophyta Gymnospermae Angiospermae

Bryophyta Pteridophyta Gymnospermae Angiospermae

Mainly Mainly Aquatic habitat habitat

Unicellular Liverworts Club mossess

Unicellular Liverworts Club mossess

Colonial

Colonial

Thalloid

Thalloid

Parenchymatous

Parenchymatous

Begining of Terrestrial of Colonisation - Amphibious

- Mosses

Mosses

Culmination of Terrestrial of Colonisation

Horsetails

Horsetails

Ferns

Ferns

Naked Naked - seeded - seeded plants plants

Cycads

Cycads

Conifers

Conifers

Gnetales

Gnetales

Closed Closed - seeded - seeded plants plants

Dicots

Dicots

Monocots

Monocots

Figure 2.1: Classification of Plant Kingdom

48

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2.2 Life Cycle Patterns in Plants

Alternation of Generation

Alternation of generation is common

in all plants. Alternation of the haploid

gametophytic phase (n) with diploid

sporophytic phase (2n) during the life

cycle is called alternation of generation.

Following type of life cycles are found in

plants (Figure 2.2).

Haplontic Life Cycle

Gametophytic phase is dominant,

photosynthetic and independent, whereas

sporophytic phase is represented by the zygote.

Zygote undergoes meiosis to restore haploid

condition. Example: Volvox, Spirogyra.

Diplontic Life Cycle

Sporophytic phase (2n) is dominant,

photosynthetic and independent. The

gametophytic phase is represented by

the single to few celled gametophyte.

The gametes fuse to form Zygote which

develops into Sporophyte. Example: Fucus,

Gymnosperms and Angiosperms

Haplodiplontic Life Cycle

This type of life cycle is found in Bryophytes

and pteridophytes which is intermediate

between haplontic and diplontic type. Both

the phases are multicellular. but they differ

in their dominant phase.

Syngamy

Gametogenesis

Zygote

(2n)

Haplontic

Gametophyte

(n)

(a)

Meiosis

Spores

(n)

Zygote (2n)

Sporophyte

(2n)

Diplontic

Syngamy

(n)

(b)

Gametogenesis

Meiosis

Zygote (2n)

Syngamy

Sporophyte

(2n)

Meiosis

Gametogenesis

Haplo-diplontic Spores(n)

Gametophyte

(n)

Figure 2.2: Life cycle patterns in plants a) Haplontic, b) Diplontic, c) Haplo-diplontic

(c)

In Bryophytes dominant independent

phase is gametophyte and it alternates

with short-lived multicellular sporophyte

totally or partially dependent on the

gametophyte.

In Pteridophytes sporophyte is

the independent phase. It alternates

with multicellular saprophytic or

autotrophic, independent, short lived

gametophyte(n).

2.3 Algae

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Rain brings joy and life to various

organisms on earth. Have you noticed

some changes in and around you after the

rain? Could you identify the reason for the

slippery nature of the terrace and green

patches on the wall of our home, green

colour of puddles and ponds? Why should

we clean our water tanks very often? The

reason is algae. Algae are simple plants that

lack true roots, true stems and true leaves.

Two-third of our earth’s surface is covered

by oceans and seas. The photosynthetic

plants called algae are present here. More

than half of the total primary productivity

of the world depends on this plant group.

Further, other aquatic organisms also

depend upon them for their existence.

M.O.Parthasarathy (1886-1963)

‘Father of Indian Phycology’.

He conducted research on structure,

cytology, reproduction and taxonomy

of Algae. He published a Monograph

on Volvocales. New algal forms like

Fritschiella, Ecballocystopsis, Charasiphon

and Cylindrocapsopsis. were reported by

him.

Algae are autotrophs, and grow in a

wide range of habitats. Majority of them

are aquatic, marine (Gracilaria, and

Sargassum) and freshwater (Oedogonium,

and Ulothrix) and also found in soils

(Fritschiella, and Vaucheria). Chlorella

lead an endozoic life in hydra and sponges

whereas Cladophora crispata grow on

the shells of molluscs. Algae are adapted

to thrive in harsh environment too.

Dunaliella salina grows in salt pans

(Halophytic alga). Algae growing in

snow are called Cryophytic algae.

Chlamydomonas nivalis grow in snow

covered mountains and impart red colour

to the snow (Red snow). A few algae grow

on the surface of aquatic plants and are

called epiphytic algae (Coleochaete, and

Rhodymenia). The study of algae is called

algology or phycology. Some of the

eminent algologists include F.E. Fritsch,

F.E. Round, R.E. Lee, M.O.Parthasarathy

Iyengar, M.S. Randhawa, Y. Bharadwaja,

V.S. Sundaralingam and T.V.Desikachary.

2.3.1 General Characteristic features

The algae show a great diversity in size,

shape and structure. A wide range of

thallus organisation is found in algae.

Unicellular motile (Chlamydomonas),

unicellular non-motile (Chlorella),

Colonial motile (Volvox), Colonial

non motile (Hydrodictyon), siphonous

(Vaucheria), unbranched filamentous

(Spirogyra), branched filamentous

(Cladophora), discoid (Coleochaete)

heterotrichous (Fritschiella), Foliaceous

(Ulva) to Giant Kelps (Laminaria and

Macrocystis). The thallus organization in

algae is given in Figure 2.3.

Algae are Eukaryotes except blue green

algae. The plant body does not show

differentiation into tissue systems. The

cell wall of algae is made up of cellulose

and hemicellulose. Siliceous walls are

present in diatoms. In Chara the thallus

is encrusted with calcium carbonate.

Some algae possess algin, polysulphate

esters of polysaccharides which are the

50

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Flagella

Chloroplast

Oogonium

Antheridium

Nucleus

Pyrenoid

Central Vacuole

a) Chlorella

b) Chlamydomonas

c) Vaucheria

Cap cell

Seta

Hold fast

e) Coleochaete

g) Ulva

f) Fritschiella

d) Oedogonium

Air vesicle

Air bladder

Lateral branch

Stipe

Hold fast

h) Fucus

i) Sargassum

Figure 2.3: Thallus organization in Algae

51

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sources for the alginate, agar agar and

Carrageenan. The cell has a membrane

bound nucleus and cell organelles like

chloroplast, mitochondria, endoplasmic

reticulum, golgi bodies etc., Pyrenoids are

present. They are proteinaceous bodies

found in chromatophores and assist in

the synthesis and storage of starch. The

pigmentation, reserve food material and

flagellation differ among the algal groups.

Algae reproduces by vegetative,

asexual and sexual methods (Figure 2.4).

Vegetative reproduction includes fission

(In unicellular forms the cell divides

mitotically to produce two daughter cells

Example: Chlamydomonas); Fragmentation

(fragments of parent thallus grow into new

individual Example: Ulothrix) Budding (A

lateral bud is formed in some members like

Protosiphon and helps in reproduction)

Bulbils, (a wedge shaped modified branch

develop in Sphacelaria) Akinetes (Thick

walled spores meant for perennation and

germinates with the advent of favourable

condition Example: Pithophora). Tubers

(Structures found on the rhizoids and the

lower nodes of Chara which store food

materials).

Asexual reproduction takesplace by

the production of zoospores(Ulothrix,

Oedogonium) aplanospore(thin walled

non motile spores Example: Vaucheria);

a) Fragmentaion-Spirogyra

b) Zoospore

formation-Cladophora

c) Isogamy

d) Anisogamy e) Oogamy f) Scalariform

conjugation- Zygnema

Figure 2.4: Reproduction in Algae

52

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Autospores (spores which look similar to

parent cell Example: Chlorella); Hypnospore

(thick walled aplanospore – Example:

Chlamydomonas nivalis); Tetraspores

(Diploid thallus of Polysiphonia produce

haploid spores after meiosis).

Sexual reproduction in algae are of three

types 1. Isogamy (Fusion of morphologically

and Physiologically similar gametes

Example: Ulothrix) 2. Anisogamy (Fusion

of either morphologically or physiologically

dissimilar gametes Example: Pandorina)

3. Oogamy (Fusion of both morphologically

and physiologically dissimilar gametes.

Example: Sargassum). The life cycle shows

distinct alternation of generation.

The Oldest recorded

alga is Grypania,

which was discovered

in the banded iron

formations of northern Michigan and

dated to approximately 2100Ma

2.3.2. Classification

F.E. Fritsch proposed a classification

for algae based on pigmentation, types

of flagella, reserve food materials, thallus

Table 2.2 Classification of Algae

Class Pigments Flagella Reserve food

Chlorophyceae Chlorophyll a and b

1,2,4 or more equal Starch

Carotenoids, Xathophyll anterior whiplash flagella

Xanthophyceae Chlorophyll a and b

2, unequal anterior 1 Fats and leucosin

Carotenoids Xathophyll tinsel and 1 whiplash

Chrysophyceae Chlorophyll a and b

Carotenoids,

1 or 2 unequal or equal

anterior both whiplash or

1 whiplash and 1 tinsel

Oils and leucosin

Bacillariophyceae Chlorophyll a and c

1 anterior (only in male Leucosin and Fats

Carotenoids,

gametes) tinsel

Cryptophyceae Chlorophyll a and c carotenoids unequal anterior both Starch

and xanthophyll

tinsel flagella

Dinophyceae Chlorophyll a and c carotenoids Two unequal (whiplash) Starch and oil

and xanthophyll

lateral flagella in different

plane

Chloromonadineae Chlorophyll a and b

2 equal flagella oil

Carotenoids, Xathophyll

Euglenophyceae Chlorophyll a and b One or two anterior tinsel

flagella

Fats and

paramylon

Phaeophyceae Chlorophyll a and c,

Xanthophyll

Two unequal whiplash and

tinsel lateral flagella

Laminarin starch

and fats

Rhodophyceae Chlorophyll a,

absent

Floridean starch

r-Phycoerthythrin

Cyanophyceae Chlorophyll a, carotenoids,

c-Phycocyanin,Allophycocyanin

absent

Cyanophycean

starch

53

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structure and reproduction. He published

his classification in the book “The structure

and reproduction of the Algae”(1935).

He classified algae into 11 classes namely

Chlorophyceae, Xanthophyceae, Chrysophyceae,

Bacillariophyceae, Cryptophyceae,

Dinophyceae, Chloromonadineae,

Euglenophyceae, Phaeophyceae, Rhodophyceae,

Cyanophyceae (Table 2.2).

The salient features of Chlorophyceae,

Phaeophyceae and Rhodophyceae are

given below.

Chlorophyceae

The members are commonly called

‘Green algae’. Most of the species are

aquatic(Fresh water-Spirogyra, Marine

-Ulva). A few are terrestrial(Trentipohlia).

Variation among the shape of the

chloroplast is found in members of algae.

It is Cup shaped (Chlamydomonas),

Discoid (Chara), Girdle shaped,

(Ulothrix), reticulate (Oedogonium),

spiral (Spirogyra), stellate(Zygnema),

plate like(Mougeoutia). Chlorophyll

‘a’ and Chlorophyll ‘b’ are the major

photosynthetic pigments. Storage bodies

called pyrenoids are present in the

chloroplast and store starch. They also

contain proteins. The cell wall is made

up of inner layer of cellulose and outer

layer of Pectin. Vegetative reproduction

takes place by means of fragmentation

and asexual reproduction is by the

production of zoospores, aplanospores

and akinetes. Sexual reproduction

is present and may be isogamous,

anisogamous or Oogamous. Examples

for this group of algae includes Chlorella,

Chlamydomonas, Volvox, Spirogyra,

Ulothrix, Chara and Ulva.

Phaeophyceae

The members of this class are called

‘Brown algae’. Majority of the

forms are found in marine habitats.

Pleurocladia is a fresh water form. The

thallus is filamentous (Ectocarpus)

frond like (Dictyota)or may be giant

kelps (Laminaria and Macrocystis).

The thallus is differentiated into leaf

like photosynthetic part called fronds,

a stalk like structure called stipe and

a holdfast which attach thallus to the

substratum.

The Pigments include Chlorophyll

a, c, carotenoids and Xanthophylls. A

golden brown pigment called fucoxanthin

is present and it gives shades of colour

from olive green to brown to the algal

members of this group. Mannitol and

Laminarin are the reserve food materials.

Motile reproductive structures are

present. Two laterally inserted unequal

flagella are present. Among these one is

whiplash and another is tinsel. Although

sexual reproduction ranges from isogamy

to Oogamy, Most of the forms show

Oogamous type. Alternation of generation

is present (isomorphic, heteromorphic

or diplontic). Examples for this group

include Sargassum, Laminaria, Fucus and

Dictyota.

Rhodophyceae

Members of this group include ‘Red algae’

and are mostly marine. The thallus is

multicellular, macroscopic and diverse in

form. Porphyridium is the unicellular form.

Filamentous (Goniotrichum) ribbon like

(Porphyra) are also present. Corallina and

Lithothamnion are heavily impregnated

with lime and form coral reefs. Apart

from chlorophyll a, r-phycoerythrin and

54

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r-phycocyanin are the photosynthetic

pigments. Asexual reproduction takes

place by means of monospores, neutral

spores and tetraspores.

The storage product is floridean

starch. Sexual reproduction is Oogamous.

Male sex organ is spermatangium which

produces spermatium. Female sex organ

is called carpogonium. The spermatium is

carried by the water currents and fuse with

egg nucleus to form zygote. The zygote

develops into carpospores. Meiosis occurs

during carpospore formation. Alternation

of generation is present. Examples for

this group of algae include Ceramium,

Polysiphonia, Gelidium, Cryptonemia and

Gigartina

A green alga

Botryococcus braunii

is employed in Biofuel

production.

Algae in Health care

Kelps are the rich source of Iodine

Chlorella is used as Single Cell Protein

(SCP).

Dunaliella salina an alga, growing

in Salt pan is complement to our

health and provide β carotene.

2.3.3 Economic Importance

The Economic importance of Algae is

given in Table 2.3

Table 2.3: Economic importance of Algae

Name of the Algae

Economic importance

Beneficial activities

Chlorella, Laminaria, Sargassum, Ulva, Food

Enteromorpha

Gracilaria, Gelidiella, Gigartina

Agar Agar – Cell wall material used for media

preparation in the microbiology lab.

Packing canned food, cosmetic, textile paper

industry

Chondrus crispus

Carrageenan – Preparation of tooth paste, paint,

blood coagulant

Laminaria, Ascophyllum

Alginate – ice cream, paints, flame proof fabrics

Laminaria, Sargassum, Ascophyllum, Fucus Fodder

Diatom (Siliceous frustules)

Diatomaceous earth– water filters, insulation

material, reinforcing agent in concrete and

rubber.

Lithophyllum, Chara, Fucus

Fertilizer

Chlorella

Chlorellin -Antibiotic

Chlorella, Scenedesmus,

Sewage treatment, Pollution indicators

Chlamydomonas

Harmful activity

Cephaleuros virescens

Red rust of coffee

55

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A Productive Cultivation

in Sea

Algae like Kappaphycus

alvarezii, Gracilaria

edulis and Gelidiella acerosa are

commercially grown in the sea for

harvesting the phycocolloids.

Sea Palm It is Postelia palmaeformis a

brown alga.

the hold fast extends to produce finger

like projections which help the filament to

attach on the substratum. The apical cell

is rounded or elongated in shape. Each

vegetative cell is cylindrical and possesses a

thick cell wall. The inner layer is cellulosic

and the outer layer is made up of pectin.

A thin layer of chitin is present above the

pectin layer. Next to the cell wall a plasma

membrane is present. A large vacuole

is present. The protoplasm contains

reticulate chloroplast and it extends from

one end of the cell to the other. A single

nucleus and many pyrenoids are present.

The distal end of some cells possess ring

like markings called apical caps. Such cells

are called cap cells. The presence of cap

cell is characteristic feature of Oedogonium

(Figure 2.5).

2.3.4 Oedogonium

Class – Chlorophyceae

Order - Oedogoniales

Family -Oedogoniaceae

Genus – Oedogonium

Oedogonium is a freshwater , filamentous

alga and occurs in ponds, lakes and

stagnant water. The filaments are attached

to rocks. Some are epiphytic on aquatic

plants. Oedogonium terrestre is a terrestrial

form and grow in moist soils. The young

filaments are attached but older ones are

free floating.

Cap cell

Chloroplast

Cell wall

Pyrenoid

Nucleus

Thallus structure

The thallus is filamentous ,multicellular

and unbranched. All the cells of the

filament are cylindrical except the basal

and apical cell. The basal cell is colourless

and forms hold fast. The proximal end of

Hold fast

a) A single b) A cell enlarged

filament

Figure 2.6

(b) A cell enlarged

oedogonium

Figure 2.5: Oedogonium

56

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Reproduction

Oedogonium reproduces by vegetative,

asexual and sexual methods. Vegetative

reproduction takes place by fragmentation

and akinete formation. During asexual

reproduction zoospores are formed.

During favourable conditions, some of the

vegetative cells function as zoosporangia.

Usually a single zoospore is produced

per zoosporangium. A ring of short

flagella is found at the base of colourless,

beak like anterior end of the zoospore.

This kind of flagellation is called

stephanokont. The zoospore is released

from the zoosporangium and swims in

water (Figure 2.6). If it reaches a suitable

substratum, it divides into two cells. The

lower cell forms holdfast. The green upper

cell divides and produces the filament.

a) Zoospore formation

b) Dwarf male

Dwarf male

Pyrenid

Nucleus

Antherozoid

Antheridium

c) Filament showing antheridium

Figure 2.6: Reproduction in Oedogonium

Sexual reproduction is Oogamous. The

male gametangium is antheridium and

female gametangium is called Oogonium.

Based on the distribution of sex organs

there are two types of species namely

Macrandrous and Nannandrous.

Macrandrous monoecious – Antheridia

and Oogonia occur on same filament –

Oedogonium fragile.

Macrandrous dioecious – Antheridia

and Oogonia occur on separate filaments

– Oedogonium crassum

In nannadrous species antheridia are

produced on reduced male filaments called

dwarf male plants(O. cancatenatum).

In nannandrous species antheridia

develop on specialised 2–4 celled

filaments called dwarf males. The dwarf

male is developed from androspores

released from the androsporangium..

If the androsporangia and oogonia

develop on same filament, it is called

gynandrosporous (O. concatenatum). If

they are borne on different filaments it is

called idioandrosporous (O. conferatum).

The antheridium produces multiflagellate

antherozoids. They are released by

57

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transverse splitting of the wall of

antheridium. Antherozoids are attracted

chemotactically towards the mature

oogonium. A single antherozoid enters

the oogonium through the opening

present on the wall of the oogonium.

The male nucleus fuses with the egg to

form a diploid zygote. After fertilization

the zygote separates from the oogonial

wall and a thick wall is secreted around

it. The diploid zygote undergoes meiosis

to produce 4 haploid multiflagellate

zoospores. The wall of the zygote ruptures

to release the zoospores.The germination

of the zoospore produces haploid filaments

of Oedogonium (Figure 2.6).

In the life cycle of Oedogonium

the diploid phase is short lived and

is represented by zygote. The haploid

phase is predominant and life cycle is of

Haplontic type (Figure 2.7).

zoospore

(n)

zoosporangium

Asexual germination

(n)

Reproduction

antheridium

(n) oogonium

(n)

antherozoid

(n)

egg

(n)

Fertilization

OEDOGONIUM

Macrandrous dioecious

filament (n)

filament (n)

Sexual

Reproduction

zygote

(2n)

germination

zoospore

(n)

Meiosis

Figure 2.7: Life cycle of Oedogonium

zoospore

(n)

2.3.5 Chara

Class – Chlorophyceae

Order – Charales

Family – Characeae

Genus – Chara

Chara is commonly called as ‘ stone wort’

It is a submerged aquatic freshwater alga

growing attached to the mud of the lakes

and slow running streams. Chara baltica

grows in saline water. The thallus is often

encrusted with calcium and magnesium

carbonate.

Thallus structure

The plant body is multicellular,

macroscopic and is differentiated into

main axis and rhizoids. The rhizoids

are thread-like, multicellular structures

arise from the lower part of the thallus or

peripheral cells of the lower node.They are

characterised by the presence of oblique

septa. The rhizoids fix the main axis on the

substratum and helps in the absorption of

salts and solutes (Figure 2.8).

The main axis is branched, long and is

differentiated into nodes and internodes.

The internode is made up of an elongated

cell in the centre called axial cell or

internodal cell. The axial cell is surrounded

by vertically elongated small cells which

originate from the node. They are called

cortical cells. In C. wallichii and C. corallina

the cortical cells are absent. Three types of

appendages arise from the node. They are

1. Branches of limited growth 2. Branches

of unlimited growth 3. Stipuloides. The

growth of the main axis and its branching

takes place by the apical cell.

The nodal cells are uninucleate with few

ellipsoidal chloroplasts. The internodal

58

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cells are elongated and possesses a

large central vacuole, many nuclei and

numerous discoidal chloroplasts.

The cytoplasm is divided into outer

ectoplasm and inner endoplasm. The

endoplasm shows cytoplasmic streaming.

Figure 2.8: Chara Habit

Reproduction

Chara reproduces by vegetative and

sexual methods. Vegetative reproduction

takes place by Amylum stars, Root bulbils,

Amorphous bulbils and secondary

protonema.

Sexual reproduction - Sexual

reproduction is Oogamous. Sex organs

are macroscopic and are produced on the

branches of limited growth. The male sex

organ is called Antheridium or Globule and

the female sex organ is called Oogonium or

Nucule (Figure 2.9). The Nucule is located

above the Globule. The antheridium is

spherical, macroscopic and its wall is

made up of eight cells called shield cells.

The antheridium has spermatogenous

filaments. These filaments produce

antherozoids. The nucule is covered by five

spirally twisted tube cells and five coronal

cells are present at the top of the nucule

(Figure 2.9). The centre of the nucule

59

Nucule

Laterals

Globule

Internode

Node

Figure 2.9: Chara sex organs

Fig 2.10 Chara sex organs

possesses a single egg. At maturity the tube

cells separate and a narrow slit is formed.

The antherozoids penetrate the oogonium

and one of them fuses with the egg to form

a diploid oospore. The oospore secretes a

thick wall around and germinates after the

resting period. The nucleus of the oospore

divides to form 4 haploid daughter nuclei

of which, three degenerate. The oospore

or zygote germinates to produce haploid

protonema. The plant body of Chara is

globule

(n)

antherozoid

(n)

nucule

(n)

amylum stars

bulbils

amorphous bulbils

secondary protonema

egg

(n)

fertilization

Asexual

Reproduction

CHARA

(n)

Sexual Reproduction

zygote

(2n)

protonema

(n)

meiosis

Figure 2.10: Life cycle of Chara

---

haploid and The oospore is the only diploid

phase in the life cycle. Therefore, the life

cycle is of haplontic type. Alternation of

generations is present (Figure 2.10).

2.4 Bryophytes

Amphibians of Plant Kingdom

In the previous

chapter we noticed

a wide range of

thallus organization

in Algae. Majority

of them are aquatic.

The development

of heterotrichous

habit, development of parenchyma

tissue, dichotomous branching in some

algae supports the view that colonization

of plants in land occurred in the past.

Bryophytes are simplest and most primitive

plant groups descended from alga – like

ancestors. They are simple embryophytes.

Let us learn about the structure and

reproduction of these primitive land plants

called Bryophytes in detail.

Shiv Ram Kashyap

(1882-1934)

Father of Indian Bryology. He

published a book-‘Liverworts of

Western Himalayas and Punjab

Plains’ He identified new genera like

Atchinsoniella, Sauchia, Sewardiella

and Stephansoniella.

Bryophytes are simplest land inhabiting

cryptogams and are restricted to moist,

shady habitats. They lack vascular tissue and

hence called ‘Non- vascular cryptogams’.

They are also called as ‘amphibians of

plant kingdom’ because they need water

for completing their life cycle.

2.4.1 General characteristic features

• The plant body of bryophyte is

gametophyte and is not differentiated

into root, stem and leaf like structure.

• Most of them are primitive land

dwellers. Some of them are aquatic

(Riella, Ricciocarpus).

• The gametophyte is conspicuous, long

lived phase of the life cycle. Thalloid

forms are present in liverworts and

Hornworts. In Mosses leaf like, stem like

structures are present. In Liverworts

thallus grows prostrate on the ground

and is attached to the substratum by

means of rhizoids. Two types of rhizoids

are present namely smooth walled and

pegged. Multicellular scales are also

present. In Moss the plant body is

erect with central axis bearing leaf like

expansions. Multicellular rhizoids are

present. The structure and reproduction

in Bryophytes is given in Figure 2.11

• Vascular tissue like xylem and phloem

are completely absent, hence called

‘Non vascular cryptogams’.

• Vegetative reproduction takes place

by the formation of adventitious

buds (Riccia fluitans) tubers develop

in Anthoceros. In some forms small

detachable branches or brood bodies

are formed, they help in vegetative

reproduction as in Bryopteris

fruticulosa. In Marchantia propagative

organs called gemmae are formed and

help in reproduction.

60

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• Sexual reproduction is Oogamous.

Antheridia and Archegonia are

produced in a protective covering and

are multicellular

• The antheridia produces biflagellate

antherozoids which swims in thin film

of water and reach the archegonium and

fuse with the egg to form diploid zygote.

• Water is essential for fertilization.

• The zygote is the first cell of the

sporophyte generation. It undergoes

mitotic division to form multicellular

undifferentiated embryo. The

embryogeny is exoscopic (the first

division of the zygote is transverse and

the apex of the embryo develops from

the outer cell). The embryo divides

and give rise to sporophyte.

• The sporophyte is dependent on

gametophyte.

• It is differentiated into three

recognizable parts namely foot, seta

and capsule. Foot is the basal portion

and is embedded in the gametophyte

through which water and nutrients

are supplied for the sporophyte. The

diploid spore mother cells found in

the capsule region undergoes meiotic

division and give rise to haploid spores.

Bryophytes are homosporous. In some

sporophytes elaters are present and

help in dispersal of spores (Example:

Capsule

a) Anthoceros

Leaf

Rhizoids

b) Funaria

c) Pegged and

smooth

walled Rhizoids

e) Fragmentation-Riccia

Tuber

Gemma Cup

d) Sphagnum

f) Tubers-Anthoceros

Figure 2.11: Structure and reproduction in Bryophytes

g) Gemmae-Marchantia

61

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Marchantia). The spores germinate to

produce gametophyte.

• The zygote, embryo and the

sporogonium constitute sporophytic

phase. The green long living haploid

phase is called gametophytic phase The

haploid gametophytic phase alternates

with diploid sporophyte and shows

heterologous alternation of generation.

2.4.2 Classification of Bryophytes

Proskauer in the year 1957 classified

Bryophytes into 3 Classes namely

i. Hepaticopsida (Riccia, Marchantia,

Porella and Riella) ii. Anthocerotopsida

(Anthoceros and Dendroceros) iii. Bryopsida

(Funaria, Polytrichum and Sphagnum).

The outline of the classification is given

below

Hepaticopsida

(Liverworts)

Bryophyta

Anthocerotopsida

(Hornworts)

Bryopsida

(Mosses)

Class: Hepaticopsida

They are lower forms of Bryophytes. They are

more simple in structure than mosses and

more confined to damp and shady places.

They have an undifferentiated thallus.

Protonernal stage is absent. Sporophyte is

very simple and short lived. In some the

foot and seta are absent. Example Riccia.

Class: Anthocerotopsida

Gametophyte is undifferentiated thallus.

Rhizoids are unicellular and unbranched.

Protonemal stage is absent. Sporophyte is

differentiated into foot and capsule and

seta is absent Example: Anthoceros.

Class: Bryopsida

These are higher forms in which the

gametophyte is differentiated into ‘stem’ like

and’leaf ’ like parts and the former showing

radial symmetry. Rhizoids are multi-cellular

and branched. Protonemal stage is present.

Sporophyte is differentiated into foot, seta

and capsule. They have a more differentiated

structure than liverworts. They often form

dense cushions. Example: Funaria.

2.4.3 Economic importance

A large amount of dead thallus of

Sphagnum gets accumulated and

compressed, hardened to form peat. In

northern Europe peat is used as fuel in

commercial scale (Netherlands). Apart

from this Nitrates, brown dye and tanning

materials are derived from peat. Sphagnum

and peat are also used in horticulture as

packing material because of their water

holding capacity. Marchantia polymorpha

is used to cure pulmonary tuberculosis.

Sphagnum, Bryum and Polytrichum are

used as food. Bryophytes play a major role

in soil formation through succession and

help in soil conservation.

2.4.4 Marchantia

Buxbaumia aphylla

and Cryptothallus mirabilis

are saprophytic

bryophytes

Class - Hepaticopsida

Order – Marchantiales

Family - Marchantiaceae

Genus - Marchantia

Marchantia grows in cool moist shady

places. Marchantia polymorpha is the

common species.

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Gametophyte

The plant body of Marchantia is a

gametophyte. It is prostrate,dorsiventral

and dichotomously branched. The thallus

on the dorsal surface possess conspicuous

median midrib which is marked by a

shallow groove on dorsal surface. The

dorsal surface appears to have rhomboidal

or polygonal diamond shaped areas which

indicate the outline of the underlying air

chambers of the thallus (Figure 2.12).

Archegoniophore

Gemma cup

Antheridiophore

Rhizoids

a) b)

Figure 2.12: Marchantia

a) Thallus with antheridiophore

b) Thallus with archegoniophore

The dorsal surface also shows crescent

shaped structures called gemma cups

which contain vegetative reproductive

structures called gemmae. The apical

notch bears an apical cell which helps

in the growth of the thallus.The ventral

surface the thallus bears multicellular

scales and rhizoids which help in fixation

and absorption of water and minerals. The

rhizoids are of two types namely smooth

walled or pegged (tuberculate) type.

On maturation the thallus bears erect

antheriophores and archegoniophores.

Internal structure of Thallus

In transverse section the Marchantia

thallus shows three parts namely:

Epidermis, Photosynthetic region and

storage region (Figure 2.13).

The epidermis has the upper and lower

layers. The upper epidermis is single layered

with thin walled parenchymatous cells.

The cells possess chloroplasts. The upper

epidermis is interrupted by many barrel

shaped air pores which communicate with

the air chambers. The pore is surrounded

by 4 to 8 superimposed tiers of cells. Below

the upper epidermis a number of air

chambers are present in a single horizontal

layer.The air chambers are separated from

one another by partitions which extend

from the epidermis to the floor of the

air chambers. The floor of the chambers

bears simple or branched green filaments.

The cells of the filaments are involved

in photosynthesis. The photosynthetic

region is followed by storage region. It is

made up of several parenchymatous cells

arranged without intercellular spaces. The

cells of this region contain starch grains

and protein granules. The lower epidermis

possesses rhizoids and multicellular scales.

Reproduction

Marchantia reproduces by vegetative and

sexual methods.

1.Vegetative Reproduction takes place

by progressive death and decay of thallus,

formation of adventitious branches and by

germination of gemmae. Death and decay of

the thallus starts from posterior end .When

it reach the point of dichotomy , two apical

parts of the thallus get separated. Each

one develops into an independent thallus.

Adventitious branches are produced on the

ventral surface of the gametophyte. The

branches get separated from the parent thallus

and grow into independent gametophytes.

Gemmae are specialized multicellular asexual

reproductive bodies. They are formed in

small cupules known as gemma cups, present

on the dorsal surface of the thallus. Usually

63

---

Figure 2.13: T.S. of Thallus

the gemmae present on the male thallus form

male plants and those on the female thallus

give rise to female plants (Figure 2.14).

a) V.S. of Gemma cup

Gemmae

Gemma cup

Oil cells

Notch

Stalk

b) A gemma enlarged

Figure 2.14: Vegetative reproduction in

Marchantia

1. Sexual reproduction:

In Marchantia, sex organs are borne

on special stalked receptacles called

the gametophores. Those bearing

antheridia are called antheridiophores

and archegonia bearing structures are

called archegoniophores (Figure 2.15).

Marchantia is heterothallic or dioecious.

i.e., male and female receptacles are

present on different thalli. The sex organs

in bryophytes are multicellular. The male

sex organ is called antheridium. It produce

biflagellate antherozoids. The female sex

organ is flask shaped called archegonium

and produces a single egg. Water is

essential for fertilization. The antherozoids

are released into water and are attracted

towards archegonium through chemotaxis.

Although many antherozoids enter the

archegonium, only one fuses with the egg to

form zygote. The zygote represent the first

cell of the sporophytic generation. Zygote

develops in to a multicellular structure

called sporophyte. (Figure 2.16).

64

---

The sporophyte is not free-living but

attached to the photosynthetic gametophyte

and derives nutrition from it. Sporophyte

is differentiated into foot, seta and capsule.

The foot is bulbous and is embedded in the

gametophyte. It derives nutrition from the

gametophyte and transfers to the sporophyte.

Seta is short and connects foot and capsule.

The capsule consists of single layered jacket

layer and encloses numerous haploid

spores and elaters. The capsule is covered

by protective covering called calyptra. On

maturation the capsule dehisces and spores

are released. Elaters helps in the dispersal

of spores. The spores under favourable

conditions germinate and develop into new

gametophyte. The haploid gametophytic

phase alternates with diploid sporophytic

phase, thus the life cycle of Marchantia shows

alternation of generation (Figure 2.17).

a) L.S. of Antheridiophore

Photosynthetic

region

Antheridium

Antheridiophore

Photosynthetic region

Archegonium

Perichaetium

Figure 2.17

V.S of marchantia sporophyte

Foot

Seta

Capsule

Spores

Elaters

Calyptra

Figure 2.16: Marchantia - V.S. of

Sporophyte

FRAGMENTATION

GEMMAE

ADVENTITIOUS

BRANCHES

(DIOECIOUS)

MALE THALLUS

(n)

FEMALE THALLUS

GERM TUBE

(n)

GERM TUBE

GERMINATION

SPORES

(n)

SPORES TETRAD

(n)

MEIOSIS

Vegetative Reproduction

GAMETOPHYTIC

GENERATION

(n)

MARCHANTIA

ARCHEGONIOPHORE

(n)

ARCHEGONIUM

(n)

EGG

(n)

ANTHERDIOPHORE

(n)

ANTHERIDIUM

(n)

ANTHEROZOID

(n)

FERTILIZATION

Archegoniophore

SPORES MOTHER

CELLS

(2n)

SPOROGONIUM

(2n)

Sexual Reproduction

SPOROPHYTIC

GENERATION

(2n)

OOSPORE

(2n)

b) L.S. of Archegoniophore

Figure 2.15: Marchantia - Sex organs

EMBRYO

(2n)

Figure 2.18 Life cycle of Marchantia

Figure 2.17: Life cycle of Marchantia

65

---

2.4.5 Funaria

Class – Bryopsida

Order- Funariales

Family – Funariaceae

Genus - Funaria

Funaria is commonly called ‘cord moss’. It

is distributed throughout the world.

Funaria hygrometrica is the common

species. It grows in close tufts on rocks,

trunks of trees, damp walls and damp

soils. They help in the process of soil

formation (Pedogenesis).

External

Capsule

features

The plant body

is a gametophyte

. It is small, 1

to 3 cm high

and consists of

slender erect

radial stem

covered with

Leaf

small, simple leaf

like structures

a r r a n g e d

in a spiral

Rhizoids

manner. The

gametophyte is Figure 2.18:

attached to the Funaria Habit

substratum by

means of multicellular rhizoids. They are

characterized by the presence of oblique

septa. The leaves are simple, sessile ovate

and have broad membranous base and

pointed apex.

Internal structure

T.S. of axis

The T.S. of axis shows the presence of

epidermis, cortex and central cylinder.

The epidermis is the outermost layer and

contain chloroplast bearing cells. The

cortex is made up of parenchymatous

tissue. The cells of the young axis

bear chloroplasts. In mature stems the

outermost cells become reddish brown

colour and become thick walled. Small

leaf traces are also noticed. The central

cylinder is made up of long, narrow,

thin walled, colourless cells which lack

protoplasts. They help in the conduction

of water and minerals.

Figure 2.19: T.S. of axis

Epidermis

Cortex

Central strand

T.S. of leaf

A well defined midrib is present. It

consists of several layers of cells but the

lateral ‘wing’ or lamina is made up of

single layer of thin walled cells which are

rich in chloroplasts. Midrib contains small

strands of slightly thickened narrow cells

which help in conduction.

Reproduction

Funaria reproduces by vegetative and

sexual methods.

Vegetative reproduction

Vegetative reproduction takes place by the

following methods (Figure 2.20):

1. Fragmentation of primary protonema,

2. Formation of secondary protonema

from any part of the gametophyte

3. Formation of gemmae on terminal

cells of the protonema.

66

---

4. Development of Bulbils on the rhizoids.

Figure 2.5 Funaria - Protonema

Figure 2.20: Vegetative reproduction

(Protonema)

Sexual reproduction

Funaria is monoecious the male and

female reproductive sex organs are

borne on different branches of the

same gametophyte. Male sex organ is

antheridium and it is formed in groups on

the antheridial branch.They are enclosed

by special leaves called perigonial leaves.

A large number of long multicellular

hairs interspersed with antherdia called

paraphysis are also present. They

contain chloroplast and are involved in

photosynthesis. They protect antheridial

head from by minimizing transpiration,

hold water between them through capillary

action and secrete mucilage which helps

in the liberation of antherozoids. Each

antheridium is protected by single layer

of jacket. It encloses a large mass of

androcytes. The androcytes transform in

to biflagellate antherozoids (Figure 2.21).

The female sex organ are the archegonia

and are borne in clusters on the archegonial

branch. Archegonial branches arise

laterally at the base of the male branch.

They are surrounded by perichaetial

leaves. Paraphyses are also present.

Each archegonium is flask shaped and is

distinguished into a large venter and long

neck region. The venter contains venter

canal cell and egg. The neck contain neck

canal cells (Figure 2.21). Water is essential

for fertilization. Rain drops help in the

transfer of antherozoids from antheridial

head to archegonial head. The antherozoids

are attracted to the archegonium through

chemotaxis. A large number of antherozoids

enter the neck of the archegonium but only

one fuses with the egg to form a diploid

zygote. The diploid zygote represents the

first cell of sporophytic generation and

divides to form a sporophyte.

Figure

a) Antheridial head

Funaria antheridial head

Paraphysis

Antheridium

Perigonial

leaves

Perichaetial Leaf

Archegonia

Paraphysis

b) Archegonial head

Figure 2.21: Funaria - Sexual

reproduction

Structure of Sporophyte or capsule

The structure of mature sporophyte of

Funaria is complex. The sporophyte is

67

---

differentiated into foot, seta and capsule

(Figure 2.22). The foot is small, conical and

is embedded in the gametophyte. The seta

Operculum

Annulus

Spores

Spores sac

Columella

Trabeculae

Epidermis

Apophysis

Seta

Figure 2.22: L.S. of capsule

is long, slender and conducts water and

nutrients to the capsule . The capsule is

differentiated into apophysis, theca proper

and operculum. The cells constituting the

wall of the capsule contain chloroplasts in

them. The apophysis is the lowermost

sterile region and connects the capsule

with seta. The epidermis contains stomata

which help in exchange of gases. The cells

of the apophysis are photosynthetic, hence

the sporophyte of Funaria partially depends

on the gametophyte. The theca proper is

the middle part and is fertile region of the

capsule. It consists of a central columella

surrounded by spore sac. The spore sac is

surrounded by a single cylindrical air sac

traversed by delicate filaments made up of

parenchyma cells called trabeculae. The

trabeculae extend from the outer wall of

the spore sac to the innermost layer of the

capsule wall. The spore sac contains spore

mother cells which undergo meiotic

division to produce haploid spores. The

apical region consists of the operculum and

peristome. The operculum is the lid of the

capsule and comes out as a circular cup

shaped lid after the dehiscence of the

capsule. The peristome has one or two rows

of thickened, tooth like projections found

on the top of the capsule. They are

hygroscopic and help in the dispersal of the

spores. During favourble conditions the

spores germinate to produce thread like

green branched structure called protonema.

It produces rhizoids and number of lateral

buds which develop into new plants. In the

life cycle of Funaria the haploid

gametophytic phase (n)alternates with

diploid sporophytic phase (2n) and shows

alternation of generation (Figure 2.23).

BUDS

(n)

PRIMARY

PROTONEMA

(n)

GERMINATION

MEIOSPORES

(n)

MEIOSIS (R/D)

SPORE MOTHER

CELLS (2n)

BULBILS (TUBERS) ON RHIZOIDS

PROTONEMA

SECONDARY PROTONEMA (n)

MULTIPLICATION OF

PROTONEMAL STAGE

BUDS

(n)

BUDS

Vegetative BUDS

Reproduction

SPORE CAVITY

(2n)

(n)

(n)

FUNARIA

(n)

Sexual

Reproduction

GAMETOPHYTE

GENERATION

(n)

SPOROPHYTE

GENERATION

(2n)

FEMALE

BRANCH

(n)

MALE

BRANCH

(n)

PERICHAETIUM

(n) PERIGONIUM

(n)

ARCHEGONIUM

(n)

OOSPHERE

(n)

ANTHERIDIUM

(n)

FERTILISATION

ZYGOTE

(2n)

ANTHEROZOID

(n)

SPOROGONIUM

(2n)

Figure 17.21. Funaria. Graphic representation

Figure 2.23: Life cycle of Funaria

of the life cycle

68

---

2.5 Pteridophytes

Seedless Vascular Cryptogams

From the previous chapter we are aware

of the salient features of amphibious

plants called Bryophytes. But there is a

plant group called Pteridophytes which

are considered as first true land plants.

Further, they were the first plants to

acquire vascular tissue namely xylem and

phloem, hence called vascular cryptogams.

Club moss, Horsetails, quill worts, water

ferns and Tree ferns belong to this group.

This chapter deals with the characteristic

features of Pteridophytes.

Pteridophytes are the vascular

cryptogams and were abundant in the

Devonian period of Palaeozoic era (400

million years ago). These plants are

mostly small, herbaceous and grow well in

moist, cool and shady places where water

is available. The photographs for some

pteridophytes are given in Figure 2.24.

2.5.1 General characteristic features of

Pteridophytes:

• Plant body is sporophyte (2n) and it is

the dominant phase. It is differentiated

into root, stem and leaves.

• Roots are adventitious.

• Stem shows monopodial or

dichotomous branching.

• Leaves may be microphyllous or

megaphyllous.

• Stele is protostele but in some forms

siphonostele is present (Marsilea)

• Tracheids are the major water

conducting elements but in Selaginella

vessels are found.

• Sporangia, spore bearing bag like

structures are borne on special leaves

called sporophyll. The sporophylls gets

organized to form cone or strobilus.

Example: Selaginella, Equisetum .

• They may be homosporous (produce

one type of spores-Lycopodium) or

Heterosporous (produce two types of

spores-Selaginella). Heterospory is the

origin for seed habit.

• Development of sporangia may be

eusporangiate (development of

sporangium from group of initials)

or leptosporangiate (development of

sporangium from single initial).

• Spore mother cells undergo meiosis

and produce spores (n).

• Spore germinates to produce haploid,

multicellular green, cordate shaped

independent gametophytes called

prothallus.

• Fragmentation, Resting buds, root

tubers and adventitious buds help in

Vegetative reproduction.

• Sexual reproduction is Oogamous.

Sex organs, namely antheridium and

archegonium are produced on the

prothallus.

• Antheridium produces spirally coiled

and multiflagellate antherozoids.

• Archegonium is flask shaped with

broad venter and elongated narrow

neck. The venter possesses egg or ovum

and neck contain neck canal cells.

69

---

• Water is essential for fertilization.

After fertilization a diploid zygote is

formed and undergoes mitotic division

to form embryo.

• Pteridophytes show apogamy and

apospory.

a) Lycopodium (club moss) b) Equisetum (Horse tail) c) Azolla (Water fern)

Figure 2.24: Pteridophytes

2.5.2 Classification of Pteridophytes

Reimer (1954) proposed a classification

for Pteridophytes. In this classification,

the Pteridophytes are divided into

2.5.3 Economic Importance

five subdivisions. 1. Psilophytopsida

2. Psilotopsida 3. Lycopsida 4. Sphenopsida

5. Pteropsida. There are 19 orders and

48 families in the classification.

The Economic importance of Pteridophyte is given in Table 2.4

Table 2.4: Economic importance of Pteridophyte

Pteridophyte

Uses

Rumohra adiantiformis (leather leaf fern) Cut flower arrangements.

Marsilea

Food

Azolla

Biofertilizer.

Dryopteris filix–mas

Treatment for tapeworm.

Pteris vittata Removal of heavy metals from soils -

Bioremediation

Pteridium sp.

Leaves yield green dye.

Equisetum sp.

Stems for scouring.

Psilotum, Lycopodium, Selaginella, Ornamental plants

Angiopteris, Marattia

The success and dominance of vascular plants is due to the development of

• Extensive root system.

• Efficient conducting tissues.

• Cuticle to prevent desiccation.

• Stomata for effective gaseous exchange.

70

---

Division-

PTERIDOPHYTA

Sub division

Psilophytopsida Psilotopsida

Lycopsida Sphenopsida Pteropsida

All are extinct plants.

Plant body had only

stem and rhizome.

Roots and leaves were

absent.

Homosporous

Spore tetrads were

borne at the terminal

sporangia.

Example: Rhynia.

The plant body is

rootless and have

fungal association.

Small, scaly

appendages represent

the leaves.

Gametophyte is

colourless and have

fungal association.

They are

homosporous and

spores are produced

in sporangia or

synangia. Example:

Psilotum.

The plant body is

differentiated into

root, stem and leaves.

Leaves are small,

univeined, spirally

arranged.

Ligules are present.

Sporophylls are

arranged in the form

of strobilus.

Both homospory

(Lycopodium)

and heterospory

(Selaginella) are

found.

Example: Selaginella.

The plant body is

differentiated into

root, stem and leaves.

Stem shows jointed

nodes and internodes.

Small, scaly leaves are

arranged at nodes in

whorls.

Peltate disc of

sporangiophore

possess compact

strobilus.

Homosporous but

incipient heterospory

is found in Equisetum

arvense.

The plant body is

differentiated into

root, stem and leaves.

Includes all the

megaphyllous

pteridophytes.

leaf gap is present

sporangia are

organized into sorus.

Both homosporus and

heterosporus forms

are present.

Example: Marsilea

71

---

2.5.4 Selaginella

Division – Lycophyta

Class – Ligulopsida

Order – Selaginellales

Family –Selaginellaceae

Genus – Selaginella

Selaginella is commonly called ‘spike moss’.

They are distributed in humid temperate and

tropical rain forests. Selaginella rupestris

and Selaginella lepidophylla are Xerophytic.

Selaginella kraussiana, Selaginella

chrysocaulos, Selaginella megaphylla are

some common species. In few Selaginella

species during dry season the entire plant

body gets curled and become fresh, green

when moisture is available. Due to this they

are called Resurrection plants. Example

S. lepidophylla

External morphology

Habit

The plant body of Selaginella is sporophyte

(2n) and it is differentiated into root,

stem, and leaves (Figure 2.25). There exist

variations in the habit of Selaginella. Some

species possess prostrate creeping system

(S. kraussiana); suberect (S. rupestris);

erect (Selaginella erythropus); Climbing

(Selaginella alligans). S. oregana is

an epiphyte. Most of the species are

perennials. on the basis of structure of

stem and arrangement of leaves, Selaginella

is divided into two sub genera namely

Homoeophyllum and Heterophyllum.

Homeophyllum include species with

erect stem and spirally arranged leaves.

(Example: S. upestris and S. oregana).

Heterophyllum include species with

prosrate stem with short erect branches

and dimorphic leaves (Example: S.

kraussiana and S. lepidophylla).

Figure 2.25: Selaginella Habit

Cone

Stem

Rhizophore

Root

Primary roots are short lived and the adult

plant has adventitious roots. The root

may arise at the point of dichotomous

branching or knot like swelling present at

the basal portion of the stem. Roots are

endogenous in origin.

Rhizophore

In many species long, cylindrical,

unbranched and leafless structures arise

from the lower side of the stem at the point

of dichotomy called rhizophores. They

grow vertically downwards and produce

tufts of adventitious roots.

Stem

The stem may be erect, dichotomously

branched or prostrate with lateral

branching. The prostrate stem is

dorsiventral.

Leaves

The leaves are microphyllous, sessile and

simple. A single midvein is present in the

leaves. The vegetative leaf as well as the

sporophyll bears a small membranous

tongue like structure on adaxial surface

called ligule. The basal part of the

ligule possess a hemispherical mass of

thin walled cells called glossopodium.

The function of ligule is not known,

72

---

but it is viewed to be associated with

water absorption, secretion and prevent

dessication of shoot. The members

belonging to Homeophyllum type possess

same type of leaves spirally arranged on

the stem whereas the Heterophyllum type

have two types of leaves- two dorsal rows

of small leaves(Microphylls) and two

ventral rows of large leaves(Megaphylls).

Internal structure

Root

The transverse section of the root reveals

an outermost layer called epidermis. It is

made up of tangentially elongated cells.

The cortex is homogeneous made up of

thin walled parenchyma . The innermost

layer of cortex is called endodermis. The

stele is a protostele, monarch and xylem is

exarch (Figure 2.26).

Epiblema

The innermost layer of cortex forms

endodermis. The stele is a protostele

Figure 2.37. It is monarch and exarch

but it is centrifugal in S. kraussiana and

crescent shaped in S. atroviridis.

Epidermis

Hypodermis

Cortex

Figure 2.27: T.S. of Rhizophore

Endodermis

Pericycle

Phloem

Metaxylem

Protoxylem

Stem

The anatomy of the stem reveals the

presence of epidermis, cortex and stelar

region (Figure 2.28).

Epidermis

Cortex

Endodermis

Protoxylem

Metaxylem

Phloem

Trabeculae

Xylem

Phloem

Cortex

Figure 2.26: T.S. of root

Rhizophore

The outermost layer of Rhizophore is

the epidermis. It is single layered and is

covered with a thick cuticle. The cortex is

differentiated into outer scelrenchymatous

and inner parenchymatous layers.

Figure 2.28: T.S. of Stem

The epidermis is parenchymatous

and is covered with a thick cuticle. The

cortex is parenchymatous with cells

arranged without intercellular spaces. A

sclerenchymatous hypodermis is noticed

in Selaginella lepidophylla. The presence

of radially elongated endodermal cells

73

---

called trabeculae is the characteristic

feature of Selaginella. The casparian strips

are found on the lateral walls. The rapid

stretching of the innermost cortical cells

in comparison with stele results in air

spaces and stele appears to be suspended

in air space with the help of trabeculae.

The stele is a protostele and exarch. A

variation in number of steles is found. It

may be monostelic (S. spinulosa); distelic

(S. kraussiana)or polystelic (S. laevigata).

The xylem is monarch(S. kraussiana) or

diarch (S. oregana). Tracheids are present

but vessels are also noticed in S. densa and

S. rupestris.

Leaf

The leaf shows upper and lower epidermis.

The epidermal cells have chloroplast.

Stomata occur on both surfaces. The

mesophyll is made up of loosely arranged

thin walled cells with intercellular spaces.

There is a median vascular bundle

surrounded by a bundle sheath. In vascular

bundle xylem is surrounded by phloem.

Reproduction

Selaginella shows both vegetative and

asexual modes of reproduction.

Sporangial wall

Tapetum

Microspore

Ligule

Figure 2.31 Mature microsporangia of Selaginella

b) A microsporangium enlarged

c) A megasporangium enlarged

Megaspore

Ligule

Figure 2.29: Reproduction in Selaginella

Axis

a) L.S. of cone

Ligule

Microsporophyll

Microsporangium

Megasporangium

Megasporophyll

Vegetative reproduction

Selaginella reproduces vegetatively by

fragmentation, bulbil formation, tuber

formation and resting buds.

Sexual reproduction

During sexual reproduction spores

are produced (Figure 2.29). Selaginella

is heterosporous and produces two

types of spores namely microspores in

74

---

microsporangium and megaspores in

megasporangium. The sporangia are borne

singly in the axils of microsporophyll

and megasporophyll respectively. The

sporophylls are arranged spirally around a

central axis and aggregate to form strobili

or cones. Variations in the distribution of

microsporangia and megasporangia among

the species are seen. In S. selaginoides and

S. rupestris megasporangia are present in

the basal part of the cone. S. kraussiana

possesses a single megasporangium at the

base of the strobilus. In S. inaequifolia one

side of the strobilus bear only megasporangia

and other microsporangia. Separate strobili

for microsporangia and megasporangia are

present in S. gracilis. and S. atro-viridis.

The development of sporangium is of

eusporangiate type. The sporangial initial

divides periclinally to form outer jacket

initials and inner archesporial initials. The

archesporial initials by repeated anticlinal

and periclinal divisions form sporogenous

cells. Microspore mother cells of

microsporangium undergo reduction division

to produce halpoid microspores. Similarly the

megaspore mother cell undergoes reduction

division to produce 4 haploid megaspores.

The microspore and megaspore represent the

male and female gametophyte and germinate

inside the sporangium. The microspores

produce biflagellate antherozoids.

Archegonia develop in the megaspore. The

antherozoids swim in water and reach the

archegonium. Fertilization brings the fusion

of male and female nucleus which result in

the formation of a diploid zygote. The diploid

zygote represents the first cell of sporophyte.

Fertilization

(Syngamy)

Embryo

(2n)

Oospore

(2n)

Antherozoid

(n)

Egg

(n) Antheridium

(n)

Archegonium

(n) Male Gametophyte

(n)

SELAGINELLA

(2n)

SPOROPHYTIC

GAMETOPHYTIC

GENERATION

(n)

GENERATION

(2n)

Microspores

(n)

Female Gametophyte

(n)

Figure 2.30: Life cycle of Selaginella

75

(2n)

Strobilus

(2n)

Microsporophyll

(2n) Megasporophyll (2n)

Microsporangium

(2n) Megasporangium

Microspore

Mother Cell

Meiosis R/D

Megaspores

(n)

Figure 2.32 Life Cycle of Selaginella

(2n)

Megaspore

Mother Cell

(2n)

---

It undergoes several mitotic division to form

embryo. The embryo develops into a mature

sporophytic plant.

In the life cycle of Selaginella alternation

of sporophytic and gametophytic

generation is present (Figure 2.30).

venation is free and dichotomous in all

the species. The vein spread in a fan-like

manner in the lamina. The leaves bear

marginal sori which are covered by a

false indusium.

2. 5.5 Adiantum

Division – Pteropsida

Class - Leptosporangiopsida

Order – Filicales

Family – Polypodiaceae

Genus – Adiantum

Adiantum is commonly known as ‘Maiden

hair fern’ or ‘Walking fern’. They are

distributed in the tropical and temperate

regions of the world. Some of the Indian

species include Adiantum capillus-veneris,

Adiantum pedatum, Adiantum caudatum

and Adiantum venustum. The sporophyte

is differentiated into rhizome, roots and

leaves Figure 2.31.

External features

Rhizome

The rhizome is a perennial, subterranean

dichotomously branched structure and is

creeping in A. capillus-veneris or may be

erect as in A. caudatum. It is covered with

persistent leaf bases and hairy outgrowths

called ramenta.

Root

The roots are adventitious and arise from

the rhizome.

Leaf

The leaves are also called fronds and are

pinnately compound (unipinnate- A.

caudatum, bipinnate- A. capillus-veneris)

the young leaves are circinately coiled.

The petiole is long, black and shiny. The

Sorus

Pinnule

Petiole

Rachis

Rhizome

Figure 2.31: Adiantum Habit

Internal structure

Root

The root is differentiated into epidermis,

cortex and central vascular cylinder.

Figure 2.32: T.S. of root

Epidermis

Outer Cortex

Inner Cortex

Phloem

Metaxylem

Protoxylem

76

Figure 2.34 Adiantum - T.S. of root

---

The epidermis is the outermost layer and

bears unicellular root hairs. The cortex is

divided into outer wide parenchymatous

and inner narrow sclerenchymatous layer.

The stele is simple and possesses a central

core of xylem in diarch condition with

phloem on either side of it (Figure 2.32).

Rhizome

The rhizome in transverse section shows a

single layered epidermis covered by cuticle.

Some epidermal cells bear multicellular

hairs. The Epidermis is followed by two

to three layered hypodermis made up of

sclerenchyma tissue. A parenchymatous

ground tissue is present. The young

rhizomes have amphiphloic siphonostele.

The older rhizomes have solenostele or

dictyostele (Figure 2.33).

Epidermis

Hypodermis

Endodermis

Meristele

Phloem

Xylem

central core surrounded by phloem

(Figure 2.34).

Figure 2.34: T.S. of Petiole

Epidermis

Ground tissue

Endodermis

Xylem

Phloem

Pinnule

The Pinnule shows upper and lower

epidermis. The cells contain chloroplasts.

Stomata are confined to lower epidermis.

The mesophyll is not differentiated

into palisade and spongy parenchyma.

The vascular bundle is surrounded by

sclerenchymatous bundle sheath.

Reproduction

Adiantum is homosporous. The

reproduction takes place by the production

of spores. The spores are produced in

sporangia. A group of sporangia forms

sori. The sori are marginal but the reflex

margins of the pinna form a protective

membranous structure called false

indusium (Figure 2.35). The development

of sporangium is of leptosporangiate type.

Figure 2.33: T.S. of Rhizome

Petiole

The petiole in T.S. shows a single layered

epidermis with thick cuticle. Epidermis

is followed by a sclerenchymatous

hypodermis which provides mechanical

support. There is an extensive

parenchymatous ground tissue. The

central region possesses a single large

horse shoe shaped stele. Xylem forms

Sporophyll

Sporangium

Annulus

Stomium

Figure 2.35: V.S. of Sporophyll

The sorus does not show any definite

sequence hence fall under mixed type.

77

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Figure 2.38. Life Cycle of Adiantum

A mature sporangium bears a multicellular

stalk and a spherical or elliptical single

layered structure called capsule. The

capsule contains haploid spores. The wall

of the capsule is differentiated into thick

walled annulus and thin walled stomium.

On maturity the sporangium bursts and

spores are released. The spores germinate

and undergo repeated division to produce

a prothallus. The prothallus is flat, green

and heart shaped. It is monoecious and

represents the gametophytic phase. Sex

organs called antheridia and archegonia

develop on the prothallus. Antheridia

release multiflagellate antherozoids which

swim in water and reach the egg of the

archegonium to accomplish fertilization.

The fertilization results in zygote(2n) and

it represents the first cell of sporophytic

generation. The zygote develops into

embryo which further differentiates

into sporophyte. Thus Adiantum shows

alternation of generation (Figure 2.36).

2.5.6 Types of Stele

The term stele refers to the central

cylinder of vascular tissues consisting of

xylem, phloem, pericycle and sometimes

medullary rays with pith (Figure 2.37).

There are two types of steles

1. Protostele

2. Siphonostele

(2n)

Oospore

Antherozoid

(n)

Embryo

(2n)

Fertilization

(Syngamy)

Oosphere (Egg)

(n)

ADIANTUM

(2n)

Sporophyll

(2n)

Sorus

(2n)

SPOROPHYTIC

GENERATION

(2n)

Sporangium

(2n)

Antheridium

(n)

Archegonium

(n)

GAMETOPHYTIC

GENERATION

(n)

Spore mother cells

(2n)

Meiosis R/D

(2n)

Prothallus

(n)

Spore

(n)

Figure 2.36: Life cycle of Adiantum

78

---

1. Protostele:

In protostele phloem surrounds xylem.

The type includes Haplostele, Actinostele,

Plectostele, and Mixed protostele.

(i) Haplostele: Xylem surrounded by

phloem is known as haplostele. Example:

Selaginella.

(ii) Actinostele: Star shaped xylem

core is surrounded by phloem is known

as actinostele. Example: Lycopodium

serratum.

(iii) Plectostele: Xylem plates alternates

with phloem plates. Example: Lycopodium

clavatum.

(iv) Mixed prototostele: Xylem groups

uniformly scattered in the phloem.

Example: Lycopodium cernuum.

Plectostele

Actinostele

Atactostele

Dictyostele

Amphiphloic

Siphonostele

Protostele

Eustele

Solenostele

Ectophloic

Siphonostele

Figure 2.37: Types of Stele

Cambium

Pith

- Xylem

- Phloem

2. Siphonostele:

In siphonostele xylem

is surrounded by

phloem with pith at

the centre. It includes

Ectophloic siphonostele,

Amphiphloic siphonostele, Solenostele,

Eustele, Atactostele and Polycylic stele.

(i) Ectophloic siphonostele: The phloem

is restricted only on the external side of

the xylem. Pith is in centre. Example:

Osmunda.

(ii) Amphiphloic siphonostele: The

phloem is present on both the sides of

xylem. The pith is in the centre. Example:

Marsilea.

(iii) Solenostele: The stele is perforated at

a place or places corresponding the origin

of the leaf trace.

(a) Ectophloic solenostele – Pith is in the

centre and the xylem is surrounded by

phloem Example Osmunda.

(b) Amphiphloic solenostele – Pith is

in the centre and the phloem is present

on both sides of the xylem. Example:

Adiantum pedatum.

(c) Dictyostele – The stele is separated

into several vascular strands and each one

is called meristele. Example: Adiantum

capillus-veneris.

(iv) Eustele: The stele is split into distinct

collateral vascular bundles around the

pith. Example: Dicot stem.

(v) Atactostele: The stele is split into

distinct collateral vascular bundles and are

scattered in the ground tissue Example:

Monocot stem.

(vi) Polycyclicstele: The vascular tissues

are present in the form of two or more

concentric cylinders. Example: Pteridium.

79

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2.6 Gymnosperms

Naked Seed producing Plants

Michael Crichton’s Science fiction in a

book transformed into a Film of Steven

Spielberg (1993) called Jurassic Park. In

this film you might have noticed insects

embedded in a transparent substance

called amber which preserves the extinct

forms. What is amber? Which group of

plants produces Amber?

Amber is a plant secretion that is a

efficient preservative that doesn’t get

degraded and hence can preserve remains

of extinct life forms. The amber is produced

by Pinites succinifera, a Gymnosperm.

In this chapter we shall discuss in detail

about one group of seed producing plants

called Gymnosperms.

Gymnosperms (Gr. Gymnos =

naked; sperma= seed) are naked seed

producing plants. They were dominant

in the Jurassic and cretaceous periods

of Mesozoic era. The members are

distributed throughout the temperate

and tropical region of the world

2.6.1 General characteristic features

• Most of the gymnosperms are

evergreen woody trees or shrubs.

Some are lianas (Gnetum)

• The plant body is sporophyte and

is differentiated into root, stem and

leaves.

• A well developed tap root system is

present. Coralloid Roots of Cycas

have symbiotic association with blue

green algae. In Pinus the roots have

mycorrhizae.

• The stem is aerial, erect and branched

or unbranched (Cycas) with leaf scars.

• In conifers two types of branches

namely branches of limited growth

(Dwarf shoot) and Branches of

unlimited growth (Long shoot) is

present.

• Leaves are dimorphic, foliage and scale

leaves are present. Foliage leaves are

green, photosynthetic and borne on

branches of limited growth. They show

xerophytic features.

• The xylem consists of tracheids but in

Gnetum and Ephedra Vessels are present.

• Secondary growth is present. The wood

may be Manoxylic (Porous, soft, more

parenchyma with wide medullary ray

-Cycas) or Pycnoxylic (compact with

narrow medullary ray-Pinus).

• They are heterosporous. The plant may be

monoecious (Pinus) or dioecious (Cycas).

• Microsporangia and Megasporangia

are produced on Microsporophyll and

Megasporophyll respectively.

• Male and female cones are produced.

• Anemophilous pollination is present.

• Fertilization is siphonogamous and

pollen tube helps in the transfer of

male nuclei.

• Polyembryony (presence of many

embryo) is Present. The naked ovule

develops into seed. The endosperm is

haploid and develop before fertilization.

• The life cycle shows alternation of

generation. The sporophytic phase is

dominant and gametophytic phase is

highly reduced. The photograph of

some of the Gymnosperms is given in

Figure 2.38

80

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a) Cycas b) Thuja c) Taxus d) Ginkgo

Figure 2.38: Gymnosperms

2.6.2 Classification of Gymnosperms

Sporne (1965) classified gymnosperms

into 3 classes, 9 orders and 31 families.

The classes include i) Cycadospsida

ii) Coniferopsida iii) Gnetopsida.

GYMNOSPERMS

Class-I Class-II Class-III

Cycadopsida Coniferopsida Gnetopsida

Orders: Orders: Order:

1. Pteridospermales

2. Bennettitales

3. Pentoxylales

4. Cycadales

1. Cordaitales

2. Coniferales

3. Taxales

4. Ginkgoales

1. Gnetales

General Characters of Main classes:

Class I – Cycadopsida

• Plants are palm-like or fern-like.

• Compound, frond-like pinnate leaves.

• Manoxylic wood.

• Sperms are motile.

• Flower like structures are absent.

Strobili are simple.

Example: Cycas, Zamia.

Class II – Coniferopsida

• Tall trees with simple leaves of varied

shape.

• Wood is pycnoxylic.

• Cone like strobili are present.

• Motile sperms are absent (except

Ginkgo biloba). Example: Pinus.

Class III – Gnetopsida

• Shrubs, trees and lianas.

• Leaves are elliptical or strap-shaped,

simple, opposite or whorled.

• Motile sperms are absent.

• Wood contains vessels.

• Strobili is called as inflorescence.

• Flower like structure with perianth is

present. Example: Gnetum, Ephedra.

2.6.2 Comparison of Gymnosperm with

Angiosperms

Gymnosperms resemble with

angiosperms in the following features

• Presence of well organised plant body

which is differentiated into roots, stem

and leaves.

• Presence of cambium in gymnosperms

as in dicotyledons.

• Flowers in Gnetum resemble to the

angiosperm male flower. The Zygote

represent the first cell of sporophyte.

• Presence of integument around the ovule.

• Both plant groups produce seeds.

• Pollen tube helps in the transfer of

male nucleus in both.

• Presence of Eustele.

81

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The difference between Gymnosperms and Angiosperms were given in Table 2.5

Table 2.5: Difference between Gymnosperms and Angiosperms

S.No Gymnosperms Angiosperms

1. Vessels are absent [except Gnetales] Vessels are present

2. Phloem lacks companion cells Companion cells are present

3. Ovules are naked Ovules are enclosed within the ovary

4. Wind pollination only Insects, wind, water, animals etc., act as

pollinating agents

5. Double fertilization is absent Double fertilization is present

6. Endosperm is haploid Endosperm is triploid

7. Fruit formation is absent Fruit formation is present

8. Flowers absent Flowers present

2.6.3 Economic importance of Gymnosperms

Table 2.6: Economic importance of Gymnosperms

S.No Plants Products uses

1. Cycas circinalis, Cycas

revoluta

Sago

Starch used as food

2. Pinus gerardiana Roasted seed Used as a food

3. Abies balsamea Resin (Canada

balsam)

4. Pinus insularis, Pinus

roxburghii

5. Araucaria (Monkey's puzzle),

Picea and Phyllocladus

Rosin and

Turpentine

Tannins

Used as mounting medium in

permanent slide preparation

Paper sizing and varnishes

Bark yield tannins and is used in

Leather industries

6. Taxus brevifolia Taxol Drug used for cancer treatment

7. Ephedra gerardiana Ephedrine For the treatment of asthma,

bronchititis

8. Pinus roxburghii Oleoresin Used to make soap, varnishes

and printing ink

9. Pinus roxburghii,

Wood pulp Used to make papers

Picea smithiana

10. Cedrus deodara wood Used to make doors, boats and

railway sleepers

11. Cedrus atlantica oil Used in perfumery

12 Thuja, Cupressus, Araucaria,

and Cryptomeria

whole plant

Ornamental plants/Floral

Decoration

82

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2.6.4 Cycas

Class – Cycadopsida

Order – Cycadales

Family- Cycadaceae

Genus - Cycas

It is widely distributed in tropical and sub

tropical region of eastern hemisphere of

the world. Cycas revoluta, Cycas beddomei,

Cycas circinalis, Cycas rumphii are some

of the common species. The plant body

is sporophyte and resemble a small palm.

The growth is very slow. It is evergreen

and xerophytic in nature.

Sporophyte:-

The sporophyte is differentiated into root,

stem and leaves. The stem is columnar

bearing a crown of spirally arranged

pinnately compound leaves (Figure 2.39).

External features

Figure 2.39: Cycas Habit

Root

Two types of roots are found in Cycas.

They are the tap root and coralloid root.

The primary root persists and forms

the tap root. Some of the lateral roots give

rise to branches which grow vertically

upward below the ground level. They

branch repeatedly to form dichotomously

branched coral- like roots called coralloid

roots. The cortical region of the coralloid

root contains the Blue green alga –

Anabaena sp. which helps in nitrogen

fixation (Figure 2.40).

Figure 2.41 Cycas - Coralloid roots

Figure 2.40: Coralloid root

Stem

The stem is columnar, unbranched and

woody. It is covered with persistent woody

leaf bases. The stem also bears adventitious

buds at the base.

Leaves

Cycas has two types of leaves

(i) Foliage or assimilatory leaves

(ii) Scale leaves

(i) Foliage or assimilatory leaves

Foliage leaves are large, pinnately

compound and form a crown at the top

of the stem. Each leaf has 80-100 pairs of

sessile leaflets. The apex is acute or spiny. The

leaflet has a single midvein. Lateral veins are

absent. Circinate vernation is present and

young leaves are covered with ramenta.

(ii) Scale leaves

Scale leaves are brown, small, triangular

and persistent which are protective in

function. They are covered with ramenta.

83

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Internal structure

T.S. of Root

The internal organization of the

primary root reveals the following parts.

1. Epiblema, 2. Cortex 3. Vascular region

(Figure 2.41). Epiblema is the outermost

layer and is made up of single layered

parenchyma. It is followed by thin walled

parenchymatous cortex. The cortex is

delimited by single layered endodermis.

A multilayered parenchymatous pericycle

is present and it surrounds the vascular

tissue. The xylem is diarch in young root

and tetrarch in older ones. Secondary

growth is present. Coralloid root also

shows similar structure but the middle

cortex is characterized by the presence

of Algal zone. Blue green alga called,

Anabaena is found in this zone. The xylem

is triarch and exarch.

Epidermis

Outer cortex

Middle cortex

Inner cortex

Mucilage cell

Tannin cell

Endodermis

Xylem

Pith

Phloem

Figure 2.41: T.S. of Coralloid root

T.S. of Stem

The cross section of young stem is

irregular in outline due to the presence

of persistent leaf bases. It is differentiated

into epidermis, cortex and vascular

cylinder. It resembles the structure of a

dicot stem (Figure 2.42).

The epidermis is the outermost layer

and is covered with thick cuticle. It is

discontinuous due to the presence of

leaf bases. The cortex constitutes the

major part and is made up of thin walled

parenchymatous cells. The cells are filled

with starch grains. Cortex also possesses

several mucilage ducts and tannin cells.

In young stem the vascular bundles are

arranged in the form of a ring. A broad

medullary ray is present. The vascular

bundles are conjoint, collateral, endarch

and open. Xylem is made up of tracheids

and phloem consists of sieve tubes and

phloem parenchyma. Companion cells

are absent. The cambium present in the

vascular bundle is active for short period.

The secondary cambium is formed from

the pericycle or cortex and helps in

secondary growth of the stem. The cortical

region shows a large number of leaf traces.

The presence of direct leaf traces and

girdling leaf trace is the unique feature of

Cycas stem. Secondary growth results in

polyxylic condition. Phellogen and cork

are formed and replace the epidermis.The

wood formed belongs to manoxylic type.

Armour of leaf bases

Cortex

Girdling leaf trace

Vascular bundles

Pith

Mucilage duct

Figure 2.42: T.S. of stem

T.S. of Rachis

The outermost layer is epidermis and is

covered by thick cuticle. The hypodermis

is made up of two layers of sclerenchyma

on the adaxial side and many layered on

the abaxial side. The ground tissue is

parenchymatous. The peculiar feature

84

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of the rachis is the arrangement of

vascular bundle i.e., in an inverted

Omega shape pattern (Figure 2.43). Each

vascular bundle is covered by a single

layered sclerenchymatous bundle sheath.

Vascular bundles are collateral, endarch

and open. A single layered endodermis

and few layered pericycle surrounds the

bundle. A diploxylic condition is present

in the vascular bundles.( presence of both

centripetal and centrifugal xylem).

Epidermis

Figure 2.43: T.S. of Rachis

Hypodermis

Ground tissue

Vascular bundle

Mucilage duct

T.S. of Leaflet

The leaflet of Cycas in transverse section

shows the presence of upper and lower

epidermis. The epidermal cells are thick

walled and are covered with thick cuticle.

The lower epidermis is not continuous

and is interrupted by sunken stomata. The

hypodermis consists of sclerenchyma cells

to prevent transpiration. The mesophyll

is differentiated into palisade and spongy

Phloem

Xylem

Transfusion

tissue

Palisade

parenchyma

Figure 2.44: T.S. of leaflet

Spongy

parenchyma

parenchyma. The cells of this layer are

involved in photosynthesis. The spongy

parenchyma present in close proximity to

the lower epidermis bear large intercellular

spaces which help in gaseous exchange.

Layers of colourless, elongated cells

which run parallel to the leaf surface from

the midrib to the margin of the leaflet are

seen. These constitute the Transfusion

tissue that helps in the lateral conduction

of water. The vascular bundle has xylem

facing upper epidermis and phloem facing

lower epidermis. The protoxylem occupies

the centre, hence the bundle is mesarch. The

vascular bundle has a sclerenchymatous

bundle sheath (Figure 2.44).

Reproduction

Cycas reproduces by both vegetative and

sexual methods

Vegetative reproduction

It takes place by adventitious buds or

bulbils. They develop in the basal part

of the stem. The bulbils on germination

produce new plants.

Sexual reproduction

Cycas is dioecious i.e., male and female

cones are produced in separate plants. It is

heterosporous and produces two types of

spores (Figure 2.45).

Male cone

The male cone or staminate cone are borne

singly on the terminal part of the stem.

The growth of the stem is continued by the

formation of axillary buds at the base of the

cone. The male cone is displaced to one side

showing sympodial growth in the stem.

Male cones are stalked, compact, oval or

conical and woody in structure. It consists

of several microphylls which are arranged

spirally around a central cone axis.

85

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a) Male cone entire

Microsporophyll

Apophysis

Microsporangia

b) A microsporophyll enlarged

Microsporangium

Microspores

c) T.S. of Microsporophyll

Ovule

d) Megasporophyll

Figure 2.45: Reproduction in Cycas

Microsporophylls

Microsporophylls are flat, leaf-like and

woody structures with narrow base and

expanded upper portion. The upper

expanded portion becomes pointed

and is called apophysis. The narrow

base is attached to the cone axis. Each

microsporophyll contains thousands of

microsporangia in groups called sori on

abaxial (lower) surface. Development

of sporangium is of Eusporangiate type.

The spore mother cell undergoes meiosis

to produce halpoid microspores. Each

Microsporangium bears large number

of microspores or pollen grains. Each

sporangium is provided with a radial line

of dehiscence, which helps in the dispersal

of spores. Each microspore (Pollen grain)

is a rounded, unicellular and uninucleate

structure surrounded by outer thick exine

and an inner thin intine. The microspore

represents the male gametophyte.

Megasporophylls

The megasporophylls of Cycas are not

organised into cones. They occur in

close spirals around the tip of the stem

of female plant. The megasporophylls are

flat and measuring 15-30 cm in length.

Each megasporophyll is differentiated

into a basal stalk and an upper leaf like

portion. The ovules are attached to the

lateral side of the sporophyll. The ovules

contain megaspore and it represent the

female gametophyte.

Structure of Ovule

Cycas produces the largest ovule of

the plant kingdom. The ovules are

orthotropous, unitegmic and possess a

short stalk. The single integument is very

thick and covers the ovule leaving a small

opening called micropyle. The integument

86

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consists of 3 layers, the outer and inner

are fleshy (sarcotesta), the middle layer

is stony called sclerotesta. The inner

layer remains fused with the nucellus.

The nucellus grows out into a beak-like

structure and the upper part dissolves and

forms a cavity-like structure called pollen

chamber. A single megaspore mother cell

undergoes meiosis to form four haploid

megaspores. The lowermost becomes

functional and others get degenerated. The

nucellus gets reduced in the form of a thin

papery layer in mature seeds and encloses

the female gametophyte An enlarged

megaspore or the embryo-sac is present

within the nucellus. An archegonial

chamber with 3-6 archegonia are present

in the archegonial chamber below the

pollen chamber (Figure 2.46).

Micropyle

Pollen Chamber

Megaspore

Female Gametophyte

Outer Layer

Middle Layer

Inner Layer

Figure 2.46: L.S. of Ovule

Seed

(2n)

Embryo

(2n)

Oospore (2n)

CYCAS (Male)

(2n)

CYCAS(female)

(2n)

SPOROPHYTIC

GENERATION

(2n)

Male cone

(2n)

Female strobilus

(2n)

Fertilization

Male nuclei

(n)

(syngamy)

GAMETOPHYTIC

GENERATION

egg

(n)

(n)

Embryo sac

(n)

Antherozoids

(n)

Megaspores

(n)

Megasporangium

(2n)

Megaspore Mother cell

Meiosis

(R/D)

(2n)

Microsporangium

(2n)

Microspore Mother cell

(2n)

Microspores

(n)

Figure 2.49 2.47: Life cycle Cycle of Cycas of Cycas

87

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Pollination and Fertilization.

Pollination is carried out by wind and

occurs at 3 celled stage(a prothallial cell, a

large tube cell and a small generative cell).

Pollen grains gets lodged in the pollen

chamber after pollination. The generative

cell divides into a stalk and a body cell.

The body cell divides to produce two large

multiciliated antherozoids or sperms.

During fertilization, one of the male

gamete or multiciliated antherozoid fuses

with the egg of the archegonium to form

a diploid zygote (2n). The endosperm is

haploid. The interval between pollination

and fertilization is 4- 6 months. The zygote

undergoes mitotic division and develops

into embryo. The ovule is transformed

into seed. The seed has two unequal

cotyledons. Germination is hypogeal. The

life cycle shows alternation of generations

(Figure 2.47).

2.6.5 Pinus

Class – Coniferopsida

Order – Coniferales

Family –Pinaceae

Genus - Pinus

Pinus is a tall tree, looks conical in

appearance and forms dense evergreen

forest in the North temperate and subalpine

regions of the world. They mostly

grow in high altitudes (ranging from

1,200 to 3,000 metres). Some species of

this genus include, Pinus roxburghii, P.

wallichiana, P. gerardiana and P. insularis.

External features

The plant body is sporophyte and is

differentiated into root, stem and leaves.

The main stem is branched. The branches

are dimorphic with long and short

branches (Figure 2.48).

Figure 2.48: Pinus Habit

Root

Tap root system is found in Pinus. The

root hairs are not well developed and

the roots are covered with fungal hyphae

called mycorrhizae.

Stem

The stem is cylindrical, erect, woody and

branched. The branches are monopodial.

The branches are of two types.

(i) Long shoots or branches of

unlimited growth, (ii) Dwarf shoot or

branches of limited growth

(i) Long shoots or branches of

unlimited growth

The long shoot is present on the main

trunk the apical buds grow indefinitely,

They shorten gradually towards the tip,

thus providing a pyramidal appearance

to the tree. These branches bear scale

leaves only.

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(ii) Dwarf shoot or branches of limited

growth

These branches do not have apical

buds and hence show only limited growth.

They develop in the axils of scale leaves

and bear both scale and foliage leaves.

Leaves

There are two types of leaves 1. scale

leaves, 2. foliage leaves

1. Scale leaves:

They are dark, brown, membranous,

thin and small. They are present on both

long and dwarf shoots. Their function is

to protect young buds. The scale leaves on

the dwarf shoots have a distinct midrib

and are called “Cataphylls”.

2. Foliage leaves:

The foliage leaves are green angular

and needle like structures. They are

borne on the dwarf shoot. A dwarf shoot

with a group of needle like foliage leaves

is known as foliar spur. The number of

needles per dwarf shoot varies among the

species. It may be one (Pinus monophylla),

two (P. sylvestris), three (P. geraradiana),

four (P. quadrifolia) and five (P. excelsa).

Internal Structure

T.S. of root

The internal structure of root reveals the

presence of epiblema, cortex and stele.

The epiblema is made up of single layer

of parenchymatous cells. Cortex is the

wide zone and consists of parenchyma.

Some of the cells have resin ducts. A

single layered endodermis with suberised

wall is present and is impregnated with

tannins.A multilayered pericycle made up

of parenchyma is present. Vascular tissue

is radial, diarch with exarch xylem. The

protoxylem bifurcates to form a ‘Y’ shaped

structure and a resin duct lies in between

the two arms of protoxylem. Secondary

growth is present (Figure 2.49).

Epiblema

Cortex

Endodermis

Pericycle

Pith

Phloem

Figure 2.49: T.S. of Pinus root

Metaxylem

Protoxylem

Resin canal

T.S. of Stem

The internal organization of the stem

shows three regions namely epidermis,

Cortex and vascular tissue (Figure 2.50).

Epidermis

Resin canal

Cortex

Endodermis

Cambium

Phloem

xylem

Pith

Medullary ray

Tannin cells

Figure 2.50: T.S. of Pinus stem

Epidermis is the outermost layer

composed of compactly arranged and

heavily cutinized cells. Epidermis is

followed by few layers of sclerenchymatous

hypodermis. The cortex consists of thin

walled parenchyma cells. Resin canals

and tannin filled cells are present in this

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region. Endodermis is indistinguishable

from cortical cells. Vascular region is

surrounded by pericycle. A ring consists

of five or six vascular bundles are present.

Vascular bundles are conjoint, collateral,

open and endarch. Pith and medullary

rays are present. Secondary growth is

present and annual rings are formed.

T.S. of needle or foliage leaf

The internal structure of needle shows

xerophytic adaptations. In cross section

the outline appears more or less triangular

and is divided into epidermis, mesophyll

and vascular bundles. The epidermis is

single layered and possesses thick cuticle

and sunken stomata.Epidermis is followed

by a few layers of sclerenchymatous

hypodermis. It is interrupted by substomatal

cavities (Figure 2.51).

pass substances from the mesophyll to

the phloem while the latter helps in water

conduction and constitutes transfusion

tissue. Two vascular bundles are present.

They are separated by sclerenchyma

tissue. The Vascular bundles are conjoint,

collateral and open.

Reproduction

Pinus is heterosporous and produces two

types of spores called. microspores and

megaspores. The plants are monoecious.

Both male and female cones or strobili

develop on the different branches of the

same plant (Figure 2.52).

Epidermis

Mesophyll

Phloem

Resin canal

Xylem

Sunken stomata

a) Pinus - A twig with male cones

Figure 2.51: T.S. of Pinus needle leaf

Mesophyll is not differentiated into

palisade and spongy parenchyma. Thin

walled cells with chloroplasts are present.

The cells are peculiar with numerous

small infoldings which project into the

cavities. The infoldings increase the

photosynthetic area of the needle leaves

Resin canal is present in the mesophyll.

A single layered endodermis separates

the vascular region from the cortex. A

multilayered pericycle containing starch

is present. Two types of specialised cells

called albuminous cells and tracheidal

cells are present. The former helps to

b) L.S. of male cone

Pollen grains

Central axis

Micro sporophyll

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Figure 2.53b Pinus Pollen Grain

c) A mature pollen grain

d) Pinus - A twig with female cone

Ovule

e) L.S. of female cone

Ovuliferous Scale

Bract Scale

Central Axis

Figure 2.52: Reproduction in Pinus

Male cone

Male cones are produced in clusters on

branches of unlimited growth. Each cone

develops on the axil of scale leaf . The

male cone consists of a centrally located

cone axis surrounded by numerous

spirally arranged microsporophyll. It

bears two microsporangia at the base of

the abaxial side of the microsporophyll.

Each sporangium bears numerous

winged microspores (n) or pollen grains.

The microspores represent the male

gametophyte

Female cone:-

Female cones are formed in the groups

of 1 to 4 in the axils of the scale leaves.

The female cone takes about three years

to mature. It has the central axis around

which megasporophylls are arranged

spirally. The megasporophyll is the

compound structure consisting of two

types of scales. 1. Bract scale (sterile), and

2. Ovuliferous scales (fertile). The dorsal

surface of each ovuliferous scale bears two

ovules. Ovules bear megaspores which

represent the female gametophyte.

Pollination and fertilization

In Pinus wind pollination takes place

(Anemophilous). The microspore or pollen

grain is released in the 4 celled stage(two

prothallial cell, 1 generative and 1 tube

cell). At the time of pollination a secretion

oozes out from the micropyle of the ovule

which entangles pollen grains which helps

to lodge them in the pollen chamber. The

tube cell protrudes to form pollen tube. The

generative cell divides to produce stalk cell

and body cell. The body cell divides into

unequal male cells. Fertilization takes place

after about a year of pollination. The pollen

tube containing two male nuclei penetrates

through the micropyle and reaches the egg.

One of the male nuclei fuses with the egg

forming diploid zygote and the remaning

one gets degenerated. The fertilized egg

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Oospore

(2n)

Seed

(2n)

Embryo

(2n)

Fertilization

(Syngamy)

SPOROPHYTIC

GENERATION

(2n)

Male gamete

(n)

Microspores

(n)

Egg

(n)

Archegonium

(n)

(zygote) undergoes mitotic division and

develops into an embryo. Polyembryony

is present. The embryo undergoes several

changes and finally becomes a winged seed.

The seed germination is epigeal. Life cycle

of Pinus shows alternation of generation

(Figure 2.53).

PINUS

(2n)

Female cone

(2n)

Male cone

(2n)

Megasporangium

(2n)

Microsporangium

Megaspore Mother cell

(2n)

(2n)

Meiosis (R/D)

Microspore Mother cell

(2n)

GAMETOPHYTIC

GENERATION

(n)

Figure 2.53: Life cycle of Pinus

Embryo sac

(n)

Figure 2.56 Life Cycle of Pinus

Megaspores

(n)

Know about Fossil plants

The National wood fossil park is

situated in Tiruvakkarai, a Village of

Villupuram district of Tamil Nadu. The

park contains petrified wood fossils

approximately 20 million years old. The

term ‘form genera’ is used to name the

fossil plants because the whole plant is

not recovered as fossils instead organs or

Prof. Birbal Sahni (1891-1949)

Father of Indian Palaeobotany. He

described Fossil plants from Rajmahal

Hills of Eastern Bihar. Pentoxylon

sahnii, Nipanioxylon are some of the

form genera described by him. Birbal

Sahni Institute of Palaebotany is

located in Lucknow

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parts of the extinct plants are obtained in

fragments. Shiwalik fossil park-Himachal

Pradesh, Mandla Fossil park-Madhya

Pradesh, Rajmahal Hills–Jharkhand,

Ariyalur – Tamilnadu are some of the

fossil rich sites of India.

Some of the fossil representatives of

different plant groups are given below

Fossil algae - Palaeoporella, Dimorphosiphon

Fossil Bryophytes – Naiadita, Hepaticites,

Muscites

Fossil Pteridophytes – Cooksonia, Rhynia,,

Baragwanthia, Calamites

Fossil Gymnosperms – Medullosa, Lepidocarpon,

Williamsonia, Lepidodendron

Fossil Angiosperms – Archaeanthus,

Furcula

2.7 Angiosperms

dominant phase and gametophyte is

highly reduced.

2.7.1 Salient features of Angiosperms

• Vascular tissue (Xylem and Phloem) is

well developed.

• Flowers are produced instead of cone

• The embryosac (Ovule) remains

enclosed in the ovary.

• Pollen tube helps in fertilization, so

water is not essential for fertilization.

• Double fertilization is present. The

endosperm is triploid.

• Angiosperms are broadly classified

into two classes namely Dicotyledons

and Monocotyledons.

2.7.2 Characteristic features of

Dicotyledons and Monocotyledons

Dicotyledons

Morphological features

In the previous lesson the characteristic

features of one of the spermatophyte

called Gymnosperms were discussed.

Spermatophytes also include plants

bearing ovules enclosed in a protective

cover called ovary, such plants are

called Angiosperms. They constitute

major plant group of our earth and are

adapted to the terrestrial mode of life.

This group of plants appeared during

the early cretaceous period (140 million

years ago) and dominates the vegetation

on a world scale. The sporophyte is the

Reticulate venation is present in the leaves.

Presence of two cotyledons in the seed.

Primary root radicle persists as Tap root.

Flowers tetramerous or pentamerous.

Tricolpate (3 furrow) pollen is present.

Anatomical features

• Vascular bundles are arranged in the

form of a ring in stem.

• Vascular bundles are open (Cambium

present).

• Secondary growth is present.

Monocotyledons

Morphological features

Parallel venation is present in the leaves.

Presence of single cotyledon in the seed.

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Radicle doesn’t persist and fibrous root is

present.

Flowers trimerous.

Monocolpate (1 furrow) Pollen is present.

Anatomical features

• Vascular bundles are scattered in

the stem

• Vascular bundles are closed (Cambium

absent).

• Secondary growth is absent.

Current Angiosperm Phylogeny Group

(APG) System of classification doesn’t

recognize dicots as a monophyletic

group. Plants that are traditionally

classified under dicots are dispersed in

several clades such as early Magnolids

and Eudicots.

Summary

Plant Kingdom includes Algae, Bryophytes,

Pteridophytes, Gymnosperms and

Angiosperms

The life cycle in plants fall under three types 1.

Haplontic,2. Diplontic and 3.Haplodiplontic

Algae are autotrophic, chlorophyll

bearing organisms. The Plant body is

not differentiated into root like, stem

like or leaf like structures. A wide range

of thallus organization is found in algae.

They reproduce vegetatively through

fragmentation, tuber and akinete formation.

Zoospores , autospores and hypnospores

are produced during asexual reproduction

.and Sexual reproduction occurs through

isogamy, anisogamy and oogamy.

Oedogonium is a fresh water, filamentous,

multicellular alga. The presence of cap cell

is the prominent characteristic feature in

addition reticulate chloroplast is present.

Asexual reproduction takes place through

Zoospores. The sexual reproduction is

Oogamous.

Chara is a fresh water alga and is

popularly called “Stone worts”. The plant

body is multicellular, macroscopic and is

differentiated into main axis and rhizoids.

Sexual reproduction is Oogamous.

Bryophytes are simplest land plants.

They are called amphibians of plant

kingdom or nonvascular cryptogams. The

plant body is gametophyte. The sporophyte

depends upon gametophyte. Conducting

tissues like xylem and phloem is absent.

Vegetative reproduction takes place through

fragmentation, formation of adventitious

bud and Gemmae. Sexual reproduction

is Oogamous. Water is essential for

fertilization.

Marchantia belongs to the class

Hepaticopsida. The thallus is dorsiventral

and is attached to the substratum by

means of rhizoids. The internal structure

of the thallus reveals the presence of

photosynthetic region and a storage region.

Vegetative reproduction takes place through

fragmentation and formation of Gemmae.

The sexual reproduction is Oogamous.

Sporophyte bears spores. Alternation of

generation is present.

Funaria belongs to the class Bryopsida.

The gametophyte is differentiated into leaflike,

stem-like structures with rhizoids.

Gemmae, Protonema and bulbils help in

asexual reproduction. Sexual reproduction

is Oogamous. Alternation of generation is

present.

Pteridophytes are also called vascular

cryptogams. The plant body is sporophyte

and is long lived ,which is differentiated

into root, stem and leaves. They may

be homosporous or heterosporous.

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The sporangia with spores are found in

sporophylls. The sporophylls organise

to form cones or strobilus. The spores

germinates to produce haploid, multicellular

heart shaped independent gametophyte

called prothallus. Sexual reproduction is

Oogamous. The life cycle shows Alternation

of generation.

The term stele includes central cylinder

of vascular tissues comprising xylem,

phloem, pericycle, endodermis and pith .

There are two major types of stele namely

Protostele and Siphonostele.

Selaginella belongs to the class

Lycopsida. The plant body is sporophyte.

It is differentiated into stem, leaf, rhizophore

and roots. Heterospory is found and two

types of spores namely microspores and

megaspores are produced in sporangia.

The microsporangia and megasporania are

borne on sporophylls. The sporophylls are

organized to form cone. Sexual reproduction

is oogamous. Alternation of generation is

present.

Adiantum belongs to Pteropsida.

The sporophyte is differentiated into

root, rhizome and leaves. The spores are

produced in sporangia and is covered by

false indusium. The sexual reproduction is

oogamous and sex organs (antheridum and

archegonium) are produced on prothallus.

Alternation of generation is present.

Gymnosperms are naked seed producing

plants. The plant body is sporophyte and it

is the dominant phase. Coralloid roots are

found in Cycas. The roots of Pinus possess

Mycorrhizal association .Two types of

branches called Long shoot and dwarf shoot

are present. Stem shows secondary growth.

Spores are produced in cones. Pollen tube

helps in fertilization.. The endosperm

is haploid . Alternation of generation is

present

Cycas belongs to Cycadopsida. The plant

body is sporophyte and looks like a small palm

tree. Apart from Taproot Coralloid roots are

present. It is dioecious, Microsporophylls

are organized into male cone. Ovules are

borne on megasporophylls which are not

organized into cone. Fertilization results

in zygote and it develops into embryo.

Alternation of generation is present.

Pinus belongs to Coniferopsida.. The

plant body is sporophyte and is differentiated

into root, stem and leaves. The main stem is

branched. The branches are dimorphic with

long and short branches. It is monoecious,

heterosporous and produces two types of

spores called microspores and megaspores.

Alternation of generation is present.

Angiosperms are highly evolved plant

group and their ovules remain enclosed in

an ovary. A wide range of habit is present..

These include trees, shrubs, herbs, climbers,

lianas. Double fertilization is present. The

endosperm is triploid. They are classified

into Dicotyledons and Monocotyledons.

Evaluation

1. Which of the plant

group has gametophyte

as a dominant phase?

a. Pteridophytes

b. Bryophytes

c. Gymnosperm

d. Angiosperm

2. Which of following represent

gametophytic generation in

pteridophytes?

a. Prothallus

b. Thallus

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c. Cone

d. Rhizophore

3. The haploid number of chromosome

for an Angiosperm is 14 , the number

of chromosome in its endosperm

would be

a. 7 b. 14 c. 42 d. 28

4. Endosperm in Gymnosperm is

formed

a. At the time of fertilization

b. Before fertilization

c. After fertilization

d. Along with the development of

embryo

5. Differentiate halpontic and diplontic

life cycle.

6. What is plectostele? give example.

7. What do you infer from the term

pycnoxylic?

8. Mention two characters shared by

gymnosperms and angiosperms.

9. Do you think shape of chloroplast

is unique for algae. Justify your

answer?

10. Do you agree with the statement

‘Bryophytes need water for

fertilization’? Justify your answer.

11. List the classes of algae.

12. Mention the pigments and storage

food of Dinophyceae.

13. What are cap cells?

14. Name the flagellation found in the

zoospore of Oedogonium

15. What is Nucule?

16. Differentiate nodal and internodal

cells of Chara.

17. What are elaters?

18. What is protonema?

19. Where do we find false indusium?

20. Explain the internal structure of

Cycas rachis.

21. Differentiate long and dwarf shoot.

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ICT Corner

Different forms of plants

Is all the plants

are same?

Steps

• Scan the QR code or go to google play store

• Type online labs and install it.

• Select biology and select Characteristics of plants

• Click theory to know the basic about Characteristics of plants

• Register yourself with mail-id and create password to access online lab simulations

Activity

• Select video and record your observations of different forms of plant group.

Step 2 Step 3

URL:

Step 1 Step 4

https://play.google.com/store/apps/details?id=in.edu.olabs.olabs&hl=en

Alternate web:

http://www.phschool.com/atschool/phbio/active_art/plant_life_cycle/

plantlifecycle.swf

* Pictures are indicative only

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Chapter

3

Unit II: Plant Morphology and

Taxonomy of Angiosperm

Vegetative Morphology

Learning Objectives

The learner will be able to,

• Explore the parts of the flowering

plants

• Differentiate vegetative morphology

and reproductive morphology

• Compare various root systems and

their modifications

• Understand the stem modifications

and functions

• Interpret the structure of leaf and

functions of leaf

Chapter Outline

3.1 Habit

3.2 Plant habitat

3.3 Life Span

3.4 Parts of a flowering plant

3.5 Root System

3.6 Shoot system

3.7 Leaf

The study of various external features of

the organism is known as morphology.

Plant morphology also known as

external morphology deals with the study

of shape, size and structure of plants

and their parts (roots, stems, leaves,

flowers, fruits and seeds). Study of

morphology is important in taxonomy.

Morphological features are important

in determining productivity of crops.

Morphological characters indicate the

specific habitats of living as well as the

fossil plants and help to correlate the

distribution in space and time of fossil

plants. Morphological features are also

significant for phylogeny.

Plant Morphology can be studied

under two broad categories:

A. Vegetative morphology – It

includes shoot system and root

system

B. Reproductive morphology – It

includes Flower/inflorescence,

Fruit and Seed

A. Vegetative morphology

Vegetative morphology deals with the

study of shape, size and structure of

plants and their parts roots, stems and

leaves. To understand the vegetative

morphology the following important

components are to be studied. They are,

1) Habit, 2) Habitat and 3) Lifespan.

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3.1 Habit

The general form of a plant is referred to as

habit. Based on habit plants are classified

into herbs, shrubs, climbers (vines) and

trees.

I. Herbs

Herbs are soft stemmed plants with less

wood or no wood. According to the

duration of their life they may be classified

as annuals, biennials and perennials.

Perennial herbs having a bulb, corm,

rhizome or tuber as the underground

stem are termed as geophytes. Example:

Phyllanthus amarus, Cleome viscosa.

II. Shrubs

A shrub is a perennial, woody plant

with several main stems arising from the

ground level. Example: Hibiscus

III. Climbers (Vine)

An elongated weak stem generally

supported by means of climbing devices

are called Climbers (vines) which may be

annual or perennial, herbaceous or woody.

Liana is a vine that is perennial and woody.

Liana’s are major components in the tree

canopy layer of some tropical forests.

Example: Ventilago, Entada, Bougainvillea.

IV. Trees

A tree is a stout, tall, perennial, woody

plant having one main stem called trunk

with many lateral branches. Example:

mango, sapota, jack, fig, teak. If the

trunk remains unbranched it is said to be

caudex. Example: Palmyra, coconut.

3.2 Plant habitat

Depending upon where plants grow

habitats may be classified into major

categories: I. Terrestrial and II.Aquatic.

I. Terrestrial

Plants growing on land are called

terrestrial plants. The following table

illustrate the types of terrestrial plants

classified based on their environmental

adaptation.

II. Aquatic

Plants that are living in water environment

are called aquatic plants or hydrophytes.

3.3 Life Span

Based on life span plants are classified

into 3 types. They are annual, biennial

and perennial

Terrestrial habitat

Types Nature of environmental adaptation Example

Mesophytes Growing in soils with sufficient water Azadirachta indica

Xerophytes Growing on dry habitats Opuntia, Euphorbia

Psammophytes Growing on sand Ipomoea pes-caprae,

Spinifex littoralis

Lithophytes Growing on rock Many algae and lichens,

Ficus spp

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Aquatic habitat

Types Nature of environmental adaptation Example

Free Floating Growing on water surface Eichhornia, Trapa, Pistia,

Lemna

Submerged Plants growing completely under water Hydrilla, Vallisneria

Emergent Plants with roots or stems anchored to Limnophyton, Typha

the substrate under water and aerial

shoots growing above water

Floating leaved Anchored at bottom but with floating Nelumbo, Nymphaea

leaves

Mangroves Plants growing emergent in marshy

saline habitat

Avicennia, Rhizophora

I. Annual (Therophyte or Ephemerals)

A plant that completes its life cycle in one

growing season. Example: Peas, maize,

water melon, groundnut, sunflower, rice

and so on.

consisting of an axis with an underground

“Root system” and an aerial “Shoot

System”. The shoot system has a stem,

branches and leaves. The root system

consists of root and its lateral branches.

II. Biennial

A plant that lives for two seasons, growing

vegetatively during the first season and

flowering and fruiting during the second

season. Example: Onion, Lettuce, Fennel,

Carrot, Radish, Cabbage and Spinach.

III. Perennial (Geophyte)

Flower

Leaf

Shoot

Root

Bud

Stem

Primary root

Secondary root

A plant that grows for many years that flowers

and set fruits for several seasons during the

life span. When they bear fruits every year,

they are called polycarpic. Example: mango,

sapota. Some plants produce flowers and

fruits only once and die after a vegetative

growth of several years. These plants are

called monocarpic. Example: Bamboo,

Agave, Musa, Talipot palm.

3.4 Parts of a flowering plant

Flowering plants are called “Angiosperms”

or Magnoliophytes. They are sporophytes

Figure: 3.1: Parts of a flowering plant

3.5 Root System

The root is non-green, cylindrical

descending axis of the plant that usually

grows into the soil (positively geotropic).

It develops from the radicle which is the

first structure that comes out when a seed

is placed in the soil. Root is responsible

for absorption of water and nutrients and

anchoring the plant.

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I. Characteristic features

• Root is the descending portion of the

plant axis.

• Generally non-green in colour as it

lacks chlorophyll.

• Does not possess nodes, internodes and

buds (Exception in sweet potato and

members of Rutaceae, roots bear buds

which help in vegetative propagation)

• It bears root hairs (To absorb water

and minerals from the soil)

• It is positively geotropic and negatively

phototropic in nature.

II. Regions of root

Root tip is covered by a dome shaped

parenchymatous cells called root cap.

It protects the meristematic cells in the

apex. In Pandanus multiple root cap is

present. In Pistia instead of root cap root

pocket is present. A few millimeters above

the root cap the following three distinct

zones have been classified based on their

meristematic activity.

1. Meristematic Zone

2. Zone of Elongation

3. Zone of Maturation

Root hair

Region of Cell

maturation

Region of cell elongation

Region of cell division

Root cap

Figure 3.2: Regions of root

Feature

Position

Table: Root zones

1. Meristematic Zone 2. Zone of

(Region of cell division ) Elongation

It lies just above the It lies just above the

root cap

meristematic zone

3. Zone of Maturation

It lies above the zone

of elongation.

Types of

cells

Functions

Meristematic cells,

actively divide and

continuously increase

in number

This is the main

growing tip of the

root

Elongated cells

The cells increase

the length and cause

enlargement of the

root.

Mature differentiated

cells

The cells differentiate

into various tissues like

epidermis, cortex and

vascular bundles. It

also produces root hairs

which absorb water and

minerals from the soil

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3.5.1 Types of root

Tap root system

Fibrous root

system

root. It may develop from the base of the

stem or nodes or internodes. Example:

Monstera deliciosa, Ficus benghalensis,

Piper nigrum. In most of the monocots

the primary root of the seedling is short

lived and lateral roots arise from various

regions of the plant body. These are

bunch of thread-like roots equal in size

which are collectively called fibrous

root system generally found in grasses.

Example: Oryza sativa, Eleusine coracana,

Pennisetum americanum.

Figure 3.3: Types of root system

I. Tap root system

Primary root is the direct prolongation

of the radicle. When the primary root

persists and continues to grow as in

dicotyledons, it forms the main root of

the plant and is called the tap root. Tap

root produces lateral roots that further

branches into finer roots. Lateral roots

along with its branches together called as

secondary roots.

II. Adventitious root system

Root developing from any part of the plant

other than radicle is called adventitious

III. Functions of root

Root performs two kinds of functions

namely primary and secondary functions.

Primary function

1. Absorb water and minerals from soil.

2. Help to anchor the plant firmly in

the soil.

Secondary function

In some plants roots perform additional

functions. These are called secondary

functions. To perform additional

functions, these roots are modified in

their structure.

Root modification

Tap root modification

Adventitious root modification

Storage

Breathing root

Storage

Mechanical support

Vital function

i. Conical

ii. Fusiform

iii. Napiform

i.Tuberous root

ii. Fasciculated root

iii. Nodulose root

iv. Moniliform root

v. Annulated root

i. Prop root

ii. Stilt root

iii. Climbing root

iv. Buttress root

i. Epiphytic root

ii. Foliar root

iii. Sucking root

iv. Photosynthetic

root

102

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3.5.2 Modifications of root

I. Tap root modification

a. Storage roots

1. Conical Root

These are cone like, broad at the base

and gradually tapering towards the apex.

Example: Daucus carota.

2. Fusiform root

These roots are swollen in the middle and

tapering towards both ends. Example:

Raphanus sativus

3. Napiform root

It is very broad and suddenly tapers like a

tail at the apex. Example: Beta vulgaris

(a) (b) (c)

(d)

Figure 3.4: Tap root modification

(a) Daucus carota (b) Raphanus sativus

(c) Beta vulgaris (d) Avicennia -

pneumatophores

b. Breathing root

Some mangrove plants like Avicennia,

Rhizophora, Bruguiera develop special kinds

of roots (Negatively geotropic) for respiration

because the soil becomes saturated with

water and aeration is very poor. They

have a large number of breathing pores or

pneumatophores for exchange of gases.

II. Adventitious root modification

a. Storage roots

1. Tuberous root

These roots are swollen without any

definite shape. Tuberous roots are

produced singly and not in clusters.

Example: Ipomoea batatas.

2. Fasciculated root

These roots are in cluster from the base

of the stem Example: Dahlia, Asparagus,

Ruellia.

3. Nodulose root

In this type of roots swelling occurs only

near the tips. Example: Maranta (arrow

root) Curcuma amada (mango ginger),

Curcuma longa (turmeric)

4. Moniliform or Beaded root

These roots swell at frequent intervals

giving them a beaded appearance.

Example: Vitis, Portulaca, Momordica,

Basella (Indian spinach).

5. Annulated root

These roots have a series of ring- like

swelling on their surface at regular

intervals. Example: Psychotria (Ipecac)

b. Mechanical support

1. Prop (Pillar) root

These roots grow vertically downward

from the lateral branches into the soil.

103

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Ipomoea batatas Dahlia Maranta Psychotria

Figure 3.5: Adventitious Root Modification for Storage

Example: Ficus benghalensis (banyan tree),

Indian rubber.

2. Stilt (Brace) root

These are thick roots growing obliquely

from the basal nodes of the main stem.

These provide mechanical support.

Example: Saccharum officinarum,

Zeamays, Pandanus, Rhizophora.

3. Climbing (clasping or clinging) roots

These roots are produced from the nodes

of the stem which attach themselves to

the support and help in climbing. To

ensure a foothold on the support they

secrete a sticky juice which dries up in

air, attaching the roots to the support.

Example: Epipremnum pinnatum, Piper

betel, Ficus pumila.

4. Buttress root

In certain trees broad plank like

outgrowths develop towards the base all

around the trunk. They grow obliquely

downwards and give support to huge

trunks of trees. This is an adaptation

for tall rain forest trees. Example:

Bombax ceiba (Red silk cotton tree),

Ceiba pentandra (white silk cotton tree),

Terminalia arjuna, Delonix regia,

Pterygota alata.

c. Vital functions

1. Epiphytic or velamen root

Some epiphytic orchids develop a special

kind of aerial roots which hang freely in

the air. These roots develop a spongy tissue

called velamen which helps in absorption

of moisture from the surrounding air.

Example: Vanda, Dendrobium, Aerides.

2. Foliar root

Roots are produced from the veins or

lamina of the leaf for the formation of new

plant. Example: Bryophyllum, Begonia,

Zamioculcas.

Ficus benghalensis Saccharum officinarum Epipremnum Bombax

pinnatum

Figure 3.6: Adventitious root modification for mechanical support

104

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3. Sucking or Haustorial roots

These roots are found in parasitic plants.

Parasites develop adventitious roots from

stem which penetrate into the tissue of the

host plant and suck nutrients.

Example: Cuscuta (dodder), Cassytha,

Orobanche (broomrape), Viscum

(mistletoe), Dendrophthoe.

4. Photosynthetic or assimilatory roots

Roots of some climbing or epiphytic

plants develop chlorophyll and turn green

which help in photosynthesis. Example:

Tinospora, Trapa natans (water chestnut),

Taeniophyllum.

3.6 Shoot system

The plumule of the embryo of a

germinating seed grows into stem. The

epicotyl elongates after embryo growth

into the axis (the stem) that bears leaves

from its tip, which contain the actively

dividing cells of the shoot called apical

meristem. Further cell divisions and

growth result in the formation of mass

of tissue called a leaf primordium. The

point from which the leaf arises is called

node. The region between two adjacent

nodes is called internode.

I. Characteristic features of the stem

1. The stem is usually the aerial portion

of the plant

2. It is positively phototropic and

negatively geotropic

3. It has nodes and internodes.

4. Stem bears vegetative bud for vegetative

growth of the plant, and floral buds for

reproduction, and ends in a terminal

bud.

5. The young stem is green and thus

carries out photosynthesis.

6. During reproductive growth stem

bears flowers and fruits.

7. Branches arise exogenously

8. Some stems bears multicellular hairs

of different kinds.

II. Functions of the stem

Primary functions

1. Provides support and bears leaves,

flowers and fruits.

2. It transports water and mineral nutrients

to the other parts from the root.

3. It transports food prepared by leaves

to other parts of the plant body.

clinging

root

hanging

root

Photosynthetic

root

Vanda Bryophyllum Cuscuta Tinospora

Figure 3.7: Adventitious Root Modification for Vital Functions

105

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Secondary functions

1. Food storage- Example: Solanum

tuberosum, Colocasia and Zingiber

officinale

2. Perennation / reproduction – Example:

Zingiber officinale, Curcuma longa

3. Water storage – Example: Opuntia

4. Bouyancy – Example: Neptunia

5. Photosynthesis – Example: Opuntia,

Ruscus, Casuarina, Euphorbia,

Caralluma.

6. Protection – Example: Citrus, Duranta,

Bougainvillea, Acacia, Fluggea, Carissa.

7. Support - Example: Passiflora,

Bougainvillea, Vitis, Cissus

quadrangularis.

3.6.1 Buds

Buds are the growing points surrounded

by protective scale leaves. The bud

primordium matures into bud. They have

compressed axis in which the internodes

are not elongated and the young leaves

are closed and crowded. When these buds

develop, the internodes elongate and the

leaves spread out. Buds have architecture

identical to the original shoot and develop

into lateral branches or may terminate by

developing into a flower or inflorescence.

Based on Origin Buds are classified into

(a) Terminal or Apical bud (b) Lateral or

Axillary or Axil bud. Based on Function

Buds classified into (a) Vegetative bud

(b) Floral or Reproductive bud

1. Terminal bud or apical bud: These

buds are present at the apex of the main

stem and at the tips of the branches.

2. Lateral bud or Axillary bud: These

buds occur in the axil of the leaves and

develop into a branch or flower.

3. Extra axillary bud : These buds are

formed at nodes but outside the axil of

the leaf as in Solanum americanum.

4. Accessory bud : An extra bud

on either side (collateral bud) or

above (superposed bud or serial bud)

the axillary bud. Example: Citrus and

Duranta

5. Adventitious buds: Buds arising at

any part other than stem are known

as adventitious bud. Radical buds

are those that arises from the lateral

roots which grow into plantlets.

Example: Millingtonia, Bergera

koenigii (Murraya koenigii), Coffea

arabica and Aegle marmelos. Foliar

buds are those that grow on leaves

from veins or from margins of the

leaves. Example: Begonia (Elephant

ear plant) and Bryophyllum (Sprout

leaf plant). Cauline buds arise directly

from the stem either from cut, pruned

ends or from branches. Adventitious

buds function as propagules which

are produced on the stem as tuberous

structures. Example: Dioscorea,

Agave.

6. Bulbils (or specialized buds) :

Bulbils are modified and enlarged

bud, meant for propagation. When

bulbils detach from parent plant and

fall on the ground, they germinate

into new plants and serve as a means

of vegetative propagation. In Agave

and Allium proliferum floral buds

get modified into bulbils. In Lilium

bulbiferum and Dioscorea bulbifera,

the bulbils develop in axil of leaves.

In Oxalis, they develop just above the

swollen root.

106

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3.6.2 Types of Stem

Majority of angiosperm possess upright,

vertically growing erect stem. They are

(i) Excurrent, (ii) Decurrent, (iii) Caudex,

(iv) Culm.

i. Excurrent

The main axis shows continuous growth

and the lateral branches gradually

becoming shorter towards the apex

which gives a conical appearance to the

trees. Example: Polyalthia longifolia,

Casuarina.

ii. Decurrent

The growth of lateral branch is more

vigorous than that of main axis. The tree

has a rounded or spreading appearance.

Example: Mangifera indica, Azadirachta

indica, Tamarindus indicus, Aegle

marmelos

iii. Caudex

It’s an unbranched, stout, cylindrical

stem, marked with scars of fallen leaves.

Example: Cocus nucifera, Borassus

flabelliformis, Areca catechu

iv. Culm

Erect stems with distinct nodes and usually

hollow internodes clasped by leaf sheaths.

Example: Majority of grasses including

Bamboo.

3.6.3 Modification of Stem

I. Aerial modification of stem

1. Creepers

These are plants growing closer

(horizontally) to the ground and produces

roots at each node. Example: Cynodon

dactylon, Oxalis, Centella

2. Trailers (Stragglers)

It is a weak stem that spreads over the

surface of the ground without rooting

at nodes. They are divided into 3 types,

i. Prostrate (Procumbent): A stem that

grows flat on the ground. Example:

Evolvulus alsinoides, Indigofera

prostrata.

ii. Decumbent: A stem that grows flat but

becomes erect during reproductive

stage. Example: Portulaca, Tridax,

Lindenbergia

iii. Diffuse: A trailing stem with spreading

branches. Example: Boerhaavia

diffusa, Merremia tridentata

3. Climbers

These plants have long weak stem and

produce special organs for attachment for

climbing over a support. Climbing helps to

display the leaves towards sunlight and to

position the flower for effective pollination.

i. Root climbers

Plants climbing with the help of

adventitious roots (arise from nodes) as

in species of Piper betel, Piper nigrum,

Hedera helix, Pothos, Hoya.

ii. Stem climbers (twiners)

These climbers lack specialised structure

for climbing and the stem itself coils

around the support. Example: Ipomoea,

Convolvulus, Dolichos, Clitoria, Quisqualis.

Stem climbers may coil around the

support clockwise or anti-clockwise.

Clockwise coiling climbers are called

dextrose. Example: Dioscorea alata. Anticlockwise

coiling climbers are called

sinistrose. Example: Dioscorea bulbifera.

107

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Stem modification

Aerial

modification

Sub-Aerial

modification

Underground

modification

Runner

Stolon

Sucker

Offset

Creepers

Trailer

Climber

Bulb

Corm

Rhizome

Tuber

Procumbent

Decumbent

Diffuse

Root Climber

Stem Climber (Twiner)

Tendril Climber

Hook climber

Lianas

iii. Hook climbers

These plants produce specialized hook

like structures which are the modification

of various organs of the plant. In

Artabotrys inflorescence axis is modified

into hook. In calamus (curved hook) leaf

tip is modified into hook. In Bignonia

unguis-cati the leaflets are modified into

curved hook (figure: 3.17). In Hugonia the

axillary buds modified into hook.

iv. Thorn climbers

Climbing or reclining on the support with

the help of thorns as in Bougainvillea and

Carissa.

v. Lianas (woody stem climber)

Woody perennial climbers found in tropical

forests are lianas. They twine themselves

around tall trees to get light. Example:

Hiptage benghalensis, Bauhinia vahlii,

Entada pursaetha.

vi. Tendril climbers

Tendrils are thread-like coiling structures

which help the plants in climbing. Tendrils

may be modifications of Stem – as in

Passiflora, Vitis and Cissus quadrangularis;

Inflorescence axis – Antigonon; Leaf –

Lathyrus; Leaflets - Pisum sativum; Petiole

– Clematis; Leaftip – Gloriosa; Stipules –

Smilax. In pitcher plant (Nepenthes) the

midrib of the leaf often coils around a

support like a tendril and holds the pitcher

in a vertical position.

Phylloclade

This is a green, flattened cylindrical

or angled stem or branch of unlimited

growth, consisting of a series of nodes

and internodes at long or short intervals.

Phylloclade is characteristic adaptation

of xerophytes where the leaves often

fall off early and modified into spines

or scales to reduce transpiration. The

phylloclade takes over all the functions of

leaves, particularly photosynthesis. The

phylloclade is also called as cladophyll.

Example: Opuntia, Phyllocactus,

Muehlenbeckia (flattened phylloclade)

Casuarina, Euphorbia tirucalli,

Euphorbia antiquorum (cylindrical

phylloclade).

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Cladode

Phylloclade

Spine

Scaly leaf

Runner

(a)

(b)

(a)

Root

Figure 3.8: (a) Phylloclade-Opuntia

(b) Cladode-Asparagus

Cladode

Cladode is a flattened or cylindrical stem

similar to Phylloclade but with one or

two internodes only. Their stem nature

is evident by the fact that they bear buds,

scales and flowers. Example: Asparagus

(cylindrical cladode), Ruscus (flattened

Cladode).

Thorns

Thorn is a woody and sharp pointed

modified stem. Either the axillary bud

or the terminal bud gets modified into

thorns. In Carissa apical bud modified

into thorns. In Citrus and Atalantia

axillary bud is modified into thorns.

II. Sub aerial stem modifications

Sub aerial stem found in plants with weak

stem in which branches lie horizontally on

the ground. These are meant for vegetative

propagation. They may be sub aerial or

partially sub terranean.

1. Runner

This is a slender, prostrate branch creeping

on the ground and rooting at the nodes.

Example: Centella (Indian pennywort),

Oxalis (wood sorrel), lawn grass (Cynodon

dactylon).

Stolon

Root

(b)

Figure 3.9: (a) Runner-Oxalis

(b) Stolon-Fragaria

2. Stolon

This is also a slender, lateral New branch plant

originating from the base of the Rootstem.

But it first grows obliquely above Suckerthe

ground, produces a loop and bends down

towards the ground. When touches the

ground it produces roots and becomes an

independent plantlet. Example: Offset Mentha

piperita (peppermint), Fragaria indica (wild

strawberry).

3. Sucker

Sucker develops from a underground stem

and grows obliquely upwards and gives rise

to a separate plantlet or new plant. Example:

Chrysanthemum, Musa, Bambusa.

Root pocket

4. Offset

Offset is similar to runner but found in

aquatic plants especially in rosette leaved

forms. A short thick lateral branch arises

from the lower axil and grows horizontally

leafless for a short distance, then it

produces a bunch of rosette leaves and

109

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Stolon

root at nodes. Example: Eichhornia Root (water

hyacinth), Pistia (water lettuce).

(c)

New plant

Root

Sucker

Offset

(d)

Figure 3.9: (c) Sucker-Chrysanthemum

(d) Offset-Eichhornia

Root pocket

III. Underground stem modifications

Perennial and some biennial herbs have

underground stems, which are generally

known as root stocks. Rootstock functions

as a storage and protective organ. It

remains alive below the ground during

unfavourable conditions and resumes

growth during the favourable conditions.

Underground stems are not roots because

they possess nodes, internodes, scale-leaves

and buds. Rootstock also lack root cap and

root hairs but they possess terminal bud

which is a characteristics of stem.

1. Bulb

It is a condensed conical or convex stem

surrounded by fleshy scale leaves. They are

of two types 1. Tunicated (coated) bulb: In

which the stem is much condensed and

surrounded by several concentric layers of

scale leaves. The inner scales commonly

fleshy, the outer ones dry. These are two

types (a) Simple Tunicated bulb Example:

Allium cepa (b) Compound Tunicated

bulb. Example: Allium sativum. 2. Scaly

bulb: They are narrow, partially overlap

each other by their margins only. Example:

Tulipa spp.

Pseudobulb is a short erect aerial

storage or propagating stem of certain

epiphytic and terrestrial sympodial

orchids. Example: Bulbophyllum.

2. Corm

This is a succulent underground stem

with an erect growing tip. The corm is

surrounded by scale leaves and exhibit nodes

and internodes. Example: Amorphophallus,

Gladiolus, Colocasia, Crocus, Colchicum

Bulb-

Allium cepa

Corm-Colocasia

Rhizome

Zingiber officinale

Tuber

Solanum tuberosum

Figure 3.10: Underground Stem

Modification

3. Rhizome

This is an underground stem growing

horizontally with several lateral growing

tips. Rhizome posses conspiquous nodes

and internodes covered by scale leaves.

Example: Zingiber officinale, Canna,

Curcuma longa, Maranta arundinacea,

Nymphaea, Nelumbo.

110

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4. Tuber

This is a succulent underground spherical

or globose stem with many embedded

axillary buds called “e yes”. Example:

Solanum tuberosum, Helianthus tuberosus

IV. Stem Branching

Branching pattern is determined by the

relative activity of apical meristems. The

mode of arrangement of branches on a

stem is known as branching. There are

two main types of branching, 1. Lateral

branching and 2. Dichotomous branching.

Based on growth pattern stems may show

indeterminate or determinate growth.

1. Indeterminate: The terminal bud

grows uninterrupted and produce

several lateral branches. This type of

growth is also known as monopodial

branching. Example: Polyalthia,

Swietenia, Antiaris.

2. Determinate: The terminal bud caese

to grow after a period of growth and the

further growth is taken care by successive

or several lateral meristem or buds.

This type of growth is also known as

sympodial branching. Example: Cycas.

3.7 Leaf

Leaves are green, thin flattened lateral

outgrowths of the stem. Leaves are the

primary photosynthetic organs and the

main site of transpiration. All the leaves

of a plant together are referred to as

phyllome.

I. Characteristics of leaf

1. Leaf is a lateral appendage of the stem.

2. It is borne at the node of the stem.

3. It is exogenous in origin.

4. It has limited growth.

5. It does not posses apical bud.

6. It has three main parts namely, leaf

base, petiole and lamina.

7. Lamina of the leaf is traversed by

vascular strands, called veins.

II. Functions of the leaf

Primary functions

1. Photosynthesis

2. Transpiration

3. Gaseous exchange

4. Protection of buds

5. Conduction of water and dissolved

solutes.

Secondary functions

1. Storage – Example: Aloe, Agave,

Kalanchoe, Sedum, Brassica oleracea.

2. Protection – Example: Berberis,

Opuntia, Argemone mexicana.

3. Support – Example: Gloriosa,

Nepenthes

4. Reproduction - Example: Bryophyllum,

Begonia, Zamioculcas.

3.7.1 Parts of the leaf

Three main parts of a typical leaf are:

i. Leaf base (Hypopodium)

ii. Petiole (Mesopodium)

iii. Lamina (Epipodium)

I. Leaf base (hypopodium)

The part of the leaf attached to the node

of the stem is called leaf base. Usually it

protects growing buds at its axil.

Pulvinus: In legumes leafbase become

broad and swollen which is known as

pulvinus. Example: Clitoria, Lablab,

Cassia, Erythrina, Butea, Peltophorum.

111

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numerous lateral veins and thin veinlets.

The lamina shows great variations in its

shape, margin, surface, texture, colour,

venation and incision.

Figure 3.11: (a) Parts of the leaf

(b) Pulvinus leaf base (c) Sheathing

leaf base

Sheathing leafbase: In many monocot

families such as Arecaceae, Musaceae,

Zingiberaceae and Poaceae the leafbase

extends into a sheath and clasps part or

whole of the internode. Such leafbase also

leave permanent scars on the stem when

they fall.

II. Petiole (stipe or mesopodium)

It is the bridge between lamina and stem.

Petiole or leaf stalk is a cylindrical or sub

cylindrical or flattened structure of a leaf

which joins the lamina with the stem. A

leaf with petiole is said to be petiolate.

Example: Ficus, Hibiscus, Mangifera,

Psidium. Leaves that do not possess petiole

is said to be sessile. Example: Calotropis,

Gloriosa.

III. Lamina (Leaf blade)

The expanded flat green portion of the

leaf is the blade or lamina. It is the seat

of photosynthesis, gaseous exchange,

transpiration and most of the metabolic

reactions of the plant. The lamina is

traversed by the midrib from which arise

Stipules

In most of the dicotyledonous plants,

the leaf base bears one or two lateral

appendages called the stipules. Leaves with

stipules are called stipulate. The leaves

without stipules are called exstipulate or

estipulate. The stipules are commonly

found in dicotyledons. In some grasses

(Monocots) an additional out growth is

present between leaf base and lamina. It

is called Ligule. Sometimes, small stipule

like outgrowths are found at the base

of leaflets of a compound leaf. They are

called stipels. The main function of the

stipule is to protect the leaf in the bud

condition.

3.7.2 Venation

The arrangement of veins and veinlets on

the leaf blade or lamina is called venation.

Internally, the vein contains vascular

tissues. Conventionally venation is

classified into two types namely, Reticulate

venation and Parallel venation.

I. Reticulate venation

In this type of venation leaf contain a

prominent midrib from which several

secondary veins arise that branch and

anastomose like a network. This type of

venation is common in all dicot leaves. It

is of two types.

1. Pinnately reticulate venation

(unicostate): In this type of venation

there is only one midrib in the centre

which forms many lateral branches to

form a network. Example: Mangifera

indica, Ficus religiosa, Nerium.

112

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2. Palmately reticulate venation

(multicostate): In this type of venation

there are two or more principal veins

arising from a single point and they

proceed outwards or upwards. The two

types of palmate reticulate venation are

i. Divergent type: When all principal

veins originate from the base and

diverge from one another towards

the margin of the leaf as in Cucurbita,

Luffa, Carica papaya, etc.,

ii. Convergent: When the veins

converge to the apex of the leaf, as

in Indian plum (Zizyphus), bay leaf

(Cinnamomum)

2. Palmate Parallel Venation

(Multicostate)

In this type several veins arise from the tip

of the petiole and they all run parallel to

each other and unite at the apex. It is of

two sub types.

i. Divergent type: All principal veins

originate from the base and diverge

towards the margin, the margin of the leaf

as in fan palm (Borassus flabelliformis)

ii. Convergent type: All principal veins

run parallel to each other from the

base of the lamina and join at the apex

as in Bamboos, rice, water hyacinth.

Rctcnngn"xgpcvcvkqp

(a) Ficus (b) Cucurbita (c) Cinnamomum

Figure 3.12: Types of reticulate venation

(a) Pinnately reticulate

(b) Palmately reticulate (Divergent)

(c) Palmately reticulate (Convergent)

II. Parallel venation

Veins run parallel to each other and do

not form a prominent reticulum. It is a

characteristic feature of monocot leaves.

It is classified into two sub types.

1. Pinnately Parallel Venation

(Unicostate)

When there is a prominent midrib in

the center, from which arise many veins

perpendicularly and run parallel to each

other. Example: Musa, Zinger, Curcuma,

Canna.

(a) Canna (b) Bamboo (c) Borassus

Figure 3.13: Types of Parallel venation

(a) Pinnately parallel venation

(b) Palmately parallel(Convergent)

(c) Palmately parallel (Divergent)

3.7.3 Phyllotaxy

The mode of arrangement of leaves on

the stem is known as phyllotaxy (Gk.

Phyllon = leaf ; taxis = arrangement).

Phyllotaxy is to avoid over crowding of

leaves and expose the leaves maximum to

the sunlight for photosynthesis. The four

main types of phyllotaxy are (1) Alternate

(2) Opposite (3) Ternate

(4) Whorled.

1. Alternate

phyllotaxy

In this type there is only

113

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Modern morphologist Hickey (1973) and Hickey and Wolf (1975)

classified the venation into following major types based on the pattern

of primary, secondary and tertiary venation.

• Craspedodromous – In which secondary veins terminate at the

leaf margin. (sub types are simplecraspedodromous, semicraspedodromous,

mixed craspedodromous).

• Camptodromous – In which secondary veins do not terminate at the margin. (sub

types are brochidodromous, eucamptodromous, cladodromous, reticulodromous).

• Hyphodromous – With only the primary midrib vein present or evident and

secondary veins either absent, very reduced or hidden with the leaf mesophyll.

• Parallellodromous – Venation is equivalent to parallel in which two or more

primary or secondary veins run parallel to one another, converging at the apex.

• Actinodromous – If three or more primary veins diverge from one point.

• Palinoactinodromous – Similar to actinodromous, but the primary veins have

additional branch in above the main point of divergence of the primaries.

• Flabellate – Venation is that in which several equal, fine veins branch toward the

apex of the leaf.

• Campylodromous – Venation is that in which several primary veins run in prominent,

recurved arches at the base, curving upward to converge at the leaf apex.

• Acrodromous – If two or more primary veins run in convergent arches toward the

leaf apex.

one leaf per node and the leaves on the

successive nodes are arranged alternate

to each other. Spiral arrangement of

leaves show vertical rows are called

orthostichies. They are two types.

a) Alternate spiral: In which the leaves are

arranged alternatively in a spiral manner.

Example: Hibiscus, Ficus.

b) Alternate distichous or Bifarious:

In which the leaves are organized

alternatively in two rows on either side of

the stem. Example: Monoon longifolium

(Polyalthia longifolia).

2. Opposite phyllotaxy

In this type each node possess two leaves

opposite to each other. They are organized

in two different types.

i. Opposite superposed: The pair of

leaves arranged in succession are

in the same direction, that is two

opposite leaves at a node lie exactly

above those at the lower node.

Example: Psidium (Guava), Eugenia

jambolana (Jamun), Quisqualis

(Rangoon creeper).

ii. Opposite decussate: In this type of

phyllotaxy one pair of leaves is placed

at right angles to the next upper

or lower pair of leaves. Example:

Calotropis, Zinnia, Ocimum

3. Ternate phyllotaxy

In this type there are three leaves attached

at each node. Example: Nerium

114

---

Alternate

Polyalthia

4. Whorled (verticillate) type of

phyllotaxy

In this type more than three leaves are

present in a whorl at each node forming

a circle or whorl. Example: Allamanda,

Alstonia scholaris.

3.7.4 Leaf mosaic

In leaf mosaic leaves tend to fit in with

one another and adjust themselves in such

a way that they may secure the maximum

amount of sunlight with minimum

amount of overlapping. The lower leaves

have longer petioles and successive upper

leaves possess decreasing length petioles.

Example: Acalypha, Begonia.

3.7.5 Leaf type

The pattern of division of a leaf into

discrete components or segments is

termed leaf type.

Based on the number of segments

I. Simple leaf

A leaf is said to be simple when the petiole

bears a single lamina; lamina may be entire

(undivided) Example: Mango or incised

to any depth but not upto the midrib or

petiole. Example: Cucurbita.

II. Compound leaf

Opposite

Superposed Guava

Compound leaf is one in which the main

rachis bears more than one lamina surface,

Opposite Decussate

Calotropis

Figure 3.14: Phyllotaxy

115

Ternate

Nerium

Whorled

Allamanda

called leaflets. Compound leaves have

evolved to increase total lamina surface.

There is one axillary bud in the axil of

the whole compound leaf. The leaflets

however, do not possess axillary buds.

1. Pinnately compound leaf

A pinnately compound leaf is defined as one

in which the rachis, bears laterally a number

of leaflets, arranged alternately or in an

opposite manner, as in tamarind, Cassia.

i. Unipinnate: The rachis is simple

and unbranched which bears leaflets

directly on its sides in alternate or

opposite manner. Example: Rose, Neem.

Unipinnate leaves are of two types.

a. when the leaflets are even in

number, the leaf is said to be

paripinnate. Example: Tamarindus,

Abrus, Sesbania, Saraca, Cassia.

b. when the leaflets are odd in

number, the leaf is said to be

imparipinnate. Example: Rosa,

Azadirachta (Neem), (Murraya

Chinese box).

ii. Bipinnate: The primary rachis

produces secondary rachii which bear

the leaflets. The secondary rachii are

known as pinnae. Number of pinnae

varies depending on the species.

Example: Delonix, Mimosa, Acacia

nilotica, Caesalpinia.

---

• Foliage leaves — are ordinary green, flat, lateral appendages of the

stem or the branch borne at the node.

• Cotyledons or seed leaves — are attached to the axis of the embryo

of the seed. As the seed germinates, they usually turn green and

become leaf-like.

• Cataphylls or scale leaves — are reduced forms of leaves, stalkless and often

brownish. They are the bud-scales, scales on the rhizome (underground stems),

and also on other parts of the plant body (Bamboo).

• Prophylls — the first formed leaves are called prophylls.

• Floral leaves — are members of a flower, forming into two accessory whorls (calyx

and corolla), two essential whorls(androecium and gynoecium).

• Hypsophylls or bract leaves — these leaves cover the flower or an inflorescence in

their axil. The main function of these leaves is to protect the flower buds.

iii. Tripinnate: When the rachis branches

thrice the leaf is called tripinnate.

(i.e) the secondary rachii produce the

tertiary rachii which bear the leaflets.

Example: Moringa, Oroxylum.

iv. Decompound: When the rachis

of leaf is branched several times it

is called decompound. Example:

Daucus carota, Coriandrum sativum,

Foeniculum vulgare.

2. Palmately compound leaf

A palmately compound leaf is defined as

one in which the petiole bears terminally,

one or more leaflets which seem to be

radiating from a common point like

fingers from the palm.

i. Unifoliolate: When a single leaflet

is articulated to the petiole is said to

be unifoliolate. Example: Citrus, Des

modium gangeticum.

ii. Bifoliolate: When there are two

leaflets articulated to the petiole it

is said to be bifoliolate. Example:

Balanites roxburghii, Hardwickia

binata, Zornia diphylla

iii. Trifoliolate: There are three leaflets

articulated to the petiole it is said to

be trifoliolate. Example: wood apple

(Aegle marmelos), Clover (Trifolium),

Lablab, Oxalis

iv. Quadrifoliolate: There are four

leaflets articulated to the petiole it is

(a) (b) (c) (d) (e)

Figure 3.15: Types of pinnately compound leaves

(a) Unipinnate (Paripinnate)-Tamarindus (b) Unipinnate (Imparipinnate)-Azadirachta

(c) Bipinnate-Caesalpinia (d) Tripinnate-Moringa (e) Decompound-Coriandrum

116

---

(a) (b) (c) (d) (e)

Figure 3.16: Types of palmately compound leaves

(a) Unifoliolate - Citrus (b) Bifoliolate – Zornia (c) Trifoliolate – Aegle marmelos

(d) Quadrifoliolate – Paris quadrifolia (e) Multifoliolate – Bombax

said to be quadrifoliolate. Example:

Paris quadrifolia, Marsilia

v. Multifoliolate or digitate: Five or

more leaflets are joined and spread

like fingers from the palm, as in

Ceiba pentandra, Cleome pentaphylla,

Bombax ceiba

3.7.6 Modification of Leaf

The main function of the leaf is food

preparation by photosynthesis. Leaves

also modified to perform some specialized

functions. They are described below.

I. Leaf tendrils

In some plants Stem is very weak and

hence they have some special organs for

attachment to the support. So some leaves

are partially or wholly modified into

tendril. Tendril is a slender wiry coiled

structure which helps in climbing the

support. Some of the modification of leaf

tendrils are given below:

Entire leaf—Lathyrus, stipules—Smilax,

terminal leaflet—Naravelia, Leaf tip—

Gloriosa, Apical leaflet—Pisum, petiole—

Clematis.

II. Leaf hooks

In some plants, leaves are modified into

hook-like structures and help the plant to

climb. In cat,s nail (Bignonia unguis-cati) an

elegant climber, the terminal leaflets become

modified into three, very sharp, stiff and

curved hooks, very much like the nails of a

cat. These hooks cling to the bark of a tree and

act as organs of support for climbing. The leaf

spines of Asparagus also act as hooks.

Floral

leaves

(Delonix)

Tendrils

(Pisum)

Phyllode

(Acacia)

Spines

(Zizyphus)

Leaf

modifications

Pitcher

(Nepenthes)

III. Leaf Spines and Prickles

Hooks

(Bignonia)

Leaf

blader

(Utricularia)

Storage

leaves

(Aloe)

Leaves of certain plants develop spinesent

structures. Either on the surface or on the

margins as an adaptation to herbivory and

xeric conditions. Example: Argemone mexicana

(Prickly poppy), Solanum trilobatum, Solanum

virginianum. In xerophytes such as Opuntia

(Prickly pear) and Euphorbia leaves and stipules

are modified into spines.

117

---

Prickles are small, sharp structure

which are the outgrowths from epidermal

cells of stem or leaf. It helps the plant in

scrambling over other plants. It is also

protective against herbivory. Example:

Rosa spp, Rubus spp.

IV. Storage Leaves

Some plants of saline and xerophytic habitats

and members of the family Crassulaceae

commonly have fleshy or swollen leaves.

These succulent leaves store water, mucilage

or food material. Such storage leaves

resist desiccation. Example: Aloe, Agave,

Bryophyllum, Kalanchoe, Sedum, Sueada,

Brassica oleracea (cabbage-variety capitata).

V. Phyllode

Phyllodes are flat, green-coloured leaflike

modifications of petioles or rachis.

The leaflets or lamina of the leaf are highly

reduced or caducous. The phyllodes perform

photosynthesis and other functions of leaf.

Example: Acacia auriculiformis (Australian

Acacia), Parkinsonia.

VI. Pitcher

The leaf becomes modified into a pitcher in

Nepenthes and Sarracenia. In Nepenthes the

basal part of the leaf is laminar and the midrib

continues as a coiled tendrillar structure.

The apical part of the leaf as modified into a

pitcher the mouth of the pitcher is closed by

a lid which is the modification of leaf apex.

VII. Bladder

In bladderwort (Utricularia), a rootless

free-floating or slightly submerged

plant common in many water bodies,

the leaf is very much segmented. Some

of these segments are modified to form

bladder-like structures, with a trap-door

entrance that traps aquatic animalcules.

VIII Floral leaves

Floral parts such as sepals, petals, stamens and

carpels are modified leaves. Sepals and petals

are leafy. They are protective in function and

considered non-essential reproductive parts.

Petals are usually coloured which attract the

insects for pollination. Stamens are considered

pollen bearing microsporophylls and carpels

are ovule bearing megasporophylls.

3.7.7 Ptyxis

Rolling or folding of individual leaves may

be as follows:

1. Reclinate - when the upper half of the

leaf blade is bent upon the lower half

as in loquat (Eriobotrya japonica).

2. Conduplicate - when the leaf is folded

lengthwise along the mid-rib, as in

guava, sweet potato and camel’s foot

tree (Bauhinia).

Leaf hooks-Bignonia Leaf spines- Zizyphus Phyllode-Acacia Pitcher-Nepenthes

Figure 3.17: Leaf Modification

118

---

3. Plicate or plaited – when the leaf is

repeatedly folded longitudinally along

ribs in a zig-zag manner, as in Borassus

flabellifer.

4. Circinate - when the leaf is rolled from

the apex towards the base like the tail

of a dog, as in ferns.

5. Convolute - when the leaf is rolled

from one margin to the other, as in

banana, aroids and Indian pennywort.

Musa and members of Araceae.

6. Involute - when the two margins are

rolled on the upper surface of the leaf

towards the midrib or the centre of the

leaf, as in water lily, lotus, Sandwich

Island Climber (Antigonon) and

Plumbago.

7. Crumpled - when the leaf is irregularly

folded as in cabbage.

3.7.8 Leaf duration

Leaves may stay and function for few days

to many years, largely determined by the

adaptations to climatic conditions.

Cauducuous (Fagacious)

Falling off soon after formation. Example:

Opuntia, Cissus quadrangularis.

Deciduous

Falling at the end of growing season so

that the plant (tree or shrub) is leafless in

winter/summer season. Example: Maple,

Plumeria, Launea, Erythrina.

Evergreen

Leaves persist throughout the year, falling

regularly so that tree is never leafless.

Example: Mimusops, Calophyllum.

Marcescent

Leaves not falling but withering on the

plant as in several members of Fagaceae.

3.7.9 Leaf symmetry

1. Dorsiventral leaf

When the leaf is flat, with the blade placed

horizontally, showing a distinct upper

surface and a lower surface, as in most

dicotyledons, it is said to be dorsiventral.

Example: Tridax.

2. Isobilateral leaf

When the leaf is directed vertically

upwards, as in many monocotyledons, it is

said to be isobilateral leaf. Example: Grass.

3. Centric leaf

When the leaf is more or less cylindrical and

directed upwards or downwards, as in pine,

onion, etc., the leaf is said to be centric.

4. Heterophylly

Occurrence of two different kinds of leaves

in the same plant is called heterophylly.

Heterophylly is found in many aquatic

plants. Here, the floating or aerial leaves and

the submerged leaves are of different kinds.

The former are generally broad, often fully

expanded, and undivided or merely lobed,

while the latter are narrow, ribbon-shaped,

linear or much dissected. Heterophylly in water

plants is, thus, an adaptation to two different

conditions of the environment. Example:

water crowfoot (Ranunculus aquatilis),

water plantain (Alisma plantago), arrowhead

(Sagittaria), Limnophila heterophylla.

Terrestrial (land) plants also exhibit this

phenomenon. Among them Sterculia villosa,

jack (in early stages), Ficus heterophylla show

leaves varying from entire to variously lobed

structures during different developmental

stages. Young leaves are usually lobed or

dissected and the mature leaves are entire. Such

type is known as developmental heterophylly.

Example: Eucalyptus, Artocarpus heterophyllus.

119

---

Summary

Flowering plants consist of two major organ

systems: Underground root system and aerial

root system. Roots perform the functions of

anchoring and absorbing nutrients from the

soil. However some roots perform additional

functions for which they undergo various

modifications in shape, form and structure.

Tap root continue the growth from the radical

which further branches into secondary roots.

Adventitious roots arise from different parts

of the plant other than radical. Stem helps to

display the leaves to get maximum sunlight

and positioning flowers and fruits to attract

pollination and dispersal agents. Apart from

the normal functions the stems are modified

to perform various functions such as food

storage, perennation and protection. Leaves

are exogenous in origin and function as food

synthesizing and gaseous exchange sites. Some

leaves also perform additional functions for

which they are modified in their morphology.

Leaves possess vascular tissues in the form of

veins which render support to the lamina and

help in transport of water, nutrients and food in

and out of leaves. Phyllotaxy is the arrangement

or distribution of leaves on the stem or its

branches in such a way that they receive

maximum sunlight to perform photosynthesis.

Activity

1. Collection of medicines prepared

from root, stem, leaf of organic plants.

2. Prepare a report of traditional

medicines.

3. Classroom level exhibition on

Siddha and Ayurvedic medicine

prepared from root, leaf, stem.

4. Growing micro greens in class room

– project work. (Green seed sprouts)

Evaluation

2. Roots are

1. Which of the

following is

polycarpic plant?

a. Mangifera

b. Bambusa

c. Musa

d. Agave

a. Descending, negatively geotropic,

positively phototropic

b. Descending, positively geotropic,

negatively phototropic

c. Ascending, positively geotropic,

negatively phototropic

d. Ascending, negatively geotropic,

positively phototropic

3. Bryophyllum and Dioscorea are

example for

a. Foliar bud, apical bud

b. Foliar bud, cauline bud

c. Cauline bud, apical bud

d. Cauline bud, foliar bud

4. Which of the following is correct

statement?

a. In Pisum sativum leaflets modified

into tendrils

b. In Atalantia terminal bud is modified

into thorns

c. In Nepenthes midrib is modified into

lid

d. In Smilax inflorescence axis is

modified into tendrils

5. Select the mismatch pair

a. Sagittaria - Heterophylly

b. Lablab - Trifoliolate

c. Begonia - Leaf mosaic

d. Allamanda - Ternate phyllotaxy

120

---

6. Draw and label the parts of regions of

root.

7. Write the similarities and differences

between

1. Avicennia and Trapa

2. Radical buds and foliar buds

3. Phylloclade and cladode

8. How root climbers differ from stem

climbers?

9. Compare sympodial branching with

monopodial branching.

10. Differentiate pinnate unicostate with

palmate multicostate venation

Climbers

Root climber - Piper betel Stem climber - Clitoria Thorn climber - Bougainvillea

Lianas - Entada

Tendril climber -

Cissus quadrangularis

121

---

ICT Corner

Monocot and Dicot plants

Is plants differ

morphologically?

Steps

• Scan the QR code or go to google play store

• Type online labs and install it.

• Select biology and select Characteristics of plants

• Click theory to know the basic about Characteristics of plants

• Register yourself with mail-id and create password to access online lab simulations

Activity

• Select video and record your observations of different forms of plant group.

Step 1 Step 2

URL:

Step 3 Step 4

https://play.google.com/store/apps/details?id=in.edu.olabs.olabs&hl=en

* Pictures are indicative only

122

---

Chapter

4

Reproductive Morphology

Learning Objectives

The learner will be able to,

• List the types of inflorescence.

• Distinguish racemose and cymose

inflorescence

• Dissect a flower and explore the

parts of a flower.

• Compare various types of

aestivation.

• Explore various types of

placentation.

• Understands the types of fruits and

seeds

Flowers of five types of land in tamil

literature.

(a)

(b)

(c)

Chapter Outline

4.1. Inflorescence

4.2. Flower

4.3. Accessory organs

4.4. Androecium

4.5. Gynoecium

4.6. Construction of floral diagram

and floral formula

4.7. Fruits

4.8. Seed

(d)

(e)

a. Kurinji (Strobilanthus kunthianus),

b. Mullai (Jasminum auriculatum),

c. Marutham (Lagerstroemia speciosa),

d. Neithal (Nymphaea pubescens),

e. Palai (Wrightia tinctoria)

123

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Flowers have been a universal cultural

object for millennia. They are an

important aesthetic element in everyday

life, and have played a highly symbolic

role in our culture throughout the ages.

Exchange of flowers marks respect,

affection, happiness, and love. However,

the biological purpose of the flower is very

different from the way we use and perceive.

Flower helps a plant to reproduce its own

kind. This chapter discusses flowers, their

arrangement, fruits and seeds which are

the reproductive units of a plant.

Floriculture

Floriculture is a branch of Horticulture.

It deals with the cultivation of

flowers and ornamental crops. The

Government of India has identified

floriculture as a sunrise industry and

accorded the status of 100% export

oriented. Agriculture and Processed

food product Export Development

Authority (APEDA) is responsible for

export promotion of agricultural and

horticultural products from India.

from a branched or unbranched axis with a

definite pattern. Function of inflorescence

is to display the flowers for effective

pollination and facilitate seed dispersal.

The grouping of flowers in one place gives

a better attraction to the visiting pollinators

and maximize the energy of the plant.

4.1.1 Types of Inflorescence

Based On Position

Have you ever noticed the inflorescence

arising from different positions? Where is

the inflorescence present in a plant? Apex

or axil?

Based on position of inflorescences, it

may be classified into three major types.

They are,

Terminal: Inflorescence grows as a

part of the terminal shoot. Example:

Raceme of Nerium oleander

Axillary: Inflorescence present in the

axile of the nearest vegetative leaf.

Example: Hibiscus rosa-sinensis

Cauliflorous: Inflorescence developed

directly from a woody trunk. Example:

Theobroma cocoa, Couroupita guianensis

Observe the inflorescence of Jackfruit

and Canon ball tree. Where does it arise?

4.1 Inflorescence

Have you seen a bouquet being used during

functions? Group of flowers arranged

together on our preference is a bouquet. But

an inflorescence is a group of flowers arising

Figure 4.1: Cauliflorous inflorescence

124

---

4.1.2 Based on branching pattern and

other characters

Inflorescences may also have classified

based on branching, number and

arrangement of flowers, and some

specialized structures.

I. Indeterminate (racemose)

II. Determinate (cymose)

III. Mixed inflorescence: Inflorescence

of some plants show a combination

of indeterminate and determinate

pattern

IV. Special inflorescence: Inflorescence

which do not confined to these

patterns

Young

flower

Old flower

I. Racemose

The central axis of the inflorescence

(peduncle) possesses terminal bud which

is capable of growing continuously and

produce lateral flowers is called racemose

inflorescence. Old flowers are at the base

and younger flowers and buds are towards

the apex. It is further divided into 3 types

based on growth pattern of main axis.

T

C

E

G

O

Q

U

G

Ockp"Czku

Gnqpicvgf

Ockp"Czku

Ujqtvgpgf

Ukorng"Tgegog

Urkmg

Ecvmkp

Urkmgngv

Urcfkz

Rcpkeng

Eqt{od

Wodgn

Figure 4.2: (a)

Racemose

Racemose

Main axis of

unlimited growth

Flowers arranged

in an acropetal

succession

Opening of flowers

is centripetal

Usually the

oldest flower at

the base of the

inflorescence axis.

Old flower

Figure 4.2: (b)

Cymose inflorescence

Cymose

Main axis of

limited growth.

Flowers arranged

in a basipetal

succession

Opening of flowers

is centrifugal

Usually the oldest

flower at the top of

the inflorescence

axis.

Ockp"Czku"

Hncvvgpgf"qt

Inqdqug

Figure 4.3: Racemose

Jgcf

1. Main axis elongated

The axis of inflorescence is elongated

and contains pedicellate or sessile flowers

on it. The following types are discussed

under main axis elongated type.

a. Simple raceme: The inflorescence

with an unbranched main axis bears

pedicellate flowers in acropetal

succession. Example: Crotalaria retusa,

mustard and radish.

b. Spike: Spike is an unbranched

indeterminate inflorescence with

sessile flowers. Example: Achyranthes,

Stachytarpheta.

c. Spikelet: Literally it is a small

spike. The Inflorescence is with

125

---

Young flower

Old flower

Figure 4.4: (a) diagrammatic,

(b) Simple raceme

Lodicules

Rachilla

Palea

Sessile flower

Figure 4.4: (c) diagrammatic, (d) Spike

branched central axis. Each branch is a

spikelet. Sessile flowers are formed in

acropetal succession on the axis. A pair

of inflorescence bracts called glumes is

present at the base. Each sessile flower has

a lemma (bract) and a palea (bracteole).

Tepals reduced to colourless scaly leaves

(lodicule). Each flower has stamen and

pistil only. Example: Paddy, Wheat,

Barley, Sorghum.

Spikelet

Sessile flower

Figure 4.4: (g) diagrammatic, (h) Catkin

called ament. Example: Acalypha hispida,

Prosopis juliflora, Piper nigrum.

e. Spadix: An inflorescence with

a fleshy or thickened central axis that

possesses many unisexual sessile flowers

in acropetal succession. Usually female

flowers are found towards the base and

male flowers are found at the apex. Entire

m

Figure 4.4: (i) diagrammatic, (j) Spadix

Hkiwtg"606"*m+"Urcfkz

inflorescence is covered by a brightly

coloured or hard bract called a spathe.

Example: Amorphophallus, Colocasia,

Phoenix, Cocos.

Lemma

Glumes

Figure 4.4: (e) diagrammatic, (f) Spikelet

d. Catkin: Pendulous spikes with

a long and drooping axis bearing small

unisexual or bisexual flowers. It is also

Hkiwtg"606"*e+"Rcpkeng

Figure 4.4: (k) diagrammatic, (l) Panicle

126

---

f. Panicle: A branched raceme is called

panicle. Example: Mangifera, neem,

Delonix regia. It is also called Compound

raceme or raceme of racemes.

2. Main axis shortened:

Inflorescence with reduced growth of

central axis. There are two types namely

corymb and umbel.

a. Corymb: An inflorescence with

shorter pedicellate flowers at the top and

longer pedicellate flowers at the bottom.

All flowers appear at the same level to

form convex or flat topped racemose

inflorescence. Example: Caesalpinia.

Compound corymb: A branched corymb

is called compound corymb. Example:

Cauliflower.

b. Umbel: An inflorescence with

indeterminate central axis and pedicellate

flowers arise from a common point of

peduncle at the apex. Example: Allium cepa,

Centella asiatica, Memecylon umbellatum.

Compound umbel: It is a branched umbel.

Each smaller unit is called umbellule.

Example: Daucas carota, Coriandrum

sativum, Memecylon edule.

Figure 4.4: (s)

Umbel

Figure 4.4: (t)

Compound umbel

Figure Hkiwtg"606"*o+"Eqt{od 4.4: (m)

Corymb

diagrammatic

Rachis

4.4 (o) Compound corymb

Figure 4.4: (n)

Compound corymb

diagrammatic

3. Main axis flattened:

The main axis of inflorescence is mostly

flattened (convex or concave) or globose.

A head or capitulum is a determinate

or indeterminate, group of sessile or sub

sessile flowers arising on a receptacle,

often subtended by an involucre.

a. Head: A head is a characteristic

inflorescence of Asteraceae and is also

found in some members of Rubiaceae.

Figure 4.4: (o)

Corymb

Figure 4.4: (p)

Compound corymb

Figure 4.4: (q)

Umbel

Hkiwtg"606"*s+"Wodgn

diagrammatic

Hkiwtg"606"*u+"Eqorqwpf"wodgn

Figure 4.4: (r)

Compound umbel

diagrammatic

Figure 4.4: (u)

Neolamarkia cadamba head

Example: Neolamarkia cadamba,

Mitragyna parvifolia and in some members

of Fabaceae-Mimosoideae. Example:

127

---

Acacia nilotica, Albizia lebbeck, Mimosa

pudica (sensitive plant).

Torus contains two types of florets:

1. Disc floret or tubular floret. 2. Ray floret

or ligulate floret.

The flower and inflorescence are

subtended by a lateral appendage

called bract. In sunflower, you may

notice that the whorl of bracts forms a

cup like structure beneath mimicking

the calyx. Such whorl of bracts is called

involucre. A group of bracts present

beneath the sub unit of inflorescence

is known as Involucel.

Heads are classified into two types.

i. Homogamous head: This type

of inflorescence exhibits single kind of

florets. Inflorescence has disc florets

alone. Example: Vernonia, Ageratum or

Ray florets alone. Example: Launaea,

Sonchus.

II. Cymose inflorescence.

Central axis stops growing and ends in

a flower, further growth is by means of

axillary buds. Old flowers present at apex

and young flowers at base

E

[

O

Q

U

G

Ukorng

E{og

Oqpqejcukcn

E{og

Ukorng

Fkejcukwo

Rqn{ejcukcn

E{og

Figure 4.5: Cyme

Jgnkeqkf

Ueqtrkqkf

1. Simple cyme (solitary): Determinate

inflorescence consists of a single flower.

It may be terminal or axillary. Example:

terminal in Trillium grandiflorum and

axillary in Hibiscus.

Figure 4.4: Homogamous head

(v) disc floret, (w) ray floret

ii. Heterogamous head: The

inflorescence possesses both types of

florets. Example: Helianthus, Tridax.

Disc florets at the centre of the head

are tubular and bisexual whereas the ray

florets found at the margin of the head

which are ligulate pistilate (unisexual).

Figure 4.6: (a) Simple cyme

2. Monochasial Cyme (uniparous): The

main axis ends with a flower. From two

lateral bracts, only one branch grows

further. It may be helicoid (bostryx) or

Scorpioid (cincinnus).

a. Helicoid: Axis develops on only one

side and forms a coil structure atleast at

the earlier development stage. Example:

Hamelia, potato.

128

---

Figure 4.6: (b) diagrammatic,

(c) Monochasial Helicoid

b. Scorpioid: Axis develops on

alternate sides and often becomes a coil

structure. Example: Heliotropium.

Figure 4.6: (h) diagrammatic,

(i) Compound dichasium

5. Polychasial Cyme (multiparous): The

central axis ends with a flower. The lateral

axes branches repeatedly. Example: Nerium

Figure 4.6: (d) diagrammatic,

(e) Monochasial Scorpioid

3. Simple dichasium (Biparous): A

central axis ends in a terminal flower;

further growth is produced by two lateral

buds. Each cymose unit consists of three

flowers of which central one is old one.

This is true cyme. Example: Jasminum.

Figure 4.6: ( j) diagrammatic,

(k) Polychasial cyme

Sympodial Cyme:

In monochasial cyme,

successive axes at first

develop in a zigzag

manner and later it

develops into a straight pseudo axis.

Example: Solanum americanum.

III. Mixed Inflorescence

Mixed inflorescence

Figure 4.6: (f) diagrammatic,

(g) Simple dichasium

4. Compound dichasium: It has many

flowers. A terminal old flower develops

lateral simple dichasial cymes on both

sides. Each compound dichasium consists

of seven flowers. Example: Clerodendron.

A small,simple dichasium is called

cymule

Thyrsus

Verticillaster

Special inflorescence

Cyathium Hypanthodium Coenanthium

Figure 4.7: Mixed and special inflorescence

129

---

Inflorescences in which both racemose

and cymose patterns of development

occur in a mixed manner. It is of the

following two types.

1. Thyrsus: It is a ‘Raceme of cymes’.

Indefinite central axis bears lateral

pedicellate cymes, (simple or compound

dichasia). Example: Ocimum, Anisomeles.

organised in a scorpioid manner. Female

flower is solitary and centrally located on

a long pedicel. Male flower is represented

only by stamens and female flower is

represented only by pistil. Cyathium may

be actinomorphic (Example: Euphorbia)

or zygomorphic (Example: Pedilanthus.).

Nectar is present in involucre.

Male flower

Female flower

Figure 4.8: (a) diagrammatic, (b) Th y r s u s

2. Verticil or Verticillaster: Main axis

bears two opposite lateral sessile cymes

at the axil of the node,each of it produces

monochasial scorpioid lateral branches so

that flowers are crowded around the node.

Example: Leonotis, Leucas.

Hkiwtg"60:"*e+"Xgtvkeknncuvgt"kphnqtguegpeg"fkcitco

Figure 4.8: (c) diagrammatic,

(d) Verticillaster

Figure 4.9: (a) diagrammatic,

(b) Cyathium

2. Hypanthodium: Receptacle is a hollow,

globose structure consisting unisexual

flowers present on the inner wall of the

receptacle. Receptacle is closed except

a small opening called ostiole which is

covered by a series of bracts. Male flowers

are present nearer to the ostiole, female

and neutral flowers are found in a mixed

manner from middle below. Example:

Ficus sp. (Banyan and Pipal).

3. Coenanthium: Circular disc like fleshy

open receptacle that bears pistillate flowers

at the center and staminate flowers at the

periphery. Example: Dorstenia

IV. Special Inflorescence

The inflorescences do not show any of the

development pattern types are classified

under special type of inflorescence.

1. Cyathium: Cyathium inflorescence

consists of small unisexual flowers

enclosed by a common involucre which

mimics a single flower. Male flowers are

Figure 4.9: (c)

Hypanthodium

Figure 4.9: (d)

Coenanthium

130

---

4.2 Flower

In a plant, which part would you like the

most? Of course, it is a flower, because

of its colour and fragrance. The flower

is a significant diagnostic feature of

angiosperms. It is a modified condensed

reproductive shoot. The growth of the

flower shoot is determinate.

Rkuvkn: The female reproductive

organ of a flower is Gynoecium or

pistil. Each member is carpel.

4.2.1 Whorls of flower

There are two whorls, accessory and

essential. Accessory whorl consists of

calyx and corolla and essential whorl

comprises of androecium and gynoecium.

Flower is said to be Complete when it

contains all four whorls. An Incomplete

flower is devoid of one or more whorls.

Rctvu"qh"Hnqygt

Uvcogp< Male organ of a

flower is androecium. Each

member is stamen.

Rgvcn : Innermost

accessory whorl of

flower is corolla. Each

member is called petal.

Ugrcn< Outermost

whorl of flower is calyx.

Each member is called

sepal.

R gtkcpvj( perigonium):

Undifferentiated calyx and

corolla. Individual members are

called tepal.

Dtcev< Subtending leaf or leaf like

structure of any flower is called

Bract.

Vjcncowu"

*vqtwu"qt"tgegrvceng+<

The part of the flower on

which other floral parts are

attached.

Dtcevgqng< A smaller bract present

on the side of pedicel is called

dtcevgqng or dtcevngv0"

A whorl of bracteoles at the base of

calyx is called grkecn{z0

Rgfkegn: stalk of the flower. Flower is

rgfkegnncvg or uguukng depending upon

presence or absence. The flowers with a short,

rudimentary pedicel are called uwduguukng"

hnqygtu.

Figure 4.10: Parts of flower

4.2.2 Flower sex

Flower sex refers to the presence or

absence of androecium and gynoecium

within a flower.

1. Perfect or bisexual(monoclinous):

When a flower contains both androecium

and gynoecium is called perfect flower.

2. Imperfect or unisexual (diclinous):

When the flower contains only one of

the essential whorls is called Imperfect

flower. It is of two types:

i) Staminate flowers: Flowers only with

androecium alone are called staminate

flowers.

131

---

le

wer

u

t"

ugz

Female

flower

Figure 4.11: (a)

Bisexual flower

c0"Dkugzwcn"hnqygt"

Female

flower

c0"Oqpqgekqwu

Figure 4.11: (b)

Male flower

d0"Ocng"hnqygt

Hkiwtg"6033"Hnqygt"ugz

"d0"Fkqgekqwu

e0"Hgocng"hnqygt

ii) Pistillate flowers: Flowers with only

gynoecium are called pistillate flowers.

4.2.3 Plant sex

Male

flower

Female

flower

Male

flower

Female

flower

c0"Oqpqgekqwu

Figure 4.12: (a)

Monoecious

Hkiwtg"6033"Hnqygt"ugz

"d0"Fkqgekqwu

Hkiwtg"6034"Rncpv"ugz""

Figure 4.12: (b)

Dioecious

e0"Hgocng"hnqygt

e0"Rqn{icoqwu

Bisexual

flower

Figure 4.11: (c) Figure 4.12: (c)

Hkiwtg"6034"Rncpv"ugz""

Female flower Polygamous

Plant sex refers to the presence and

distribution of flowers with different sexes

in an individual plant.

1. Hermaphroditic: All the flowers of the

plant are bisexual.

2. Monoecious (mono-one; oikos-house):

Both male and female flowers are present

in the same plant Example: Coconut.

3. Dioecious (di-two: oikos-house): Male

and Female flowers are present on separate

plants. Example: Papaya, Palmyra.

132

Types of Polygamous:

Andromonoecious: A plant with both

Female

flower male flowers and bisexual flowers.

Male

Gynomonoecious: Male A plant with

flower both pistillate and flower bisexual flowers.

"d0"Fkqgekqwu

Polygamomonoecious: A plant

with pistillate, staminate and bisexual

Hkiwtg"6034"Rncpv"ugz""

flowers. It is also called trimonoecious.

d0"Ocng"hnqygt

Androdioecious:

e0"Hgocng"hnqygt

A plant with

staminate flowers on one individual

and bisexual flower on other

individual

Male

Bisexual

flower

flower Gynodioecious: A plant with

e0"Rqn{icoqwu

pistillate flowers on one individual and

bisexual flowers on other individual.

e0"Rqn{icoqwu

Polygamodioecious: A plant with

staminate flowers and bisexual in one

individual and pistillate flowers and

bisexual flowers in other individual.

Trioecious: A plant with

staminate,pistillate and bisexual

flowers on different individuals

4. Polygamous: The condition in which

bisexual and unisexual (staminate/

pistillate) flowers occur in a same plant is

called polygamous. It is of several types.

See box. Example: Musa, Mangifera.

4.2.4 Flower symmetry

What is the radius of a circle? Cut a

paper into round shape, fold it so as

to get two equal halves. In how many

planes will you get equal halves? In

how many planes you can divide a

cucumber in two equal halves? A flower

is symmetrical when it is divided into

equal halves in any plane running

through the center. Flower symmetry

Bisexual

flower

---

Figure 4.13: (a)

Actinomorphic

Figure 4.13: (b)

Zygomorphic

Figure 4.13: (c)

Asymmetric

is an important structural adaptation

related to pollination systems.

1. Actinomorphic (or) radial or

polysymmetric: The flower shows two

mirror images when cut in any plane or

radius through the centre.Normally there

are more than two planes of symmetry.

Example: Hibiscus, Datura, water lily.

2. Zygomorphic (bilateral symmetry)

or monosymmetric: The flower can be

divided into equal halves in only one plane.

Zygomorphic flower can efficiently transfer

pollen grains to visiting pollinators. Example:

Pisum, Bean, Cassia, Gulmohar, Salvia,

Ocimum.

3. Asymmetric (amorphic): Flower lacks

any plane of symmetry and cannot be

divided into equal halves in any plane. Parts

of such flowers are twisted. Example: Canna

indica.

4.3 Accessory organs

4.3.1 Arrangement of whorls

The position of perianth (sepals, petals,

tepals) parts relative to one another is

called perianth arrangement.

1. Cyclic or whorled: All the floral

parts are arranged in definite whorls.

Example: Brassica,Solanum.

2. Acyclic or spiral: The floral parts

are arranged in spirals on the elongated

fleshy torus. Example: Magnolia.

3. Spirocyclic or hemicyclic: Some parts

are in whorls and others parts are in spirals.

Example: Nymphaea, Annona, Polyalthia

4.3.2 Cycly

It explains the number of whorls of floral

parts. Perianth cycly is the number of

whorls of perianth (sepals, petals) parts.

Figure 4.14: (a) Cyclic Figure 4.14: (b) Acyclic Figure 4.14: (c)

Spirocyclic

133

---

1. Uniseriate: It is a single whorl of

accessory(non-essential) floral part. It is

less common.Example: Sterculia.

2. Biseriate (dicyclic): It is with

two whorls of accessory floral parts.

(outer=lower,inner=upper)It is the most

common type of perianth cycly. Example:

Hibiscus.

3. Multiseriate: (triseriate,tetraseriate)

More than two whorls of non–essential

floral parts.Example: Chrysanthemum.

4. Dichlamydeous: A flower is composed

of distinct outer calyx and inner corolla.

5. Homochlamydeous: Perianth is undifferentiated

into calyx and corolla and composed

of similar parts called tepals. Most

monocots have a homochlamydeous perianth.

6. Achlamydeous: Perianth is absent

altogether.Flowers without petals are

called apetalous and flowers without

sepals are called asepalous.

Figure 4.15: (a)

Uniseriate

Figure 4.15: (b)

Biseriate

Figure 4.15: (c)

Multiseriate

Figure 4.16: (a)

Dichlamydeous

4.3.3 Merosity

Figure 4.16: (b)

Homochlamydeous

Number of floral parts per whorl is called

merosity. Perianth merosity is the number

of perianth parts per whorl.

1. Isomerous: Presence of same number

of perianth parts in different whorls of a

flower. (five sepals, five petals). Example:

Hibiscus.

2. Anisomerous: Each whorl of flower

contains different number of members.

Example: Annona.

3. Bimerous: Floral parts in two or

multiples of two. Example: Ixora

4. Trimerous: Floral parts in three or

multiples of three. Example: Allium,

Monocots.

5. Tetramerous: Floral parts in four or

multiples of four. Example: Brassica juncea.

6. Pentamerous: Floral parts in five or

multiples of five. Example: Hibiscus,

Dicots.

4.3.4 Calyx

Calyx protects the flower in bud stage.

Outermost whorl of flower is calyx.

Unit of calyx is sepal. Normally green in

colour.

134

---

Figure 4.17: (a)

Trimerous

Figure 4.17: (b)

Tetramerous

Figure 4.17: (c)

Pentamerous

1. Fusion: a. Aposepalous (polysepalous

or chorisepalous): The flower with distinct

sepals. Example: Brassica, Annona.

a. Caducous or fugacious calyx: Calyx that

withers or falls during the early development

stage of flower. Example: Papaver.

Figure 4.18 (a): Aposepalous

b. Synsepalous: The flower with united or

fused sepals. Example: Hibiscus, Brugmansia.

Figure 4.19: (a)

Caducous bud

with sepal

Figure 4.19: (b)

Caducous flower

without sepal

b. Deciduous: Calyx that falls after

the opening of flower (anthesis) Example:

Nelumbo.

Figure 4.18: (b) Synsepalous

2. Duration of floral parts:

What is the green part of brinjal fruit?

Have you seen similar to this in any other

fruits?

Figure 4.19: (c) Deciduous

c. Persistant: Calyx that persists

and continues to be along with the fruit

and forms a cup at the base of the fruit.

Example: Brinjal.

135

---

d. Accrescent: Calyx that is persistent,

grows along with the fruit and encloses

the fruit either completely or partially.

Example: Physalis, Palmyra.

Figure 4.19: (d)

Persistant calyx

Figure 4.19: (e)

Accrescent

3. Shapes of calyx

Have you noticed the shoe flower’s calyx?

It is bell shaped called Campanulate. The

fruiting calyx is urn shaped in Withania

and it is called urceolate. In Datura calyx

is tube like and it is known as tubular.

Two lipped calyx is present in Ocimum.

Sometimes calyx is coloured and called

petaloid. Example: Saraca, Sterculia. Calyx

is distinctly leafy,large and often yellow

or orange coloured sometimes white as

in Mussaenda.

It is modified

into hair like

structure or scaly

called pappus

as in Tridax of

Compositae.

Figure 4.20: (c)

Mussaenda

Figure 4.20: (a)

Companulate

Figure 4.20: (b)

Pappus

136

What is the use of pappus ?

4.3.5 Corolla

Corolla is the most attractive part in

majority of the flowers and is usually

brightly coloured. Corolla helps to display

the flower and attracts the pollinators.

1. Fusion:

a. Apopetalous (polypetalous,

choripetalous): Petals are distinct.

Example: Hibiscus.

b. Sympetalous (gamopetalous):

Petals are fused. Example: Datura.

2. Shapes of corolla

I. Apopetalous Actinomorphic

1. Cruciform: Four petals arranged in

the form of a cross. Example: Brassica,

mustard, radish, cauliflower.

2. Caryophyllaceous: Five petals with long

claws with limb at right angles to the claw.

Example: Caryophyllaceae. Dianthus.

3. Rosaceous: Five to many sessile or

minutely clawed petals with radiating

limbs. Example: Rose, Tea.

Figure 4.21: (a)

Cruciform

Figure 4.21: (b)

Caryophyllaceous

II. Apopetalous Zygomorphic

1. Papilionaceous:

Made up of five distinct petals organized

in a butterfly shape. Corolla has three types

of petals. One usually large posterior petal

called vexillum(standard)two lateral petalswings

(alae) and two anterior sympetalous

petals called carina. Example: Clitoria

ternatea, Pea, Bean.

---

Figure 4.21: (d)

Campanulate

Figure 4.21: (e)

Infundibuliform

Figure 4.21: (c) Papilionaceous

Figure 4.21: (f)

Rotate

Figure 4.21: (g)

Salvershaped

Apopetalous

Sympetalous

Actinomorphic Zygomorphic Actinomorphic Zygomorphic

III. Sympetalous Actinomorphic

1. Tubular:

Petals united to form a narrow tubular

structure with very short limbs. Example:

Disc floret of sunflower.

2. Campanulate:

Petals fused to form a bell-shaped corolla.

Example: Physalis,Cucurbita maxima,

Campanula.

3. Infundibuliform:

Petals fused to form funnel-shaped

corolla. Tube gradually widens into limbs.

Example: Datura, Ipomoea.

4. Rotate:

Petals fused to form a wheel shaped corolla

with very short tube and a spreading

circular limb. Example: brinjal, Evolvulus

5. Salver shaped or Hypocrateriform;

Petals fused to form a long narrow

tube with spreading limbs. Example:

Catharanthus, Ixora,

Tabernaemontana

6. Urceolate:

Petals fused to form

urn-shaped or potshaped

corolla.Example:

Bryophyllum calycinum, Figure 4.21:

Diospyros.

(h) Urceolate

137

---

IV. Sympetalous Zygomorphic

1. Bilabiate:

Corolla with two lips. Example:

Ocimum,Leucas,Adhatoda.

Tubular corolla with a single strapshaped

limb. Example: Ray floret of

Helianthus

2. Personate:

Corolla made up of two lips with the

upper arched and the lower protruding

into the corolla throat. Example:

Antirrhinum,Linaria.

3. Ligulate:

Tubular corolla with a single strapshaped

limb. Example: Ray floret of

Helianthus.

C0"Xcnxcvg<"Margins of sepals or

petals do not overlap but just touch

each other.

Example: Calyx in members of

Malvaceae, Calotropis, Annona.

Figure 4.21: (i)

Bilabiate

4.3.6 Perianth

Figure 4.21: (j)

Personate

Can you recall the term homochlamydeous?

undifferentiated calyx and corolla in a

flower is called perianth. Each member is

called tepal. If the tepals are distinct they

are called Apotepalous (Polyphyllous).

Example: Allium sativum. Fused tepals

are called Syntepalous. (Gamophyllous).

Example: Allium cepa.

B. Vykuvgf" qt" eqpxqnwvg" qt"

eqpvqtvgf<

One margin of each petal or sepal

overlapping on the other petal

Example:Petals of chinarose

Cguvkxcvkqp"

Arrangement of sepals and petals in the flower bud.

D. Quincuncial: It is a

type of imbricate

aestivation in which two

petals are external and two

internal and one petal with

one margin internal and the

other margin external.

Example:Guava,calyx of

Ipomoea, Catharanthus.

C. Imbricate: Sepals and petals

irregularly overlap on each

other; one member of the whorl

is exterior, one interior and rest

of the three having one margin

exterior and the other interior.

Example: Cassia, Delonix

There are 3 types.

1.Ascendingly imbricate.

2.Quincuncial.

3.Vexillary.

E. Vexillary:Large

posterior petals both

margins overlap

lateral petals.

Lateral petals other

margin overlaps

anterior petals

Example: Pea,bean.

138

---

4.3.7 Aestivation: Arrangement of sepals and petals in the flower bud is said to be

aestivation.

C0Xcnxcvg D0Vykuvgf E0Kodtkecvg F0Swkpewpekcn G0Xgzknnct{

Figure 4.22: Aestivation

Lodicule: Reduced scale like perianth

in the members of Poaceae is called

lodicule.

Ikebana

A creative mind can earn more

money in floral art industry. Ikebana

is a Japanese form of floral art.

Ikebana is all about flowers arranged

in angles. Floral art is not just an

arrangement of flowers, but it is

also about coordinating colours and

texture. Ikebana experts are needed

for marriages, other functions and in

star hotels.

Essential Parts of Flower

4.4 Androecium

Androecium: Third

whorl of flower is the

male reproductive

part of the flower.

It is composed of

stamens(microsporophylls). Each Stamen

consist of 3 parts,

a. Filament b. Anther c. Connective

Anther

Connective

Filament

Dorsal view

Ventral view

Figure 4.23: Stamen

139

---

Anther: Upper swollen part with microsporangia.

Filament: Stalk of stamen

Connective: Tissue connecting anther

lobes with filament

Anther typically contains two compartments

called thecae (singular theca).

Each theca consists of two microsporangia.

Two microsporangia fused to form a locule.

Sterile stamens are called Staminodes.

Example: Cassia. Distinct: stamens which

do not fuse to one another. Free: stamens

which do not fuse with other parts of

flower. Apostemonous: flowers with

stamens that are free and distinct.

4.4.1 Fusion of stamens: Refers to the

stamens fusing among themselves or with

other parts of flower. Two types.

1. Connation and 2. Adnation

1. Connation: Refers to the fusion of

stamens among themselves. It is of

3 types. a. Adelphy. b. Syngenecious.

c. Synandrous.

a. Adelphy: Filaments connate into

one or more bundles but anthers are free.

It may be the following types.

1. Monadelphous: Filaments of

stamens connate into a single bundle.

Example: malvaceae (chinarose,cotton).

Figure 4.24: (a)

Monadelphous

2. Diadelphous: Filaments of

stamens connate into two bundles.

Example: Fabaceae, pea.

3. Polyadelphous: Filaments

connate into many bundles. Example:

Citrus, Bombax

Anthers (united)

Filaments (free)

Figure 4.24: (d)

Syngenesious

Figure 4.24: (e)

Synandrous

Figure 4.24: (b)

Diadelphous

140

Figure 4.24: (c)

Polyadelphous

b. Syngenesious: Anthers connate,

filaments free. Example: Asteraceae.

c. Synandrous: Filaments and anthers

are completely fused. Example: Coccinea.

2. Adnation: Refers to the fusion of stamens

with other floral parts. Epipetalous

(petalostemonous): Stamens are adnate to

petals .Example: brinjal,Datura.

a. Episepalous:

stamens are adnate

to sepals. Example:

Grevillea (Silver oak)

b. Epitepalous

( epiphyllous) :

stamens are adnate

to tepals. Example:

Asphodelus, Asparagus.

Stamen

Petal

Figure 4.25: (a)

Epipetalous

---

c. Gynostegium:Connation product of

stamens and stigma is called gynostegium.

Example: Calotropis and Orchidaceae.

d. Pollinium: Pollen grains are fused

together as a single mass

Figure 4.26: (b)

Tetradynamous

Figure 4.26: (c)

Heterostemonous

4.4.3 Stamen insertion

1.Inserted: Shorter than the corolla tube

and included within. Example: Datura.

Figure 4.25: (b)

Gynostegium

Figure 4.25: (c)

Pollinium

4.4.2 Arrangement of stamens relate to

length of stamens:

1. Didynamous (di-two, dynamisstrength):

Four stamens in which two

with long filaments and two with short

filaments. Example: Lamiaceae, Ocimum.

If all four stamens are in two equal pairs

then the condition is called didynamous.

Stamen

Petal

Figure 4.27: (a)

Inserted

Figure 4.27: (b)

Exserted

2.Exserted:Longer than the corolla tube

and project out.Example: Mimosa, Acacia

arabica

The number of whorls of stamens

present in a flower is called stamen cycly.

Two major types are 1.uniseriate,a single

whorl of stamens and 2.biseriate,two

whorls of stamens.

4.4.4 Anther types

Figure 4.26: (a)

Didynamous

2. Tetradynamous(tetra-four): Six stamens

of which four with long filaments and

two with short filaments. Example: Brassicaceae,

(Brassica).

3. Heterostemonous: stamens are of

different lengths in the same flower.

Example: Cassia, Ipomoea.

1. Monothecal: One lobe with two

microsporangia. They are kidney shaped

in a cross section. Example: Malvaceae

Figure 4.28: (a)

Monothecal

Figure 4.28: (b)

Dithecal

141

---

Some other types: a) Haplostemonous:

stamens are uniseriate and equal in

number to the petals and opposite the

sepals (antisepalous)

b) Obhaplostemonous: Stamens

are uniseriate, number equal to petals

and opposite the petals (antipetalous)

c) Diplostemonous: Stamens are

biseriate, outer antisepalous, inner

antipetalous. Example: Murraya.

d) Obdiplostemonous: Stamens

are biseriate, outer antipetalous, inner

antisepalous. Example: Caryophyllaceae.

e) Polystemonous: Numerous stamens

are normally many more than

the number of petals.

c d e

2. Dithecal: It is a typical type,having two

lobes with four microsporangia.They are

butterfly shaped in cross section. Example:

solanaceae.

4.4.5 Anther attachment

1. Basifixed:(Innate) Base of anther is

attached to the tip of filament. Example:

Brassica, Datura.

2. Dorsifixed: Apex of filament is attached

to the dorsal side of the anther. Example:

Citrus, Hibiscus.

3. Versatile: Filament is attached to the

anther at midpoint. Example: Grasses.

4. Adnate: Filament is continued from

the base to the apex of anther. Example:

Verbena, Ranunculus, Nelumbo

C0"Dcukhkzgf

Filament

D0"Fqtukhkzgf

Filament

E0"Xgtucvkng

F0"Cfpcvg

Figure 4.29: Anther attachment

4.4.6 Anther dehiscence

It refers to opening of anther to disperse

pollen grains.

1. Longitudinal: Anther dehisces along a

suture parallel to long axis of each anther

lobe. Example: Datura, chinarose, cotton.

2. Transverse: Anther dehisces at right

angles to the long axis of anther lobe.

Example: Malvaceae.

3. Poricidal: Anther dehisces through

pores at one end of the thecae. Example:

Ericaceae, Solanum, potato, brinjal, Cassia.

4. Valvular: Anther dehisces through a

pore covered by a flap of tissue. Example:

Lauraceae, Cinnamomum.

C0"Nqpikvwfkpcn

E0"Rqtkekfcn

Filament

Apical pore

Filament

D0"Vtcpuxgtug

F0"Xcnxwnct

Pollengrain

Valve

Pollengrains

Figure 4.30: Anther dehiscence

142

---

4.4.7 Anther dehiscing direction

It shows the position of anther opening

relative to the anther of the flower.

1.Introrse: Anther dehisces towards the

center of the flower. Example: Dianthus.

4.5.2 Fusion of carpels

It is an important systematic character.

Apocarpous gynoecium is generally

thought to be ancestral condition in

Angiosperms.

Apocarpous

A pistil contains

two or more

distinct carpels.

Example: Annona.

Syncarpous

A pistil contains

two or more carpels

which are connate.

Example: Citrus,

tomato.

Figure 4.31: (a)

Introrse

Figure 4.31: (b)

Extrorse

2. Extrorse: Anther dehisces towards periphery

of the flower. Example: Argemone.

4.5 Gynoecium

Gynoecium or pistil is

the female reproductive

part of the flower.

A pistil consists of an

expanded basal portion

called the ovary, an

elongated section called

a style and an apical

structure that receives

pollen called a stigma.

Ovary with stipe is

called stipitate ovary.

Stigma

Style

Ovary

Figure 4.32:

Pistil

Carpel: They are

components of a gynoecium. Gynoecium

is made of one or more carpels. Carpels

may be distinct or connate.

4.5.1 Number of carpel

c0"Crqectrqwu

Carpels 3 locules 1

d0"U{pectrqwu"wpknqewnct

Stipe

C.S.

Septum

Carpels 4 locules 4

e0"u{pectrqwu"vgvtcnqewnct

Figure 4.33: Fusion of

carpels

Unicarpellary

(monocarpellary)

Single carpel

Example: Fabaceae

Bicarpellary

Two carpels

Example:

Rubiaceae

Tricarpellary

Three carpels

Example:

Cucurbitaceae

Tetracarpellary

Four carpels

Example:

Lamiaceae.

Multicarpellary

Many carpels

Example:

Nymphaeceae.

143

---

4.5.3 Number of locules

Ovary bears ovules on a specialized

tissue called placenta. A septum is a

crosswall or partition of ovary. The

walls of ovary and septa form a cavity

called locule.

b. Bifid: A style branched into two.

Example: Asteraceae

Style

Apical part of ovary

C0"Dknqewnct

Ovule

D0Vtknqewnct

Figure 4.35: (a)

Simple style

Figure 4.35: (b)

Bifid style

N

N

N

N

E0"Vgvtcnqewnct

Ovule

Figure 4.34: Locules

Number of locules

Unilocular

Ovary

with one

chamber

Example:

pea,

groundnut.

Bilocular

Ovary

with two

chambers

Example:

mustard,

Crossandra.

N

N

N

N

N

F0"Rgpvcnqewnct

Trilocular

Ovary with

three

chambers

Example:

banana,

Euphorbia.

Like that tetralocular and pentalocular

ovaries are present according to the locule

numbers four and five. More than one

locule ovaries are called plurilocular.

4.5.4 Style and stigma

1. Style is a stalk like structure of a pistil

connecting ovary and stigma.

a. Simple: Single unbranched style.

Example: Hibiscus.

c. Gynobasic style:

arising from base of

the ovary. Example:

Lamiaceae (Ocimum),

characteristic of

Boraginaceae.

d. Lateral style:

Style arises from the

side of ovary. Example:

Mangifera.

2. Stigma: A stigma is

a structure present at

the tip of a pistil which

receives the pollen grains.

Figure 4.35:

(c) Gynobasic

style,

(d) Lateral

style

a. Discoid: A disk-shaped stigma is

called discoid.

b. Capitate: Stigma appearing like a

head. Example: Alchemilla

c. Globose: Stigma is spherical in

shape is called globose.

d. Plumose stigma: Stigma feathery

which is unbranched or branched as in

Asteraceae, Poaceae.

3. Pistillode: A reduced sterile pistil.

Example: ray floret of head infloresence

in Helianthus.

144

---

Corolla

Anthophore

Calyx

Saffron flower stigma is costly. One

gram of saffron is around Rs.300.

In traditional texts ascribe a few

medicinal properties to saffron

stigma.It is also used as a flavoring

substance.

Figure 4.36: C0"Cpvjqrjqtg (a) Anthophore

Androecium

Corolla

4. Gynandrophore or Androgynophore:

The unified internodal elongation between

corolla and androecium and androecium

and gynoecium. Example: Gynandropsis.

Androphore

Figure D0"Cpftqrjqtg

4.36: (b) Androphore

Figure 4.36: (d) Androgynophore

4.5.5 Extension of the condensed

internode of the receptacle

1. Anthophore:The internodal elongation

between calyx and corolla. Example:

caryophyllaceae (Silene conoidea)

2. Androphore: The internodal elongation

between the corolla and androecium.

Example: Grewia.

3. Gynophore: The internodal elongation

between androecium and gynoecium.

Example: Capparis.

Figure 4.36: (c) Gynophore

4.5.6 Ovary position

Hypanthium: (staminal disk); a fleshy,

elevated often nectariferous cup like

thalamus.

The position or attachment of ovary

relative to the other floral parts. It may be

classified into

1. Superior ovary: It is the ovary with the

sepals, petals and stamens attached at the

base of the ovary.

2. Inferior ovary: It is the ovary with the

sepals, petals and stamens attached at the

apex of the ovary.

3. Half-inferior ovary: It is the ovary

with the sepals, petals and stamens or

hypanthium attached near the middle of

the ovary.

145

---

Hypogynous:

The term is used for sepals,

petals and stamens attached

at the base of a superior

ovary. Example: Malvaceae

Epihypogynous:

The term is used for sepals,

petals and stamens attached

at the middle of the ovary

(half-inferior). Example:

Fabaceae, Rosaceae.

Perigynous:

The term is used for a

hypanthium attached at the

base of a superior ovary.

Epigynous:

The term is used for sepals,

petals and stamens attached

at the tip of an inferior

ovary. Example: cucumber,

apple, Asteraceae.

Epiperigynous:

The term is used for

hypanthium attached at the

apex of an inferior ovary.

4.5.7 Perianth / androecial position on thalamus:

It describes placement of the perianth and androecium relative to the ovary and to a

hypanthium, if present.

Hypanthium

absent

Hypanthium

present

Hypanthium

absent

Hypanthium

Ovary

superior

Ovary

inferior

Figure 4.37: Perianth / androecial position on thalamus

Ovary

half-inferior

Hkiwtg"6062"Rgtkcpvj1cpftqgekcn"rqukvkqp"qp"vjcncowu

Parietal axile:

It is with the placentae at the junction of

the septum and ovary wall of a two or more

locular ovary. Example: Brassicaceae.

Parietal septate:

It is with placentae on the inner ovary walls

but within septate locules as in Aizoaceae.

Apical pendulous

It is with placenta at the top of ovary. Ovules

hanging down.

Apical axile

It is with two or more placentae at the top of

a septate ovary. Example: Apiaceae.

146

---

4.6 Construction of floral diagram

and floral formula

A floral formula is a simple way to explain

the salient features of a flower. The floral

diagram is a representation of the cross

section of the flower. It represents floral

whorls arranged as viewed from above.

Floral diagram shows the number and

arrangement of bract, bracteoles and floral

parts, fusion, overlapping and placentation.

The branch that bears the flower is

called mother axis.

147

---

The side of the flower facing the

mother axis is called posterior side. The

side facing the bract is the anterior side.

Floral formula and floral diagram of

The members of different floral whorls

are shown arranged in concentric rings.

Figure 4.38: (a) Hibiscus rosa-sinensis

Figure 4.38: (b) Brassica compestris

Br Brl K (5) C 5 A (∞) G (5)

Br Brl K 2+2 C 2+2 A 2+4 G (2)

Figure 4.38: (c) Crotalaria juncea

Figure 4.38: (d) Ixora coccinea

Br Ebrl % K (5) C 1+2+ (2) A 5+5 G- (1)

Br Brl K (4) C (4) A 4 G (2)

Ocng"hnqygt

Hgocng"hnqygt

Figure 4.38: (e) Phyllanthus amarus

Ocng"Hnqygt

Hgocng"Hnqygt

Figure 4.38: (f) Cocos nucifera

Br Ebrl P 3+3 A (3) G 0

Br Brl P (3)+3 A 3+3 G 0

Br Ebrl P 3+3 A 0 G (3) Br Brl P (3)+3 A 0 G (3)

148

---

Br : Bracteate.

Ebr : Ebracteate

Brl : Bracteolate

Ebrl : Ebracteolate

: Actinomorphic flower or

polysymmetric

% : Zygomorphic or monosymmetric

: Staminate

: Pistillate

: Bisexual flower

K : Calyx, K 5 five sepals, aposepalous,

K( 5 ) five sepals synsepalous.

C : Corolla, C 5 five petals ,apopetalous,

C( 5 ) five petals sympetalous C (2+3) corolla

bilabiate with upper lib two lobes.

A : Androecium A 3 three stamens free,

A 2 + 2 , Stamens 4, two whorls (didynamous)

each whorl two stamens (free)

A (9)+1 – stamens ten, two bundles

(diadelphous) 9 stamens unite to one

bundle,1 another bundle.

C 5 A 5 —Epipetalous represents by

an arc.

A 0 :Staminode(sterile stamen)

G. Gynoecium or pistil – G 2 – Carpels

two, free (apocarpous)

G (3) – Carpels three, united

(syncarpous)

G 0 – pistillode (sterile carpel)

G – superior ovary, the line under G

G inferior ovary, the line above G

G– – semi-inferior ovary, the line

before middle of G.

∞ – Indefinite number of units

Can

you

imagine a man sized

inflorescence? The

largest unbranched

inflorescence is a spadix of titan

arum(Amorphophallus titanium).It

can grow upto 6 feet.Though the male

and female flowers are very small,they

combine to form a huge spadix

surrounded by a huge modified leaf

and appear like a single flower.The

largest inflorescence of any flowering

plant is Corypha umbraculifera.It

grows upto 6 to 8 feet.

Do you accept a flower weigh

as much as 11 kg.The largest single

flower of giant refflesia(Refflesia

arnoldi)grows up to 3 feet and weighs

as much.

Titan arum

4.7 Fruits

Corypha

Refflesia

We know about several kinds of fruits, but

by botanical study we will be surprised

to know the types of fruits and how they

are produced by plants. Fruits are the

products of pollination and fertilization,

usually containing seeds inside. In

common person perpective a fruit may be

defined as an edible product of the entire

gynoecium and any floral part which is

sweet, juicy or fleshy, coloured, aromatic

and enclosing seeds. However the fruit is

149

---

a fertilized and ripened ovary. The branch

of horticulture that deals with the study

of fruits and their cultivation is called

pomology.

4.7.1 Structure of Fruit

Fruit has a fruit wall. It is otherwise called

pericarp. It is differentiated into outer

epicarp, middle mesocarp and inner

endocarp. The inner part of the fruit is

occupied by the seed.

4.7.2 Types of Fruit

Fruits are classified into various types:

Simple Fruits

The fruits are derived from a single ovary

of a flower Example: Mango, Tomato.

Simple fruits are classified based on the

nature of pericarp as follows

A. Fleshy Fruit

The fruits are derived from single pistil

where the pericarp is fleshy, succulent and

differentiated into epicarp, mesocarp and

endocarp. It is subdivided into the following.

a) Berry: Fruit develops from bicarpellary

or multicarpellary, syncarpous ovary.

Here the epicarp is thin, the mesocarp

and endocarp remain undifferentiated.

They form a pulp in which the seeds are

embedded. Example: Tomato, Date Palm,

Grapes, Brinjal.

b) Drupe: Fruit develops from

monocarpellary, superior ovary. It

is usually one seeded. Pericarp is

differentiated into outer skinny epicarp,

fleshy and pulpy mesocarp and hard and

stony endocarp around the seed. Example:

Mango, Coconut.

c) Pepo: Fruit develops from

tricarpellary inferior ovary. Pericarp

terns leathery or woody which encloses,

fleshy mesocarp and smooth endocarp.

Example: Cucumber, Watermelon, Bottle

gourd, Pumpkin.

d) Hesperidium: Fruit develops from

multicarpellary, multilocular, syncarpous,

Fruits

True fruit

False fruit

Parthenocarpic fruit

Ovary develops into

fruit without any

non-carpellary part.

Example: Tomato,

Mango

In addition to the ovary

the non- carpellary (floral)

parts like thalamus (Apple),

perianth ( jack fruit) and

involucre and perianth (English

walnut) develop into fruit.

Development

of fruits without

fertilization. They

are seedless fruits.

Example: Banana

Figure 4.39: Classification of fruits based on formation

150

---

Berry (Tomato)

Drupe (Mango)

Pepo (Cucumber)

Hesperidium (Orange)

Pome (Apple)

Figure 4.40: Simple fleshy fruits

Balausta (Pomegranate)

superior ovary. The fruit wall is differentiated

into leathery epicarp with oil glands, a

middle fibrous mesocarp. The endocarp

forms distinct chambers, containing juicy

hairs. Example: Orange, Lemon.

e) Pome: It develops from

multicarpellary, syncarpous, inferior

ovary. The receptacle also develops

along with the ovary and becomes fleshy,

enclosing the true fruit. In pome the

epicarp is thin skin like and endocarp is

cartilagenous. Example: Apple, Pear.

f) Balausta: A fleshy indehiscent

fruit developing from multicarpellary,

multilocular inferior ovary whose

pericarp is tough and leathery. Seeds are

attached irregularly with testa being the

edible portion. Example: Pomegranate.

B. Dry Fruit

They develops from single ovary where

the pericarp is dry and not differentiated

into epicarp, mesocarp and endocarp. It is

further subdivided into three types.

1) Dry dehiscent fruit

Pericarp is dry and splits open

along the sutures to liberate seeds.

They can be classified into following types.

a) Follicle: Fruit develops from

monocarpellary, superior ovary and

dehisces along one suture. Example:

Calotropis.

b) Legume or pod: Fruit

develops from monocarpellary,

superior ovary and dehisces through

both dorsal and ventral sutures. Example:

Pisum.

c) Siliqua: Fruit develops from

bicarpellary, syncarpous, superior ovary

initially one chambered but subsequently

becomes two chambered due to the

formation of false septum (replum). The

fruit dehisces along two suture. Example:

Brassica.

151

---

Follicle (Calotropis)

Siliqua (Brassica)

Legume (Pisum)

Silicula (Capsella)

iv) Poricidal: Dehiscence through

terminal pores. Example: Papaver.

v) Denticidal: Capsule opening at

top exposing a number of teeth. Example:

Primula, Cerastium.

vi) Circumscissile: (pyxidium)

Dehisces transversely so that top comes off

as a lid or operculum. Example: Anagallis

arvensis, Portulaca, Operculina.

2) Dry indehiscent fruit

Dry fruit which does not split open at

maturity. It is subdivided into.

a) Achene: Single seeded dry fruit

developing from single carpel with

superior ovary. Achenes commonly

develop from apocarpous pistil, Fruit wall

Loculicidal

Septifragal (Datura)

(Lady’s finger)

Figure 4.41: Dry dehiscent fruit

d) Silicula: Fruit similar to siliqua but

shorter and broader. Example: Capsella,

Lepidium, Alyssum.

e) Capsule: Fruit develops from

multicarpellary, syncarpous, superior

ovary. Based on the dehiscence pattern

they are sub divided into.

i) Septicidal: Capsule splitting

along septa and valves remaining attached

to septa. Example: Linum, Aristolochia.

ii) Loculicidal: Capsule splitting

along locules and values remaining

attached to septa. Example: Lady’s finger.

iii) Septifragal: Capsule splitting

so that valves fall off leaving seeds attached

to the central axis. Example: Datura.

Achene (Clematis)

Caryopsis (Oryza)

Cypsela (Tridax)

Nut (Anacardium)

Samara (Acer)

Utricle

(Chenopodium)

Figure 4.42: Dry indehiscent fruit

152

---

is free from seed coat. Example: Clematis,

Delphinium, Strawberry.

b) Cypsela: Single seeded dry fruit,

develops from bicarpellary, syncarpous,

inferior ovary with reduced scales, hairy

or feathery calyx lobes. Example: Tridax,

Helianthus.

c) Caryopsis: It is a one seeded fruit

which develops from a monocarpellary,

superior ovary. Pericarp is inseparably

fused with seed. Example: Oryza, Triticum.

d) Nut: They develop from

mulicarpellary, syncarpous, superior

ovary with hard, woody or bony pericap.

It is a one seeded fruit. Example: Quercus,

Anacardium.

e) Samara: A dry indehiscent, one

seeded fruit in which the pericarp devlops

into thin winged structure around the

fruit. Example: Acer, Pterocarpus.

f) Utricle: They develops from

bicarpellary, unilocular, syncarpus,

superior ovary with pericarp loosely

enclosing the seeds. Example:

Chenopodium.

3) Schizocarpic Fruit

This fruit type is intermediate between

dehiscent and indehiscent fruit. The fruit

instead of dehiscing rather splits into

number of segments, each containing

one or more seeds. They are of following

types.

a) Cremocarp: Fruit develops from

bicarpellary, syncarpous, inferior ovary

and splitting into two one seeded segments

known as mericarps. Example: Coriander,

Carrot.

b) Carcerulus: Fruit develops from

bicarpellary, syncarpous, superior

ovary and splitting into four one seeded

Cremocarp (Coriander)

Lomentum (Mimosa)

segments known as nutlets. Example:

Leucas, Ocimum, Abutilon

c) Lomentum: The fruit is derived

from monocarpellary, unilocular ovary.

A leguminous fruit, constricted between

the seeds to form a number of one seeded

compartments that separate at maturity.

Example: Desmodium, Mimosa

d) Regma: They develop from

tricarpellary, syncarpous, superior,

trilocular ovary and splits into oneseeded

cocci which remain attached to

carpophore. Example: Ricinus, Geranium

Aggregate Fruits

Carcerulus (Abutilon)

Regma (Castor)

Figure 4.43: Schizocarpic Fruit

Aggregate fruits develop from a single

flower having an apocarpous pistil. each

of the free carpel is develops into a simple

fruitlet. A collection of simple fruitlets

makes an aggregate fruit. An individual

ovary develops into a drupe, achene,

follicle or berry. An aggregate of these

fruits borne by a single flower is known as

153

---

an etaerio. Example: Magnolia, Raspberry,

Annona, Polyalthia

Annona

Polyalthia

Figure 4.44: Aggregate Fruits

Multiple or Composite Fruit

A Multiple or composite fruit develops

from the whole inflorescence along with

its peduncle on which they are borne.

a) Sorosis: A fleshy multiple fruit which

develops from a spike or spadix. The

flowers fused together by their succulent

perianth and at the same time the axis

bearing them become fleshy or juicy and

the whole inflorescence forms a compact

mass. Example: Pineapple, Jack fruit,

Mulberry

b) Syconus: A multiple fruit which develops

from hypanthodium inflorescence. The

receptacle develops further and converts

into fleshy fruit which encloses a number

of true fruit or achenes which develops

from female flower of hypanthodium

inflorescence. Example: Ficus

Sorosis (Jack fruit)

Syconus (Ficus)

Figure 4.45: Multiple or composite fruit

• Lodoicea maldivica

is the world's largest

fruit. The size of

mature fruit is

40–50 cm in diameter and weights

15–30 kg.

• Progesterone which supports

pregnancy is obtained naturally

from a fruit of Balanites aegyptiaca

and Trigonella foenum - graecum.

4.7.3 Functions of Fruit

1. Edible part of the fruit is a source of

food, energy for animals.

2. They are source of many chemicals like

sugar, pectin, organic acids, vitamins

and minerals.

3. The fruit protects the seeds from

unfavourable climatic conditions and

animals.

4. Both fleshy and dry fruits help in the

dispersal of seeds to distant places.

5. In certain cases, fruit may provide

nutrition to the developing seedling.

6. Fruits provide source of medicine to

humans.

• Lupinus arcticus

(legume family) of

Artic Tundra is the

oldest viable seed

remained dormant for 10,000 years.

• Pheonix dactylifera (date palm) of

king Herod's palace near dead sea

has viable seed for 20,000 years.

• Powdered seeds of Moringa

oleifera is used to purify water.

154

---

Fruits

Simple

Aggregate

Multiple

Etaerio of follicle (Calotropis)

Etaerio of achena (Clematis)

Etaerio of drupe (Raspberry)

Etaerio of berries (Polyalthia)

Sorosis (Jack fruit)

Syconus (Ficus)

Fleshy fruit

a. Berry (Tomato)

b. Drupe (Mango)

c. Pepo (Cucumber)

d. Hesperidium (Orange)

e. Pome (Apple)

f. Balausta (Pomogranate)

Dry

dehiscent

Dry fruit

Indehiscent

(Achenial)

Schizocarpic

(Splitting)

a. Follicle (Calotropis)

b. Legume (Pisum)

c. Siliqua (Brassica)

d. Silicula (Capsella)

e. Capsule

i. Septicidal (Linum)

ii. Loculicidal (Lady’s finger)

iii. Septifragal (Datura)

iv. Poricidal (Papaver)

v. Denticidal (Primula)

vi. Circumscissile (Anagallis)

a. Achene (Clematis)

b. Cypsela (Tridax)

c. Caryopsis (Oryza)

d. Nut (Anacardium)

e. Samara (Acer)

f. Utricle (Chenopodium)

a. Cremocarp

(Coriander)

b. Carcerulus

(Abutilon)

c. Lomentum

(Mimosa)

d. Regma (Castor)

Figure 4.46: Types of fruits

155

---

Edible Parts of Fruit

Type of Fruit Common Name Botanical Name Edible Part

Berry Tomato Lycopersicon Whole fruit

esculentum

Brinjal

Solanum

Tender fruit

melongena

Guava Psidium guajava Whole fruit

Date Phoenix dactylifera Pericarp

Drupe Mango Mangifera indica Mesocarp

Coconut Cocos nucifera Endosperm (both cellular

and liquid)

Pepo Cucumber Cucumis sativus Whole fruit

Hesperidium Citrus (Orange, Citrus sinensis Juicy hairs on the endocarp

Lemon)

Pome Apple Pyrus malus Thalamus (false fruit) and a

part of pericarp

Balausta Pomegranate Punica granatum Succulent testa of the seeds

Legume Pea Pisum sativum Seed

Siliqua Mustard Brassica campestris Seed

var.

Poricidal Poppy

Papaver

Seeds

capsule

somniferum

Loculicidal Lady’s finger Abelmoschus Tender fruit

capsule

esculentus

Cypsela Sunflower Helianthus annuus Seed (for oil)

Caryopsis Maize Zea maize Seed

Paddy Oryza sativa Seed

Nut Cashew nut Anacardium

occidentale

Pedicel (false fruit) and

cotyledons (true fruit)

Cremocarp Coriander Coriandrum Mericarps

sativum

Lomentum Touch-me-not Mimosa pudica Seed

Aggregate fruit Custard apple Annona squamosa Pericarps

Composite

fruits

Sorosis Jack fruit Artocarpus Perianth, seeds

heterophyllus

Pine apple Ananas comosus Perianth, rachis

Mulberry Morus alba Whole fruit

Syconus Fig Ficus carica Whole inflorescence

156

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4.8 Seed

Do all fruits contain seeds? No, triploid

fruits do not. The seed is a fertilized

mature ovule which possess an embryonic

plant, usually stores food material and

has a protective coat. After fertilization,

changes occur in various parts of the ovule

and transforms into a seed.

4.8.1 Types of Seed

Do seeds germinate as soon as they are

dispersed

I. Based on the number of cotyledons

present two types of seeds are recognized.

i. Dicotyledonous seed: Seed with

two cotyledons.

ii. Monocotyledonous seed: Seed with

one cotyledon.

II. Based on the presence or absence

of the endosperm the seed is of two types.

i. Albuminous or Endospermous

seed: The cotyledons are thin,

membranous and mature seeds have

endosperm persistent and nourishes the

seedling during its early development.

Example: Castor, sunflower, maize.

ii. Ex-albuminous or nonendospermous

seed: Food is utilized by

the developing embryo and so the mature

seeds are without endosperm. In such

seeds, colyledons store food and become

thick and fleshy. Example: Pea, Groundnut.

4.8.2 Significance of Seeds:

v The seed encloses and protects the

embryo for next generation.

v It contains food for the development of

embryo.

v It is a means for the dispersal of new

individuals of the species.

v A seed is a means for perpetuation of

the species. It may lie dormant during

unfavorable conditions but germinates

on getting suitable conditions.

v Seeds of various plants are used as

food, both for animals and men.

v They are the basis of agriculture.

v Seeds are the products of sexual

reproduction so they provide genetic

variations and recombination in a plant.

Activity

Prepare a diet chart to provide

balanced diet to an adolescent

(a school going child) which includes

food items (fruits, vegetable and

seeds) which are non - expensive and

are commonly available.

Summary

Inflorescence is a group of flowers present

on a common stalk. Inflorescence may be

classified into 3 types based on position.

Inflorescence classified into racemose,

cymose, mixed and special type based on

the flower arrangement and branching of

axis. Flower is a modified shoot and meant

for sexual reproduction. Flower has various

parts to enhance reproduction. Flower

can be explained by its sex, symmetry and

arrangement of whorls, merosity. Calyx is

outermost whorl of flower and many types.

Corolla is second whorl of flower and used

for pollination. Corolla may be united or

free and has various forms in different

flowers. Aestivation is arrangement of

sepals, petals in bud condition and is of

many types. Androecium is the male part

of flower and made up of stamens. Stamens

contain filament,anther and connective.

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Gynoecium is female part of flower.

Ovary, style and stigma are parts of pistil.

According to number of carpels it is divided

into monocarpellary, bicarpellary etc. It

may be apocarpous or syncarpous. Locule

number may be one to many. The ovary

is superior or inferior or semi inferior.

Mode of distribution of placenta inside

the ovary is placentation. Construction

of floral diagram and floral formula for

given flower with some examples.

Fruits are the products of pollination

and fertilization. Fruit developed from

single ovary of flower is called simple

fruit. Simple fruits are two types based on

the fruit wall as simple fleshy and simple

dry. An intermediate between dehiscent

and indehiscent fruit is called schizocarpic

fruit. The simple fruits could be fleshy

or dry which could again be dehiscent

or indehiscent. Fruits that are developed

from multicarpellary, apocarpus pistil is

called aggregate. Multiple or composite

fruit develops from the flowers of the

complete inflorescence. Seed is a ripened

ovule which contains the embryo or the

miniature of plant body. Seeds with one

cotyledon are monocotyledonous and

with two cotyledons are dicotyledonous.

Evalution

1. Vexillary

aestivation is

characteristic of the

family

a. Fabaceae

b. Asteraceae

c. Solanaceae d. Brassicaceae

2. Gynoecium with united carples is

termed as

a. Apocarpous b. Multicarpellary

c. Syncarpous d. None of the above

3. Aggregate fruit develops from

a. Multicarpellary, apocarpous ovary

b. Multicarpellary, syncarpous ovary

c. Multicarpellary ovary

d. Whole inflorescence

4. In an inflorescence where flowers

are borne laterally in an acropetal

succession the position of the youngest

floral bud shall be

a. Proximal b. Distal

c. Intercalary d. Anywhere

5. A true fruit is the one where

a. Only ovary of the flower develops

into fruit

b. Ovary and calyx of the flower

develops into fruit

c. Overy, calyx and thalamus of the

flower develops into fruit

d. All floral whorls of the flower

develops into fruit

6. Find out the floral formula for a

bisexual flower with bract, regular,

pentamerous, distinct calyx and

corolla, superior ovary without

bracteole.

7. Give the technical terms for the

following: -

a. A sterile stamen

b. Stamens are united in one bunch

c. Stamens are attached to the petals

8. Explain the different types of

placentation with example.

9. Differenciate between aggregate fruit

with multiple fruit.

10. Explain the different types of fleshy

fruit with suitable example.

158

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ICT Corner

Floral diagram and floral formula

Let’s generate

Floral diagram and

Floral formula.

Steps

• Scan the QR code

• Enter sepal, petal, androecium & Gynoecium

• Select enable colour

• Select shape of sepal & petal, fused (if so)

• Enter carpel number & position submit the from

• Click formula to generate floral formula

Activity

• Make floral diagram and formula of various flower by changing numbers and

positions of floral parts.

• You can edit the floral diagram using Inkscape, which is denoted in help tap.

Step 1 Step 2

Step 3

URL:

http://kvetnidiagram.8u.cz/index_en.php

* Pictures are indicative only

159

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Chapter

5

Taxonomy and

Systematic Botany

Learning Objectives

The learner will be able to,

• Differentiate systematic botany

from taxonomy.

• Explain the ICN principles and to

discuss the codes of nomenclature.

• Compare the national and

international herbaria.

• Appreciate the role of morphology,

anatomy, cytology, DNA sequencing

in relation to Taxonomy,

• Describe diagnostic features of

families Fabaceae, Apocynaceae,

Solanaceae, Euphorbiaceae, Musaceae

and Liliaceae.

Chapter Outline

5.1 Taxonomy and Systematics

5.2 Taxonomic Hierarchy

5.3 Concept of species – Morphological,

Biological and Phylogenetic

5.4 International Code of

Botanical Nomenclature

5.5 Type concept

5.6 Taxonomic Aids

5.7 Botanical Gardens

5.8 Herbarium – Preparation and uses

5.9 Classification of Plants

5.10 Types of classification

5.11 Modern trends

in taxonomy

5.12 Cladistics

5.13 Selected Families

of Angiosperms

Plants are the prime companions of

human beings in this universe. Plants

are the source of food, energy, shelter,

clothing, drugs, beverages, oxygen and

the aesthetic environment. Taxonomic

activity of human is not restricted to

living organisms alone. Human beings

learn to identify, describe, name and

classify food, clothes, books, games,

vehicles and other objects that they come

across in their life. Every human being

thus is a taxonomist from the cradle to

the grave.

Taxonomy has witnessed various

phases in its early history to the present day

modernization. The need for knowledge

on plants had been realized since human

existence, a man started utilizing plants

for food, shelter and as curative agent for

ailments.

Theophrastus (372 – 287 BC), the

Greek Philosopher known as “Father of

Botany”. He named and described some 500

plants in his “De Historia Plantarum”. Later

Dioscorides (62 – 127 AD), Greek physician,

described and illustrated in his famous

“Materia medica” and described about 600

medicinal plants. From 16 th century onwards

Europe has witnessed a major developments

in the field of Taxonomy. Some of the key

contributors include Andrea Caesalpino, John

Ray, Tournefort, Jean Bauhin and Gaspard

Bauhin. Linnaeus ‘Species Plantarum' (1753)

160

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laid strong foundation for the binomial

nomenclature.

Taxonomy is no more classical

morphology based discipline but

become a dynamic and transdisciplinary

subject, making use of many branches of

botany such as Cell Biology, Physiology,

Biochemistry, Ecology, Pharmacology

and also Modern Biotechnology,

Molecular Biology and Bioinformatics. It

helps to understand biodiversity, wildlife,

forest management of natural resources

for sustainable use of plants and eco

restoration.

5.1 Taxonomy and Systematics

The word taxonomy is derived from Greek

words “taxis” (arrangement) and “nomos”

(rules or laws). Davis and Heywood (1963)

defined taxonomy as “the science dealing

with the study of classification including

the bases, principles, rules and procedures”.

Though there were earlier usages of

the term ‘systematics’, only during the

latter half of 20 th century ‘Systematics’

was recognized as a formal field of study.

Simpson (1961) defined systematics as

“Scientific study of the kinds and diversity

Differences between Taxonomy and Systematics

Taxonomy

• Discipline of classifying organisms into

taxa.

• Governs the practices of naming,

describing, identifying and specimen

preservation.

• Classification + Nomenclature =

Taxonomy

of organisms and all relationships among

them”. Though there are two terms are

used in an interchangeable way, they differ

from each other.

5.2 Taxonomic Hierarchy

Taxonomic hierarchy was introduced by

Carolus Linnaeus. It is the arrangement

of various taxonomic levels in descending

order starting from kingdom up to

species.

Species is the lowest of classification

and shows the high level of similarities

among the organisms. For example,

Helianthus annuus and Helianthus

Systematics

• Broad field of biology that studies the

diversification of species.

• Governs the evolutionary history and

phylogenetic relationship in addition to

taxonomy.

• Taxonomy + Phylogeny = Systematics

tuberosus. These two species differ in their

morphology. Both of them are herbs but

Helianthus tuberosus is a perennial herb.

Genus consist of multiple species

which have similar characters but differ

from the species of another genus.

Example: Helianthus, Tridax.

Family comprises a number of genera

which share some similarities among

them. Example: Asteraceae.

Order includes group of families

which show less similarities among them.

Class consists of group of orders which

share few similarities.

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Division is the next level of classification

that consists of number of classes.

Example: Magnoliophyta.

Kingdom is the highest level or rank

of the classification. Example: Plantae

Rank Ending Example

Kingdom - Plantae

Phylum = Division -phyta Magnoliophyta

Subphylum = Sub division -phytina Magnoliophytina

Class -opsida Asteropsida

Sub class -idea Asteridea

Order -ales Asterales

Suborder -ineae Asterineae

Family -aceae Asteraceae

Sub family -oideae Asteroideae

Tribe -eae Heliantheae

Genus - Helianthus

Sub genus - Helianthus subg. Helianthus

Series - Helianthus ser. Helianthus

Species - Helianthus annuus

5.3 Concept of species-Morphological,

Biological and Phylogenetic

Species is the fundamental unit of taxonomic

classification. Greek philosopher Plato

proposed concept of “eidos” or species and

believed that all objects are shadows of the

“eidos”. According to Stebbins (1977) species

is the basic unit of evolutionary process.

Species is a group of individual organisms

which have the following characters.

1. A population of organisms which

closely resemble each other more than

the other population.

2. They descend from a common

ancestor.

3. In sexually reproducing organisms,

they interbreed freely in nature,

producing fertile offspring.

4. In asexually reproducing organisms,

they are identified by their

morphological resemblance.

5. In case of fossil organisms, they are

identified by the morphological and

anatomical resemblance.

Species concepts can be classified into

two general groups. Concept emphasizing

process of evolution that maintains the

species as a unit and that can result in

evolutionary divergence and speciation.

162

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Another concept emphasises the product

of evolution in defining a species.

Types of Species

There are different types of species and

they are as follows:

1. Process of evolution - Biological Species

2. Product of evolution - Morphological

Species and Phylogenetic Species

Morphological Species (Taxonomic

species)

When the individuals are similar to one

another in one or more features and

different from other such groups, they

are called morphological species. These

species are defined and categorized with

no knowledge of phylogenetic history, gene

flow or detailed reproductive mechanisms.

Biological Species (Isolation Species)

According to Ernest Mayr 1963,“ these

are groups of populations that interbreed

and are reproductively isolated from other

such groups in nature”.

Phylogenetic Species

This concept was developed by Meglitsch

(1954), Simpson (1961) and Wiley (1978).

Wiley defined phylogenetic species as “an

evolutionary species is a single lineage of

ancestor descendent populations which

maintains its identity from other such

lineages which has its own evolutionary

tendencies and historical fate”.

5.4 International Code of Botanical

Nomenclature

Assigning name for a plant is known as

Nomenclature. This is based on the rules

and recommendations of the International

Code of Botanical Nomenclature. ICBN

deals with the names of existing (living)

and extinct (fossil) organisms. The

elementary rule of naming of plants

was first proposed by Linnaeus in 1737

and 1751 in his Philosophia Botanica.

In 1813 a detailed set of rules regarding

plant nomenclature was given by A.P. de

Candolle in his famous work “Theorie

elementaire de la botanique”. Then the

present ICBN was evolved by following the

same rules of Linnaeus, A.P. de Candolle

and his son Alphonse de Candolle.

ICBN due to specific reasons and in

order to separate plant kingdom from

other organisms, is redesignated as

ICN. The International Botanical

Congress held in Melbourne in July

2011 brought this change. The ICN

stands for International Code of

Nomenclature for Algae, Fungi and

Plants.

ICN Principles

International Code of Nomenclature is

based on the following six principles.

1. Botanical nomenclature is independent

of zoological and bacteriological

nomenclature.

2. Application of names of taxonomic

group is determined by means of

nomenclatural types.

3. Nomenclature of a taxonomic group is

based on priority of publication.

4. Each taxonomic group with a particular

circumscription, position and rank

can bear only one correct name, the

earliest that is in accordance with the

rules except in specified cases.

163

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5. Scientific names of taxonomic groups

are treated as Latin regardless of their

derivation.

6. The rules of nomenclature are

retroactive unless expressly limited.

Codes of Nomenclature

ICN has formulated a set of rules and

recommendations dealing with the

botanical name of plants. International

Botanical Congress is held at different

places every six years. Proposals for

nomenclatural changes and changes in

rules are discussed and implemented.

Changes are published in their website.

18 th International Botanical Congress

held in 2011at Melbourne, Australia made

the following major changes.

1. The code now permits electronic

publication of names of new taxa.

2. Latin diagnosis or description is not

mandatory and permits the use of

English or Latin for the publication of a

new name (Art-39).

3. “One fungus, one name” and “one fossil

one name” are important changes, the

concept of anamorph and telomorph

(for fungi) and morphotaxa (for fossils)

have been eliminated. (Previously,

sexual and asexual stages of the fungus/

fossils were provided with different

names).

Anamorph – Asexual reproductive

stage of fungus.

Telomorph – Sexual reproductive

stage of fungus.

4. As an experiment with “registration

of names” new fungal descriptions

require the use of an identifier from

a “recognized repository”. There are

two recognized repositories Index

fungorum and Myco Bank.

19 th International Botanical Congress

was held in Shenzhen in China in 2017.

Changes accepted by International

Botanical Congress are yet to be published.

Vernacular names (Common names)

Vernacular names are known as common

names. They are very often descriptive

and poetic references to plants. Common

name refer to more than one plant or many

plants may have same common name.

These names are regional or local and are

not universal. Example: Albizia amara . L

belongs to Mimosaceae is called as Usilai

in South Tamilnadu and Thurinji in North

Tamilnadu.

Activity

Write common name and scientific

name of 10 different plants around

your home.

Scientific Names / Botanical Names

Each and every taxon as per the ICN

(species, genus, family etc) can have only

one correct scientific name. Scientific

name of a species is always a binomial.

These names are universally applied.

Example: Oryza sativa L. is the scientific

name of paddy.

Polynomial

Polynomial is a descriptive phrase of a

plant. Example: Ranunculus calycibus

retroflexis pedunculis falcatis caule

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erecto folius compositis. It means butter

cup with reflexed sepals, curved flower

stalks, erect stem and compound leaves.

Polynomial system did not hold good

as it was cumbersome to remember and

use. Polynomial system of naming a

plant is replaced by a binomial system by

Linnaeus.

Binomial

Binomial nomenclature was first

introduced by Gaspard Bauhin and it

was implemented by Carolus Linnaeus.

Scientific name of a species consists of

two words and according to binomial

nomenclature, the first one is called

genus name and second one is specific

epithet. Example: Mangifera indica.

Mangifera is a genus name and indica is

specific epithet. This system is in vogue

even now.

Author citation

This refers to valid name of the taxa

accompanied by the author’s name who

published the name validly. Example:

Solanum nigrum L. There are two types of

author citation.

Single author: When a single author

proposed a valid name, the name

of the author alone is accompanied

by his abbreviated name. Example:

Pithecellobium cinereum Benth.

Multiple authors: When two or more

authors are associated with a valid

publication of name, their names should be

noted with the help of Latin word et or &.

Example: Delphinium viscosum Hook. f. et

Thomson.

Standard form of author’s abbreviations

has to be followed.

Author

Standard form of

Abbreviation

Linnaeus L.

G.Bentham

Benth.

William Hooker

Hook.

Robert Brown

R.Br.

J.P.Lamarck

Lamk.

A.P.de Candolle

DC.

Wallich

Wall.

Alphonse de Candolle A. DC.

5.5 Type concept

ICN’s second principle states that a

specimen must be associated with the

scientific name known as nomenclatural

type. A nomenclatural type is either

a specimen or may be an illustration.

Example: Herbarium sheet for vascular

plants.

There are different nomenclatural types.

Holotype: A specimen or illustration

originally cited by the author in

protologue. It is a definitive reference

source for identity. Citation of holotype

and submission of it is one of the criteria

for valid publication of a botanical name.

Isotype: Duplicate specimen of the

holotype collected from same population by

same person on same date with same field

number. They are the reliable duplicates of

holotype and may be distributed to various

herbaria of various regions.

Lectotype: Specimen selected from

original material serves as a type, when

no holotype was designated at the time of

publications or if holotype is missing or

destroyed.

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Syntype: When more than one specimen

cited by the author in the protologue

without designating holotype.

Neotype: Specimen derived from nonoriginal

collection selected as the type,

when original specimen is missing or

destroyed.

Paratype: Specimen cited in the protologue

is other than holotype, isotype or syntype.

Epitype: Specimen or illustration serves

as an interpretive type, when holotype,

neotype or lectotype is ambiguous.

5.6 Taxonomic Aids

Taxonomic aids are the tools for the

taxonomic study. Some techniques,

procedures and stored information

that are useful in identification and

classification of organisms are called

taxonomical aids. They are required

in almost all branches of biological

studies for their proper identification

and for finding their relationship with

others. Some of the taxonomical aids

are keys, flora, revisions, monograph,

catalogues, herbarium, botanical

gardens etc.

1. Keys

Taxonomic keys are the tools for the

identification of unfamiliar plants. These

keys are based on characters which are

stable and reliable. The most common type

of key is a dichotomous key. It consists of a

sequence of two contrasting statements. A

pair of contrasting statements is known as

couplet. Each statement is known as lead.

The plant is correctly identified with keys

by narrowing down the characters found

in plant.

Example:

1. a) Flowers cream-coloured; fruiting calyx

enclosing the berry ......Physalis

b) Flowers white or violet; fruiting calyx

not enclosing the berry ....2

2. a) Corolla rotate;

fruit a berry

.....Solanum

b) Corolla funnel-form or salver-form;

fruit a capsule: ....3

3. a) Radical leaves present; flowers in

racemes; fruits without prickles

...Nicotiana

b) Radical leaves

absent; flowers solitary; fruits with

prickles.....Datura

Another type of key for identification

is the Polyclave or Multi-entry key. It

consists of a list of numerous character

states. The user selects all states that

match the specimen. Polyclave keys are

implemented by a computer algorithm.

2. Flora

Flora is the document of all plant species in

a given geographic area. Flora consists of

total number of plant species in an area and

gives information about flowering season,

fruiting season and distribution for the given

geographic area. It also provides details

on rare and endemic species of that area.

Example: Flora of Tamil Nadu Carnatic by

K.M.Matthew. Floras are categorized based

on the scope and area covered.

Local Flora

It covers the limited areas, usually

state, country, city or mountain range.

Example: ‘Flora of Thiruvannamalai

District’ by R. Vijaysankar, K. Ravikumar

and P. Ravichandran.

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Regional Flora

It includes large geographical area or

a botanical region. Example: ‘Flora of

Tamil Nadu’ Carnatic by K.M.Matthew

(1983), ‘Flora of Madras Presidency’ by

J.S. Gamble and Fischer.

Continental Flora

This flora covers the entire continent.

Example: ‘Flora of Europaea’ by D.A.Web.

Electronic Floras (e - floras)

It is nothing but the digitized form of a

flora published online. Example: ‘e – Flora

China’. This provides the information and

also functions as an identification tool.

3. Monograph

A Monograph is a complete global account

of a taxon of any rank – family, genus or

species at a given time. This includes the

existing taxonomic knowledge and all

relevant information about the group

concerned such as Anatomy, Biochemistry,

Palynology, Chromosome Number and

Phylogeny. It also includes extensive

literature review, all nomenclatural

information, identification key to all

taxa, citation of specimens examined and

distribution map.

Example: The Family Lentibulariaceae by

Peter Tylor.

Revisions

Taxonomic revision is carried out for

a family or genus. Usually taxonomic

revision is less comprehensive than a

monograph for a given geographical area.

Revisions normally incorporate keys

to identify the taxa, short descriptions,

often confined to diagnostic characters,

distribution maps and a classification.

Illustrations mostly in the form of line

drawings are included both in monographs

and revisions. There are difficulties in

identifying various members within a taxon.

If there is inconsistency of the characters

within the taxon’s geographic range then a

revision is needed. Taxonomic revisions are

primarily based on original research work.

Example: Malvaceae of India by T.K.Paul,

Venu. P. 2006 Strobilanthes (Acanthaceae)

in Peninsular India.

Catalogues

Catalogues are the books of libraries rich

in botanical titles. They have special value

in taxonomic studies. To refer a catalogue,

one should know full name of the author,

exact title of the book, exact date of

publication the particulars of edition.

Example: Catalogue of the Library of British

Museum (of Natural History) Catalogue

of the Library of the Massachusetts

Horticultural Society.

5.7 Botanical Gardens

In true sense all gardens are not botanical

gardens. Botanical gardens are centres

for collection of plants in their various

stages of living. Gardens existed for

growing ornamental plants for aesthetic

value, religious and status reasons. The

famous “hanging gardens” of Babylon

in Mesopotamia is an example. For the

purpose of science and education the first

garden was maintained by Theophrastus

in his public lecture hall at Athens.

First modern botanical garden was

established by Luca Ghini (1490-1556) a

professor of Botany at Pisa, Italy in 1544.

167

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National Botanical Gardens

National

Botanical garden

Lucknow

AJCB

Indian

Botanical garden

Kolkata

Established in

1948

Arboretum-

500 species of trees

Established in

1786 by

Lt. Col. Robert Kyd

500 species

of Rose hybrids

JNTBGRI

Trivandrum

Kerala

Established in

1979

Conserving

tropical plant:

Genetic resources

4,000 species

The National

Orchidarium

Yercaud

Established in

1963

Maintained by

Southern circle

of BSI

3,000 trees and

1,800 shrubs

Largest and

oldest

15,000

species of

plants

Major attractiongerm

plasm

collection &

ex-situ

conservation

plants &

300 species of

plants

Major Attraction-

Insectivorous plants

Major Attraction-

The Great

Banyan Tree

Major attraction-

Bambusetum

(69 species)

Figure 5.1: National Botanical Garden

168

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Botanical garden contains special plant

collections such as cacti, succulent, green

house, shade house, tropical, alpine and

exotic plants. Worldwide there are about

1800 botanical gardens and arboreta.

Role of Botanical Garden: Botanical

Gardens play the following important roles.

1. Gardens with aesthetic value which

attract a large number of visitors. For

example, the Great Banyan Tree (Ficus

benghalensis) in the Indian Botanical

Garden at Kolkata.

2. Gardens have a wide range of species

and supply taxonomic material for

botanical research.

3. Garden is used for self-instruction or

demonstration purposes.

4. It can integrate information of diverse

fields like Anatomy, Embryology,

Phytochemistry, Cytology, Physiology

and Ecology.

5. Act as a conservation centre for diversity,

rare and endangered species.

6. It offers annual list of available species

and a free exchange of seeds.

7. Botanical garden gives information

about method of propagation, sale of

plant material to the general public.

Royal Botanic garden,

Kew- England

Royal Botanic garden Kew- England

is a non- departmental public body

in the United Kingdom. It is the

largest botanical garden in the world,

established in 1760, but officially opened

in the year 1841.

Figure 5.2: Royal Botanic garden,

Kew - England

Plant collections include Aquatic

garden, Arboretum with 14,000 trees,

Bonsai collection, Cacti collection,

Carnivorous plant collection.

5.8 Herbarium – Preparation and uses

Herbaria are store houses of preserved

plant collections. Plants are preserved in

the form of pressed and dried specimens

mounted on a sheet of paper. Herbaria act

as a centre for research and function as

sources of material for systematic work.

Preparation of herbarium Specimen

Herbarium Specimen is defined as a

pressed and dried plant sample that is

permanently glued or strapped to a sheet

of paper along with a documentation label.

Preparation of herbarium specimen

includes the following steps.

1. Plant collection: Field collection,

Liquid preserved collection, Living

collection, Collection for molecular

studies.

2. Documentation of field site data

3. Preparation of plant specimen

4. Mounting herbarium specimen

5. Herbarium labels.

6. Protection of herbarium sheets against

mold and insects

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Preparation of herbarium Specimen

Plant Collection

Plant specimen with flower or fruit is collected

Documentation of field site data

Certain data are to be recorded at the

time of plant collection. It includes date,

time, country, state, city, specific locality

information, latitude, longitude, elevation

and land mark information. These data

will be typed onto a herbarium label.

Preparation of plant specimen

Plant specimen collected from the field

is pressed immediately with the help of

portable field plant press. plant specimen

is transferred to a standard plant press

(12” x 18”) which between two outer

12” x 18” frames and secured by two straps.

Mounting herbarium specimen

The standard size of herbarium sheet is used

for mounting the specimen (29cm x 41cm).

specimens are affixed to herbarium

sheet with standard white glue

or solution of Methyl cellulose.

Herbarium label

Herbarium label size is generally 4-5’’ wide

and 2-3’’tall. A typical label contains all information

like habit, habitat, vegetation type,

land mark information, latitude, longitude,

image document, collection number, date

of collection and name of the collector.

Protection of herbarium sheets against

mold and insects

Applycation of 2% Mercuric chloride,

Naphthalene, DDT, carbon disulphide. Fumigation

using formaldehyde. Presently deep

freezing(-20 o C) method is followed throughout

the world.

World’s smallest

water – lily Nymphaea

thermarum was saved

f r o m

extinction when it was

grown from seed at Kew

in 2009.

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International Herbarium

S.No Herbarium Year Established Acronym

Number of

specimens

1. Museum National d’Histoire

1635 P ,PC 10,000,000

Naturelle, Paris, France

2. New York Botanical Garden,

1891 NY 72,00,000

Bronx, New York, U.S.A

3. Komarov Botanical Institute,

1823 LE 71,60,000

St.Petersburg (Leningrad), Russia

4. Royal Botanic Gardens, Kew,

England, U.K

1841 K 70,00,000

National Herbarium

S.No Herbarium Year Established Acronym

Number of

specimens

1. Madras Herbarium

1955 MH 4,08,776

BSI campus, Coimbatore

2. Central National Herbarium

1795 CAL 2,00,000

West Bengal

3. Jawaharlal Nehru Tropical Botanical 1979 TBGT 30,500

Garden and Research Institute

Thiruvananthapuram, Kerala

4. Presidency College Herbarium,

Chennai.

1844 PCM 15,000

Uses of Herbarium

1. Herbarium provides resource material

for systematic research and studies.

2. It is a place for orderly arrangement of

voucher specimens.

3. Voucher specimen serves as a reference

for comparing doubtful newly collected

fresh specimens.

4. Voucher specimens play a role in studies

like floristic diversity, environmental

assessment, ecological mechanisms

and survey of unexplored areas.

5. Herbarium provides opportunity for

documenting biodiversity and studies

related to the field of ecology and

conservation biology.

Kew Herbarium

Kew Garden is situated in South West London

that houses the “largest and most diverse

botanical and mycological collections in

the world” founded in the year 1840. Living

collection includes more than 30,000 different

kinds of plants. While herbarium which is

one of the largest in the world has over seven

million preserved plant specimens. The library

contains more than 7,50,000 volumes and the

illustrations and also a collection of more than

1,75,000 prints, books, photographs, letters,

manuscripts, periodicals, maps and botanical

illustrations.

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International Botanic Garden

New York Botanic garden, USA.

Royal Botanic Garden, Kew - England.

Botanical Gardens of the New South

Wales, Sydney.

Rio- de jenerio Botanic Garden, Brazil.

Botanical Survey of India

On 13 February 1890, a survey was

formally constituted and designated

as the Botanical Survey of India. After

independence, the need was felt for a

more comprehensive documentation

of the country’s plant resources to

boost the economy. Padmashree

Dr.E.K.Janaki Ammal was appointed

as officer on special Duty on 14th Oct

1952. Then reorganization plan was

finally approved by the Govt. of India

on 29 March 1954, with Calcutta as

the headquarters of BSI. Jammu Tavi

Botanical Garden has been named

after Dr. E. K. Janaki Ammal.

Figure 5.3: Dr. E.K. Janaki Ammal

Activity

Prepare herbarium of 5 common

weed plants found inside your school

campus /nearby garden /waste land.

5.9 Classification of Plants

Imagine walking into a library and

looking for a Harry Potter story book.

As you walk into the library you notice

that it is under renovation and all the

books are scattered. Will it not be hard

to find the exact book you are looking

for? It might take hours. So you decide

to come the next day when all the books

are arranged according to the genres. One

rack for adventure, another for Detective,

Fantasy, Horror, Encyclopaedia and so

on. You automatically know Harry Potter

is in the fantasy section and it takes less

than ten minutes for you to find it. That

is because the books have been classified

and arranged according to a system.

Similarly there is a vast assemblage of

group of plants in the world. Is it possible

to study and understand all of these? No.

Since it is difficult to study all these plants

together, it is necessary to device some

means to make this possible.

Classification is essential to biology

because there is a vast diversity of organisms

to sort out and compare. Unless they are

organized into manageable categories

it will be difficult for identification.

Biological classifications are the inventions

of biologists based upon the best evidence

available. The scientific basis for

cataloguing and retrieving information

about the tremendous diversity of flora is

known as classification.

Classification paves way for the

arrangement of organisms into groups

on the basis of their similarities,

dissimilarities and relationships. The

purpose of classification is to provide a

systematic arrangement expressing the

relationship between the organisms.

172

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Taxonomists have assigned a method

of classifying organisms which are called

ranks. These taxonomical ranks are

hierarchical. The scheme of classification

has to be flexible, allowing newly

discovered living organisms to be added

where they fit best.

5.9.1 Need for Classification

• Understanding the classification of

organisms can gives an insight in to other

fields and has significant practical value.

• Classification helps us to know about

different taxa, their phylogenetic

relationship and exact position.

• It helps to train the students of plant

sciences with regard to the diversity of

organisms and their relationship with

other biological branches.

5.10 Types of classification

Taxonomic entities are classified in three

ways. They are artificial classification,

natural classification and phylogenetic

classification.

5.10.1 Artificial system of classification

Carolus Linnaeus (1707 -1778) was a great

Swedish Botanist and said to be the “Father

of Taxonomy.”

He outlined an

artificial system

of classification

in “Species

Plantarum” in

1753, wherein he

listed and described

7,300 species and

arranged in 24

classes mostly

on the basis of Figure 5.4:

number, union Carolus Linnaeus

24 classes recognized by Linnaeus in his

Species Plantarum (1753) on the basis of

stamens.

No Classes Characters

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

Monandria

Diandria

Triandria

Tetrandria

Pentandria

Hexandria

Heptandria

Octandria

Ennandria

Decandria

Dodecandria

Icosandria

Polyandria

Didynamia

Tetradynamia

Monadelphia

Diadelphia

Polyadelphia

Syngenesia

Gynandria

Monoecia

Dioecia

Polygamia

Cryptogamia

stamen one

stamens two

stamens three

stamens four

stamens five

stamens six

stamens seven

stamens eight

stamens nine

stamens ten

stamens 11-19

stamens 20 or more,

on the calyx

stamens 20 or more,

on the receptacle

stamens didynamous;

2 short, 2 long

stamens tetradynamous;

4 long, 2 short

stamens

monadelphous; united

in 1 group

stamens diadelphous;

united in 2 groups

stamens

polyadelphous; united

in 3 or more groups

stamens syngenesious;

united by anthers only

stamens united with

the gynoecium

plants monoecious

plants dioecious

plants polygamous

flowerless plants

173

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(adhesion and cohesion), length, and

distribution of stamens. The classes were

further subdivided on the basis of carpel

characteristics into orders. Hence the

system of classification is also known as

sexual system of classification.

This system of classification though

artificial, was continued for more than

100 years after the death of Linnaeus,

due to its simplicity and easy way of

identification of plants.

However the system could not hold

good due to the following reasons.

1. Totally unrelated plants were kept in

a single group, whereas closely related

plants were placed in widely separated

groups. Example:

a. Zingiberaceae of monocotyledons

and Anacardiaceae of dicotyledonous

were placed under the class

Monandria since these possess

single stamens.

b. Prunus was classified along with

Cactus because of the same number

of stamens.

No attempts were made to classify

plants based on either natural or

phylogenetic relationships which exist

among plant groups.

5.10.2 Natural system

Botanists who came after Linnaeus realised

that no single character is more important

than the other characters. Accordingly

an approach to a natural system of

classification sprouted in France. The first

scheme of classification based on overall

similarities was presented by Antoine

Laurent de Jessieu in 1789.

Bentham and Hooker system of

classification

Figure 5.5: George Bentham and

J.D. Hooker.

A widely followed natural system of

classification considered the best was

proposed by two English botanist

George Bentham (1800 - 1884) and

Joseph Dalton Hooker (1817–1911). The

classification was published in a three

volume work as “Genera Plantarum”

(1862–1883) describing 202 families

and 7569 genera and 97, 205 species.

In this system the seeded plants were

classified into 3 major classes such as

Dicotyledonae, Gymnospermae and

Monocotyledonae.

Class I Dicotyledonae: Plants contain

two cotyledons in their seed, leaves with

reticulate venation, tap root system and

tetramerous or pentamerous flowers come

under this class. It includes three subclasses

– Polypetalae, Gamopetalae and

Monochlamydeae.

Sub-class 1. Polypetalae: Plants with

free petals and dichlamydeous flowers

come under polypetalae. It is further

divided into three series – Thalamiflorae,

Disciflorae and Calyciflorae.

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Seed plants

Class I

Dicotyledonae

Class II

Gymnospermae

3 families

1. Gnetaceae

2. Coniferae

3. Cycadaceae

Class III

Monocotyledonae

7series and 34 families

Sub-class I

Polypetalae

Series (i) Thalamiflorae

6 orders and 34 families

Sub-class II

Gamopetalae

Series (i) Inferae

3 orders and 9 families

Sub-class III

Monochlamydeae

8 series and 36 families

Series (ii) Disciflorae

4orders and 23 families

Series (ii) Heteromerae

3 orders and 12 families

Series (iii) Calyciiflorae

5orders and 27 families

Series (iii) Bicarpellatae

4 orders and 24 families

Figure 5.6: Bentham and Hooker system of classification

Series (i) Thalamiflorae: Plants

having flowers with dome or conical

shaped thalamus and superior ovary are

included in this series. It includes 6 orders

and 34 families.

Series (ii) Disciflorae: Flowers having

prominent disc shaped thalamus with

superior ovary come under this series. It

includes 4 orders and 23 families.

Series (iii) Calyciflorae: It includes plants

having flowers with cup shaped thalamus

and with inferior or sometimes with half

inferior ovary. Calyciflorae includes 5 orders

and 27 families.

Sub-class 2. Gamopetalae: Plants with

united petals, which are either partially

or completely fused to one another

and dichlamydeous are placed under

Gamopetalae. It is further divided into

three series – Inferae, Heteromerae and

Bicarpellatae.

Series (i) Inferae: The flowers are

epigynous and with inferior ovary. Inferae

includes 3 orders and 9 families.

Series (ii) Heteromerae: The flowers

are hypogynous, superior ovary and with

more than two carpels. Heteromerae

includes 3 orders and 12 families.

Series (iii) Bicarpellatae: The flowers

are hypogynous, superior ovary and with

two carpels.Bicarpellatae includes 4 orders

and 24 families.

Sub-class 3. Monochlamydeae: Plants

with incomplete flowers either apetalous

175

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or with undifferenciated calyx and corolla

are placed under Monochlamydeae. The

sepals and petals are not distinguished and

they are called perianth. Sometimes both

the whorls are absent. Monochlamydeae

includes 8 series and 36 families.

Class II Gymnospermae: Plants that

contain naked seeds come under this class.

Gymnospermae includes three families –

Gnetaceae, Coniferae and Cycadaceae.

Class III Monocotyledonae: Plants

contain only one cotyledon in their seed,

leaves with parallel venation, fibrous root

system and trimerous flowers come under

this class. The Monocotyledonae has

7 series and 34 families.

The Bentham and Hooker system of

classification is still supposed to be the best

system of classification. It has been widely

practiced in colonial countries and herbaria

of those countries were organised based on

this system and is still used as a key for the

identification of plants in some herbaria of

the world due to the following reasons:

• Description of plants is quite accurate

and reliable, because it is mainly based on

personal studies from actual specimens

and not mere comparisons of known

facts.

• As it is easy to follow, it is used as a key

for the identification of plants in several

herbaria of the world.

Though it is a natural system,

this system was not intended to be

phylogenetic.

5.10.3 Phylogenetic system of

classification

The publication of the Origin of Species

(1859) by Charles Darwin has given

stimulus for the emergence of phylogenetic

system of classification.

I Adolph Engler and Karl A Prantl

system of classification

One of the earliest phylogenetic system of

classification of the entire plant Kingdom

was jointly proposed by two German

botanists Adolph Engler ( 1844 -1930) and

Karl A Prantl (1849 - 1893). They published

their classification in a monumental work

“Die Naturelichen Pflanzen Familien” in

23 volumes (1887- 1915)

In this system of classification the plant

kingdom was divided into 13 divisions. The

Division: Embryophyta (Siphonogama)

Sub-division:Gymnospermae

Sub-division: Angiospermae

Class: Monocotyledonae

(includes 11 orders 45 families)

Class: Dicotyledonae

(includes 44 orders)

Archichlamydeae

(Apetalae)

(i) Corolla polypetalous

(ii) Perianth single or double

(iii) Includes 33 orders 201 families

176

Metachlamydeae

(Sympetalae)

(i) Corolla Gamopetalous

(ii) Perianth in two whorls

(iii) Includes 11 orders 57 families

Figure 5.7: Outline of Engler and Prantl classification

---

Figure 5.8: Adolph Engler and Karl A

Prantl

first 11 divisions are Thallophytes, twelfth

division is Embryophyta Asiphonogama

(plants with embryos but no pollen tubes;

Bryophytes and Pteridophytes) and the

thirteenth division is Embryophyta

Siphonogama (plants with embryos and

pollen tubes) which includes seed plants.

II Arthur Cronquist system of

classification

Arthur Cronquist (1919 - 1992) an eminent

American taxonomist proposed

phylogenetic classification of flowering

plants based on a wide range of taxonomic

characters including anatomical and

phytochemical characters of phylogenetic

importance. He has presented his

classification in 1968 in his book titled

“The evolution and classification of

flowering plants.” His classification

is broadly based on the Principles of

phylogeny that finds acceptance with

major contemporary authors.

Figure 5.9: Arthur Cronquist

Cronquist classified the angiosperms

into two main classes Magnoliopsida

(=dicotyledons) and Liliopsida

Hamamelidae (2)

Rosidae (5)

Magnoliidae

(1)

Asteridae (6)

Dilleniidae (4)

Caryophyllidae (3)

4. Zingiberidae

3. Commelinidae

2. Arecidae

Sub-class

5. Lilidae

Sub-class

1. Alismatidae

Class: Magnoliopsida

Class: Liliopsida

Figure 5.10: Diagramatic representation of the relationship between class

Magnoliopsida and Liliopsida.

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(= monocotyledons). There are

6 subclasses, 64 orders, 320 families and

about 165,000 species in Magnoliopsida,

whereas in Liliopsida there are 5 sub

classes, 19 orders, 66 families and about

50,000 species.

Cronquist system of classification

also could not persist for a long time

because, the system is not very useful

for identification and cannot be adopted

in herbaria due to its high phylogenetic

nature.

5.10.4 Angiosperm phylogeny group

(APG) classification

The most recent classification of

flowering plants based on phylogenetic

data was set in the last decade of

twentieth century. Four versions of

Angiosperm Phylogenetic Group

classification (APG I, APG II, APG III

& APG IV) have been published in 1998,

2003, 2009 and 2016 respectively. Each

version supplants the previous version.

Recognition of monophyletic group

based on the information received

from various disciplines such as gross

morphology, anatomy, embryology,

palynology, karyology, phytochemistry

and more strongly on molecular data

with respect to DNA sequences of two

chloroplast genes (atpB and rbcL) and

one nuclear gene (nuclear ribosomal

18s DNA).

The most recent updated version,

APG IV (2016) recognised 64 orders and

416families. Of these, 416 families 259 are

represented in India.

The outline of APG IV classification is

given below.

EUDICOTS EARLY

ANGIOSPERMS

MONOCOTS

Early

diverging

eudicots

Super

rosids

Super

asterids

Amborellales

Nymphaeales

Austrobaileyales

Magnoliids

Chloranthales

Monocots

Family: Musaceae

Liliaceae

Ceratophyllales

Ranunculales

Proteales

Torchodendrales

Buxales

Gunnerales

Dilleniales

Saxifragales

Rosids

Family: Fabaceae

Euphorbiaceae

Berberidopsidales

Santalales

Caryophyllales

Asterids

Family: Apocynaceae

Solanaceae

Figure 5.11: Simplified version of APG IV

( Source: Plant Gateway's The Global Flora,

Vol. I January 2018 )

Angiosperms are classified into three

clades early angiosperms, monocots

and eudicots. Early angiosperms

are classified into 8 orders and

26 families (ANA-grade + magnoliids

+ Chloranthales)

Amborellales

Nymphaeales

Austrobaileyales

➢ Seeds always with two cotyledons.

➢ Presence of ethereal oils.

➢ Leaves are always simple net-veined.

➢ Each floral whorls with many parts.

➢ Perianth usually spirally arranged

or parts in threes.

➢ Stamens with broad filaments.

➢ Anthers tetrasporangiate.

➢ Pollen monosulcate.

➢ Nectaries are rare.

➢ Carpels usually free and.

➢ Embryo very small.

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Monocots are classified into 11 orders

and 77 families (basal monocots + lilioids

+ commelinids)

➢ Seeds with single cotyledon.

➢ Primary root short-lived.

➢ Single adaxial prophyll.

➢ Ethereal oils rarely present.

➢ Mostly herbaceous, absence of

vascular cambium.

➢ Vascular bundles are scattered in the

stem.

➢ Leaf simple with parallel-veined.

➢ Floral parts usually in threes.

➢ Perianth often composed of tepals.

➢ Pollen monosulcate.

➢ Styles normally hollow and.

➢ Successive microsporogenesis.

Eudicots are divided into 45 orders and

313 families (early diverging eudicots +

super rosids + super asterids).

➢ Seeds with always two cotyledons.

➢ Nodes trilacunar with three leaf traces.

➢ Stomata anomocytic.

➢ Ethereal oils rarely present.

➢ Woody or herbaceous plants.

➢ Leaves simple or compound, usually

net-veined.

➢ Flower parts mostly in twos, fours

or fives.

➢ Microsporogenesis simultaneous.

➢ Style solid and .

➢ Pollen tricolpate.

APG system is an evolving system that

might undergo change periodically based on

the new sets of data from various disciplines

of Botany. It is the currently accepted

system across the world and followed by

all the leading taxonomic institutions and

practising taxonomists. However, it is

yet to percolate into the Indian botanical

curriculum.

Changes in earlier taxonomic understanding.

The newly proposed APG classification system has brought many changes in our earlier

understanding on the concept of primitive flowering plant families. Some of them are

given below:

• The real Ranalean families, especially the arborescent ones are no more the primitive

families. But as per APG classification system, Amborellaceae, Nymphaceae,

Austrobaileyaceae, Magnoliaceae and Chloranthaceae form the early angiosperms.

• Monocots are recognised as a monophyletic group and hence terminology is retained.

• Dicots are polyphyletic group and as a result the use of the term dicotyledons as a

group becomes outdated.

• Liliaceae (Sensu lato) is split into 14 families.

• Molluginaceae and Gisekiaceae are recognised separately from Aizoaceae.

• Euphorbiaceae (s.l.) is split in to Phyllanthaceae, Picrodendraceae and Putranjivaceae.

• Asclepiadaceae are merged with Apocynaceae (s.l.)

• Many genera that were conventionally treated under Verbenaceae such as Clerodendron,

Tectona and Vitex are transferred to Lamiaceae based on the modified circumscription

of these families.

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202 303

Families

386 462 457 413 416

Bentham and

Hooker 1883

Engler and

Prantl1915

Arthur Cronquist

1981

Classification reflects the state of our

knowledge at a given point of time. It will

continue to change as we acquire new

information.

A significant number

of major herbaria,

including Kew are

changing the order of

their collections in accordance with APG.

The influential world checklist

of selected plant families (also from

kew) is being updated to the APG III

system.

A recent photographic survey

of the plants of USA and Canada is

organized according to the APG III

system.

In UK, the latest edition of the

standard flora of the British Isles

written by Stace is based on the APG

III system.

5.11 Modern trends in taxonomy

Taxonomists now accept that, the

morphological characters alone should not

be considered in systematic classification

of plants. The complete knowledge of

APG I

1998

APG II

2003

taxonomy is possible with the principles of

various disciplines like Cytology, Genetics,

Anatomy, Physiology, Geographical

Distribution, Embryology, Ecology,

Palynology, Phenology, Bio-Chemistry,

Numerical Taxonomy and Transplant

Experiments. These have been found to be

useful in solving some of the taxonomical

problems by providing additional

characters. It has changed the face of

classification from alpha (classical) to omega

(modern kind). Thus the new systematic has

evolved into a better taxonomy.

5.11.1 Chemotaxonomy

APG III

2009

APG IV

2016

Figure 5.12: A timeline showing the history of classifying flowering plants into families.

( Source: Royal Botanic Gardens Kew State of World's Plant 2017 )

Various medicines, spices and preservatives

obtained from plant have drawn the

attention of Taxonomists. Study of

various chemicals available in plants help

to solve certain taxonomical problems.

Chemotaxonomy is the scientific approach

of classification of plants on the basis of their

biochemical constituents. As proteins are

more closely controlled by genes and less

subjected to natural selection, it has been

used at all hierarchical levels of classification

starting from the rank of ‘variety’ up to the

rank of division in plants. Proteins, amino

acids, nucleic acids, peptides etc. are the most

studied chemicals in chemotaxonomy.

The chemical characters can be divided

into three main categories.

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1. Easily visible characters like starch

grains, silica etc.

2. Characters detected by chemical tests

like phenolics, oil, fats, waxes etc.

3. Proteins

Aims of chemotaxonomy

1. To develop taxonomic characters

which may improve existing system

of plant classification.

2. To improve present day knowledge

of phylogeny of plants.

5.11.2 Biosystematics

Biosystematics is an “Experimental,

ecological and cytotaxonomy” through

which life forms are studied and their

relationships are defined. The term

biosystematics was introduced by Camp

and Gilly in 1943. Many authors feel

Biosystematics is closer to Cytogenetics

and Ecology and much importance given

not to classification but to evolution.

Aims of biosystematics

The aims of biosystematics are as follows:

1. To delimit the naturally occurring

biotic community of plant species.

2. To establish the evolution of a

group of taxa by understanding

the evolutionary and phylogenetic

trends.

3. To involve any type of data

gathering based on modern

concepts and not only on

morphology and anatomy.

4. To recognize the various groups as

separate biosystematic categories

such as ecotypes, ecospecies,

cenospecies and comparium.

5.11.3 Karyotaxonomy

Chromosomes are the carriers of genetic

information. Increased knowledge about

the chromosomes have been used for

extensive biosystematic studies and

resolving many taxonomic problems.

Utilization of the characters and

phenomena of cytology for the explanation

of taxonomic problem is known as

cytotaxonomy or karyotaxonomy. The

characters of chromosome such as number,

size, morphology and behaviour during

meiosis have proved to be of taxonomic

value.

5.11.4 Serotaxonomy (immunotaxonomy)

Systematic serology or serotaxonomy had

its origin towards the end of twentieth

century with the discovery of serological

reactions and development of the discipline

of immunology. The classification of very

similar plants by means of differences in the

proteins they contain, to solve taxonomic

problems is called serotaxonomy.

Smith (1976) defined it as “the study of

the origins and properties of antisera.”

Importance of serotaxonomy

It determines the degree of similarity

between species, genera, families etc. by

comparing the reactions of antigens from

various plant taxa with antibodies raised

against the antigen of a given taxon.

Example: 1. The assignment of

Phaseolus aureus and P. mungo to the genus

Vigna is strongly supported by serological

evidence by Chrispeels and Gartner.

5.11.5 Molecular taxonomy (molecular

systematics / molecular phylogenetics)

Molecular Taxonomy is the branch

of phylogeny that analyses hereditary

181

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molecular differences, mainly in DNA

sequences, to gain information and to

establish genetic relationship between the

members of different taxonomic categories.

The advent of DNA cloning and sequencing

methods have contributed immensely to the

development of molecular taxonomy and

population genetics over the years. These

modern methods have revolutionised the

field of molecular taxonomy and population

genetics with improved analytical power

and precision.

The results of a molecular

phylogenetic analysis are expressed in

Molecular Markers

Allozyme electrophoresis is a method which can identify genetic variation at the

level of enzymes that are directly encoded by DNA.

Mitochondrial DNA markers are non- nuclear DNA located within organelles in

the cytoplasm called mitochondria. The entire genome undergoes transcription as one

single unit. They are not subjected to recombination and thus they are homologous

markers.

Microsatellite is a simple DNA sequence which is repeated several times across

various points in the DNA of an organism. These (usually 2-5) repeats are highly

variable and these loci can be used as markers. (Example: TGTGTG, in which two

base pairs repeat, the region are termed tandem repeat.)

Single nucleotide polymorphisms arise due to single nucleotide substitutions

(transitions/transversions) or single nucleotide insertions/deletions. SNPs are the

most abundant polymorphisms in the genome (coding and non-coding) of any

organism. These single nucleotide variants can be detected using PCR, microchip

arrays or fluorescence technology.

DNA microarray or DNA chip consists of small glass microscope slides, silicon

chip or nylon membranes with many immobilized DNA fragments arranged in a

standard pattern. A DNA microarray can be utilized as a medium for matching a

reporter probe of known sequence against the DNA isolated from the target sample

which is of unknown origin. Species-specific DNA sequences could be incorporated

to a DNA microarray and this could be used for identification purposes.

Arbitrary markers are sometimes used to target a segment of DNA of unknown

function. The widely used methods of amplifying unknown regions are RAPD and

AFLP DNA.

Specific Nuclear DNA markers: Variable Number of Tandem Repeat is a segment

of DNA that is repeated tens or even hundreds to thousands of times in nuclear

genome. They repeat in tandem; vary in number in different loci and differently in

individuals. There are two main classes of repetitive and highly polymorphic DNA

viz. minisatellite DNA referring to genetic loci with repeats of length 9-65 bp and

microsatellite DNA with repeats of 2-8 bp (1-6) long. Microsatellites are much more

numerous in the genome of vertebrates than minisatellites.

182

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the form of a tree called phylogenetic

tree. Different molecular markers

like allozymes, mitochondrial DNA,

micro satellites, RFLP (Restriction

Fragment Length Polymorphism), RAPD

(Random amplified polymorphic DNA),

AFLPs (Amplified Fragment Length

Polymorphism), single nucleotide

polymorphism- SNP, microchips or arrays

are used in analysis.

Uses of molecular taxonomy

1. Molecular taxonomy helps in

establishing the relationship of

different plant groups at DNA level.

2. It unlocks the treasure chest of

information on evolutionary history of

organisms.

RFLP (Restriction Fragment Length

Polymorphism)

RFLPs is a molecular method of genetic

analysis that allows identification of taxa

based on unique patterns of restriction

sites in specific regions of DNA. It refers

to differences between taxa in restriction

sites and therefore the lengths of fragments

of DNA following cleavage with restriction

enzymes.

Amplified Fragment Length

Polymorphism (AFLP)

This method is similar to that of

identifying RFLPs in that a restriction

enzyme is used to cut DNA into

numerous smaller pieces, each of which

terminates in a characteristic nucleotide

sequence due to the action of restriction

enzymes.

AFLP is largely used for population

genetics studies, but has been used in

studies of closely related species and even

in some cases, for higher level cladistic

analysis.

Random Amplified Polymorphic DNA

(RAPD)

It is a method to identify genetic markers

using a randomly synthesized primer

that will anneal (recombine (DNA) in the

double stranded form) to complementary

regions located in various locations of

isolated DNA. If another complementary

site is present on the opposing DNA

strand at a distance that is not too great

(within the limits of PCR) then the

reaction will amplify this region of DNA.

RAPDs like microsatellites may often

be used for genetic studies within species

but may also be successfully employed

in phylogenetic studies to address

relationships within a species or between

closely related species. However RAPD

analysis has the major disadvantage that

results are difficult to replicate and in that

the homology of similar bands in different

taxa may be nuclear.

Significance of Molecular Taxonomy

1. It helps to identify a very large number

of species of plants and animals by the

use of conserved molecular sequences.

2. Using DNA data evolutionary patterns

of biodiversity are now investigated.

3. DNA taxonomy plays a vital role in

phytogeography, which ultimately

helps in genome mapping and

biodiversity conservation.

4. DNA- based molecular markers used

for designing DNA based molecular

probes, have also been developed under

the branch of molecular systematics.

5.11.6 DNA Barcoding

Have you seen how scanners are used in

supermarkets to distinguish the Universal

Product Code (UPC)? In the same way we

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can also distinguish one species from another.

DNA barcoding is a taxonomic method that

uses a very short genetic sequence from

a standard part of a genome. The genetic

sequence used to identify a plant is known

as “DNA tags” or “DNA barcodes”. Paul

Hebert in 2003 proposed ‘DNA barcoding’

and he is considered as ‘Father of barcoding’.

The gene region that is being used as

an effective barcode in plants is present

in two genes of the chloroplast, matK

and rbcL, and have been approved as the

barcode regions for plants.

Sequence of unknown species can be

matched from submitted sequence in

GenBank using Blast (web-programme for

searching the closely related sequence).

Significance of DNA barcoding

1. DNA barcoding greatly helps in

identification and classification of

organism.

2. It aids in mapping the extent of

biodiversity.

DNA barcoding techniques require a

large database of sequences for comparison

and prior knowledge of the barcoding region.

However, DNA barcoding is a helpful

tool to determine the authenticity of

botanical material in whole, cut or

powdered form.

List of conferences of International

Barcode was held

S.No. Year Place

1. 2005 London, United Kingdom

2. 2007 Taipei, Taiwan

3. 2009 Mexico City, Mexico

4. 2011 Adelaide, Australia

5. 2013 Yunnan, China

6. 2015 Guelph, Canada

7. 20-24

Nov' 2017

Skukuza, South Africa

5.11.7 Differences between classical and

modern taxonomy

Classical Taxonomy

It is called old

systematics or Alpha

(ἀ) taxonomy or

Taxonomy

It is pre Darwinean

Species is considered

as basic unit and is

static

Classification is

mainly based on

morphological

characters

This system is based

on the observation of

a few samples/

individuals

5.12 Cladistics

Modern Taxonomy

It is called

Neosystematics or

Biosystematics or

Omega (Ω) taxonomy

It is post Darwinean

species is considered

as dynamic entity and

ever changing

Classification is

based on morphological,

reproductive

characters and

phylogenetic (evolutionary)

relationship

of the organism

This system is based

on the observation of

large number of samples/individuals

Analysis of the taxonomic

data, and the types of

characters that are used in

classification have changed

from time to time. Plants

have been classified based

on the morphology before

the advancement of microscopes, which

help in the inclusions of sub microscopic

and microscopic features. A closer study

is necessary while classifying closely

related plants. Discovery of new finer

molecular analytical techniques coupled

with advanced software and computers

has ushered in a new era of modern or

phylogenetic classification.

The method of classifying organisms into

monophyletic group of a common ancestor

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based on shared apomorphic characters is

called cladistics (from Greek, klados-branch).

The outcome of a cladistic analysis is

a cladogram, a tree-shaped diagram that

represent the best hypothesis of phylogenetic

relationships. Earlier generated cladograms

were largely on the basis of morphological

characters, but now genetic sequencing data

and computational softwares are commonly

used in phylogenetic analysis.

Cladistic analysis

Cladistics is one of the primary methods of

constructing phylogenies, or evolutionary

histories. Cladistics uses shared, derived

characters to group organisms into clades.

These clades have atleast one shared, derived

character found in their most recent common

ancestor that is not found in other groups

hence they are considered more closely related

to each other. These shared characters can

be morphological such as, leaf, flower, fruit,

seed and so on; behavioural, like opening of

flowers nocturnal/diurnal; molecular like,

DNA or protein sequence and more.

Cladistics accept only monophyletic

groups. Paraphyletic and polyphyletic

taxa are occasionally considered when

such taxa conveniently treated as one

group for practical purposes. Example:

dicots, sterculiaceae. Polyphyletic groups

are rejected by cladistics.

i. Monophyletic group; Taxa

comprising all the descendants of a

common ancestor.

C A D B

ii. Paraphyletic group; Taxon that

includes an ancestor but not all of the

descendants of that ancestor.

A C B D

CB, CBD

and ACB are

paraphyletic

group

iii. Polyphyletic group; Taxa that

includes members from two different

lineages.

C A D B W X Z Y

Need for cladistics

1. Cladistics is now the most commonly

used and accepted method for

creating phylogenetic system of

classifications.

2. Cladistics produces a hypothesis about

the relationship of organisms to predict

the morphological characteristics of

organism.

3. Cladistics helps to elucidate mechanism

of evolution.

5.13 Selected Families of Angiosperms

Dicot Families

Plant kingdom is so vast and varied.

For the purpose of study, they have

been classified into Artificial, Natural,

Phylogenetic and APG system in

course of time. Bentham and Hooker

system of classification is followed

in India till recently. Great variation

occurs not only in different families,

but also varies in genera and species

185

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which are included within the

family. Variation occurs in number,

arrangement, adhesion and cohesion

of the floral parts. We study a few

families for understanding the process

and purpose of classification.

5.13.1 Family: Fabaceae (Pea family)

Systematic position

APG classification

Bentham and Hooker

classification

Kingdom Plantae Kingdom Plantae

Clade Angiosperms Class Dicotyledonae

Clade Eudicots Sub-class Polypetalae

Clade Rosids Series Calyciflorae

Order Fabales Order Rosales

Family Fabaceae Family Fabaceae

Diagnostic features

• Leaves simple or imparipinnately

compound or palmate, leaf base

pulvinate, leaflets stipellate.

• Flowers Zygomorphic

• Corolla: Papilionaceous, descendingly

imbricate aestivation, posterior petal

outermost,

• Petals clawed.

• Stamens: Monadelphous, diadelphous

• Ovary stipitate (a short stalk as the

base), monocarpellary, unilocular with

marginal placentation.

• Fruit a legume or lomentum.

General characters

Distribution: Fabaceae includes about 741

genera and more than 20,200 species. The

members are cosmopolitan in distribution

but abundant in tropical and subtropical

regions.

Habit: All types of habits are

represented in this family. Mostly herbs

(Indigofera, Crotalaria), prostrate

(Indigofera enneaphylla) erect (Crotalaria

verrucosa), shrubs (Cajanus cajan), small

trees (Sesbania), climbers (Clitoria), large

tree (Pongamia, Dalbergia, Erythrina,

Butea), woody climber (Mucuna),

hydrophyte (Aeschynomene aspera)

commonly called pith plant.

Root: Tap

root system,

roots are

nodulated,

have tubercles

containing

nitrogen – fixing Root nodule

bacteria (Rhizobium leguminosarum)

Stem: Aerial, herbaceous, woody

(Dalbergia) twining or climbing Clitoria.

Leaf: Leaf simple or unifoliate

(Desmodium gangeticum) bifoliate (Zornia

diphylla,), Trifoliate (Lablab purpureus),

unipinnate or simple pinnate (Clitoria),

alternate, stipulate, leaf base, pulvinate,

stipulus 2, free. Leaves showing reticulate

venation terminal leaflet modifies into a

tendril in Pisum sativum.

Inflorescence: Raceme (Crotalaria

verrucosa), panicle (Dalbergia latifolia)

axillary solitary (Clitoria ternatea)

186

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Flowers: Bracteate, bracteolate

(Sesbania), pedicellete, complete, bisexual,

pentamerous, heterochlamydeous,

zygomorphic hypogynous or sometimes

perigynous.

Calyx: Sepals 5, green, synsepalous,

more or less united in a tube and persistant,

valvate or imbricate, odd sepal is anterior

in position.

Corolla: Petals 5, apopetalous,

unequal and papilionaceous, vexillary

or descendingly imbricate aestivation

all petals have claw at the base. The

outer most petal is large called standard

petal or vexillum, Lateral 2 petals are

lanceolate and curved. They are called

wing petals or alae. Anterior two petals

are partly fused and are called keel

petals or carina which encloses the

stamens and pistil.

Androecium: Stamens 10, diadelphous,

usually 9+1 (Clitoria ternatea). The

odd stamen is posterior in position.

In Aeschynomene aspera, the stamens

are fused to form two bundles each

containing five stamens (5)+5. Stamens

are monadelphous and dimorphic

ie. 5 stamens have longer filaments and

other 5 stamens have shorter filaments

thus the stamens are found at two levels

and the shape of anthers also varies in

(Crotalaria verrucosa). (5 anthers are long

and lanceolate, and the other 5 anthers are

short and blunt). Anthers are dithecous,

basifixed and dehiscing longitudinally.

Gynoecium: Monocarpellary,

unilocular, ovary superior, with two

alternating rows of ovules on marginal

placentation. Style simple and bent, stigma

flattened or feathery.

Fruit: The characteristic fruit of

Fabaceae is a legume (Pisum sativum),

sometimes indehiscent and rarely a

lomentum (Desmodium).

In Arachis hypogea the fruit is

geocarpic (fruits develops and matures

from underground). After fertilization

the stipe of the ovary becomes

meristematic and grows down into the

soil. This ovary gets buried into the soil

and develops into fruit.

Seed: Endospermic or nonendospermic

(Pisum sativum), mostly

reniformed.

Botanical description of Clitoria

ternatea (Sangu pushpam)

Habit: Twining climber

Root: Branched tap root system having

nodules.

Stem: Aerial, weak stem and a twiner

Leaf: Imparipinnately compound,

alternate, stipulate showing reticulate

venation. Leaflets are stipellate. Petiolate

and stipels are pulvinated.

Inflorescence: Solitary and axillary

Flower: Bracteate, bracteolate, bracteoles

usually large, pedicellate, heterochlamydeous,

complete, bisexual, pentamerous, zygomorphic

and hypogynous.

Calyx: Sepals 5, synsepalous, green

showing valvate aestivation. Odd sepal is

anterior in position.

Corolla: Petals 5, white or blue

apopetalous, irregular papilionaceous

corolla showing descendingly imbricate

aestivation.

Androecium: Stamens 10, diadelphous

(9)+1 nine stamens fused to form a bundle

and the tenth stamen is free. Anthers

187

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Standard petal

Stigma

Stamen

Style

Ovary

Calyx

Stipe

L.S of flower

Anther

Filament

Sepal

Habit

Standard

petal

Single stamen

Androecium

Calyx

Wing petal

Stigma

Style

Ovary

Stipe

Gynoecium

Corolla

C.S.of Ovary

Ovule

Locule

Keel petal

Floral formula

Br.,Brl.,%, , K (5)

,C 5

,A (9)+1

,G 1

Figure 5.13: Clitoria ternatea

Floral diagram

188

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are dithecous, basifixed, introse and

dechiscing by longitudinal slits.

Gynoecium: Monocarpellary, unilocular,

with many ovules on mariginal

placentation, ovary superior, style simple

and incurved with feathery stigma.

Fruit: Legume

Seed: Non-endospermous, reniform.

Floral Formula: Dt0.Dtn0.'.""."M *7+

.E 7

.C *;+-3

.I 3

Botanical description of Pisum sativum

(Pea Plant)

Habit: Cultivated herb, becoming shrubby.

Root: Branched tap root system,

nodulated due to the presence of

nitrogen fixing bacteria (Rhizobium

leguminosorum).

Stem: Erect and climbing, one to three

feet high, young stem densely pubescent,

somewhat angular, herbaceous, green and

branched.

Leaves: Alternate, petiolate, stipulate,

stipules ¼ to ½ inch long attached near

the base, compound (trifoliate), leaflets

dark green, entire, acuminate, pubescent

on both the sides, reticulate venation.

Inflorescence: Clustered axillary

racemes.

Flower: Bracteate (small

and deciduous), bracteolate

(usually persistent), pedicellate,

heterochlamydeous, complete, bisexual,

pentamerous, zygomorphic and

hypogynous.

Calyx: Sepals 5, green synsepalous,

companulate, showing valvate aestivation.

Odd sepal is anterior in position.

Corolla: Petals 5, apopetalous,

irregular papillionaceous, consisting of

a posterior standard, two lateral wings,

two anterior ones forming a keel which

encloses stamen and pistil, vexillary /

descendingly imbricate aestivation.

Androecium: Stamens 10, diadelphous

(9)+1 nine stamens fused to form a bundle

and the tenth one is posterior and free.

Anthers dithecous, basifixed, introse and

dehisce longitudinally.

Gynoecium: Monocarpellary, ovary

superior, unilocular, with many ovules on

marginal placentation, style simple and

curved, stigma capitate.

Fruit: Legume

Seed: non-endospermous with thick

cotyledons.

Floral Formula: Dt0.Dtn0.'.""."M *7+

.E 7

.C *;+-3

.I 3

Arachis hypogea

Crotalaria verrucosa

Indigofera tinctoria Aeschynomene aspera

Figure 5.14: Selected plants belongs to

the Family Fabaceae

189

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Tendril

Flower

Standard petal

Stigma

Stamen

Style

Ovary

Habit

L.S.of flower

Calyx

Stipe

Sepal

Standard

petal

Wing petal

Keel petal

Anther

Filament

Single stamen

Calyx

Corolla

Androecium

Stigma

Style

Gynoecium

Ovary

Stipe

C.S.of Ovary

Ovule

Locule

Floral formula

Br.,Brl.,%, , K (5)

,C 5

,A (9)+1

,G 1

Figure 5.15: Pisum sativum

Floral diagram

190

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Economic Importance

Economic

importance

Binomial

Useful

part

Uses

Pulses

Cajanus cajan

(Pigeon Pea)

Phaseolus vulgaris (French bean)

Cicer arietinum

(Chick pea / Channa /

கொண்டைக்கடலை)

Vigna mungo

(black gram / உளுந்து)

Vigna radiata

(green gram / பாசிபபயறு)

Vigna unguiculata

(cow pea / தட்டைபபயறு)

Glycine max (soya bean)

Macrotyloma uniflorum

(Horse gram / கொள்ளு)

Seeds

Sources of protein and starch of our food.

Food plants

Lablab purpureus

(field bean)

Sesbania grandiflora (agathi,

vegetable humming bird)

Cyamopsis tetragonoloba

(cluster bean)

Tender

fruits

Leaves

Tender

fruits

Vegetable

Greens

Vegetable

Oil Plants

Arachis hypogea (Ground nut)

Pongamia pinnata (Pungam)

Seeds

Seeds

Oil extracted from the seeds is edible and

used for cooking.

Pongam oil has medicinal value and is

used in the preparation of soap.

Timber

Plants

Dalbergia latifolia

(rose wood)

Pterocarpus santalinus

(red sandalwood)

P.dalbergioides

(Padauk)

P.marsupium (வேங்)

Timber

Timber is used for making furniture, cabinet

articles and as building materials.

Medicinal

Plants

Crotalaria albida

Psoralea corylifolia

(கார்போக அரிசி)

Glycirrhiza glabra

(Licorice root / அதிமதுரம்)

Mucuna pruriens

(பூனைகொலி)

Roots

Seeds

Roots

Seeds

Used as purgative

Used in leprosy and leucoderma

Immuno modulater

Neurological remedy

Fibre Plants

Crotalaria juncea

(sunhemp / சணப்ப)

Sesbania sesban (aegyptiaca)

Stem

fibres

(Bast)

Used for making ropes.

Continued

191

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Economic

importance

Binomial

Useful

part

Pith Plant Aeschynomene aspera Stem

pith

Dye

Plants

Indigofera tinctoria (Avuri)

Leaves

Uses

Used for packing, handicraft and fishing

floats

Indigo dye obtained from leaves is used

to colour printing and in paints.

Clitoria ternatea

Butea monosperma

Flowers

and

seeds

Flowers

Blue dye is obtained

Natural dye

Green

Manuring

Indigofera tinctoria

Tephrosea purpurea

Gliricidia sepium

Entire

plant

Used as green manure because of the

presence of nitrogen fixing bacteria in

the lateral roots.

Ornamental

Plants

Butea frondosa

(Flame of the forest),

Clitoria ternatea,

Lathyrus odoratus

(Sweet pea) and

Lupinus hirsutus (Lupin)

Entire

plant

Grown as ornamental plants.

Diabetes Remedy

The aerial parts of Galega officinalis

(Fabaceae) contains Metformin (dimethyl

biguanide). It is now reputed to be the

most widely prescribed agent in the treatment

of diabetes all over the world.

The seeds of Abrus precatorius are

used in necklaces and rosaries, but are

extremely poisonous and can be fatal if

ingested.

INTERNATIONAL

YEAR OF PULSES

The attractive seeds of Adenanthera

pavonina (Family: Caesalpiniaceae)

have been used as units of weight for

the measures of gold throughout India.

The Food and Agriculture Organization

(FAO) of the United Nations has been

nominated to declare 2016 as the year

for pulses, to make people more aware

of the nutritional value of pulses.

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5.13.2 Family: Apocynaceae (milk weed family) (including Asclepiadaceae)

Systematic position

APG classification

Bentham and Hooker

classification

Kingdom Plantae Kingdom Plantae

Clade Angiosperms Class Dicotyledonae

Clade Eudicots Sub-class Gamopetalae

Clade Asterides Series Bicarpellatae

Order Gentianales Order Gentianales

Family Apocynaceae Family Apocynaceae

Diagnostic features

• Plants with milky sap.

• Leaves opposite or whorled, exstipulate.

• Flowers pentamerous.

• Stamens epipetalous, connate with

corona.

• Fruit a follicle.

• Stigma is thick and massive often

connate to stamen to form Gynostegium

• Seeds often with coma (hair).

• Presence of nectariferous disc.

General Characters

Distribution:

This family is represented by 345 genera,

4,675 species. Mostly tropical and

subtropical whereas a few species found

in temperate region.

Habit: Tree (Alstonia), shrub,

(Nerium), herb (Catharanthus), woody

twiner (Allamanda, Succulent, Adenium

usually twining shrubs with milky sap in

laticiferous vessels.

Root: Branched tap root system

Stem: The stems are succulent in some

taxa (Stapelia, caralluma), usually erect,

branched solid, glabrous, rarely tube like

and thick.

Leaves: Simple, undivided, sometimes

reduced, exstipulate, opposite decusate

(Calotropis) or sometimes alternate

(Thevetia) or in whorls of 3 (Nerium),

entire, rarely stipulate (Tabernaemontana).

Inflorescence: A Panicle, dichasial

cyme, often umbelliform in (Asclepiadoids)

or raceme, or axillary cluster of two

flowers each (Catharanthus).

Flowers: Bracteate, bracteolate, pedicellate,

complete, bisexual, actinomorphic, zygomorphic

in Ceropegia heterochlamydeous ,

pentamerous, hypogynous but rarely perigynous

or epigynous (Plumeria)

Ceropegia spp

Calyx: Sepals 5, synsepalous (at least basally)

sometimes aposepalous (Catharanthus) deeply

lobed ; valvate or quincuncial (Thevetia),

odd sepal posterior, glandular appendages

(Squamellae) present on the adaxial side.

Corolla: Petals 5, sympetalous united

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into a tube, salver or funnel shaped; twisted

or rarely valvate, often hairy within or

contain some corona like out growths at

the mouth of the corolla tube.

Androecium: Stamens 5 , alternipetalous,

often epipetalous, apostemonous to

monadelphous, In Asclepiadoids the

stamens are connate to the styles to form a

gynostegium, pollen grains of each theca of

an anther are fused into a waxy mass called

pollinium. The right pollinium of each anther

attached to the left pollinium of the adjacent

anther by a hair like translator, translator arms

(retinacula) attached together with the gland

like structure called corpusculum. Anthers

are dithecous, basifixed, often sagitate, introse;

dehisce longitudinally, anthers basally awned;

sometimes bear hairy appendages over the

lobes (Nerium).

Gynoecium: Bicarpellary, carpels apically

united, superior, or rarely half inferior

(Plumeria) 1 to 2 locule with 2 to many ovules

in each locule on marginal placentation. Style

one and simple, stigma is characteristically

thickened, massive and bilobed. A

nectariferous disc is often present around

or at the base of the gynoecium, (Thevetia,

Catharanthus, Allamanda and Rauvolfia).

Fruit: The fruit is variable and can be a

berry (Landolphia), drupe (Cerbera) follicle

(Asclepias), capsule (Allamanda).

Seed: Seeds are endospermous often with

crown of hairs.

Botanical description of Catharanthus

roseus

Habit: Erect ever blooming ornamental

plant with milky latex.

Root: Branched tap root system

Stem: Aerial, erect, cylindrical reddish

green, glabrous and branched.

Leaves: Usually simple, opposite

decussate, exstipulate, subsessile,

or petiolate, elliptic – ovate, entire,

mucronate, unicostate reticulate venation.

Inflorescence: cymose, axillary pairs.

Flower: Ebracteate, Ebracteolate,

subsessile, complete, bisexual,

heterochlamydeous, actinomorphic,

hypogynous, pentamerous, rosy purple,

white or pink.

Calyx: Sepals 5, slightly synsepalous,

green showing valvate aestivation.

Corolla: Petals 5, sympetalous, throat

of corolla tube hairy forming a corona,

twisted (hypocrateriform).

Androecium: Stamens 5,

apostemanous, epipetalous, inserted at the

mouth of the corolla tube, filaments short,

anthers sagittate, dithecous, dorsifixed,

introse.

Gynoecium: Bicarpellary, apocarpous,

ovaries superior, unilocular, ovules many,

placentation marginal, style simple, stigma

hour-glass shaped. Two scaly nectaries are

present one on the anterior and another

on the posterior side of the ovary.

Fruit: A pair of elongated follicles.

Floral Formula: Ebr.,Ebrl., , ,K (5)

,C (5)

,A 5

,G (2)

194

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Flower

Leaf

Fruit

Corolla

Sepal

Calyx

L.S. of the flower

Habit

Corolla

Epipetalous

stamens

Stigma

Style

Ovary

Gynoecium

Flower entire

Stigma

(hour - glass shaped)

Style

Ovary

Scaly nectary

Calyx

Scaly

nectary

Ovule

Apocarpous

ovary

A pair of

elongated

follicles

C.S. of the ovary Fruit Seed Floral diagram

Floral formula

Ebr.,Ebrl., , ,K (5)

,C (5)

,A 5

,G 2

Figure 5.16: Catharanthus roseus

Figure 5.51 Catharanthus roseus

195

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Figure 5.17: Calotropis gigantea

196

---

Economic importance of the family Apocynaceae

S.No

Economic

importance

Binomial Useful part Uses

1 Food plant Carissa carandas (பெரும்களா)

2 Medicinal

plant

Carissa spinarum (சிறுகளா)

Rauvolfia serpentina

(Indian snake root /

sarpagandha)

Thevetia peruviana

(lucky nut/ தஙஅலரி)

Vallaris solanacea

Cerbera odollam

Alstonia scholaris

Strophanthus hispidus

Wrightia tomentosa (பாலை)

Catharanthus roseus

Caralluma umbellate

(களிமுளியான்)

Fruits

Shoot

Dried roots

Seeds

Latex

Latex

Bark

Seeds

Bark and

Roots

Aerial

parts

Succulent

stem

Edible and used in

pickles

To treat hypertension

and mental disorders

Alkaloid (reserpine)

obtained from the

dried roots, of the

plant can lower the

blood pressure and

used as sedative for

patients suffering from

Schizophrenia.

Used in rheumatism

Useful in toothache and

to treat inflated gums.

Used as an emetic and

purgative.

Used in malaria and

dysentery.

Yield the drug

strophanthin

Used as antidote to

snakebite.

Used to treat muscle

pain, the alkaloids like

vinblastine and vincristine

are mainly used

to treat various human

cancers.

Antiobesity

197

---

3. Dye yielding

plant

4. Ornamental

plants

Wrightia tinctoria Seeds An indigo- like dye

is obtained from the

seeds.

Allamanda nerifolia (golden

trumpet),

Alstonia scholaris,

Beaumontia grandiflora,

Catharanthus roseus,

Nerium indicum

Plumeria obtusa,

Plumeria alba,

Stapelia spp, Hoya, Asclepias,

and Cryptostegia.

plant

Grown as ornamentals

plants.

Thevetia

Plumeria

Rauvolfia

Tabernaemontana

Figure 5.18: Selected plants belongs to the family Apocynaceae

198

---

5.13.3 Family: Solanaceae (Potato Family / Night shade family)

Systematic Position

APG system of classification

Bentham and Hooker system

of classification

Kingdom Plantae Kingdom Plantae

Clade Angiosperms Class Dicotyledonae

Clade Eudicot Subclass Gamopetalae

Clade Asterids Series Bicarpellatae

Clade Solanales Order Polemoniales

Family Solanaceae Family Solanaceae

Diagnostic Features

• Leaves alternate, exstipulate.

• Flowers actinomorphic, pentamerous.

• Calyx often persistence / accrescent.

• Stamens 5, epipetalous, poricidal in

dehiscence.

• Carpels 2, ovary superior, 2 chambered,

obliquely placed, falsely four chambered

placenta swollen, ovule numerous.

• Fruits berry or capsule, vascular

bundles with both outer and inner

phloem (Bicollateral vascular bundle).

General Characters

Distribution:

Family Solanaceae includes about 88

genera and about 2650 species, of these

Solanum is the largest genus of the

family with about 1500 species. Plants

are worldwide in distribution but more

abundant in South America.

Habit: Mostly annual herbs, shrubs,

small trees (Solanum violaceum) lianas

with prickles (Solanum trilobatum),

many with stellate trichomes; rarely vines

(Lycium sinensis)

Root: Branched tap root system.

Stem: Herbaceous or woody; erect or

twining, or creeping; sometimes modified

into tubers (Solanum tuberosum) often

with bicollateral vascular bundles.

Leaves: Alternate, simple, rarely

pinnately compound(Solanum tuberosum

and (Lycopersicon esculentum) exstipulate,

opposite or sub-opposite in upper part,

unicostate reticulate venation.

Inflorescence: Generally axillary or

terminal cymose (Solanum) or solitary

flowers (Datura stramonium). Extra

axillary scorpiod cyme called rhiphidium

(Solanum nigrum) solitary and axillary

(Datura and Nicotiana) umbellate cyme

(Withania somnifera).

Flowers: Bracteate (Petunia), or

ebracteate (Withania) pedicellate, bisexual,

heterochlamydeous, actinomorphic or

weakly zygomorphic due to oblique position

of ovary pentamerous, hypogynous.

Calyx: Sepals 5, rarely 4 or 6, Synsepalous,

valvale peristaent, often accrescent

(enlarging to envelop the fruit) occasionally

enclosing the fruit ( Physalis, Withania)

Corolla: Petals 5, sympetalous, rotate,

tubular (Solanum) or bell- shaped (Atropa)

199

---

or infundibuliform (Petunia) usually

alternate with sepals; rarely bilipped

and zygomorphic (Schizanthus) usually

valvate, sometimes convolute (Datura).

Androecium: Stamens 5, epipetalous,

filaments usually unequal in length,

stamens only 2 in Schizanthus(others 3 are

reduced to staminode), 4 and didynamous

in (Salpiglossis) Anthers dithecous, dehisce

longitudinally or poricidal.

Gynoecium: Bicarpellary, syncarpous

obliquely placed, ovary superior, bilocular

but looks tetralocular due to the formation

of false septa, numerous ovules in each

locule on axile placentation.

Fruit: A capsule or berry. In

Lycopersicon esculentum, Capsicum, the

fruit is a berry and in species of Datura

and Petunia, the fruit is a capsule.

Seed: Endospermous.

Botanical description of Datura metel

Habit: Large, erect and stout herb.

Root: Branched tap root system.

Stem: Stem is hollow, green and

herbaceous with strong odour.

Leaf: Simple, alternate, petiolate, entire

or deeply lobed, glabrous exstipulate

showing unicostate reticulate venation.

Inflorescence: Solitary and axillary cyme.

Flower: Flowers are large, greenish

white, bracteate, ebracteolate, pedicellate,

complete,

heterochlamydeous,

pentamerous, regular, actinomorphic,

bisexual and hypogynous.

Calyx: Sepals 5, green synsepalous

showing valvate aestivation. Calyx is mostly

persistant, odd sepal is posterior in position.

Corolla: petals 5, greenish white,

sympetalous, plicate (folded like a fan)

showing twisted aestivation, funnel

shaped with wide mouth and 10 lobed.

Androecium: Stamens 5, free from

one another, epipetalous, alternipetalous

and are inserted in the middle of the

corolla tube. Anthers are basifixed,

dithecous, with long filament, introse and

longitudinally dehiscent.

Gynoecium: Ovary bicarpellary,

syncarpous superior ovary, basically

biloculear but tetralocular due to the

formation of false septum. Carpels are

obliquely placed and ovules on swollen

axile placentation. Style simple long and

filiform, stigma two lobed.

Fruit: Spinescent capsule opening by

four apical valves with persistent calyx.

Seed: Endospermous.

Floral Formula: Dt0.Gdtn0.""".""".M *7+

.E *7+

.C 7

.I *4+

Solanum trilobatum

Withania somnifera

Atropa belladonna

Schizanthus pinnatus

Figure 5.19: Selected plants belongs to

the Family Solanace

200

---

Leaf

Stamen

Corolla

Stamen

Corolla

Calyx

Calyx

Habit

Flower entire

Corolla

Stigma

Sepal

Anther

Epipetalous

stamens

Style

Ovary

C.S. of Ovary

Ovule

Swollen

placenta

Calyx

Corolla cut open

Gynoecium

Spiny

outgrowth

Persistent

calyx

Valve

Seed

Spiny

outgrowth

Persistent

calyx

Fruit: Spinescent

capsule

Fruit - After

dehiscence

Floral formula

Br.,Ebrl., , ,K (5)

,C (5)

,A 5

,G (2)

Floral Diagram

Figure 5.20: Datura metel

201

---

Botanical description of Solanum americanum

Corolla

Stamen

Fruit

Extra - Axillary

scorpioid cyme

Inflorescence

Corolla

Stamen

Habit

Entire flower

Sepal

Corolla

Epipetalous

stamens

Apical pore

Anther lobe

Connective

Filament

Stigma

Style

Ovary

Calyx

Corolla cut open

Stamen

Gynoecium

Persistent

calyx

Berry

Ovary wall

Placenta

Ovule

Fruit

C.S.of ovary

Floral formula

Ebr.,Ebrl., , ,K (5)

,C (5)

,A 5

,G (2)

Floral diagram

Figure 5.58 Solanum nigrum

Figure 5.21: Solanum americanum

202

---

Habit: A small annual herb

Root: Branched tap root system.

Stem: Aerial, erect, green and

herbaceous

Leaf: Simple, alternate but opposite

in the floral region, petiolate, exstipulate

ovate, entire or slightly lobed, acute

unicostate reticulate venation.

Inflorescence: Extra-axillary (due to

fusion of floral axis) scorpioid cyme called

rhiphidium

Flower: Ebracteate, pedicellate,

white, bisexual, actinomorphic,

heterochlamydeous, pentamerous,

hypogynous white.

Calyx: Sepals 5, synsepalous, green,

persistent and showing valvate aestivation.

Corolla: petals 5, sympetalous, white,

showing valvate aestivation.

Androecium: Stamens 5,

apostamenous, epipetalous, filaments

short, anthers conniving and forming

an envelope around the style dithecous,

basifixed with apical pores.

Gynoecium: Bicarpellary, syncarpous,

superior, bilocular, many ovules in each

locule on axile placentation, septum

oblique, highly swollen placenta, style

long and hairy at the base, stigma bifid.

Fruit: Berry

Floral Formula: Ebr.,Ebrl., , ,K (5)

,C (5)

,A 5

,G (2)

Economic importance

Economic importance of the family solanaceae

S.No Economic

importance

Binomial Useful part Uses

1. Food plant Solanum tuberosum

(potato)

Underground

stem tubers

Used as vegetables and also

used for the production of

starch.

Lycopersicon esculentum

(tomato)

Solanum melongena

(brinjal)

Capsicum annuum (bell

peppers & chilli papers)

C. frutescens (மிளகாய்)

Physalis peruviana (cape

gooseberry / கசொடக்கு

தகொளி)

Ripened fruits

Tender fruits

Fruits

Fruit

Used as delicious vegetable

and eaten raw.

Cooked and eaten as

vegetable.

Used as vegetables and

powdered chilli is the dried

pulverized fruit which

is used as spice to add

pungency or piquancy and

flavour to dishes .

Used as delicious fruit.

203

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Economic importance of the family solanaceae

S.No Economic Binomial Useful part Uses

importance

2. Medicinal

plant

Atropa belladonna

(deadly nightshade)

Roots

A powerful alkaloid

‘atropine’ obtained from

root is used in belladona

plasters, tinctures etc. for

relieving pain and also for

dialating pupils of eyes for

eye –testing.

Datura stramonium

(ஊமத்த)

Solanum trilobatum

(தூதுவளை)

Leaves and

roots

Leaves, flowers

and berries

Stramonium drug obtained

from the leaves and roots

of this is used to treat

asthma and whooping

cough.

Used to treat cough.

Withania somnifera

(Ashwagandha /

அமுகொரா)

3. Tobacco Nicotiana tabaccum

(tobacco / புகையிலை)

4. Ornamental

plants

Cestrum diurnum

(Day Jasmine)

Cestrum nocturnum

(Night Jasmine)

Nicotiana alata

Petunia hybrida,

Schizanthus pinnatus

Brugmansia species

(Angel trumpet)

Roots

Leaves are

dried and

made into

tobacco.

Plant

Used in curing cough and

rheumatism.

Used in cigarette, beedi,

hukkah, pipes as well as

for chewing and snuffing,

alkaloids like nicotine,

nornicotine and anabasin

are present in tobacco.

Grown in garden as

ornamental plants for their

aesthetic nature.

Do tomatoes come

from a tree?

Solanum betaceum

(Tree tomato)

204

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5.13.4 Family: Euphorbiaceae (Castor Family / Spurge Family )

(In APG classification Peraceae, Phyllanthaceae and Picrodendraceae are excluded

from the family Euphorbiaceae)

Systematic position

APG Classification

Bentham and Hooker

Classification

Kingdom Plantae Kingdom Plantae

Clade: Angiosperms Class: Dicotyledonae

Clade: Eudicots Sub-class: Monochlamydeae

Clade: Rosids Series: Unisexuales

Order: Malpighiales Order: Euphorbiales

Family: Euphorbiaceae Family: Euphorbiaceae

Diagnostic features

• Latex is present either milky or watery.

• Inflorescence generally cymose, catkin in

Acalypha, cyathium in Euphorbia sp.

• Flowers apetalous, unisexual.

• Ovary tricarpellary, distinctly trilobed.

• Fruit capsule or regma.

General characters

Distribution: Euphorbiaceae includes

214 genera and about 5600 species. The

plants of this family are found throughout

the world. Well represented in Africa and

South America.

Habit: Mostly shrubs (Ricinus

communics, Jatropha gossypifolia) or tree

Emblica officinalis, herbs (Phyllanthus

amarus) , twiners (Tragia involucrata)

some are xerophytic (Euphorbia) with

cactus – like (phylloclades) plants usually

contain milky or watery sap.

Root: Well branched tap root system.

Stem: Aerial, erect or prostrate

(E.prostrata), herbaceous or woody. Stem

becomes modified into flattened, leaflike

and becomes succulent in several

species of Euphorbia. Such modified

stem is called phylloclades. Cylindrical,

branched, solid or hollow, usually contain

latex either milky (E.tirucalli) or watery

(Jatropha curcas).

Leaf: Stipulate or exstipulate.

Mostly simple, alternate, often reduced

or deciduous as in several species of

Euphorbia, palmately lobed in Ricinus

or deeply lobed in Manihot. The stiplues

are modified into a pair of spines

(E.splendens) or glandular hairs (Jatropha

curcas ). The leaves around the cyathium

inflorescence become beautifully coloured

in E.pulcherrima (Paalperukki tree) with

unicostate or multicostate reticulate

205

---

venation.

Inflorescence: The inflorescence of

Euphorbiaceae varies greatly, Terminal

raceme – Croton, Ricinus,

Catkin – Acalypha hispida Cyme -

Jatropha, solitary axillary – Phyllanthus

asperulatus, cyathium – Euphobia

species.

Cyathium is the an unique and special

inflorescence of this family. Each cyathium

contains centrally a single, naked terminal

female flower, usually represented by a

tricarpellary gynoecium. The female flower

is surrounded by a cup-like involucre

formed by 4 or 5 connate sepaloid bracts.

In the axil of each bract develops a group of

stamens in a scorpioid manner. Each stamen

represents a naked male flower because it is

a jointed structure, its upper portion is the

filament bearing the anther and its lower

portion represents the pedicel of the male

flower bearing stamen. A nectar secreting

gland is present on the rim of the involucre.

Glands are oval or crescent shaped and

often brightly coloured. Though cyathium

appears like a single flower, it actually

an inflorescence.

Flowers: Flowers are always unisexual,

and are highly variable. Bracteate,

ebracteolate, generally unisexual,

homochlamydeous,

rarely

heterochlamydeous, monoecious

(Baliospermum) or dioecious (Bridelia),

actinomorphic, rarely zygomorphic,

hypogynous, rearly perigynous (Bridelia).

Perianth: Tepals 0 to 5 biseriate

(male flowers of Croton bonplandianum)

uniseriate or aphyllous (Euphorbia),

valvate or imbricate when present,

apophyllous or synphyllous.

Androecium: The number of stamens

vary from 1 to many. In Euphorbia a

single stalked stamen represents a single

male flower. In Ricinus usually 5 stamens

are present, but each stamen is profusely

branched. In Jatropha they are arranged in

two whorls each of 5 stamens. The stamens

are indefinite (Crotons), the filaments

may be free or connate. The anthers are

dithecous, dehisce either by apical or by

transverse or longitudinal slits.

Gynoecium: Tricarpellary, rarely

bicarpellary (Bridelia, Mercurialis), tetra

or pentacarpellary

(Wielandia), syncarpous, ovary

superior, rarely semi-inferior, ovules one

or two in each locule on axile placentation,

rarely locule splits into two forming six

chambers (Phyllanthus). Styles 3, each

split into two feathery stigma. Nectaries

are usually present, gynoecium is present

as a pistillode in staminate flowers.

Fruit: Fruits are capsule or schizocarp.

It breaks violently and dehisce into three

one seeded cocci called regma (Ricinus ),

drupe in Emblica officinalis and berry or

samara.

Seed: Seeds are endospermous. In

Ricinus knob-like caruncle develops from

the micorpyle,that absorbs and temporarily

retains water enabling germination.

Ricinus

206

---

Botanical Description Of Ricinus communis (Castor)

Female flower

Male flower

Stigma

Style

Ovary

Perianth

Habit

Ovule

Stigma

Style

Ovule

Ovary

Female flower

Crowded and

connate stamen

Perianth

C.S.of Ovary

Stamen

Stipitate phalanges

Branched

filament

L.S.of female flower

Anther

Filament

Male flower Polyadelphous stamens Stamen

Floral formula of male flower

Br.,Ebrl., , ,P (5)

,A ,G 0

Floral formula of female flower

Br.,Ebrl., , ,P (3)

,A 0

,G (3)

Floral diagram of male flower

Floral diagram of female flower

Figure Figure 5.64 5.22: Ricinus communis

207

---

Habit: Tall perennial shrub

Root: Branched tap root system

Stem: Aerial, erect, cylindrical, branched

and hollow, solid at the base, glabrous,

Leaf: Simple, petiolate, hollow, exstipulate,

alternate, broad, palmately lobed, usually 7-9

lobes, serrate, palmately reticulate divergent

venation.

Inflorescence: Terminal panicle.

Male Flower Bracteate, ebracteolate,

pedicellate, male flowers (open for one day)

towards lower portion of the inflorescence,

actinomorphic, incomplete.

Perianth: Tepals 5, apophyllous,

uniseriate, green, valvate aestivation, odd

tepal posterior in position.

Androecium: Stamens numerous (upto

1000) crowded and connate into about 8mm

long cluster of stipitate phalanges, each stamen

profusely branded, anthers globose basifixed.

Gynocium: usually absent rarely

represented by pistillode.

Female Flower Bracteate, ebracteolate,

pedicellate, female flowers (open for

fourteen days) found towards the apical

portion of inflorescence, actinomorphic,

incomplete and hypogynous.

Perianth: Tepals 3, apophyllous, green

valvate.

Androecium: Absent but staminode is

present.

Gynoecium: Tricarpellary, syncarpous,

ovary superior, distinctly trilobed, trilocular,

covered with spiny outgrowth, single large

ovule in each locule on axile placentation,

style three with three bifid stigma.

Fruit: A schizocarp with spiny

outgrowth, splits into three one seeded

cocci.

Seed: Endospermous, knob-like

caruncle develops from the micorpyle,

that absorbs and temporarily retains water

enabling germination.

Floral Formula:

Male flower: Br.,Ebrl., , ,P (5)

,A ,G 0

Female flower: Br.,Ebrl., , ,P (3)

,A 0

,G (3)

Hevea brasiliensis

Euphorbia pulcherrima

Euphorbia splendens

Croton tiglium

Figure 5.23: Selected plants belongs to the Family Euphorbiaceae

208

---

Economic importance of the family Euphorbiaceae

Economic

importance

Food plant

Binomial Useful part Uses

Emblica officinalis (Nellikai)

P. acidus (அரைநெல்லி)

Manihot esculenta (Maravalli

kizhanku / Tapioca)

Sauropus androgynous

Fruits

Tuberous

roots

Leaves

Rich in vitamin C, which

are edible and pickled.

Roots are rich in starch

and used for preparing

bread, biscuits, chips and

other food stuffs.

Greens (multi vitamin

plant)

Oil plant

Croton oil

Croton tiglium

Seed

Used as a powerful

purgative and also to treat

skin diseases.

Castor Oil

Ricinus communis

(Amanakku/Castor)

Seeds

Used as vegetable oil,

ricinoleic acid present

in this oil eliminate acne

causing bacteria apart

from that it acts as laxative

and lubricant.

Jatropha Oil

Jatropha curcas (Kattamanakku)

Seeds

Used for biofuels.

Rubber:

Hevea brasiliensis

(Para rubber)

Manihot glaziovii (Manicoba rubber)

Coagulated

latex

Latex is used in rubber

products like tube and

tyre.

Medicinal

plants

Euphorbia resinifera

Euphorbia hirta

(அம்மான் பசசரிசி)

Latex

Whole plant

Euphorbium drug is

obtained from the latex

and used as a purgative.

Lactogogue

Mallotus philippenensis

Phyllanthus amarus (Keezhanelli)

Fruits

Entire shoot

system

Used as anthelmintic.

Used to treat Jaundice.

209

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Economic

importance

Dye yielding

plants

Kamela dye,

Blue dye

Purple dye

Red dye

Jatropha gossypifolia

Binomial Useful part Uses

Croton tiglium (நேரேொளம்)

Ricinus communis

Mallotus philippenensis

Jatropha curcas

Chrozophora tinctoria

Phyllanthus reticulatus

Timber plant Aporosa dioica,

Bischofia javanica,

(வரொமவிருடசம்)

Drypetes roxburghii (வீரைமரம்)

Ornamental

plant

Acalypha ciliata,

A. hispida,

Codiaeum varigatum

Croton tiglium

Euphorbia antiquorum,

E.pulcherrima, E.splendens.

E. tirucalli

Jatropha gossypifolia

Leaves and

roots

Seed

Seed oil

Fruits

Bark

Bark

Roots

Timber

Plants

Used in the treatment of

leprosy and snakebite.

Purgative

Purgative

Used for dyeing wool and

silk.

Used for dyeing clothes

and fishing nets.

Used in textile Industry

Used for tanning and

dyeing fishing lines and

nets

Used for packing cases,

tea boxes, veneers,

plywood, match industry

and several other similar

purpose.

Grown as ornamental

plants.

5.13.5 Family Musaceae – Banana Family

Diagnostic Features

• Perennial giant herbs with pseudostems

formed by leaf sheaths.

• Leaves are large with thick midrib,

parallel venation.

• Flowers are zygomorphic, unisexual,

inflorescence spadix covered by spathe.

• Corolla 2 lipped.

• Ovary tricarpellary, inferior.

• Fruit elongated berry.

• Septal nectaries are present.

210

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Heliconiaceae

Systematic Position

APG Classification

Bentham and Hooker

Classification

Kingdom Plantae Kingdom Plantae

Clade Angiosperms Class: Monocotyledonae

Clade Monocots Subclass Zingiberidae

Clade Commelinids Series Epigynae

Order Zingiberales Order Zingiberales

Family Musaceae Family Musaceae

Musa velutina

Zingiberaceae

Marantaceae

Cannaceae

Costaceae

Lowiaceae

Strelitziaceae

Musaceae

Note: Earlier Musaceae was a large family with 6 genera viz. Musa, Ensete, Ravenala,

Strelitzia, Orchidantha and Heliconia. In APG only Musa and Ensete are retained while

Ravenala, Strelitzia, Orchidantha and Heleconia are separated.

General Characters

Rhizogram of the Zingiberales

Distribution

Musaceae includes only 2 genera (Musa

and Ensete) and 81 species. The members

of this family are mainly wet tropical

lowlands from West Africa to Pacific

(southern Japan to Queensland). (Musa

is the most common plant of the family

found in India)

211

Habit: Large perennial herbs

perennating by means of rhizome ( Musa

paradisiaca), raraly trees as in Ravenala

madagascariensis.

Root: Fibrous adventitious root

system.

Stem: In Musa the real stem is

found underground called rhizomatous

(dichotomously branching in atleast

---

some spp). The apparent aerial erect,

unbranched tall pseudostem is formed by

the long stiff and sheathy leaf bases which

are rolled around one another to form an

aerial pseudostem. The central axis that is

concealed at the bottom of the pseudostem

in called shaft, which elongates and pierces

through the pseudostem at the time of

flowering and produces inflorescence

terminally. monocorpic in Musa.

(produces flowers and fruits once during

its life time). Stem is aerial and woody in

Ravenala madagascariensis.

Leaf: Simple with long and strong

petiole the leaf blade is large and broad

with sheathy leaf base. The leaf is

exstipulate. Oval, obtuse or oblong with

a stout midrib, entire, numerous parallel

veins extending up to the margin, rolled

in bud . Phyllotaxy is spiral in Musa

and distichous i.e. leaves are arranged

alternately in two opposite vertical rows

in Ravenala.

Inflorescence: Terminal or axillary

thyrse of one to many monochasial

branched spadix in Musa, Usually the

flowers are protected by large brightly

coloured, spirally arranged, boat shaped

bract called spathe. Compound cyme in

Ravenala.

Flowers: Bracteate, ebracteolate,

sessile, trimerours, unisexual, or bisexual

or polygamous, when unisexual the

flowers are monoecious. Flowers are

zygyomorphic and epigynous. (In Musa

flowers are polygamous i.e. staminate

flowers, pistilate flowers and bisexual

flowers are present in the same plant).

Perianth: Tepals 6, biseriate,

arranged in two whorls of 3 each and

homochlamydeous, 3 +3 syntepalous. In

most of the species of Musa, the three

outer tepals and two lateral tepals of the

inner whorl are fused to form 5 toothed

tube like structure called abaxial lip. The

posterior inner median tepal alone is free,

which is distinctly broad and membranous

called labellum.

Androecium: Stamens 5 or 6,

arranged in two whorls of 3 each opposite

and adnate to the tepals. In Musa only 5

stamens are fertile and the inner posterior

stamen is either absent or represented by a

staminode. In Ravenala all the six stamens

are fertile. Filaments free, anthers linear,

dithecous dehisce by longitudinal slits,

and with sticky pollen.

Gynoecium: Tricarpallary, syncarpous,

the median carpel is anterior in position,

trilocular ovary inferior, ovules many,

placentation axile, style filiform, stigma

three lobed septal nectaries are present.

Fruit: Elongated berry containing

numerous seeds, fruits forming compact

bunches, seeds with copious and small

embryo in Musa. Capsule in Ravenala.

Seed: Starch rich endosperm and

starchless perisperm. Species of Ensete are

distinguished from those of Musa by their

larger seeds.

Botanical Description of Musa

paradisiaca.

Habit: Monocarpic gigantic herb.

Root: Fibrous adventitious root

system.

Stem: The real stem is underground

called rhizomatous. The apparent, aerial

erect unbranched pseudo stem is formed

by the long, stiff and sheathy leaf bases

which are rolled around one another to

form an aerial pseudostem. The central

212

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Leaf

Spathe

Flower

Fruit

Branched

spadix

Inflorescence

Spathe with flowers

Pseudo

stem

Outer tepal

Inner tepal

Stigma

Anther

Abaxial lip

Labellum

Habit

Bisexual flower

Ovary

Fused tepals

Labellum

Anther

Stigma

Filament

Style

Stamens

C.S of ovary

Locule

Ovary

Ovule

Anterior median

carpel

Gynoecium

Floral diagram

Floral formula : Bisexual flower

Br.,Ebrl.,%, , P (3+2)+1

,A 3+3

,G (3)

Figure 5.68 5.24: Musa paradisiaca

213

---

axis that is concealed at the bottom of

the pseudostem is called shaft. The shaft

elongates, pierces through the pseudostem

and produces an inflorescence terminally.

Leaf: Simple with a long and strong

petiole. The leaf blade is large and broad

with sheathy leaf base. Leaf exstipulate and

obtuse pinnately parallel venation which

extends upto the leaf margin phyllotaxy is

spiral.

Inflorescence: Terminal branched

spadix. Flowers are protected by large,

brightly coloured spirally arranged, boat

shaped bracts called spathe. When the

flowers open, spathe rolls back and falls off.

Flower: Bracteate, ebracteolate, sessile,

trimerous, unisexual or bisexual, flowers

are zygomorphic and epigynous.

Perianth: Tepals 6, biseriate, 3+3

syntepalous, arranged in two whorls of

3 each and homochlamydeous, the three

tepals of the outer whorl and the two lateral

tepals of the inner whol are fused by valvate

aestivation to form 5 toothed tube like

structure called abaxial lip, the posterior

inner median tepal is distinctly broad

membrancus and free called labellum.

Androecium: Stamens 6, arranged in

two whorls of 3 each, arranged opposite to

the tepals. Only five stamens are fertile and

the inner posterior stamen is either absent

or represented by staminode. Anthers are

dithecous and they dehisce by vertical

slits. Filament is simple and filiform and

rudimentary ovary or pistillode is often

present in the male flower.

Gynoecium: Tricarpellary, syncarpous,

the median carpel anterior, trilocular,

ovary inferior, numerous ovules on axile

placentation. Style is simple and filiform,

stigma trilobed. Septal nectaries are

present.

Fruit: An elongated fleshy berry and

seeds are not produced in cultivated

varieties.

Floral Formula

Male flower:

Br,Ebrl,%, ,P (3+2)+1 ,A 3+3 ,G 0 .

Female flower:

Br,Ebrl,%, ,P (3+2)+1 ,A 0 ,G (3) .

Bisexual flower:

Br,Ebrl,%, ,P (3+2)+1 ,A 3+3 ,G (3) .

Ensete ventricosum

Ravenala

madagascariensis

Strelitzia reginae Heliconia spp

Figure 5.25: Selected plants belongs to the Family Musaceae

214

---

Economic Importance of The Family Musaceae

S.No Economic

Binomial Useful part Uses

importance

1 Food plant Musa paradisiaca. The raw (tender

green) bananas, the

Cooked and eaten

as vegetable.

shaft and male buds.

Leaves

Commonly used

as plates on festive

occasions and are

widely used to

wrap food items

Fruit

when cooking.

Crunchy and salty

fried plantain chips

are delicious.

Flower stalk (Shaft) Edible after

Ensete ventricosa

cooking.

2. Medicinal

plant

Musa chinensis

(Chinea kela)

Musa spp.

Fruits

Sap obtained from

the sheathy leaf

base.

Edible bananas

which are sweet,

rich in starch and

vitamins.

Considered to be

an antidote for

cobra bite.

3. Starch Ensete ventricosum

(Ethiopean banana)

4. Fibre yielding

plant

5. Ornamental

plant

Musa textilis

(Manila hemp)

Musa coccinea

(a wild banana species).

(M. acuminata, M.

velutina and M. ornata)

Ensete ventricosum

The swollen basal

parts of leaf sheaths

Fibre

Plant

Used as a source

of starch and

vitamins.

Fibre is woven and

made into abaca

cloth, also used for

twine, bagging and

wrapping paper.

Have ornamental

scarlet flowers.

Cultivated as

ornamentals

Continued

215

---

*Ravenala

madagascariensis

(traveller’s palm),

Plant

*Strelitzia reginae (bird of

paradise ) and *Heliconia

spp.

Grown as

ornamental plants

5.13.6 Monocot Family

Family: Liliaceae (Lily Family)

Systematic position

APG Classification

Bentham and Hooker

Classification

Kingdom Plantae Kingdom Plantae

Clade Angiosperms Class Monocotyledons

Clade Monocots Series Coronarieae

Order Liliales Order Liliales

Family Liliaceae Family Liliaceae

Diagnostic Features

• Perennial herbs often with bulbous

stem / rhizomes.

• Radical leaves.

• Perianth showy.

• Stamens six.

• Ovary superior .

General Characters

Distribution: Liliaceae are fairly large

family comprising about 15 genera and

550 species. Members of this family are

widely distributed over most part of the

world.

Habit: Mostly perennial herbs

persisting by means of a sympodial

rhizome (Polygonatum), by a bulb

(Lilium) corm (Colchicum), shrubby or

tree like (Yucca and Dracaena). Woody

climbers, climbing with the help of

stipular tendrils in Smilax. Trees in

Xanthorrhoea, succulents in Aloe.

Note: Liliaceae of Bentham and

Hooker included Allium, Gloriosa,

Smilax, Asparagus, Scilla, Aloe,

Dracaena etc. Now under APG, it

includes only Lilium and Tulipa.

All others are placed under different

families.

Root: Adventitious and fibrous, and

typically contractile.

Stem: Stems usually bulbous,

rhizomatous in some, aerial, erect

(Dracaena) or climbing (Smilax) in

Ruscus the ultimate branches are modified

into phylloclades, In Asparagus stem is

modified into cladodes and the leaves are

reduced to scales.

Leaf: Leaves are radical (Lilium) or

cauline (Dracaena), usually alternate,

opposite (Gloriosa), sometimes fleshy

and hollow, reduced to scales (Ruscus and

Asparagus). The venation is parallel but

216

---

in species of Smilax it is reticulate. Leaves

are usually exstipulate, but in Smilax, two

tendrils arise from the base of the leaf,

which are considered modified stipules.

Inflorescence: Flowers are usually

borne in simple or branched racemes

(Asphodelus) spikes in Aloe, huge terminal

panicle in Yucca, solitary and axillary in

Gloriosa, solitary and terminal in Tulipa.

Flowers: Flowers are often showy,

pedicellate, bracteate, usually ebracteolate

except Dianella and Lilium, bisexual,

actinomorphic, trimerous, hypogynous,

rarely unisexual (Smilax) and are dioecious,

rarely tetramerous (Maianthemum), slightly

zygomorphic (Lilium) and hypogynous.

Perianth: Tepals 6 biseriate arranged

in two whorls of 3 each, apotepalous or

rarely syntepalous as in Aloe. Usually

petaloid or sometimes sepaloid, odd tepal

of the outer whorl is anterior in position,

valvate or imbricate, tepals more than six

in Paris quadrifolia.

Androecium: Stamens 6, arranged

in 2 whorls of 3 each: rarely stamens are

3 (Ruscus),4 in Maianthemum, or up to

12, apostamenous, opposite to the tepals,

sometimes epitepalous; filaments distinct

or connate, anthers dithecous, basifixed

or versatile, extrose, or intrese, dehiscing

usually by vertical slit and sometimes

by terminal pores; rarely synstamenous

(Ruscus).

Gynoecium:

Tricarpallary,

syncarpous, the odd carpel usually

anterior, ovary superior, trilocular, with

2 rows of numerous ovules on axile

placextation; rarely unilocular with

parietal placentation, style usually one;

stigmas 1 or 3; rarely the ovary is inferior

(Haemodorum), nectar – secreting septal

glands are present in the ovary.

Fruit: Fruit usually a septicidal

or loculicidal capsule or a berry as in

Asparagus & Smilax.

Botanical description of Allium cepa

(In APG classification, Allium cepa is

placed under the family Amaryllidaceae)

Habit: Perennial herb with bulb.

Root: Fibrous adventitious root system

Stem: Underground bulb

Leaf: a cluster of radical leaves emerges

from the underground bulb, cylindrical

and fleshy having sheathy leaf bases with

parallel venation.

Inflorescence: Scapigerous i.e. the

inflorescence axis (peduncle) arising from

the ground bearing a cluster of flowers

at its apex. Pedicels are of equal length,

arising from the apex of the peduncle

which brings all flowers at the same level.

Flower: Small, white, bracteate,

ebrcteolate, pedicellate, complete,

trimerous, actinomorphic and

hypogynous. Flowers are protandrous.

Perianth: Tepals 6, white,arranged

in two whorls of three each, syntepalous

showing valvate aestivation.

Androecium: Stamens 6, arranged

in two whorls of three each, epitepalous,

apostamenous /free and opposite to tepals.

Anthers dithecous, basifixed, introse, and

dehiscing longitudinally.

Gynoecium: Tricarpellary and

syncarpous. Ovary superior, trilocular with

two ovules in each locule on axile placentation.

Style simple, slender with simple stigma.

Fruit: A loculicidal capsule.

Seed: Endospermous

Floral Formula:

Br.,Ebrl., , ,P (3+3)

+A 3+3

,G (3)

217

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Inflorescence

Bract

Peduncle

Cylindrical fleshy leaf

Pedicel

Flower

Bract

Peduncle

Inflorescence

Epitepalous stamen

Filament

Bulbose

stem

Ovary

Perianth

Pedicel

Habit

Flower entire

L.s of flower

Anther

Stigma

Style

Ovary

Pedicel

Stigma

Style

Ovary

Gynoecium

C.S. of ovary

Locule

Ovule

Carpel

Floral formula

Br.,Ebrl., , ,P (3+3)

+A 3+3

,G (3)

Figure 5.26: Allium cepa

Floral diagram

218

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Economic importance of the family liliaceae

S.No Economic Binomial Useful part Uses

importance

1 Food plant Allium cepa Bulbs Used as vegetable,

stimulative, diuretic,

expectorant with

bactericidal properties.

2. Medicinal

plant

Allium sativum

Asparagus officinalis

A. racemosus

Aloe barbadense

Aloe vera

Asparagus racemosus

Colchichum luteum

Gloriosa superba

Scilla hyacinthiana;

Smilax glabra; and

S.ovalifolia;

Bulbs

Fleshy

shoots

Tuberous

roots

Leaves

Leaves

Roots

Roots

Tubers

Bulbs

Roots

Used as condiment and also

good for heart.

Used as vegetables.

Used as vegetables.

Leaves are the source of

resinous drug, used as a

purgative.

Gelatinous glycoside

called aloin from

succulent leaves are

used in soothing lotions,

piles and inflammations,

hemorrhoidal salves and

shampoos.

Medicinal oil is prepared

from the root is used for

nervous and rheumatic

complaints and also in skin

diseases.

Used in the treatment of

gout and rheumatism.

Tubers helpful in promoting

labour pains in women.

Used as heart stimulant.

Used in the treatment of

venereal diseases.

4. Fibre

yielding

plant

5. Raticides

Insecticides

Phormium tenax Fibre Used for cordage, fishing

net, mattings, twines

Urginea indica

Veratrum album

Bulbs

Bulbs

Used for killing rats

Used as insecticide.

219

Continued

---

S.No Economic Binomial Useful part Uses

importance

6. Polyploidy Colchicum luteum Corm Colchicine (alkaloid)

used to induce polyploidy.

7. Ornamental

plants

Agapanthus

africanus

(Africian Lilly)

Hemerocallis fulva

(Orange Day Lilly)

Gloriosa superba

(Malabar glory lilly)

Lilium candidum

Lilium giganteum

Ruscus aculeatus

(Butchers Broom)

Tulipa suaveolens

Yucca alcifolia and

Y.gloriosa

Plant

Some of the well known

garden ornamentals.

Can you identify

this?

a. Name the family.

b. Write the binomial.

c. List the economic

uses.

In Yucca the crosspollination

carried

out by special moth,

Pronuba yuccasella.

Fully opened flowers

emit perfumes

and are visited by

the female moth,

especially during

nights. This

moth collects

a lot of pollen

grains from one

flower and visits

another flower.

Life history of

this moth is intimately associated with

the pollination mechanism in Yucca.

Lilium nilgiriensis

Tulipa

Smilax

Ruscus

Figure 5.27: Selected plants belongs to the

Family Liliaceae

220

---

State Flower of Tamil Nadu

Gloriosa superba

Ascrambling or

climbing plant.

Anthers extrose

and versatile.

The flower petals, wavy on

the edges, greenish yellow

when bloom, turn flame red

at the tips when matures

leaves subopposite, the

leaf tip is modified into

tendril.

The plant contain the

alkaloid colchicine. It

is widely used as an

experimental tool

in the study of cell

division.

Fruit is a fleshy capsule

.

Petals have wavy edges

and are strongly turned

backwards.

The name of Gloriosa superba is composed of two greek words

Gloriosa means full of glory, superba means superb.

This plant was placed earlier in Liliaceae.

221

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Summary

Taxonomy deals with the identification,

naming and classification of plants. But

systematics deals with evolutionary

relationship between the organisms in

addition to taxonomy. Taxonomic hierarchy

was introduced by Carolus Linnaeus. It also

includes ranks. Species is the fundamental

unit of taxonomic classification. Species

concept can be classified into two groups

based on the process of evolution and

product of evolution. There are three

types of species, morphological, biological

and phylogenetic species. Type concept

emphasizes that a specimen must be

associated with the scientific name which

is known as nomenclatural type. There are

different types and they are holotype, isotype,

lectotype etc. Taxonomic aids are the tools

for the taxonomic study such as keys, flora,

revisions, catalogues, botanical gardens and

herbaria. Botanical gardens serve different

purposes. They have aesthetic value, offers

scope for botanical research, conservation

of rare species and propagation of many

species. Botanical survey of India explores

and documents biodiversity all over India. It

has 11 regional centres in India. Herbarium

preparation includes plant collection,

documentation of field data, preparation of

plant specimens, mounting and labelling.

There are several national and international

herbaria. National herbaria include MH,

PCM, CAL etc. Kew herbarium is the world’s

largest one.

Classification is the basis for cataloguing

and retrieving information about the

tremendous diversity of flora. It helps us

to know about different varieties, their

phylogenetic relationship and exact position.

Some important systems of classification are

fall in to three types; artificial, natural and

phylogenetic. Carolus Linnaeus outlined an

artificial system of classification in “Species

Plantarum” in 1753. The first scheme of

classification based on overall similarities

was presented by Antoine Laurent De Jessieu

in 1789. A widely followed natural system

of classification was proposed by George

Bentham (1800 - 1884) and Joseph Dalton

Hooker. This system was not intended

to be phylogenetic. One of the earliest

phylogenetic systems of classification

was jointly proposed by Adolf Engler

and Karl A Prantl in a monumental work

“Die Naturelichen Pflanzen Familien”.

Arthur Cronquist proposed phylogenetic

classification of flowering plants based

on a wide range of taxonomic characters

including anatomical and phytochemical

of phylogenetic importance in his book

titled “The evolution and classification of

flowering plants.”Angiosperm phylogeny

group (APG) classification is the most

recent classification of flowering plants

based on phylogenetic data. APG system

is an evolving and currently accepted

system across the world and followed by

all the leading taxonomic institutions and

practising taxonomists.

Cladistics is the methodology, used

to classify organisms into monophyletic

groups, consisting of all the descents of

the common ancestors. The outcome

of a cladistic analysis is a cladogram

and is constructed to represent the best

hypothesis of phylogenetic relationships.

Chemotaxonomy is the scientific approach

of classification of plants on the basis of

their biochemical constituents in them.

Utilization of the characters of chromosome

for the taxonomic inference is known

222

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as karyotaxonomy. The application of

serology in solving taxonomic problems

is called serotaxonomy. Molecular

Taxonomy is the branch of phylogeny that

analyses hereditary molecular differences,

mainly in DNA nuclear and chloroplast

sequences, to gain information and to

establish genetic relationship between the

members of different taxonomic categories.

Different molecular markers like allozymes,

mitochondrial DNA, microsatellites,

RAPDs, AFLPs, single nucleotide

polymorphism- SNP, microchips or arrays

are used in analysis. Molecular Taxonomy

unlocks the treasure chest of information

on evolutionary history of organisms.It

plays a vital role in phytogeography, which

ultimately helps in genome mapping and

biodiversity conservation. DNA barcoding

is a taxonomic method that uses a very

short genetic sequence from a standard part

of a genome. It helps in identification of

organisms.

Evaluation

1. Specimen derived

from non-original

collection serves as

the nomenclatural

type, when original

specimen is missing.

It is known as

a. Holotype b. Neotype

c. Isotype d. Paratype

2. Phylogenetic classification is the

most favoured classification because

it reflects

a. Comparative Anatomy

b. Number of flowers produced

c. Comparative cytology

d. Evolutionary relationships

3. The taxonomy which involves the

similarities and dissimilarities among

the immune system of different taxa

is termed as

a. Chemotaxonomy

b. Molecular systematics

c. Serotaxonomy

d. Numerical taxonomy

4. Which of the following is a flowering

plant with nodules containing

filamentous nitrogen fixing micro -

organisms?

a. Crotalaria juncea

b. Cycas revoluta

c. Cicer arietinum

d. Casuarina equisetifolia

5. Flowers are zygomorphic in

a. Ceropegia b. Thevetia

c. Datura d. Solanum

6. What is the role of national gardens

in conserving biodiversity – discuss

7. Where will you place the plants which

contain two cotyledons with cup

shaped thalamus?

8. How does molecular markers work

to unlock the evolutionary history of

organisms?

9. Give the floral characters of Clitoria

ternatea.

10. How will you distinguish Solanaceae

members from Liliaceae members?

223

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ICT Corner

Characteristics of flowers

Look inside the Flower.

Steps

• Scan the QR code or go to google play store

• Type online labs and install it.

• Select biology and select Character of flower

• Click theory to know the basic about Character of flower

• Register yourself with mail-id and create password to access online lab simulations

Activity

• Select simulation and dissect the different flowers

• Record your observations

Step 2

Step 4

URL:

Step 1 Step 3

https://play.google.com/store/apps/details?id=in.edu.olabs.olabs&hl=en

* Pictures are indicative only

224

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Chapter

6

Unit III: Cell biology and

Biomolecules

Cell: The Unit of Life

Learning Objectives

The learner will be able to,

• Describe the cell and contributions

of early scientist towards its

discovery

• Appreciate the use of light and

electron microscopes for better

understanding of the cell

• Understand the ideas of cell theory

and the different concepts associated

with it

• Distinguish the significant characters

of various groups of life forms

• Recognize the basic structure of cell

and differentiate the cells of animals,

plants, bacteria and viruses

• Explain the structure and functions

of cell organelles including nucleus

• Recognize the structure of

chromosome and its types

• Describe the flagellar structure,

types and movements

• Get acquainted with the cytological

techniques

Chapter Outline

6.1. Discovery

6.2. Microscopy

6.3. Cell theory

6.4. Cell types

6.5. Plant cell and Animal cell

6.6. Cell organelles

6.7. Nucleus

6.8. Flagella

6.9. Cytological techniques

The word ‘cell’ comes from the Latin word

‘Celle” which means ‘a small compartment’.

The word cell was first used by Robert

Hooke (1662) therefore the term ‘cell’ is as

old as 300 years.

6.1. Discovery

Aristotle (384-322BC),

was the one who first

recognised that animals and plants

consists of organised structural units but

unable to explain what it was. In 1660’s

Robert Hooke observed something

which looks like ‘honeycomb with a

great little boxes’ which was later called

as ‘cell’ from the cork tissue in 1665. He

compiled his work as Micrographia. Later,

Antonie von Leeuwenhoek observed

unicellular particles which he named as

‘animacules’. Robert Brown (1831-39)

described the spherical body in the plant

225

---

Scientist

Aristotle (384–322BC)

cells as nucleus. H. J. Dutrochet (1824),

a French scientist, was the first to give idea

on cell theory. Later, Matthias Schleiden

(German Botanist) and Theodor Schwann

(German Zoologist) (1833) outlined the

basic features of the cell theory. Rudolf

Virchow (1858) explained the cell theory

by adding a feature stating that all living

cells arise from pre-existing living cells by

‘cell division’.

6.2. Microscopy

Microscope is an inevitable instrument

in studying the cell and subcellular

structures. It offers scope in studying

Robert Hooke (1635–1703)

Antonie von Leeuwenhoek

(1632–1723)

Schleiden (1804–1881) &

Schwann (1810–1882)

Rudolf Virchow (1821–1902)

Figure 6.1

Resolution: The term resolving

power or resolution refers to the

ability of the lenses to show the details

of object lying between two points. It

is the finest detail available from an

object. It can be calculated using the

following formula

Resolution = 0.61λ

NA

Where, λ= wavelength of the light and

NA is the numerical aperture.

Numerical Aperture: It is an important

optical constant associated with the

optical lens denoting the ability to resolve.

Higher the NA value greater will be the

resolving power of the microscope.

Magnification: The optical increase

in the size of an image is called

magnification. It is calculated by the

following formula

Magnification =

size of image seen with the microscope

size of the image seen with normal eye

226

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microscopic organisms therefore it is

named as microscope (mikros – small;

skipein – to see) in Greek terminology.

Compound microscope was invented by

Z. Jansen.

Microscope works on the lens system

which basically relies on properties of light

and lens such as reflection, magnification

and numerical aperture. The common

light microscope which has many lenses

are called as compound microscope. The

microscope transmits visible light from

sources to eye or camera through sample,

where interaction takes place.

6.2.1 Bright field Microscope

Bright field microscope is routinely

used microscope in studying various

aspects of cells. It allows light to pass

directly through specimen and shows a

well distinguished image from different

portions of the specimen depending upon

the contrast from absorption of visible

light. The contrast can be increased by

staining the specimen with reagent that

reacts with cells and tissue components

of the object.

The light rays are focused by

condenser on to the specimen on a

microslide placed upon the adjustable

platform called as stage. The light comes

from the Compact Flourescent Lamp

(CFL) or Light Emitting Diode (LED)

light system. Then it passes through two

lens systems namely objective lens (closer

to the object) and the eye piece (closer to

eye). There are four objective lenses (5X,

10X, 45X and 100X) which can be rotated

and fixed at certain point to get required

magnification. It works on the principle

of numerical aperture value and its own

resolving power.

The first magnification of the

microscope is done by the objective lens

which is called primary magnification

and it is real, inverted image. The second

magnification of the microscope is

obtained through eye piece lens called

as secondary magnification and it is

virtual and inverted image (Figure 6.2 a,

b and c).

6.2.2 Dark Field Microscope

The dark field microscope was discovered

by Z. Sigmondy (1905). Here the field will

be dark but object will be glistening so the

appearance will be bright. A special effect

in an ordinary microscope is brought

about by means of a special component

called ‘Patch Stop Carrier’. It is fixed in

metal ring of the condenser component.

Patch stop is a small glass device which has

a dark patch at centre of the disc leaving

a small area along the margin through

which the light passes. The light passing

through the margin will travel oblique like

a hollow cone and strikes the object in the

periphery, therefore the specimen appears

glistening in a dark background. (Figure

6.2 d and e).

6.2.3 Phase contrast microscope

This was invented by Zernike (1935). It is

a modification of light microscope with all

its basic principle. The objects observed by

increasing the contrast by bringing about

change in amplitude of the light waves. The

contrast can be increased by introducing the

‘Phase Plate’ in the condenser lens. Phase

plate is a circular component with circular

annular etching.

227

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Eye

Initial image

Eye Lens

Final Image

Objective Lens

Object

(a)

(b)

(c)

Objective lens

Stage

Condenser lens

Patch stop

Light source

(d)

(e)

(f)

Figure 6.2: a. Light microscope; b. Ray diagram - light path; c. Image taken using light

microscope; d. Light path in dark field; e. Image taken using dark field microscope;

f. Light path in phase contrast microscope; g. Image taken using phase contrast microscope

228

(g)

---

Microscopic measurements:

The microscope also has facility to measure microscopic objects

through a technique called ‘micrometry’. There are two scales

involved for measuring.

1. Ocular Micrometer

2. Stage Micrometer

Ocular Micrometer: It is fixed inside the eye piece lens. It is a thin transparent glass

disc where there are lines divided into 100 equal units. The scale has no value.

Stage Micrometer:This is a slide with a line divided into 100 units. The line is about

1mm. The distance between two adjacent lines is 10 µm. The known value of the stage

micrometer is transferred to the ocular micrometer, thereby the measurements can be

made using ocular micrometer.

The distance between two adjacent line of ocular meter= Number of stage divisions

Number of ocular divisions × 10

0 10 20 30 40 50

(a)

(b)

Figure 6.3: a. Ocular micrometer; b. Stage micrometer

Light passes with different velocity after

coming out of the thinnest and thickest

areas of the phase plate thereby increasing

the contrast of the specimen. A hollow cone

of light passes through the condenser. Direct

light pass through thin area of phase plate,

whereas light passing from the specimen

reaches thick area of phase plate. The light

passing through thicker area travel at low

speed, on the other hand the light passing

through thin area reach fast therefore

contrast is increased in the specimen. Phase

contrast microscope is used to observe

living cells, tissues and the cells cultured

invitro during mitosis (Figure 6.2 f and g).

6.2.4 Electron Microscope

Electron Microscope was first introduced

by Ernest Ruska (1931) and developed

by G Binning and H Roher (1981). It is

used to analyse the fine details of the cell

and organelles called ultrastructure. It uses

beam of accelerated electrons as source of

illumination and therefore the resolving

power is 1,00,000 times than that of light

microscope.

The specimen to be viewed under

electron microscope is dehydrated

and impregnated with electron opaque

chemicals like gold or palladium. This is

essential for withstanding electrons and

229

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also for contrast of the image.

There are two kinds of electron

microscopes namely

1. Transmission Electron Microscope (TEM)

2. Scanning Electron Microscope (SEM)

1. Transmission electron microscope:

This is the most commonly used

electron microscope which provides two

dimensional image. The components of

the microscope are as follows:

a. Electron Generating System

b. Electron Condensor

c. Specimen Objective

d. Tube Lens

e. Projector

(a)

(b)

Figure 6.4: a. Transmission electron microscope; b. Image of TEM

(a)

(b)

Figure 6.5: a. Scanning electron microscope; b. Image of SEM

A beam of electron passes through the

specimen to form an image on fluorescent

screen. The magnification is 1–3 lakhs

times and resolving power is 2–10 Å. It

is used for studying detailed structrue of

viruses, mycoplasma, cellular organelles,

etc (Figure 6.4 a and b).

230

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Comparison of Microscopes

Features

Source of

illumination

for Image

Formation

Types of cells

visualized

Light Dark Field

Microscope Microscope

Visible

light

Individual

cells can be

visualised,

even living

ones.

Phase Contrast Transmission

Microscope Electron

Microscope

Scanning

Electron

Microscope

Visible light Visible light Electrons Electrons

Individual

cells can be

visualised,

even living

ones.

Individual cells

can be

visualised, even

living ones.

Thin sections of

the specimen are

obtained. The

electron beam

pass through

the sections

and form an

image with high

magnification

and high

resolution.

Image 2-D 2-D 2-D 2-D 3-D

Nature of

Lenses

Glass

lenses

Glass lenses Glass lenses

One electrostatic

lens with few

electromagnetic

lenses

The specimen

is coated with

gold and the

electrons

are reflected

back and give

the details

of surface

topography of

the specimen.

One

electrostatic

lens with few

electromagnetic

lenses

Medium Air/oil Air/oil Air/oil Vacuum Vacuum

Specimen Glass slides Glass slides Glass slides

mounting

Focusing and

Magnification

Adjustments

Means for

obtaining

specimen

Contrast

Microscope

picture

Changing

objectives

Light

diffraction

Changing

objectives

Through

patch stop

Changing

objectives

Through phase

plate

Mounted

on coated

or uncoated

copper grids

Electrical, using

deflection coil

Electron

scattering

Mounted on

aluminium

stubs and are

coated in gold

Electrical,

using

deflection coil

Electron

scattering

231

---

2. Scanning Electron Microscope:

This is used to obtain three dimensional

image and has a lower resolving power than

TEM. In this, electrons are focused by means

of lenses into a very fine point. The interaction

of electrons with the specimen results in the

release of different forms of radiation (such

as auger electrons, secondary electrons, back

scattered electrons) from the surface of the

specimen. These radiations are then captured

by an appropriate detector, amplified and

then imaged on fluorescent screen. The

magnification is 2,00,000 times and resolution

is 5–20 nm (Figure 6.5 a and b).

6.3. Cell Theory

In 1833, German botanist Matthias

Schleiden and German zoologist Theodor

Schwann proposed that all plants and

animals are composed of cells and that

cells were the basic building blocks of life.

These observations led to the

formulation of modern cell theory.

• All organisms are made up of cells.

• New cells are formed by the division of

pre-existing cells.

• Cells contains genetic material, which is

passed on from parents to daughter cells.

• All metabolic reactions take place

inside the cells.

6.3.1 Exception to Cell Theory

Viruses are puzzle in biology. Viruses,

viroids and prions are the exception to

cell theory. They lack protoplasm, the

essential part of the cell and exists as

obligate parasites which are sub-cellular

in nature.

6.3.2 Cell Doctrine (Cell Principle)

The features of cell doctrine are as follows:

• All organisms are made up of cells.

• New cells are produced from the

pre-existing cells.

• Cell is a structural and functional unit

of all living organisms.

• A cell contains hereditary information

which is passed on from cell to cell

during cell division.

• All the cells are basically the same in

chemical composition and metabolic

activities.

• The structure and function of cell is

controlled by DNA.

• Sometimes the dead cells may remain

functional as tracheids and vessels in

plants and horny cells in animals.

6.3.3 Protoplasm Theory

Corti first observed protoplasm. Felix

Dujardin (1835) observed a living juice

in animal cell and called it “Sarcode”.

Purkinje (1839) coined the term

protoplasm for sap inside a plant cell. Hugo

Van Mohl (1846) indicated importance of

protoplasm.

Max Schultze (1861) established

similarity between Protoplasm and

Sarcode and proposed a theory which

later on called “Protoplasm Theory”

by O. Hertwig (1892). Huxley (1868)

proposed Protoplasm as a “physical

basis of life”.

Protoplasm as a Colloidal System

Protoplasm is a complex colloidal system

which was suggested by Fisher in 1894

and Hardy in 1899. It is primarily made of

water contents and various other solutes

of biological importance such as glucose,

fatty acids, amino acids, minerals,

vitamins, hormones and enzymes.

232

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These solutes may be homogeneous

(soluble in water) or heterogeneous

mass (insoluble in water) which forms

the basis for its colloidal nature.

Physical Properties of Protoplasm

The protoplasm exist either in semisolid

(jelly-like) state called ‘gel᾿ due to

suspended particles and various chemical

bonds or may be liquid state called ‘sol᾿.

The colloidal protoplasm which is in gel

form can change into sol form by solation

and the sol can change into gel by gelation.

These gel-sol conditions of colloidal

system are prime basis for mechanical

behaviour of cytoplasm.

1. Protoplasm is translucent, odourless

and polyphasic fluid.

2. It is a crystal colloid solution which

is a mixture of chemical substances

forming crystalloid i.e. true solution

(sugars, salts, acids, bases) and others

forming colloidal solution (Proteins

and lipids)

3. It is the most important property of the

protoplasm by which it exhibits three

main phenomena namely Brownian

movement, amoeboid movement and

cytoplasmic streaming or cyclosis.

Viscosity of protoplasm is 2–20

centipoises. The Refractive index of the

protoplasm is 1.4.

4. The pH of the protoplasm is around 6.8,

contain 90% water (10% in dormant

seeds)

5. Approximately 34 elements are present

in protoplasm but only 13 elements are

main or universal elements i.e. C, H, O, N,

Cl, Ca, P, Na, K, S, Mg, I and Fe. Carbon,

Hydrogen, Oxygen and Nitrogen form the

96% of protoplasm.

6. Protoplasm is neither a good nor a

bad conductor of electricity. It forms

a delimiting membrane on coming in

contact with water and solidifies when

heated.

7. Cohesiveness: Particles or molecules

of protoplasm are adhered with each

other by forces, such as Van der

Waal’s bonds, that hold long chains

of molecules together. This property

varies with the strength of these

forces.

8. Contractility: The contractility of protoplasm

is important for the absorption

and removal of water especially stomatal

operations.

9. Surface tension: The proteins and

lipids of the protoplasm have less

surface tension, hence they are found

at the surface forming the membrane.

On the other hand the chemical

substances (NaCl) have high surface

tension, so they occur in deeper parts

of the cell protoplasm.

6.3.4 Cell sizes and shapes

Cell greatly vary in size, shape and

also in function. Group of cells with

similar structures are called tissue they

integrate together to perform similar

function, group of tissue join together

to perform similar function called

organ, group of organs with related

function called organ system, organ

system coordinating together to form

an organism.

Shape

The shape of cell vary greatly from

organism to organism and within the

organism itself. In bacteria cell shape

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1 cm = 1/100 meter

1 mm = 1/1000 meter =1/10 cm

1 µm = 1/1000,000 meter = 1/10,000 cm

1 nm = 1/1,000,000,000 meter = 1/10,000,000 cm

1 Å = 1/10,000,000,000 meter =1/100,000,000 cm

or

1 m = 10 2 cm = 10 3 mm = 10 6 µm = 10 9 nm = 10 10 Å

m = meter cm = centimetre mm = millimeter µm = micrometer

nm = nanometer Å=Angstrom

vary from round (cocci) to rectangular

(rod). In virus, shape of the envelope

varies from round to hexagonal or ‘T’

shaped. In fungi, globular to elongated

cylindrical cells and the spores of fungi

vary greatly in shape. In plants and

animals cells vary in shape according

to cell types such as parenchyma,

mesophyll, palisade, tracheid, fiber,

epithelium and others (Figure 6.6).

Size:

Mycoplasma

0.15 - 0.3 µm

RBC

7 -8 µm

Plant cell

10 - 100 µm

Chicken Egg

65mm

Ostrich Egg

50 - 150 mm

Virus

0.004 - 0.1 µm

Bacteria

0.5 - 5 µm

BGA

1 -60 µm

Ultra microscope Light microscope Naked Eye

Figure 6.6: Cell size variation of few organisms

6.4. Types of cells

On the basis of the cellular organization

and the nuclear characteristics, the cell

can be divided into

• Prokaryotes

• Mesokaryotes and

• Eukaryotes

6.4.1 Prokaryotes

Those organisms with primitive nucleus

are called as prokaryotes (pro – primitive;

karyon – nucleus). The DNA lies in the

‘nucleoid’ which is not bound by the

nuclear membrane and therefore it is not

a true nucleus and is also a primitive type

234

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of nuclear material. The DNA is without

histone proteins. Example: Bacteria, blue

green algae, Mycoplasma, Rickettsiae and

Spirochaetae.

6.4.2 Mesokaryotes

In the year 1966, scientist Dodge and his

coworkers proposed another kind of organisms

called mesokaryotes. These organisms

which shares some of the characters of both

prokaryotes and eukaryotes. In other words

these are organisms intermediate between

pro and eukaryotes. These contains well

organized nucleus with nuclear membrane

and the DNA is organized into chromosomes

but without histone protein components

divides through amitosis similar with

prokaryotes. Certain Protozoa like

Noctiluca, some phytoplanktons like

Gymnodinium, Peridinium and

Dinoflagellates are representatives of

mesokaryotes.

6.4.3 Eukaryotes

Comparison between types of cellular organisation

Those organisms which have true nucleus

are called Eukaryotes (Eu – True;

karyon – nucleus). The DNA is associated

with protein bound histones forming

the chromosomes. Membrane bound

organelles are present. Few organelles may

be arisen by endosymbiosis which is a cell

living inside another cell. The organelles

like mitochondria and chloroplast well

support this theory.

Features Prokaryotes Mesokaryotes Eukaryotes

Size of the cell ~1-5µm ~5-10µm ~10-100µm

Nuclear character Nucleoid, no true

nucleus,

Nucleus with nuclear

membrane

True nucleus with

nuclear membrane

DNA

Usually circular

without histone

proteins

Usually linear but

without histone

proteins

Usually linear with

histone proteins

RNA/Protein

synthesis

Couples in

cytoplasm

Similar with

eukaryotes

RNA synthesis Inside

nucleus/ Protein

synthesis in cytoplasm

Ribosomes 50S+ 30S 60S + 40S 60S + 40S

Organelles Absent Present Numerous

Cell movement Flagella Gliding and flagella Flagella and cilia

Organization Usually single cell Single and colony Single, colonial and

multicellular

Cell division Binary fission Binary fission Mitosis and meiosis

Examples Bacteria and

Archaea

Origin of Eukaryotic cell:

Dinoflagellate,

Protozoa

Fungi, plants and

animals

Endosymbiont theory: Two eukaryotic organelles believed to be the descendants of the

endosymbiotic prokaryotes. The ancestors of the eukaryotic cell engulfed a bacterium

and the bacteria continued to function inside the host cell.

235

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Nucleoid

(containing DNA)

Cell Membrane

Prokaryotic Cell

ORIGIN OF EUKARYOTES

Cytoplasm

1 A prokaryote grows In size

and develops infoldings in its

Cell Membrane to increase tts

surface area to volume ratio.

Cell Membrane Infoldings

2 eventually pinch off from

the cell membrane, forming an early endomembrane

system. It encloses the nucleoid,

maling a membrane-bound nucleus. This is

the first eukaryote.

Nucleus

Endomembrane System

Nuclear Membrane

Endoplasmic Reticulum

3 An aerobic(oxygen using)proteobacterium

Enters the eukaryote, either as prey or a

parasite, and manages to avoid digestion.it

becomes an endosymbiont, or a cell living

Inside another cell.

Proteobacterium

First eukaryote

4 e’s ability to use oxygen to make energy becomes an asset for

the host,allowing it to thrive in an increasingly oxygen-rich environment

as the other eukaryotes go extinct, the proteobacterium is eventually

assimilated and becomes a mitochondrion.

Mitochondria

Cyanobacterium

Mitochondrion

Ancestor of Animals, fungi, and other Heterotrophs

Chloroplasts

5 Some eukaryotes go on to acquire additional

endosymbionts-the cyanobacteria, a group of bacteria

capable of photosynthesis. They become chloroplasts.

Figure 6.7: A model of endosymbiotic theory

236

Ancestor of Plants and Algae

---

The first cell might have evolved

approximately 3.8 billion years ago. The

primitive cell would have been similar

to present day protists (Figure 6.7).

6.5. Plant and Animal cell

6.5.1 Ultra Structure of Eukaryotic Cell

The eukaryotic cell is highly distinct

in its organisation. It shows several

variations in different organisms.

For instance, the eukaryotic cells

Figure 6.8: Animal and Plant cell

in plants and animals vary greatly

(Figure 6.8).

Animal Cell

Animal cells are surrounded by cell

membrane or plasma membrane.

Inside this membrane the gelatinous

matrix called protoplasm is seen to

contain nucleus and other organelles

which include the endoplasmic

reticulum, mitochondria, golgi bodies,

centrioles, lysosomes, ribosomes and

cytoskeleton.

Plant cell

A typical plant cell has prominent

cell wall, a large central vacuole and

plastids in addition to other organelles

present in animal cell (Figure 6.9

and 6.10).

Figure 6.9: Ultra Structure of Plant Cell

237

---

Difference between plant and animal cells

S. No Plant cell Animal Cell

1 Usually they are larger than animal cells Usually smaller than plant cells

2 Cell wall present in addition to plasma

membrane and consists of middle

lamellae, primary and secondary walls

Cell wall absent

3 Plasmodesmata present Plasmodesmata absent

4 Chloroplast present Chloroplast absent

5 Vacuole large and permanent Vacuole small and temporary

6 Tonoplast present around vacuole Tonoplast absent

7 Centrioles absent except motile cells of

lower plants

8 Nucleus present along the periphery of

the cell

Centrioles present

Nucleus at the centre of the cell

9 Lysosomes are rare Lysosomes present

10 Storage material is starch grains Storage material is a glycogen granules

6.5.2 Protoplasm

Protoplasm is the living content of the cell

that is surrounded by plasma membrane.

It is a colourless material that exists

throughout the cell together with the

cytoplasm, nucleus and other organelles.

Protoplasm is composed of a mixture of

small particles, such as ions, amino acids,

monosaccharides, water, macromolecules

like nucleic acids, proteins, lipids and

Figure 6.10: Cell structure and components

polysaccharides. It appears colourless,

jelly like gelatinous, viscous elastic and

granular. It appears foamy due to the

presence of large number of vacuoles. It

responds to the stimuli like heat, electric

shock, chemicals and so on.

6.5.3 Cell Wall

Cell wall is the outermost protective

cover of the cell. It is present in

bacteria, fungi and plants whereas

it is absent in animal cell. It was first

observed by Robert Hooke. It is an

actively growing portion. It is made up

of different complex material in various

organism. In bacteria it is composed

of peptidoglycan, in fungi chitin and

fungal cellulose, in algae cellulose,

galactans and mannans. In plants it is

made up of cellulose, hemicellulose,

pectin, lignin, cutin, suberin and silica.

238

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In plant, cell wall shows three distinct

regions (a) Primary wall (b) Secondary

wall (c) Middle lamellae (Figure 6.11).

a. Primary wall

It is the first layer inner to middle

lamellae, primarily consisting of loose

network of cellulose microfibrils in a gel

matrix. It is thin, elastic and extensible.

In most plants the microfibrils are made

up of cellulose oriented differently based

on shape and thickness of the wall. The

matrix of the primary wall is composed

of hemicellulose, pectin, glycoprotein and

water. Hemicellulose binds the microfibrils

with matrix and glycoproteins control the

orientation of microfibrils while pectin

serves as filling material of the matrix.

Cells such as parenchyma and meristems

have only primary wall.

b. Secondary wall

Secondary wall is laid during maturation.

It plays a key role in determining the shape

of a cell. It is thick, inelastic and is made

up of cellulose and lignin. The secondary

wall is divided into three sublayers

termed as S 1, S 2 and S 3 where the cellulose

microfibrils are compactly arranged with

different orientation forming a laminated

structure and the cell wall strength is

increased.

c. Middle lamellae

It is the outermost layer made up of calcium

and magnesium pectate, deposited at the

time of cytokinesis. It is a thin amorphous

layer which cements two adjacent cells. It

is optically inactive (isotropic).

Plasmodesmata and Pits

Plasmodesmata act as a channel between

the protoplasm of adjacent cells through

which many substances pass through.

Moreover, at few regions the secondary

wall layer is laid unevenly whereas the

primary wall and middle lamellae are laid

continuously such regions are called pits.

The pits of adjacent cells are opposite to

each other. Each pit has a pit chamber

and a pit membrane. The pit membrane

has many minute pores and thus they

are permeable. The pits are of two types

namely simple and bordered pit.

Middle lamella

Primary wall

Middle lamella

Primary wall

S 1

S 2

S 3

Cell Lumen

Secondary

wall

S 1

S 2

S 3

Cell Lumen

Secondary wall

T.S. of a Plant cell

(details of cell wall)

Portion enlarged with

adjacent cells

Figure 6.11: Plant cell wall

239

---

Functions of cell wall

The cell wall plays a vital role in holding

several important functions given below

1. Offers definite shape and rigidity to

the cell.

2. Serves as barrier for several molecules

to enter the cells.

3. Provides protection to the internal

protoplasm against mechanical injury.

4. Prevents the bursting of cells by

maintaining the osmotic pressure.

5. Plays a major role by acting as a

mechanism of defense for the cells.

6.5.4 Cell Membrane

The cell membrane is also called cell

surface (or) plasma membrane. It is a thin

structure which holds the cytoplasmic

content called ‘cytosol’. It is extremely

thin (less than 10nm).

Figure 6.12: Model of Cell membrane

Fluid Mosaic Model

Jonathan Singer and Garth Nicolson

(1972) proposed fluid mosaic model.

It is made up of lipids and proteins

together with a little amount of

carbohydrate. The lipid membrane is made

up of phospholipid. The phospholipid

molecule has a hydrophobic tail and

hydrophilic head. The hydrophobic tail

Water-loving

polar molecule are

called hydrophilic

molecule. They have

polar phosphate group responsible for

attracting water.

Water hating non-polar molecule

are called as hydrophobic molecule.

They have fatty acid which is nonpolar

which cannot attract water

repels water and hydrophilic head attracts

water. The proteins of the membrane

are globular proteins which are found

intermingled between the lipid bilayer

most of which are projecting beyond the

lipid bilayer. These proteins are called as

integral proteins. Few are superficially

attached on either surface of the lipid

bilayer which are called as peripheral

proteins. The proteins are involved

in transport of molecules across the

membranes and also act as enzymes,

receptors (or) antigens.

The Carbohydrate molecules

of cell membrane are short chain

polysaccharides. These are either bound

with ‘glycoproteins’ or ‘glycolipids’ and

form a ‘glyocalyx’ (Figure 6.12).

The movement of membrane lipids from

one side of the membrane to the other

side by vertical movement is called flip

flopping or flip flop movement. This

movement takes place more slowly

than lateral diffusion of lipid molecule.

The phospholipids can have flip flop

movement because the phospholipids

have smaller polar regions, whereas the

proteins cannot flip flop because the polar

region is extensive.

240

---

Figure 6.13: Transport of molecules through cell membrane

Function of Cell Membrane

The functions of the cell membrane is

enormous which includes cell signalling,

transporting nutrients and water,

preventing unwanted substances entering

into the cell, and so on.

Cell Transport

Cell membrane act as a channel of transport

for molecules. The membrane is selectively

permeable to molecules. It transports

molecules through energy dependant

process and energy independent process.

The membrane proteins (channel and

carrier) are involved in movement of

ions and molecules across the membrane

(Figure 6.13).

Endocytosis and Exocytosis

Cell surface membrane are able to

transport individual molecules and ions.

There are processes in which a cell can

transport a large quantity of solids and

liquids into cell (endocytosis) or out of

cell (exocytosis) (Figure 6.14).

Endocytosis: During endocytosis

the cell wraps the cell surface membrane

around the material and brings it into

Figure 6.14: Endocytosis and exocytosis

241

---

cytoplasm inside a vesicle. There are two

types of endocytosis:

1. Phagocytosis – Particle is engulfed by

membrane, which folds around it and

forms a vesicle. The enzymes digest the

material and products are absorbed by

cytoplasm.

2. Pinocytosis – Fluid droplets are

engulfed by membrane, which forms

vesicles around them.

Exocytosis: Vesicles fuse with plasma

membrane and eject contents. This

passage of material out of the cell is known

as exocytosis. This material may be a

secretion in the case of digestive enzymes,

hormones or mucus.

Signal Transduction

The process by which the cell receive

information from outside and respond is

called signal transduction. Plants, fungi

and animal cell use nitric oxide as one

of the many signalling molecules. The

cell membrane is the site of chemical

interactions of signal transduction.

Receptors receives the information from

first messenger and transmit the message

through series of membrane proteins.

It activates second messenger which

stimulates the cell to carry out specific

function.

cellular organelles are suspended and bound

together by a lipid bilayer plasma membrane.

It constitutes dissolved nutrients, numerous

salts and acids to dissolve waste products.

It is a very good conductor of electricity.

It gives support and protection to the cell

organelles. It helps movement of the cellular

materials around the cell through a process

called cytoplasmic streaming. Further,

most cellular activities such as many

metabolic pathways including glycolysis

and cell division occur in cytoplasm.

6.6 Cell Organelles

6.6.1 Endomembrane System

The system of membranes in a eukaryotic

cell, comprising the plasma membrane,

nuclear membrane, endoplasmic

reticulum, golgi apparatus, lysosomes

and vacuolar membranes (tonoplast).

Endomembranes are made up of

phospholipids with embedded proteins

that are similar to cell membrane

which occur within the cytoplasm. The

endomembrane system is evolved from

the inward growth of cell membrane

in the ancestors of the first eukaryotes

(Figure 6.15).

6.6.2 Endoplasmic Reticulum

Cytoplasm

Cytoplasm is the main arena of various

activities of a cell. It is the semifluid

gelatinous substance that fills the cell. It

is made up of eighty percent water and is

usually clear and colourless. The cytoplasm

is sometimes described as non nuclear

content of protoplasm. The cytoplasm

serves as a molecular soup where all the

Figure 6.15: Structure of Endoplasmic

reticulum

242

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The largest of the internal membranes is

called the endoplasmic reticulum (ER).

The name endoplasmic reticulum was given

by K.R. Porter (1948). It consists of double

membrane. Morphologically the structure

of endoplasmic reticulum consists of:

1. Cisternae are long, broad, flat, sac like

structures arranged in parallel bundles

or stacks to form lamella. The space

between membranes of cisternae is

filled with fluid.

2. Vesicles are oval membrane bound

vacuolar structure.

3. Tubules are irregular shape, branched,

smooth walled, enclosing a space

Endoplasmic reticulum is associated

with nuclear membrane and cell surface

membrane. It forms a network in cytoplasm

and gives mechanical support to the cell.

Its chemical environment enables protein

folding and undergo modification necessary

for their function. Misfolded proteins are

pulled out and are degraded in endoplasmic

reticulum. When ribosomes are present in the

outer surface of the membrane it is called as

rough endoplasmic reticulum(RER), when

the ribosomes are absent in the endoplasmic

reticulum it is called as smooth Endoplasmic

reticulum(SER). Rough endoplasmic

reticulum is involved in protein synthesis and

smooth endoplasmic reticulum are the sites

of lipid synthesis. The smooth endoplasmic

reticulum contains enzymes that detoxify

lipid soluble drugs, certain chemicals and

other harmful compounds.

6.6.3 Golgi Body (Dictyosomes)

In 1898, Camillo Golgi visualized a netlike

reticulum of fibrils near the nucleus, were

named as Golgi bodies. In plant cells they

are found as smaller vesicles termed as

dictyosomes. Golgi apparatus is a stack of

flat membrane enclosed sacs. It consist of

cisternae, tubules, vesicles and golgi vacuoles.

In plants the cisternae are 10-20 in number

placed in piles separated from each other

by a thin layer of inter cisternal cytoplasm

often flat or curved. Peripheral edge of

cisternae forms a network of tubules and

vesicles. Tubules interconnect cisternae and

are 30-50nm in dimension. Vesicles are large

round or concave sac. They are pinched off

from the tubules.They are smooth/secretary

or coated type. Golgi vacuoles are large

spherical filled with granular or amorphous

substance, some function like lysosomes.

The Golgi apparatus compartmentalises a

series of steps leading to the production of

functional protein.

Figure 6.16: Structure of Golgi apparatus

Small pieces of rough endoplasmic

reticulum are pinched off at the ends to

form small vesicles. A number of these

vesicles then join up and fuse together

to make a Golgi body. Golgi complex

plays a major role in post translational

modification of proteins and glycosidation

of lipids (Figure 6.16 and 6.17).

Functions:

• Glycoproteins and glycolipids are

produced

• Transporting and storing lipids.

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• Formation of lysosomes.

• Production of digestive enzymes.

• Cell plate and cell wall formation

• Secretion of Carbohydrates for the

formation of plant cell walls and insect

cuticles.

• Zymogen granules (proenzyme/precursor

of all enzyme) are synthesised.

the mitochondrion is filled with proteinaceous

material called mitochondrial matrix. The

inner membrane consists of stalked particles

called elementary particles or Fernandez

Moran particles, F1 particles or Oxysomes.

Each particle consists of a base, stem and

a round head. In the head ATP synthase is

present for oxidative phosphorylation. Inner

membrane is impermeable to most ions,

small molecules and maintains the

proton gradient that drives oxidative

phosphorylation (Figure 6.18).

Figure 6.17: Exocytosis

6.6.4 Mitochondria

It was first observed by A. Kolliker (1880).

Altmann (1894) named it as Bioplasts.

Later Benda (1897, 1898), named as

mitochondria. They are ovoid, rounded,

rod shape and pleomorphic structures.

Mitochondrion consists of double

membrane, the outer and inner membrane.

The outer membrane is smooth, highly

permeable to small molecules and it

contains proteins called Porins, which

form channels that allows free diffusion of

molecules smaller than about 1000 daltons

and the inner membrane divides the

mitochondrion into two compartments,

outer chamber between two membranes

and the inner chamber filled with matrix.

The inner membrane is convoluted

(infoldings), called crista (plural: cristae).

Cristae contain most of the enzymes for

electron transport system. Inner chamber of

Figure 6.18: Structure of Mitochondria

Mitochondria contain 73% of proteins,

25-30% of lipids, 5-7 % of RNA, DNA

(in traces) and enzymes (about 60 types).

Mitochondria are called Power house of a

cell, as they produce energy rich ATP.

All the enzymes of Kreb’s cycle are

found in the matrix except succinate

dehydrogenase. Mitochondria consist of

circular DNA and 70S ribosome. They

multiply by fission and replicates by strand

displacement model. Because of the presence

of DNA it is semi-autonomous organelle.

Unique characteristic of mitochondria is

that they are inherited from female parent

only. Mitochondrial DNA comparisons are

used to trace human origins. Mitochondrial

DNA is used to track and date recent

evolutionary time because it mutates 5 to 10

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time faster than DNA in the nucleus.

6.6.5 Plastids

The term plastid is derived from the Greek

word Platikas (formed/moulded) and used

by A.F.U. Schimper in 1885. He classified

plastids into following types according to

their structure, pigments and function.

Plastids multiply by fission.

Plastids

Chromoplasts Leucoplasts

(Coloured Plastids) (Colourless

Plastids store food

materials)

Chloroplast Amyloplast –

Occurs in green stores – starch

algae and higher

plants

Pigments

chlorophyll a and b

Phaeoplast

Brown algae and

dinoflagellates

Pigment

fucoxanthin

Rhodoplast

Red algae

Pigment

Phycoerythrin

Elaioplast – store –

lipids (oils)

Seed of monocot

and dicots.

Aleuroplast (or)

Proteoplast

store – Protein

According to Schimper, different kind

of plastids can transform into one another.

Chloroplasts

6.6.6 Chloroplast

Chloroplasts are vital organelle found in

green plants. Chloroplast has a double

membrane the outer membrane and

the inner membrane separated by a

space called periplastidial space. The

space enclosed by the inner membrane

of chloroplast is filled with gelatinous

matrix, lipo-proteinaceous fluid called

stroma. Inside the stroma there is flat

interconnected sacs called thylakoid. The

membrane of thylakoid enclose a space

called thylakoid lumen.

Grana (singular: Granum) are

formed when many of these thylakoids

are stacked together like pile of coins.

Light is absorbed and converted into

chemical energy in the granum, which is

used in stroma to prepare carbohydrates.

Thylakoid contain chlorophyll pigments.

The chloroplast contains osmophilic

granules, 70s ribosomes, DNA

(circular and non histone) and RNA.

These chloroplast genome encodes

approximately 30 proteins involved in

photosynthesis including the components

of photosystem I & II, cytochrome bf

complex and ATP synthase. One of

the subunits of Rubisco is encoded by

chloroplast DNA. It is the major protein

component of chloroplast stroma,

single most abundant protein on earth.

The thylakoid contain small, rounded

photosynthetic units called quantosomes.

It is a semi-autonomous organelle and

divides by fission (Figure 6.19).

Chromoplasts

(contains

carotenoids)

Leucoplasts

Functions:

• Photosynthesis

• Light reactions takes place in granum,

• Dark reactions take place in stroma,

• Chloroplast is involved in photorespiration.

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Figure 6.19: Structure of Chloroplast

6.6.7 Ribosome

Types of Ribosomes

Ribosomes were first observed by George

Palade (1953) as dense particles or granules

in the electron microscope. Electron

microscopic observation reveals that

ribosomes are composed of two rounded

sub units, united together to form a complete

unit. Mg 2+ is required for structural cohesion

of ribosomes. Biogenesis of ribosome are

denova formation, auto replication and

nucleolar origin. Each ribosome is made

up of one small and one large sub-unit

Ribosomes are the sites of protein synthesis

in the cell. Ribosome is not a membrane

bound organelle (Figure 6.20).

70S Ribosomes (sub

unit 30S and 50S)

3 RNA molecule

(i) 16SrRNA in

30S subunit

(ii) 23S and 5S

in 50S large

subunit

(Prokaryotic

cells of Bluegreen

algae Bacteria,

Mitochondria

and Chloroplast

of many Algae

and higher

plants)

80S Ribosomes (sub

units 40S and 60S)

4 RNA molecule

(i) 18SrRNA in

40S small

subunit

(ii) 28S, 5.8S and

5S in larger

60S subunit

(Eukaryotic cells

of Plants and

animals)

Figure 6.20: Structure of Ribosomes

Svedberg unit (s).

The size of ribosomes

and their subunits

are usually given in

Svedberg unit (named after Theoder

Svedberg, Swedish Chemist Noble

Laureate 1929), a measure of a

particle size dependent on the speed

with which particle sediment in the

ultracentrifuge.

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Ribosome consists of RNA and

protein: RNA 60 % and Protein 40%.

During protein synthesis many ribosomes

are attached to the single mRNA is called

polysomes or polyribosomes. The

function of polysomes is the formation of

several copies of a particular polypeptide

during protein synthesis. They are free in

non-protein synthesising cells. In protein

synthesising cells they are linked together

with the help of Mg 2+ ions.

6.6.8 Lysosomes (Suicidal Bags of Cell)

Lysosomes were discovered by Christian

de Duve (1953), these are known as

suicidal bags. They are spherical bodies

enclosed by a single unit membrane.

They are found in eukaryotic cell.

Lysosomes are small vacuoles formed

when small pieces of golgi body are

pinched off from its tubules.

They contain a variety of hydrolytic

enzymes, that can digest material within

the cell. The membrane around lysosome

prevent these enzymes from digesting the

cell itself (Figure 6.21).

like mitochondria and endoplasmic

reticulum

• Autolysis: Lysosome causes self

destruction of cell on insight of disease

they destroy the cells.

• Ageing: Lysosomes have autolytic

enzymes that disrupts intracellular

molecules.

• Phagocytosis: Large cells or contents

are engulfed and digested by

macrophages, thus forming a phagosome

in cytoplasm. These phagosome fuse

with lysosome for further digestion.

• Exocytosis: Lysosomes release their

enzymes outside the cell to digest other

cells (Figure 6.22).

Acid Hydrolases

Nuclease, Proteases

Glycosidases

Lipases

Phophatases

Sulphatases

Phospholipidases

pH 7.2

ATP

ADP+ iP

Enzymes of Lysosome

Figure 6.22: Enzymes of Lysosome

6.6.9 Peroxisomes

Figure 6.21: Structure of Lysosome

Functions:

• Intracellular digestion: They digest

carbohydrates, proteins and lipids

present in cytoplasm.

• Autophagy: During adverse condition

they digest their own cell organelles

Figure 6.23: Structure of Peroxisome

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Peroxisomes were identified as organelles

by Christian de Duve (1967). Peroxisomes

are small spherical bodies and single

membrane bound organelle. It takes part

in photorespiration and associated with

glycolate metabolism. In plants, leaf

cells have many peroxisomes. It is also

commonly found in liver and kidney of

mammals. These are also found in cells of

protozoa and yeast (Figure 6.23).

in centriole (non-membranous organelle)

(Figure 6.24).

6.6.10 Glyoxysomes

Glyoxysome was discovered by Harry

Beevers (1961). Glyoxysome is a single

membrane bound organelle. It is a sub

cellular organelle and contains enzymes

of glyoxylate pathway. β-oxidation of fatty

acid occurs in glyoxysomes of germinating

seeds Example: Castor seeds.

6.6.11 Microbodies

Eukaryotic cells contain many enzyme

bearing membrane enclosed vesicles

called microbodies. They are single

unit membrane bound cell organelles:

Example: peroxisomes and glyoxysomes.

6.6.12 Sphaerosomes

It is spherical in shape and enclosed by

single unit membrane. Example: Storage

of fat in the endosperm cells of oil seeds.

6.6.13 Centrioles

Centriole consist of nine triplet peripheral

fibrils made up of tubulin. The central part

of the centriole is called hub, is connected to

the tubules of the peripheral triplets by radial

spokes (9+0 pattern). The centriole form

the basal body of cilia or flagella and spindle

fibers which forms the spindle apparatus

in animal cells. The membrane is absent

Figure 6.24: Structure of Centriole

6.6.14 Vacuoles

In plant cells vacuoles are large, bounded by

a single unit membrane called Tonoplast.

The vacuoles contain cell sap, which is a

solution of sugars, amino acids, mineral

salts, waste chemical and anthocyanin

pigments. Beetroot cells contains

anthocyanin pigments in their vacuoles.

Vacuoles accumulate products like tannins.

The osmotic expansion of a cell kept in

water is chiefly regulated by vacuole and

the water enters the vacuoles by osmosis.

The major function of plant vacuole

is to maintain water pressure known

as turgor pressure, which maintains

the plant structure. Vacuoles organises

itself into a storage/sequestration

compartment. Example: Vacuoles store,

most of the sucrose of the cell.

i. Sugar in Sugar beet and Sugar cane.

ii. Malic acid in Apple.

iii. Acids in Citrus fruits.

iv. Flavonoid pigment Cyanidin

3 rutinoside in the petals of

Antirrhinum.

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v. Tannins in Mimosa pudica.

vi. Raphide crystals in Dieffenbachia.

vii. Heavy metals in Mustard (Brassica).

viii. Latex in Rubber tree and Dandelion

stem.

Cell Inclusions

The cell inclusions are the non-living

materials present in the cytoplasm. They

are organic and inorganic compounds.

Inclusions in prokaryotes

In prokaryotes, reserve materials such

as phosphate granules, cyanophycean

granules, glycogen granules, poly

β-hydroxy butyrate granules, sulphur

granules, carboxysomes and gas vacuoles

are present. Inorganic inclusions in

bacteria are polyphosphate granules

(volutin granules) and sulphur granules.

These granules are also known as

metachromatic granules.

Inclusions in Eukaryotes

• Reserve food materials: Starch grains,

glycogen granules, aleurone grains, fat

droplets

• Secretions in plant cells are essential oil,

resins, gums, latex and tannins

• Inorganic crystals – plant cell have

calcium carbonate, calcium oxalate and

silica

• Cystolith – hypodermal leaf cells of

Ficus bengalensis, calcium carbonate

• Sphaeraphides – star shaped calcium

oxalate, Colocasia

• Raphides – calcium oxalate, Eichhornia

• Prismatic crystals – calcium oxalate,

dry scales of Allium cepa

6.7. Nucleus

Nucleus is an important unit of cell which

control all activities of the cell. Nucleus

holds the hereditary information. It is the

largest among all cell organelles. It may be

spherical, cuboidal, ellipsoidal or

discoidal.

It is surrounded by a double

membrane structure called nuclear

Figure 6.25: Structure of a Nucleus

envelope, which has the inner and

outer membrane. The inner membrane

is smooth without ribosomes and

the outer membrane is rough by the

presence of ribosomes and is continues

with irregular and infrequent intervals

with the endoplasmic reticulum. The

membrane is perforated by pores known

as nuclear pores which allows materials

such as mRNA, ribosomal units,

proteins and other macromolecules to

pass in and out of the nucleus. The pores

enclosed by circular structures called

annuli. The pore and annuli forms the

pore complex. The space between two

membranes is called perinuclear space.

Nuclear space is filled with nucleoplasm,

a gelatinous matrix has uncondensed

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chromatin network and a conspicuous

nucleoli. The chromatin network is the

uncoiled, indistinct and remain thread like

during the interphase. It has little amount of

RNA and DNA bound to histone proteins in

eukaryotic cells (Figure 6.25).

Chromatin is a

viscous gelatinous

substance that contains

DNA, histone &

non–histone proteins and RNA. H1,

H2A, H2B, H3 and H4 are the different

histones found in chromatin. It is formed

by a series of repeated units called

nucleosomes. Each nucleosome has a

core of eight histone subunits.

During cell division chromatin is

condensed into an organized form called

chromosome. The portion of Eukaryotic

chromosome which is transcribed into

mRNA contains active genes that are not

tightly condensed during interphase is

called Euchromatin. The portion of a

Eukaryotic chromosome that is not

transcribed into mRNA which remains

condensed during interphase and stains

intensely is called Heterochromatin.

I Nucleolus is a small, dense, spherical

structure either present singly or in

multiples inside nucleus and it’s not

membrane bound. Nucleoli possesses genes

for rRNA and tRNA.

Functions of the nucleus

• Controlling all the cellular activities

• Storing the genetic or hereditary

information.

• Coding the information in the DNA for

the production of enzymes and proteins.

• DNA duplication and transcription takes

place in the nucleus.

• In nucleolus ribosomal biogenesis takes

place.

6.7.1 Chromosomes

Strasburger (1875) first reported its

present in eukaryotic cell and the term

‘chromosome’ was introduced by Waldeyer

in 1888. Bridges (1916) first proved that

chromosomes are the physical carriers of

genes. It is made up of DNA and associated

proteins.

Structure of chromosome

The chromosomes are composed of thread

like strands called chromatin which is

made up of DNA, protein and RNA. Each

chromosome consists of two symmetrical

structures called chromatids. During cell

division the chromatids forms well organized

chromosomes with definite size and shape.

They are identical and are called sister

chromatids. A typical chromosome has

narrow zones called constrictions. There are

two types of constrictions namely primary

constriction and secondary constriction.

The primary constriction is made up of

centromere and kinetochore. Both the

chromatids are united at centromere,

whose number varies. The monocentric

chromosome has one centromere and

the polycentric chromosome has many

centromeres. The centromere contains a

complex system of protein fibres called

kinetochore. Kinetochore is the region

of chromosome which is attached to the

spindle fibre during mitosis.

Besides primary there are secondary

constrictions, represented with few

occurrence. Nucleoli develop from these

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secondary constrictions are called nucleolar

organizers. Secondary constrictions

contains the genes for ribosomal RNA

which induce the formation of nucleoli

and are called nucleolar organizer regions

(Figure 6.26).

Figure 6.26: Structure of a Chromosome

A satellite or SAT Chromosome are

short chromosomal segment or rounded

body separated from main chromosome

by a relatively elongated secondary

constriction. It is a morphological entity

in certain chromosomes.

Based on the position of centromere,

chromosomes are called telocentric

(terminal centromere), Acrocentric

(terminal centromere capped by telomere),

Sub metacentric (centromere subterminal)

and Metacentric (centromere median).

The eukaryotic chromosomes may be rod

Satellite

Metacentric Sub-Metacentric Acrocentric Telocentric

Figure 6.27: Types of chromosomes

based on centromere

Chromonema fiber:

It is a chromatin

fibre, 100 – 130 nm in

diameter thought to

be an element of higher order packing

of chromatin within chromosome.

During prophase the chromosomal

material becomes visible as very

thin filaments called chromonemata,

which is called as chromatids in early

stages of condensation. Chromatid

and chromonema are the two names

for the same structure a single linear

DNA molecule with its associated

proteins

Chromomeres: Chromomeres are

bead like accumulations of chromatin

material which are visible along

interphase chromosomes. They can

be seen in polytene chromosomes. At

metaphase they are not visible.

shaped (telocentric and acrocentric),

L-shaped (sub-metacentric) and V-shaped

(metacentric) (Figure 6.27).

Telomere is the terminal part of

chromosome. It offers stability to the

chromosome. DNA of the telomere

has specific sequence of nucleotides.

Telomere in all eukaryotes are composed

of many repeats of short DNA sequences

(5’TTAGGG3’ sequence in Neurospora

crassa and human beings). Maintenance

of telomeres appears to be an important

factor in determining the life span and

reproductive capacity of cells so studies

of telomeres and telomerase have the

promise of providing new insights into

conditions such as ageing and cancer.

Telomeres prevents the fusion of

chromosomal ends with one another.

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Holocentric chromosomes have

centromere activity distributed along

the whole surface of the chromosome

during mitosis. Holocentric condition

can be seen in Caenorhabditis elegans

(nematode) and many insects. There are

three types of centromere in eukaryotes.

They are as follows:

Point centromere: the type of

centromere in which the kinetochore

is assembled as a result of protein

recognition of specific DNA sequences.

Kinetochores assembled on point

centromere bind a single microtubule.

It is also called as localized centromere.

It occurs in budding yeasts

Regional centromere: In regional

centromere where the kinetochore

is assembled on a variable array of

repeated DNA sequences. Kinetochore

assembled on regional centromeres

bind multiple microtubules. It occurs

in fission yeast cell, humans and so on.

Holocentromere- The microtubules

bind all along the mitotic chromosome.

Example: Caenorhabditis elegans

(nematode) and many insects.

Based on the functions of chromosome

it can be divided into autosomes and sex

chromosomes.

Autosomes are present in all cells

controlling somatic characteristics

of an organism. In human diploid

cell, 44 chromosomes are autosomes

whereas two are sex chromosomes.

Sex chromosomes are involved in the

determination of sex.

Special types of chromosomes are

found only in certain special tissues.

These chromosomes are larger in size and

are called giant chromosomes in certain

plants and they are found in the suspensors

of the embryo. The polytene chromosome

and lamp brush chromosome occur

in animals and are also called as giant

chromosomes.

Polytene chromosomes observed in the

salivary glands of Drosophila (fruit fly) by

C.G. Balbiani in 1881. In larvae of many

flies, midges (Dipthera) and some insects

the interphase chromosomes duplicates

and reduplicates without nuclear division.

A single chromosome which is present

in multiple copies form a structure called

polytene chromosome which can be seen

in light microscope. They are genetically

active. There is a distinct alternating dark

bands and light inter-bands. About 95%

of DNA are present in bands and 5% in

inter-bands. The polytene chromosome has

extremely large puff called Balbiani rings

which is seen in Chironomous larvae. It is

also known as chromosomal puff. Puffing

of bands are the sites of intense RNA

synthesis. As this chromosome occurs in the

salivary gland it is known as salivary gland

chromosomes. Polyteny is achieved by

repeated replication of chromosomal DNA

several times without nuclear division and

the daughter chromatids aligned side by side

and do not separate (called endomitosis).

Gene expression, transcription of genes and

RNA synthesis occurs in the bands along

the polytene chromosomes. Maternal and

paternal homologues remain associated side

by side is called somatic pairing.

Lampbrush chromosomes occur at the

diplotene stage of first meiotic prophase

in oocytes of an animal Salamandar and

in giant nucleus of the unicellular alga

Acetabularia. It was first observed by

Flemming in 1882. The highly condensed

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chromosome forms the chromosomal axis,

from which lateral loops of DNA extend

as a result of intense RNA synthesis.

6.8. Flagella

6.8.1 Prokaryotic Flagellum

Check your grasp ?

When E-coli are cultured in medium

rich in glucose they lack flagella. When

grown in nutritionally poor medium

they possess flagella. What does this

indicate about the value of flagella?

Flagella is essential to seek out

a nutritionally more favourable

environment

Bacterial flagella are helical appendages

helps in motility. They are much thinner

than flagella or cilia of eukaryotes.

The filament contains a protein called

flagellin. The structure consists of a

basal body associated with cytoplasmic

membrane and cell wall with short hook

and helical filament. Bacteria rotates

their helical flagella and propels rings

present in the basal body which are

involved in the rotary motor that spins

the flagellum.

Structure of flagella in Bacteria

The gram positive bacteria contain only two

basal rings. S-ring is attached to the inside

of peptidoglycan and M-ring is attached

to the cell membrane. In Gram negative

bacteria two pairs of rings proximal and

distal ring are connected by a central

rod. They are L-Lipopolysaccharide ring

P-Peptidoglycan ring, S-Super membrane

ring and M-membrane ring. The outer pair

L and P rings is attached to cell wall and the

inner pair S and M rings attached to cell

membrane (Figure 6.28).

Mechanism of flagellar movement –

proton motive force

In flagellar rotation only proton

movements are involved and not ATP.

Protons flowing back into the cell

through the basal body rings of each

flagellum drives it to rotate. These

rings constitute the rotary motor.

The proton motive force (The force

derived from the electrical potential

and the hydrogen ion gradient

across the cytoplasmic membrane)

drives the flagellar motor. For the

rotation of flagellum the energy is

derived from proton gradient across

the plasma membrane generated

by oxidative phosphorylation. In

bacteria flagellar motor is located

in the plasma membrane where the

oxidative phosphorylation takes place.

Therefore, plasma membrane is a site

of generation of proton motive force.

6.8.2 Eukaryotic Flagellum– Cell Motility

Figure 6.28: Structure of Bacterial

Flagellum

Structure

Eukaryotic Flagella are enclosed by unit

membrane and it arises from a basal body.

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Flagella is composed of outer nine pairs

of microtubules with two microtubules

in its centre (9+2 arrangement). Flagella

are microtubule projection of the plasma

membrane. Flagellum is longer than cilium

(as long as 200µm). The structure of flagellum

has an axoneme made up microtubules and

protein tubulin (Figure 6.29).

Movement

Outer microtubule doublet is associated

with axonemal dynein which generates

force for movement. The movement is

ATP driven. The interaction between

tubulin and dynein is the mechanism

for the contraction of cilia and flagella.

Dynein molecules uses energy from

ATP to shift the adjacent microtubules.

This movement bends the cilium or

flagellum.

membrane bound structure made up of

basal body, rootlets, basal plate and shaft.

The shaft or axoneme consists of nine

pairs of microtubule doublets, arranged

in a circle along the periphery with a two

central tubules, (9+2) arrangement of

microtubules is present. Microtubules are

made up of tubulin. The motor protein

dynein connects the outer microtubule

pair and links them to the central pair.

Nexin links the peripheral doublets of

microtubules (Figure 6.30).

Figure 6.30: Structure of Cilia & flagella

6.9. Cytological Techniques

6.9.1 Preparation of Slides

Figure 6.29: Structure of Eukaryotic

flagellum

6.8.3 Cilia

Cilia (plural) are short cellular, numerous

microtubule bound projections of

plasma membrane. Cilium (singular) is

There are different

types of mounting based

on the portion of a

specimen to be observed

a. Whole mount: The

whole organism or

smaller structure is

mounted over a slide and observed.

b. Squash: Is a preparation where the

material to be observed is crushed/

squashed on to a slide so as to reveal

their contents. Example: Pollen grains,

mitosis and meiosis in root tips and

flower buds to observe chromosomes.

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c. Smears: Here the specimen is in the

fluid (blood, microbial cultures etc.,)

are scraped, brushed or aspirated from

surface of organ. Example: Epithelial cells.

d. Sections: Free hand sections from a

specimen and thin sections are selected,

stained and mounted on a slide.

Example: Leaf and stem of plants.

6.9.2 Recording the Observations

The observations made through a

microscope can be recorded by hand

diagrams or through microphotographs.

Hand diagrams: Hand diagrams are

drawn using ordinary pencil by observing

the slide and drawing manually.

Microphotograph: Images of structures

observed through microscopes can be

further magnified, projected and saved by

attaching a camera to the microscope by

a microscope coupler or eyepiece adaptor.

Picture taken using a inbuilt camera in a

microscope is called microphotography or

microphotograph.

6.9.3 Staining Techniques

Staining is very important to observe different

components of the cell. Each component

of the cell has different affinity towards

different stains. The technique of staining

the cells and tissue is called ‘histochemical

staining’ or ‘histochemistry’.

Common stains used in Histochemistry

S. No. Stain Colour of staining Affinity

1. Eosin Pink, Red Cytoplasm, cellulose

2. Acetocarmine/

Pink/ Red

Nucleus, Chromosomes

Haematoxylin

3. Methylene Blue Blue Nucleus

4. Saffranine Red Cell wall (Lignin)

5. Cotton blue Blue Fungal Hyphae

6. Sudan IV, Sudan Black Scarlet Red/Black Lipids

7. Coomasie brilliant Blue Blue Protein

8. Janus Green Greenish Blue Mitochondria

9. I 2 KI Bluish black to brown Starch

10. Toluidine blue Blue, greenish blue Xylem, Parenchyma &

Epidermis

Summary

Cell is the fundamental unit of all organisms

which was identified 300 years ago. Microscope

offers scope for observing smaller objects and

organisms. It works on the principle of light

and lenses. Different microscope offers clarity

in observing objects depending on the features

to be observed. Micrometric techniques

are used in measurement of microscopic

objects. Electron microscopes are used in

understanding the ultra-structural details of

cell. Cell theory and doctrine states that all

organism are made up of cell and it contains

genetic material. Protoplasm theory explains

nature and different properties of protoplasm.

Cell size and shape differ from type of tissue

or organs and organisms. Based on cellular

organization and nuclear characters the

255

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Concept Map

Cell

(The basic unit of life)

Cell wall & Plasmamembrane Protoplasm

Cytoplasm Nucleus

Cell organelles

Cytoplasmic inclusions

DNA

RNA

Proteins

Storage

Substance

carbohydrates, fats

& proteins

Secretory

substance

Pigments &

Enzymes

Excretory

substance

glycosides, tannins

& gums

Mitochondria

generation

of ATP

Chloroplast

Photosynthesis

Endoplasmic

Reticulum

transport

substance

synthesis

lipoprotein &

glycogen

Golgi bodies

Packaging &

Secretion

Ribosomes

Protein

Synthesis

Centrosomes

give rise spindle

fiber in animal

cells

Vacuoles

facilitate

transport

of ions &

materials

in plant cell

Microbodies

Peroxisomes

Glyoxysomes

256

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organisms are classified into prokaryote,

eukaryote and mesokaryote.

The eukaryotic cells originated by

endosymbiosis of prokaryotic organism. Key

difference between plant cell and animal cell

is the cell wall. Protoplasm is the colourless

mass includes the cytoplasm, cell organelles

and nucleus. Cell wall is the outermost

protective covering with three regions

primary, secondary wall and middle lamellae.

Cell membrane holds the cytoplasmic

content called cytosol. Cytoplasm includes

the matrix and the cell organelles excluding

nucleus. Endomembrane system includes

endoplasmic reticulum, golgi apparatus,

chloroplast, lysosomes, vacuoles, nuclear

membrane and plasma membrane. Nucleus

is the control unit of the cell, it carries

hereditary information. Chromosomes are

made up of DNA and associated proteins.

Bacterial flagella are made up of helical

polymers of a protein called flagellin.

Proton motive force are involved in flagellar

rotation. In Eukaryotes flagella are made up

microtubules and protein called dynein and

nexin and the movement is

driven by ATP. Cytological

techniques include

preparation of slides,

staining and recording the

observation.

Evaluation

1. The two subunits of ribosomes remain

united at critical ion level of

a. Magnesium b. Calcium

c. Sodium d. Ferrous

2. Sequences of which of the following

is used to know the phylogeny

a. mRNA b. rRNA

c. tRNA d. Hn RNA

3. Many cells function properly and

divide mitotically even though they

do not have

a. Plasma membrane b. cytoskeleton

c. mitochondria d. Plastids

4. Keeping in view the fluid mosaic

model for the structure of cell

membrane, which one of the following

statements is correct with respect to

the movement of lipids and proteins

from one lipid monolayer to the other

a. Neither lipid nor proteins can flip-flop

b. Both lipid and proteins can flip flop

c. While lipids can rarely flip-flop

proteins cannot

d. While proteins can flip-flop lipids

cannot

5. Match the columns and identify the

correct option:

Column-I

Column-II

(a) Thylakoids (i) Disc-shaped sacs

in Golgi apparatus

(b) Cristae (ii) Condensed

structure of DNA

(c) Cisternae (iii) Flat membranous

sacs in stroma

(d) Chromatin (iv) Infoldings in

mitochondria

(a) (b) (c) (d)

(1) (iii) (iv) (ii) (i)

(2) (iv) (iii) (i) (ii)

(3) (iii) (iv) (i) (ii)

(4) (iii) (i) (iv) (ii)

6. Bring out the significance of phase

contrast microscopy

7. State the protoplasm theory

8. Distinguish between prokaryotes and

eukaryotes

9. Difference between plant and animal cell

10. Draw the ultra structure of plant cell

257

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Giant Chromosomes

Chromosome puff

Inter band

Dark band

Chromonemata

Polytene chromosomes

Chromosome axis

Matrix

Chromosomal fibre

Lampbrush chromosomes

258

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ICT Corner

Cell structure

Cell-The unit of Life

Steps

• Scan the QR code & install the app from Android app store

• Open the app & move the cell organelles by moving left bottom button

• Select the cell organelles by pointer

• Play the audio notes of cell organelles by click the right center button

• Use pointer & observe the structure of cell organelles

Activity

• Observe the structures of cell organelles and record it.

Step 2

Step 4

Step 1

Step 3

Step 5

URL:

https://play.google.com/store/apps/details?id=com.VIEW.CellWorld&hl=en

* Pictures are indicative only

259

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Chapter

7

Cell Cycle

Learning Objectives

The learner will be able to,

• Outline the cell cycle and different

stages in cell division.

• Recognise the importance of mitosis

in the production of genetically

identical cells.

• Have an insight on the significant

of mitosis and meiosis.

• Understand how a single cell divides

to a whole organism.

• Familiarize the behaviour of

chromosomes in plants and animal

cells during meiosis.

• Know about crossing over and

random assortment of homologous

chromosomes and its importance.

Chapter Outline

7.1 History

of cell division

7.2 Cell cycle

7.3 Cell Division

7.4 Difference between Mitosis and Meiosis

7.5 Mitogens

One of the most important features of

the living cells is their power to grow

and divide. New cells are formed by

the division of pre-existing cells. Cells

increase in number by cell division. The

parent cell divides and passes on genetic

material to the daughter cells.

Neurons can be

replaced!

Stem cells in the

human brain - most

neurons are in G 0

and do not divide.

As neurons and

neuroglia die or

injured they are

replaced by neural

stem cells

Edouard Van Beneden, a Belgian

cytologist, embryologist and marine

biologist. He was Professor of Zoology at

the University of Liège. He contributed

to cytogenetics by his works on the

roundworm Ascaris. In his work he

discovered how chromosomes organized

meiosis (the production of gametes).

260

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7.1 History of a Cell

Table 7.1: History of Cell

Year Scientist Events

1665 Robert Hooke Coined word “Cell”

1670–74 Antonie van Leeuwenhoek First living cells observed in

microscope - Structure of bacteria

1831–33 Robert Brown Presence of nucleus in cells of orchid

roots

1839 Jan Evangelista Purkyne Coined “protoplasm”

(J.E. Purkinje)

1838–39 Schleiden & Schwann Cell theory

1858 Rudolph Ludwig Carl Virchow Cell theory ‘omnis cellula e cellula’

1873 Anton Schneider Described chromosomes (Nuclear

filaments) for the first time

1882 Walther Flemming Coined the word mitosis; chromosome

behaviour

1883 Edouard Van Beneden Cell division in round worm

1888 Theodor Boveri Centrosome; Chromosome Theory

7.1.1 The Role of the Nucleus

As studied earlier, the nucleus is the

organising centre of the cell. The

information in the nucleus is contained

within structures called chromosomes.

These uniquely:

• Control activities of the cell.

• Genetic information copied from cell

to cell while the cell divides.

• Hereditary characters are passed on

to new individuals when gametic cells

fuse together in sexual reproduction.

7.1.2 Chromosomes

At the time when a nucleus divides,

the chromosomes become compact

and multicoiled structure. Only in this

condensed state do the chromosomes

become clearly visible in cells. All other

times, the chromosomes are very long,

thin, uncoiled threads. In this condition

they give the stained nucleus the granular

appearance. The granules are called

chromatin.

The four important features of the

chromosome are:

• The shape of the chromosome is

specific: The long, thin, lengthy

structured chromosome contains

a short, constricted region called

centromere. A centromere may occur

anywhere along the chromosome, but

it is always in the same position on any

given chromosome.

• The number of chromosomes per

species is fixed: for example the mouse

has 40 chromosomes, the onion has 16

and humans have 46.

261

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• Chromosomes occur in pairs: The

chromosomes of a cell occur in

pairs, called homologous pairs. One

of each pair come originally from

each parent. Example, human has 46

chromosomes, 23 coming originally

from each parent in the process of

sexual reproduction.

• Chromosomes are copied: Between

nuclear divisions, whilst the

chromosomes are uncoiled and cannot

be seen, each chromosome is copied.

The two identical structures formed

are called chromatids.

7.1.3 Nuclear Divisions

There are two types of nuclear division,

as mitosis and meiosis. In mitosis, the

daughter cells formed will have the same

number of chromosomes as the parent

cell, typically diploid (2n) state. Mitosis is

the nuclear division that occurs when cells

grow or when cells need to be replaced and

when organism reproduces asexually.

In meiosis, the daughter cells contain

half the number of chromosomes of

the parent cell and is known as haploid

state (n).

Whichever division takes place, it

is normally followed by division of the

cytoplasm to form separate cells, called as

cytokinesis.

7.2 Cell Cycle

Definition: A series of events leading to

the formation of new cell is known as cell

cycle. The phenomenonal changes leading

to formation of new population take place

in the cell cycle. It was discovered by

Prevost and Dumans (1824). The series

of events include several phases.

7.2.1 Duration of Cell Cycle

Different kinds of cells have varied

duration for cell cycle phases. Eukaryotic

cell divides every 24 hours. The cell cycle

is divided into mitosis and interphase.

In cell cycle 95% is spent for interphase

whereas the mitosis and cytokinesis last

only for an hour.

Table 7.2: Cell cycle of a proliferating

human cell

Phase Time duration (in hrs)

G 1 11

S 8

G 2 4

M 1

The different phases of cell cycle are as

follows (Figure 7.1).

7.2.2 Interphase

Longest part of the cell cycle, but it is of

extremely variable length. At first glance

the nucleus appears to be resting but this

is not the case at all. The chromosomes

previously visible as thread like structure,

have dispersed. Now they are actively

involved in protein synthesis, at least for

most of the interphase.

C-Value is the amount in picograms

of DNA contained within a haploid

nucleus.

7.2.3 G 1 Phase

The first gap phase – 2C amount of DNA in

cells of G 1 . The cells become metabolically

active and grows by producing proteins,

lipids, carbohydrates and cell organelles

including mitochondria and endoplasmic

reticulum. Many checkpoints control

262

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Figure 7.1: Cell cycle

the cell cycle. The checkpoint called

the restriction point at the end of G 1 ,

determines a cells fate whether it will

continue in the cell cycle and divide or

enter a stage called G 0 as a quiescent stage

and probably as specified cell or die. Cells

are arrested in G 1 due to:

• Nutrient deprivation

• Lack of growth factors or density

dependant inhibition

• Undergo metabolic changes and enter

into G 0 state.

Biochemicals inside cells activates the

cell division. The proteins called kinases

and cyclins activate genes and their proteins

to perform cell division. Cyclins act as

major checkpoint which operates in G 1 to

determine whether or not a cell divides.

Dolly

Since the DNA of cells

in G 0 , do not replicate.

The researcher are

able to fuse the

donor cells from a sheep’s mammary

glands into G 0 state by culturing in

the nutrient free state. The G 0 donor

nucleus synchronised with cytoplasm

of the recipient egg, which developed

into the clone Dolly.

7.2.4 G 0 Phase

Some cells exit G 1 and enters a quiescent

stage called G 0 , where the cells remain

metabolically active without proliferation.

Cells can exist for long periods in G 0 phase.

In G 0 cells cease growth with reduced rate of

RNA and protein synthesis. The G 0 phase is

263

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not permanent. Mature neuron and skeletal

muscle cell remain permanently in G 0 .

Many cells in animals remains in G 0 unless

called on to proliferate by appropriate

growth factors or other extracellular

signals. G 0 cells are not dormant.

7.2.5 S phase – Synthesis phase – cells

with intermediate amounts of DNA.

Growth of the cell continues as replication

of DNA occur, protein molecules called

histones are synthesised and attach to

the DNA. The centrioles duplicate in the

cytoplasm. DNA content increases from

2C to 4C.

7.2.6 G 2 – The second Gap phase – 4C

amount of DNA in cells of G 2 and

mitosis

Cell growth continues by protein and cell

organelle synthesis, mitochondria and

chloroplasts divide. DNA content remains as

4C. Tubulin is synthesised and microtubules

are formed. Microtubles organise to form

spindle fibre. The spindle begins to form and

nuclear division follows.

One of the proteins synthesized only

in the G 2 period is known as Maturation

Promoting Factor (MPF). It brings about

condensation of interphase chromosomes

into the mitotic form.

DNA damage checkpoints operates in

G 1 S and G 2 phases of the cell cycle.

7.3 Cell Division

7.3.1 Amitosis (Direct

Cell Division)

Amitosis is also called

direct or incipient cell division. Here there

is no spindle formation and chromatin

material does not condense. It consist of two

steps: (Figure 7.2).

Karyokinesis:

• Involves division of nucleus.

• Nucleus develops a constriction at

the center and becomes dumbell

shaped.

• Constriction deepens and divides

the nucleus into two.

Cytokinesis:

• Involves division of cytoplasm.

• Plasma membrane develops a

constriction along nuclear constriction.

• It deepens centripetally and finally

divides the cell into two cells.

Example: Cells of mammalian cartilage,

macronucleus of Paramecium and old

degenerating cells of higher plants.

Figure 7.2: Amitosis

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Drawbacks of Amitosis

• Causes unequal distribution of

chromosomes.

• Can lead to abnormalities in

metabolism and reproduction.

7.3.2 Mitosis

The most important part of cell division

concerns events inside the nucleus. Mitosis

occurs in shoot and root tips and other

meristematic tissues of plants associated

with growth. The number of chromosomes

in the parent and the daughter (Progeny)

cells remain the same so it is also called as

equational division.

7.3.3 Closed and Open Mitosis

In closed mitosis, the nuclear envelope

remains intact and chromosomes migrate

to opposite poles of a spindle within the

nucleus (Figure 7.3).

Example: Many single celled eukaryotes

including yeast and slime molds.

In open mitosis, the nuclear envelope

breaks down and then reforms around the

2 sets of separated chromosome.

Example: Most plants and animals

• Some animals are able to regenerate

the whole parts of the body.

Mitosis is divided into four stages

prophase, metaphase, anaphase and

telophase (Figure 7.6).

Prophase

Prophase is the longest phase in mitosis.

Chromosomes become visible as long

thin thread like structure, condenses to

form compact mitotic chromosomes.

In plant cells initiation of spindle

fibres takes place, nucleolus disappears.

Nuclear envelope breaks down. Golgi

apparatus and endoplasmic reticulum

are not seen.

Closed mitosis

Spindle

Open mitosis

Spindle

Figure 7.3: Closed and Open mitosis

265

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Fibrous

corona

Inner

kinetochore

Outer

kinetochore

Microtubule

Inner

centromere

where the chromosome morphology can

be easily studied.

Kinetochore is a DNA–Protein

complex present in the centromere DNA

where the microtubules are attached. It is

a trilaminar disc like plate.

The spindle assembly checkpoint

which decides the cell to enter anaphase.

Figure 7.4: Centromere

In animal cell the centrioles extend a

radial array of microtubules (Figure 7.4)

towards the plasma membrane when they

reach the poles of the cell. This arrangement

of microtubules is called an aster. Plant cells

do not form asters.

Metaphase

Chromosomes (two sister chromatids)

are attached to the spindle fibres by

kinetochore of the centromere. The

spindle fibres is made up of tubulin. The

alignment of chromosome into compact

group at the equator of the cell is known

as metaphase plate. This is the stage

Anaphase

Each chromosome split simultaneously and

two daughter chromatids begins to migrate

towards two opposite poles of a cell. Each

centromere splits longitudinally into two,

freeing the two sister chromatids from

each other. Shortening of spindle fibre and

longitudinal splitting of centromere creates

a pull which divides chromosome into two

halves. Each half receive two chromatids

(that is sister chromatids are separated).

When the sister chromatids separate the

actual partitioning of the replicated genome

is complete.

A ubiquitine ligase is activated called

as the anaphase-promoting complex

cyclosome (APC/C) leads to degradation of

Figure 7.5: Anaphase promoting complex cyclosome

266

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the key regulatory proteins at the transition

of metaphase to anaphase. APC is a cluster of

proteins that induces the breaking down of

cohesion proteins which leads to the separation

of chromatids during mitosis (Figure 7.5).

Telophase

Two sets of daughter chromosomes reach

opposite poles of the cell, mitotic spindle

disappears. Division of genetic material is

completed after this karyokinesis, cytokinesis

(division of cytoplasm) is completed,

nucleolus and nuclear membranes reforms.

Nuclear membranes form around each set of

sister chromatids now called chromosomes,

each has its own centromere. Now the

chromosomes decondense. In plants,

phragmoplast are formed between the

daughter cells. Cell plate is formed between

the two daughter cells, reconstruction of

cell wall takes place. Finally the cells are

separated by the distribution of organelles,

macromolecules into two newly formed

daughter cells.

A Culture of animal cells in which

the cell cycles were asynchronous was

incubated with 3H-Thymidine for

10 minutes. Autoradiography showed

that 50% of the cells were labelled. If

the cell cycle time (generation time)

was 16 hrs how long was the S period?

Length of the S period = Fraction of

cells in DNA replication × generation

time

Length of the S period = 0.5 × 16

hours = 8 hours

Activity

Squash preparation of onion root tip

to visualize and study various stages of

mitosis.

Figure 7.6: Mitosis

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7.3.4 Cytokinesis

Cytokinesis in Animal Cells

It is a contractile process. The contractile

mechanism contained in contractile ring

located inside the plasma membrane. The

ring consists of a bundle of microfilaments

assembled from actin and myosin.

This fibril helps for the generation of a

contractile force. This force draws the

contractile ring inward forming a cleavage

furrow in the cell surface dividing the cell

into two.

Check your grasp!

What effect does mitosis have on

transcription?

During mitosis transcription stops.

Cytokinesis in Plant Cell

Division of the cytoplasm often starts during

telophase. In plants, cytokinesis cell plate

grows from centre towards lateral walls -

centrifugal manner of cell plate formation.

Phragmoplast contains microtubules,

actin filaments and vesicles from golgi

apparatus and ER. The golgi vesicles

contains carbohydrates such as pectin,

hemicellulose which move along the

microtubule of the pharagmoplast to

the equator fuse, forming a new plasma

membrane and the materials which are

placed their becomes new cell wall.

The first stage of cell wall construction

is a line dividing the newly forming

cells called a cell plate. The cell plate

eventually stretches right across the cell

forming the middle lamella. Cellulose

builds up on each side of the middle

lamella to form the cell walls of two new

plant cells.

Skin cells and the cells

lining your gut are

constantly dying and

are being replaced by

identical cells.

7.3.5 Significance of Mitosis

Exact copy of the parent cell is produced

by mitosis (genetically identical).

1. Genetic stability – daughter cells are

genetically identical to parent cells.

2. Growth – as multicellular organisms

grow, the number of cells making up

their tissue increases. The new cells

must be identical to the existing ones.

3. Repair of tissues - damaged cells must

be replaced by identical new cells by

mitosis.

4. Asexual reproduction – asexual

reproduction results in offspring that

are identical to the parent. Example

Yeast and Amoeba.

5. In flowering plants, structure such

as bulbs, corms, tubers, rhizomes

and runners are produced by mitotic

division. When they separate from the

parent, they form a new individual.

The production of large numbers of

offsprings in a short period of time,

is possible only by mitosis. In genetic

engineering and biotechnology, tissues

are grown by mitosis (i.e. in tissue culture).

6. Regeneration – Arms of star fish

7.3.6 Meiosis

In Greek meioum means to reduce. Meiosis

is unique because of synapsis, homologous

recombination and reduction division.

Meiosis takes place in the reproductive

268

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organs. It results in the formation of gametes

with half the normal chromosome number.

Haploid sperms are made in testes;

haploid eggs are made in ovaries of animals.

In flowering plants meiosis occurs

during microsporogenesis in anthers and

megasporogenesis in ovule. In contrast to

mitosis, meiosis produces cells that are

not genetically identical. So meiosis has a

key role in producing new genetic types

which results in genetic variation.

Stages in Meiosis

Meiosis can be studied under two divisions

i.e., meiosis I and meiosis II. As with

mitosis, the cell is said to be in interphase

when it is not dividing.

Prophase I is the longest and most

complex stage in meiosis. Pairing of

homologous chromosomes (bivalents).

Meiosis I-Reduction Division

Prophase I – Prophase I is of longer

duration and it is divided into 5 substages –

Leptotene, Zygotene, Pachytene, Diplotene

and Diakinesis (Figure 7.7).

Leptotene – Chromosomes are visible

under light microscope. Condensation of

chromosomes takes place. Paired sister

chromatids begin to condense.

Zygotene – Pairing of homologous

chromosomes takes place and it is known

as synapsis. Chromosome synapsis is

made by the formation of synaptonemal

complex. The complex formed by the

homologous chromosomes are called as

bivalent (tetrads).

Pachytene – At this stage bivalent

chromosomes are clearly visible as

tetrads. Bivalent of meiosis I consists of 4

chromatids and 2 centromeres. Synapsis

is completed and recombination nodules

appear at a site where crossing over takes

place between non-sister chromatids of

homologous chromosome. Recombination

of homologous chromosomes is completed

by the end of the stage but the chromosomes

are linked at the sites of crossing over. This is

mediated by the enzyme recombinase.

Diplotene – Synaptonemal complex

disassembled and dissolves. The

homologous chromosomes remain attached

at one or more points where crossing over

has taken place. These points of attachment

where ‘X’ shaped structures occur at the

sites of crossing over is called Chiasmata.

Chiasmata are chromatin structures at sites

where recombination has been taken place.

They are specialised chromosomal structures

that hold the homologous chromosomes

together. Sister chromatids remain closely

associated whereas the homologous

chromosomes tend to separate from each

other but are held together by chiasmata.

This substage may last for days or years

depending on the sex and organism. The

chromosomes are very actively transcribed

in females as the egg stores up materials

for use during embryonic development. In

animals, the chromosomes have prominent

loops called lampbrush chromosome.

Diakinesis – Terminalisation of

chiasmata. Spindle fibres assemble. Nuclear

envelope breaks down. Homologous

chromosomes become short and condensed.

Nucleolus disappears.

Metaphase I

Spindle fibres are attached to the

centromeres of the two homologous

chromosomes. Bivalent (pairs of

homologous chromosomes) aligned at the

269

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Figure 7.7: Prophase I

equator of the cell known as metaphase

plate. Each bivalent consists of two

centromeres and four chromatids.

The random distribution of homologous

chromosomes in a cell in Metaphase I is

called independent assortment.

Anaphase I

Homologous chromosomes are separated

from each other. Shortening of spindle

fibers takes place. Each homologous

chromosomes with its two chromatids

and undivided centromere move towards

the opposite poles of the cells. The actual

reduction in the number of chromosomes

takes place at this stage. Homologous

chromosomes which move to the opposite

poles are either paternal or maternal in

origin. Sister chromatids remain attached

with their centromeres.

Telophase I

Haploid set of chromosomes are present

at each pole. The formation of two

daughter cells, each with haploid number

of chromosomes. Nuclei are reassembled.

Nuclear envelope forms around the

chromosome and the chromosomes

becomes uncoiled. Nucleolus reappears.

In plants, after karyokinesis cytokinesis

takes place by which two daughter cells are

formed by the cell plate between 2 groups

of chromosomes known as dyad of cells

(haploid).

The stage between the two meiotic

divisions is called interkinesis which is

short-lived.

Meiosis II – Equational division.

This division is otherwise called mitotic

meiosis. Since it includes all the stages of

mitotic divisions.

Prophase II

The chromosome with 2 chromatids

becomes short, condensed, thick and

becomes visible. New spindle develops

at right angles to the cell axis. Nuclear

membrane and nucleolus disappear.

Metaphase II

Chromosome arranged at the equatorial

plane of the spindle. Microtubules of

spindle gets attached to the centromere of

sister chromatids.

Anaphase II

Sister chromatids separate. The daughter

chromosomes move to the opposite

poles due to shortening of microtubules.

Centromere of each chromosome split,

allowing to move towards opposite

poles of the cells holding the sister

chromatids.

270

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Figure 7.8: Meiosis

Telophase II

Four groups of chromosomes are organised

into four haploid nuclei. The spindle

disappears. Nuclear envelope, nucleolus

reappear.

After karyokinesis, cytokinesis follows

and four haploid daughter cells are formed,

called tetrads.

7.3.7 Significance of Meiosis

• This maintains a definite constant

number of chromosomes in organisms.

• Crossing over takes place and

exchange of genetic material leads

to variations among species. These

variations are the raw materials to

evolution. Meiosis leads to genetic

variability by partitioning different

combinations of genes into gametes

through independent assortment.

• Adaptation of organisms to various

environmental stress.

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7.4 Difference Between Mitosis and

Meiosis

Table 7.3: Difference between mitosis

in Plants and Animals

Plants

Animals

Centrioles are Centrioles are

absent

present

Asters are not Asters are formed

formed

Cell division Cell division

involves

involves furrowing

formation of a and cleavage of

cell plate cytoplasm

Occurs mainly at

meristem

Occurs in tissues

throughout the body

Table 7.4: Difference Between Mitosis

and Meiosis (Figure 7.8)

Mitosis

Meiosis

One division Two divisions

Number of Number of

chromosomes chromosomes is

remains the same halved

Homologous

chromosomes line

up separately on

the metaphase

plate

Homologous

chromosome do

not pair up

Chiasmata do not

form and crossing

over never occurs

Daughter cells

are genetically

identical

Two daughter cells

are formed

Homologous

chromosomes line

up in pairs at the

metaphase plate

Homologous

chromosome

pairup to form

bivalent

Chiasmata form

and crossingover

occurs

Daughter cells

are genetically

different from the

parent cells

Four daughter cells

are formed

7.5 Mitogens

The factors which promote cell cycle

proliferation is called mitogens. Plant

mitogens include gibberellin, ethylene,

Indole acetic acid, kinetin. These increase

mitotic rate.

Mitotic Poisons (Mitotic Inhibitors)

Certain chemical components act as

inhibitors of the mitotic cell division and

they are called mitotic poisons.

Endomitosis

The replication of chromosomes in

the absence of nuclear division and

cytoplasmic division resulting in

numerous copies within each cell is

called endomitosis. Chromonema do

not separate to form chromosomes, but

remain closely associated with each other.

Nuclear membrane does not rupture. So

no spindle formation. It occurs notably

in the salivary glands of Drosophila and

other flies. Cells in these tissues contain

giant chromosomes (polyteny), each

consisting of over thousands of intimately

associated, or synapsed, chromatids.

Example: Polytene chromosome.

Anastral

This is present only in plant cells. No asters

or centrioles are formed only spindle

fibres are formed during cell division.

Amphiastral

Aster and centrioles are formed at each

pole of the spindle during cell division.

This is found in animal cells.

272

---

Summary

273

---

Evaluation

1. The correct sequence in cell cycle is

a. S-M-G1-G2

b. S-G1-G2-M

c. G1-S-G2-M

d. M-G-G2-S

2. If cell division is

restricted in G1 phase of the cell cycle

then the condition is known as

a. S Phase

b. G2 Phase

c. M Phase

d. G 0 Phase

3. Anaphase promoting complex APC

is a protein degradation machinery

necessary for proper mitosis of animal

cells. If APC is defective in human cell,

which of the following is expected to

occur?

a. Chromosomes will be fragmented

b. Chromosomes will not condense

c. Chromosomes will not segregate

d. Recombination of chromosomes

will occur

4. In S phase of the cell cycle

a. Amount of DNA doubles in each

cell

b. Amount of DNA remains same in

each cell

c. Chromosome number is increased

d. Amount of DNA is reduced to half

in each cell

5. Centromere is required for

a. transcription

b. crossing over

c. Cytoplasmic cleavage

d. movement of chromosome towards

pole

274

6. Synapsis occur between

a. mRNA and ribosomes

b. spindle fibres and centromeres

c. two homologous chromosomes

d. a male and a female gamete

7. In meiosis crossing over is initiated at

a. Diplotene

b. Pachytene

c. Leptotene

d. Zygotene

8. Colchicine prevents the mitosis of the

cells at which of the following stage

a. Anaphase

b. Metaphase

c. Prophase

d. interphase

9. The paring of homologous

chromosomes on meiosis is known as

a. Bivalent

b. Synapsis

c. Disjunction

d. Synergids

10. Anastral mitosis is the characteristic

feature of

a. Lower animals

b. Higher animals

c. Higher plants

d. All living organisms

11. Write any three significance of mitosis

12. Differentiate between mitosis and

meiosis

13. Given an account of G 0 phase

14. Differentiate cytokinesis in plant cells

and animal cells

15. Write about Pachytene and Diplotene

of Prophase I

---

ICT Corner

Cell division

How cells are multiply?

Steps

• Scan the QR code

• Click Mitosis and start the animation press play

• Select mitosis in the top of the page – play it - use forward button to slow down

• Select meiosis in the top of the page – play it - use forward button to slow down

Activity

• Select meiosis and cell cycle.

• Record your observations.

Step 1

Step 3

Step 2

Step 4

URL:

https://www.cellsalive.com/

* Pictures are indicative only

275

---

Chapter

8

Biomolecules

Learning Objectives

The learner will be able to,

• List out the inorganic and organic

components of a cell.

• Understand about bonding pattern

of water and properties of water.

• Familiarise with the classification

of carbohydrates and its functions.

• Recognise the basic structure of

carbohydrates, proteins, lipids and

nucleic acids and differentiate the

various pattern of classification

with respect to structure.

• Identify the structure and functions

of carbohydrates.

• Familiarise with the general

structure of amino acids and

its classification based on the

functional group.

• Comparative study of the primary,

secondary, tertiary and quaternary

structure of proteins.

• Know the structure and

classification of enzymes.

• Know about the factors affecting

the mode of action of enzymes with

relevant examples.

• Understand lipids as a biomolecule

and discuss the properties of lipids.

• Have a deeper knowledge about

structure of nucleic acids.

• Recognize nucleic acids as a

polymer which plays a vital role in

carrying the genetic information.

• Learn about the different forms of

DNA and types of RNA.

Chapter Outline

8.1 Water

8.2 Primary and Secondary Metabolites

8.3 Carbohydrates – Classification and

Structure

8.4 Lipids – Classification and Structure

8.5 Proteins and Amino Acids –

Classification and Structure,

8.6 Enzymes – Classification, Nomenclature,

Structure and Concepts, Mechanism

of Enzyme Action, Activation energy,

factors affecting enzyme action.

8.7 Nucleic Acids general Structure and

composition – Forms of DNA and

Types of RNA.

276

---

2

2

2

2

2

2

Biomolecules

Organic compounds:

Biomolecules

Level 4:

The cell

and its organelles

Level 3:

Supramolecular

complexes

Level 2:

Macromolecules

Level 1:

Monomeric units

NH

N

O

O P O CH

O

H

H

O N

O

H

H

OH H

Chromosome

DNA

Nucleotides

H N

H

C COO

CH

Plasma membrane

Protein

Amino acids

CH

OH

O

H

H

OH

H

OH

HO

H

OH

Cell wall

Cellulose

Sugars

H

CH OH

Oo

Figure 8.1: Components of cell

Having learnt the structure of the

cell, we can now understand that each

component of the cell is responsible for

a specific function. The cell components

are made of collection of molecules

called as cellular pool, which consists of

both inorganic and organic compounds.

Inorganic compounds include salts,

mineral ions and water.

Organic compounds are carbohydrates,

lipids, amino acids, proteins, nucleotides,

hormones and vitamins. Some organic

molecules remain in colloidal form in the

aqueous intracellular fluid. Others exist in

non-aqueous phases like the lipid membrane

and cell walls. The cell maintains this

pool by the intake and elimination of specific

molecules (Figure 8.1).

The minerals essential for plant

growth are of two types: macronutrients,

which are required in larger amounts

(Eg. Potassium, phosphorus, calcium,

magnesium, sulphur and iron) and

micronutrients, which are required in

trace amounts (Eg. Cobalt, zinc, boron,

copper, molybdenum and manganese)

and are essential for enzyme action.

Example, Manganese is required for

activity of enzyme needed for synthesis

of oligosaccharides and glycoproteins.

Molybdenum is necessary for fixation of

nitrogen by enzyme nitrogenase.

Component % of the total

cellular mass

Water 70

Proteins 15

Carbohydrates 3

Lipids 2

Nucleic acids 6

Ions 4

277

---

30%

70%

30%

Chemical

70%

Water

Water is a tiny polar molecule and

can readily pass through membranes.

Two electronegative atoms of oxygen

share a hydrogen bonds of two water

molecule. Thus, they can stick together

by cohesion and results in lattice

formation (Figure 8.4).

(15%)

Proteins

(4%) Small

molecules

(6%) RNA

(2%) Phospholipids

(1%) DNA

(2%) Polysacharides

Figure 8.2: Percentage of biomolecules

in cell

H

O

H

Covalent Bond

8.1 Water

Water is the most abundant component

in living organisms. Life on earth is

inevitably linked to water. Water makes

up 70% of human cell and upto 95% of

mass of a plant cell (Figure 8.2).

Masaru Emoto discovered

that crystals

formed in frozen water

reveal changes when

specific, concentrated

thoughts are

directed toward

them. This crystal

structure shows

joy mood Figure 8.3

8.1.1 Chemistry of Water

Figure 8.4: Water molecule

8.1.2 Properties of Water

• Adhesion and cohesion property

• High latent heat of vaporisation

• High melting and boiling point

• Universal solvent

• Specific heat capacity

Figure 8.5: Synthesis of metabolites

during growth

278

---

8.2 Primary and Secondary

Metabolites

Most plants, fungi and other microbes

synthesizes a number of organic

compounds. These components are called

as metabolites which are intermediates

and products of metabolism. The term

metabolite is usually restricted to small

molecules. It can be catergorized into

two types namely primary and secondary

metabolites based on their role in

metabolic process (Figure 8.5).

Primary metabolites are those that are

required for the basic metabolic processes

like photosynthesis, respiration, protein

and lipid metabolism of living organisms.

Secondary metabolites does not

show any direct function in growth and

development of organisms.

Metabolites

Enzymes

Amino acid

Organic acid

Vitamins

Pigments

Alkaloids

Essential oil

Toxins

Lectins

Drugs

Polymeric

substances

Primary

Examples

Protease, lipase,

peroxidase

Proline, leucine

Acetic acid, lactic acid

A, B, C

Secondary

Carotenoids,

anthocyanins

Morphine, codeine

Lemon grass oil, rose oil

Abrin, ricin

Concanavalin A

Vinblastin, curcumin

Rubber, gums, cellulose

somniferum).

It is used as a

pain reliever in

patients with

severe pain levels

and cough

suppressant.

8.2.1 Organic Molecules

Morphine is the first

alkaloid to be found. It

comes from the plant

Opium poppy (Papaver

Organic molecules may be small and

simple. These simple molecules assemble

and form large and complex molecules

called macromolecules. These include

four main classes – carbohydrates,

lipids, proteins and nucleic acids.

All macromolecules except lipids are

formed by the process of polymerisation,

a process in which repeating subunits

termed monomers are bound into chains

of different lengths. These chains of

monomers are called polymers.

8.3 Carbohydrates

Carbohydrates are organic compounds

made of carbon and water. Thus one

molecule of water combines with a carbon

atom to form CH 2 O and is repeated

several (n) times to form (CH 2 O) n where

n is an integer ranging from 3–7. These

are also called as saccharides. The

common term sugar refers to a simple

carbohydrate such as a monosaccharide

or disaccharide that tastes sweet are

soluble in water (Figure 8.7).

279

---

Monosaccharides

(simple sugars)

Carbohydrates

(Saccharides or sugars)

Oligosaccharides

( 2 to 10 sugar units)

Polysaccharides

( more than10 sugar units)

Functional

group

Number of

carbon atoms

Di - Tri - Tetra - Penta -

saccharides saccharides saccharides saccharides

Homo

polysaccharides

Hetero

polysaccharides

Aldoses

Glucose

Trioses

Glyceraldehyde

Maltose Raffinose Stachyose Verbascose Starch

Peptidoglycan

Ketose

Fructose

Tetroses

Erythrose

Lactose

Glycogen

Hyaluronic acid

Pentoses

Ribose

Hexose

Glucose

Sucrose Cellulose Chondroitin

sulphate

Chitin

Inulin

Keratan sulphate

Agar agar

8.3.1 Monosaccharides – The Simple

Sugars

Monosaccharides are relatively small

molecules constituting single sugar

unit. Glucose has a chemical formula of

C 6 H 12 O 6 . It is a six carbon molecule and

hence is called as hexose (Figure 8.6).

All monosaccharides contain one

of two functional groups. Some are

aldehydes, like glucose and are referred as

aldoses; other are ketones, like fructose

and are referred as ketoses.

Glucose is one of the

most well-known

molecules due to its

nature as an essential

nutrient for human

health. You ingest glucose in your

food, and then your body uses blood

to carry the glucose to the cells of

every organ for the purpose of energy

production.

Figure 8.6: Structure of Glucose

280

---

8.3.2 Disaccharides

Disaccharides are formed when two

monosaccharides join together. An example

is sucrose. Sucrose is formed from a molecule

of α-glucose and a molecule of fructose.

This is a condensation reaction releasing

water. The bond formed between the glucose

and fructose molecule by removal of water

is called glycosidic bond. This is another

example of strong, covalent bond.

Figure 8.7: structure of carbohydrates

In the reverse process, a disaccharide is

digested to the component monosaccharide

in a hydrolysis reaction. This reaction

involves addition of a water (hydro)

molecule and splitting (lysis) of the

glycosidic bond.

8.3.3 Polysaccharides

These are made of hundreds of

monosaccharide units. Polysaccharides

also called "Glycans". Long chain of

branched or unbranched monosaccharides

are held together by glycosidic bonds.

Polysaccharide is an example of giant

molecule, a macromolecule and

consists of only one type of monomer.

Polysaccharides are insoluble in water and

are sweetless. Cellulose is an example built

from repeated units of glucose monomer.

Depending on the function,

polysaccharides are of two types -

storage polysaccharide and structural

polysaccharide (Figure 8.8).

8.3.4 Starch

Starch is a storage polysaccharides made

up of repeated units of amylose and

amylopectin. Starch grains are made

up of successive layers of amylose and

amylopectin, which can be seen as growth

rings. Amylose is a linear, unbranched

polymer which makes up 80% of starch.

Amylopectin is a polymer with some 1, 6

linkages that gives it a branched structure.

Figure 8.8: Branched and linear polysaccharides

281

---

8.3.5 Test for Starch

We test the presence of starch by adding a

solution of iodine in potassium iodide. Iodine

molecules fit nearly into the starch helix,

creating a blue-black colour (Figure 8.9).

a

b

Glucose chain

8.3.7 Celluloses

Cellulose is a structural polysaccharide

made up of thousands of glucose units. In

this case, β-glucose units are held together

by 1,4 glycosidic linkage, forming long

unbranched chains. Cellulose fibres

are straight and uncoiled. It has many

industrial uses which include cellulose

fibres as cotton, nitrocellulose for

explosives, cellulose acetate for fibres of

multiple uses and cellophane for packing

(Figure 8.11).

c

Tri-iodide ion

Figure 8.9: Test for starch

a. Test on potato; b. test on starch at varied

concentrations; c. starch – iodine reaction

8.3.6 Glycogen

Glycogen is also a storage polysaccharide

otherwise called as animal starch. It is

the only carbohydrate stored in animals

and fungi. Like amylopectin glycogen is

a polymer of glucose with (α1-6) linked

branches. Glycogen is seen in liver cells,

skeletal muscle fibre and throughout the

human body except brain (Figure 8.10).

The liver stores

glucose as glycogen

Figure 8.11: Cellulose molecule

?

Most herbivores have a problem:

➢ Cellulose is one of the most

abundant organic compound in

the biosphere.

Glycogenesis

Glycogenolysis

➢

eat grass: principle component is

cellulose

Glucose

Figure 8.10: Glycogen: Glycogen in liver

➢ cannot produce cellulase

Solution: Mutualistic bacteria in

digestive system produce cellulases.

282

---

8.3.8 Chitin

Chitin is a homo polysaccharide with amino

acids added to form mucopolysaccharide.

The basic unit is a nitrogen containing glucose

derivative known as N-acetyl glucosamine.

It forms the exoskeleton of insects and other

arthropods. It is also present in the cell walls

of fungi (Figure 8.12).

Figure 8.12: Structure of Chitin molecule

Does mushroom cells

have cell wall?

My cell walls are made of

chitin. Chitin is made of

glucose and chitin is primarily

used as a structural

component, strengthening

exoskeletons, shells, and

cell walls of fungus.

My hard

shells are

made of

chitin too

used as test for reducing sugar and is known

as Benedict’s test. The results of benedict’s

test depends on concentration of the sugar.

If there is no reducing sugar it remains blue

(Figure 8.14).

Mine

too

Figure 8.13

8.3.9 Test for Reducing Sugars

Blue

Solution

Green/yellow

precipitate

Orange

precipitate

Brick-red

precipitate

Aldoses and ketoses are reducing sugars.

This means that, when heated with an

alkaline solution of copper (II) sulphate

(a blue solution called benedict’s solution),

the aldehyde or ketone group reduces

Cu 2+ ions to Cu + ions forming brick red

precipitate of copper(I) oxide. In the process,

the aldehyde or ketone group is oxidised to

a carboxyl group (–COOH). This reaction is

None

Trace of Moderate

reducing sugar reducing sugar

Figure 8.14: Test for sugar

• Sucrose is not a reducing sugar

Large

amount of

reducing sugar

• The greater the concentration of

reducing sugar, the more is the

precipitate formed and greater is the

colour change.

283

---

Other Sugar Compounds

Other

Polysaccharides

Structure

Functions

Inulin Polymer of fructose It is not metabolised in the

human body and is readily

filtered through the kidney

Hyaluronic acid

Agar

Heparin

Chondroitin

sulphate

Keratan sulphate

Heteropolymer of d

glucuronic acid and D-N

acetyl glucosamine

Mucopolysaccharide from red

algae

Glycosamino glycan contains

variably sulphated disaccharide

unit present in liver

Sulphated glycosaminoglycan

composed of altering sugars

(N-acetylglucosamine and

glucuronic acid)

Sulphated glycosaminoglycan

and is a structural

carbohydrate

It accounts for the toughness

and flexibility of cartilage and

tendon

Used as solidifying agent in

culture medium in laboratory

Used as an anticoagulant

Dietery supplement for

treatment of osteoarthritis

Acts as cushion to absorb

mechanical shock

Human can’t digest

cellulose but herbivores

can digest them

with the help of bacteria

present in the gut

which produces enzyme cellulase.

This is an example of mutualism.

8.4 Lipids

The term lipid is derived from greek word

lipos, meaning fat. These substances are

not soluble in polar solvent such as water

but dissolve in non-polar solvents such as

benzene, ether, chloroform. This is because

they contain long hydrocarbon chains

that are non-polar and thus hydrophobic.

The main groups of compounds classified

as lipids are triglycerides, phospholipids,

steroids and waxes.

8.4.1 Triglycerides

Triglycerides are composed of single

molecule of glycerol bound to 3 fatty acids.

These include fats and oils. Fatty acids are

long chain hydrocarbons with a carboxyl

group at one end which binds to one of the

hydroxyl groups of glycerol, thus forming an

ester bond. Fatty acids are structural unit of

lipids and are carboxylic acid of long chain

hydrocarbons. The hydrocarbon can vary in

length from 4 – 24 carbons and the fat may

be saturated or unsaturated. In saturated

fatty acids the hydrocarbon chain is single

bonded (Eg. palmitic acid, stearic acid) and

in unsaturated fatty acids (Eg. Oleic acid,

284

---

linoleic acid) the hydrocarbon chain is double

bonded (one/two/three). In general solid fats

are saturated and oils are unsaturated, in

which most are globules.

8.4.2 Membrane Lipids

A class of lipids that serves as major

structural component of cell membrane is

phospholipids. These contain only 2 fatty

acids attached to the glycerol, while the third

glycerol binding site holds a phosphate group.

This phosphate group is in turn bonded to an

alcohol. These lipids have both hydrophobic

and hydrophilic regions. The structure of

lipid bilayer helps the membrane in function

such as selective permeability and fluid

nature (Figure 8.15).

8.4.3 Steroids

These are complex compounds

commonly found in cell membrane

and animal hormones. Eg. Cholesterol

which reinforces the structure of the

cell membrane in animal cells and in

an unusual group of cell wall deficient

bacteria – Mycoplasma.

Fungal cell

Cell membrane and cell wall

Not in humans

Ergosterol

synthesis

pathway

Ergosterol

Squalene

Mannoproteins

b-(1,6)-glucan

b-(1,3)-glucan

Chitin

Phospholipid bilayer

of cell membrane

b-(1,3)-glucan synthase

DNA/RNA synthesis

Figure 8.15: Complex molecules in cell wall

8.4.4 Waxes

These are esters formed between a long

chain alcohol and saturated fatty acids.

Fur, feathers, fruits, leaves, skin and insect

exoskeleton are naturally waterproofed with

a coating of wax (Figure 8.16 and 8.17).

Figure 8.16: Lecithin

Lecithin is a food additive and dietery

supplement

Figure 8.17: Wax D present in cell

wall of TB and Leprosy causing

bacteria is infectious

285

---

Carbohydrate

Cellular Structure

Polymer

Monomer

Starch grains in a

chloroplast Starch Monosaccharide

H

HO

CH2OH

O

H H

OH H

OH

H OH

Nucleic acid

P

Phosphate

group

Nitrogenous base

o

5-carbon

sugar

Chromosome DNA strand Nucleotide

Protein

Ala

Val Ser

Val

Ala

H

H

CH 3

N C C OH

H O

Intermediate

Polypeptide

Amino acid

H

H

H

C

H

C

H

C

H

H

Lipid

H H H H H

C C C C C

H H H

H

Adipose cell with

fat droplets

Triglyceride

O

HO C

C

H H H

Fatty acid

286

---

8.5 Proteins

Proteins are the most diverse of all

macromolecule. Proteins make up 2/3 of

total dry mass of a cell. The term protein

was coined by Gerardus Johannes Mulder

and is derived form a greek word proteos

which means of the first rank.

H

H

N

Amino Group

H

C

R

Variable

Side Chain

O

C

OH

Carboxyl Acid

Group

Figure 8.18: Structure of basic amino acid

Amino acids are building blocks of

proteins. There are about 20 different

amino acids exist naturally. All amino

acids have a basic skeleton consisting of a

carbon (a-carbon) linked to a basic amino

group.

(NH 2 ), an acidic carboxylic group

(COOH) and a hydrogen atom (H) and

side chain or variable R group. The amino

acid is both an acid and a base and is called

amphoteric.

A zwitterion also called as dipolar ion,

is a molecule with two or more functional

groups, of which at least one has a positive

and other has a negative electrical charge and

the net charge of the entire molecule is zero.

The pH at which this happens is known as

the isoelectric point (Figure 8.19).

8.5.1 Classification of Amino acids

Figure 8.19: Structure of amino acid

Based on the R group amino acids are

classified as acidic, basic, polar, non-polar.

The amino group of one amino acid

reacts with carboxyl group of other

amino acid, forming a peptide bond. Two

amino acids can react together with the

loss of water to form a dipeptide. Long

strings of amino acids linked by peptide

bonds are called polypeptides. In 1953

Fred Sanger first sequenced the Insulin

protein (Figure 8.18 and 8.20 a and b).

Figure 8.20(a): Amino acid reaction

287

---

Figure 8.20(b): Classification of Amino Acids

First protein Insulin

was sequenced by Fred

Sanger

Figure 8.22

Figure 8.21

Linus Pauling and Robert Corey in

1951 proposed the α-helix and β sheet

secondary structures of proteins. They

were awarded nobel prize in 1954

288

---

8.5.2 Structure of Protein

Protein is synthesised

on the ribosome as

a linear sequence of

amino acids which are

held together by peptide

bonds. After synthesis,

the protein attains conformational

change into a specific 3D form for

proper functioning. According to the

mode of folding, four levels of protein

organisation have been recognised

namely primary, secondary, tertiary

and quaternary (Figure 8.23).

Primary

structure

C

C

C

O

H

N

H

N

C

O

HO

C

C

C

O

C

N

H

O

N

H

O

C

Primary structure

C

C

b Pleated sheet

Tertiary

structure

C

O

H

N

H

N

C

O

Quaternary

structure

C

C

O

C

N

H

Secondary

structure

N

H

O

C

C

C

C

O

H

N

H

N

C

O

C

C

C

C

C

O

C

O

H

N

H

N

H O

C

H

O

C

O

N

H

N C

H

N

C

C

H

O

C

C

H

C

C

O

C

N

N

N

H

H

N

C O

C

O

N

C

C

H

Alpha helix

Figure 8.23: Structure of Protein

• The primary structure is linear

arrangement of amino acids in a

polypeptide chain.

• Secondary structure arises when

various functional groups are exposed

on outer surface of the molecular

interaction by forming hydrogen

bonds. This causes the aminoacid

chain to twist into coiled configuration

called α-helix or to fold into a flat

β-pleated sheets.

• Tertiary protein structure arises

when the secondary level proteins fold

into globular structure called domains.

• Quaternary protein structure may

be assumed by some complex proteins

in which more than one polypeptide

forms a large multiunit protein. The

individual polypeptide chains of

the protein are called subunits and

the active protein itself is called a

multimer.

For example: Enzymes serve as catalyst

for chemical reactions in cell and are

non-specific. Antibodies are complex

glycoproteins with specific regions of

attachment for various organisms.

8.5.3 Protein Denaturation

Denaturation is the loss of 3D structure

of protein. Exposure to heat causes atoms

to vibrate violently, and this disrupts the

hydrogen and ionic bonds. Under these

conditions, protein molecules become

elongated, disorganised strands. Agents

such as soap, detergents, acid, alcohol and

some disinfectants disrupt the interchain

bond and cause the molecule to be nonfunctional

(Figure 8.25).

289

---

Figure 8.24

(a)

Albumen

Water _ soluble

Christian Anfinsen explained

denaturation of

proteins by heat treatment

leading to breakage

of non-covalent

bond.

Insoluble

positive charge and oxygen and nitrogen

have small negative charge. Opposite

charges attract to form hydrogen bonds.

Though these bonds are weak, large

number of them maintains the molecule

in 3D shape (Figure 8.26).

Ionic Bond

It is formed between any charged groups

that are not joined together by peptide

bond. It is stronger than hydrogen bond

and can be broken by changes in pH and

temperature.

(b)

Protein thermal lrreversible denaturation

Native albumen Denaturation ti Crosslinking

_ SH

_

S-S

Figure 8.25: Protein denaturation

8.5.4 Protein Bonding

There are three types of chemical bonding

CH

Hydrophobic Interactions

and van der Waals Interactions

Disulfide Bond

Some amino acids like cysteine and

methionine have sulphur. These form

disulphide bridge between sulphur atoms

and amino acids.

Hydrophobic Bond

This bond helps some protein to maintain

structure. When globular proteins are in

solution, their hydrophobic groups point

inwards away from water.

Hydrogen

bond

OH

CH 2

O

H

O

C

CH 2

HC 3

CH 3

HC 3

CH 3

CH

CH 2 S S CH 2

Disulfide bond

O

Polypeptide

backbone

The more the distance

between the sulphur

a t o m s ,

the more

the proteins bend; the

more the hair curls.

CH 2

CH 2

CH 2

CH 2

NH 3 O C CH 2

Ionic bond

Figure 8.26: Protein bonding

Hydrogen Bond

It is formed between some hydrogen atoms

of oxygen and nitrogen in polypeptide

chain. The hydrogen atoms have a small

8.5.5 Test for Proteins

The biuret test is used as an indicator of the

presence of protein because it gives a purple

colour in the presence of peptide bonds (–C–

N–). To a protein solution an equal quantity of

sodium hydroxide solution is added and mixed.

Then a few drops of 0.5% copper (II) sulphate

is added with gentle mixing. A distinct purple

290

---

colour develops without heating (Figure 8.27 a

and b).

foods and the breaking down of sugar

in respiration are examples of catabolic

reactions (Figure 8.28).

Figure 8.27(a): Biuret test

Figure 8.28: Enzyme reaction

Figure 8.27(b): Colour intensity

increases with increase in concentration

8.6 Enzymes

Enzymes are globular proteins that catalyse

the many thousands of metabolic reactions

taking place within cells and organism. The

molecules involved in such reactions are

metabolites. Metabolism consists of chains and

cycles of enzyme-catalysed reactions, such as

respiration, photosynthesis, protein synthesis

and other pathways. These reactions are

classified as

• anabolic (building up of organic

molecules). Synthesis of proteins

from amino acids and synthesis of

polysaccharides from simple sugars

are examples of anabolic reactions.

• catabolic (breaking down of larger

molecules). Digestion of complex

Enzymes can be extracellular enzyme as

secreted and work externally exported from

cells. Eg. digestive enzymes; or intracellular

enzymes that remain within cells and work

there. These are found inside organelles or

within cells. Eg. insulin

8.6.1 Properties of Enzyme

• All are globular proteins.

• They act as catalysts and effective even

in small quantity.

• They remain unchanged at the end of

the reaction.

• They are highly specific.

• They have an active site where the

reaction takes place.

• Enzymes lower activation energy of

the reaction they catalyse.

RUBISCO is the

abundant protein in

the whole biosphere

291

---

As molecules react they become

unstable, high energy intermediates,

but they are in this transition state

only momentarily. Energy is required

to raise molecules to this transition

state and this minimum energy needed

is called the activation energy. This

could be explained schematically

by ‘boulder on hillside’ model of

activation energy (Figure 8.29).

Enzyme

Activation energy

without enzymes

Energy in the reaction

Reactant

Activation energy

with enzymes

Product

Time

This graph shows the activation energies of a reaction with and without enzymes

Figure 8.29: Activation energy

8.6.2 Lock and Key Mechanism of

Enzyme

In a enzyme catalysed reaction, the

starting substance is the substrate. It is

converted to the product. The substrate

binds to the specially formed pocket in the

enzyme – the active site, this is called lock

and key mechanism of enzyme action.

As the enzyme and substrate form a ES

complex, the substrate is raised in energy

to a transition state and then breaks down

into products plus unchanged enzyme

(Figure 8.30).

Substrate

Product

Enzyme

Enzyme - Substrate

complex

Enzyme

Figure 8.30: Enzyme mechanism

292

---

8.6.3 Factors Affecting the Rate of

Enzyme Reactions

Enzymes are sensitive to environmental

condition. It could be affected by

temperature, pH, substrate concentration

and enzyme concentration.

The rate of enzyme reaction is

measured by the amount of substrate

changed or amount of product formed,

during a period of time.

8.6.4 Temperature

Heating increases molecular motion.

Thus the molecules of the substrate and

enzyme move more quickly resulting in

a greater probability of occurence of the

reaction. The temperature that promotes

maximum activity is referred to as

optimum temperature (Figure 8.31a).

Increasing enzyme

activity

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

pH

Enzyme Pepsin Catalase

Figure 8.31(b): pH

8.6.6 Substrate Concentration

Optimum

pH

For a given enzyme concentration, the rate of

an enzyme reaction increases with increasing

substrate concentration (Figure 8.32).

8.6.7 Enzyme Concentration

The rate of reaction is directly proportional

to the enzyme concentration.

V max

Rate of reaction

Too cold for the

enzyme to

operate

Optimum temperature

for the enzyme

Rapid denaturation

at high temperature

Rate of reaction

K m

Substrate concentration

8.6.5 pH

Temperature

Figure 8.31(a): Temperature

The optimum pH is that at which the

maximum rate of reaction occurs. Thus the

pH change leads to an alteration of enzyme

shape, including the active site. If extremes

of pH are encountered by an enzyme, then it

will be denatured (Figure 8.31b).

Figure 8.32: Rate of enzyme reaction

8.6.8 Introducing the Michaelis-Menton

Constant (Km) and Its Significance

When the initial rate of reaction of an

enzyme is measured over a range of

substrate concentrations (with a fixed

amount of enzyme) and the results plotted

on a graph. With increasing substrate

concentration, the velocity increases –

rapidly at lower substrate concentration.

293

---

However the rate increases progressively,

above a certain concentration of

the substrate the curve flattened out. No

further increase in rate occurs.

This shows that the enzyme is working

at maximum velocity at this point. On the

graph, this point of maximum velocity is

shown as V max .

8.6.9 Inhibitors of Enzyme

Certain substances present in the cells may

react with the enzyme and lower the rate

of reaction. These substances are called

inhibitors. It is of two types competitive

and non-competitive (Figure 8.33).

V i

No inhibitor

K m

K m

[S]

V max

Competitive

inhibition

V max

Noncompetitive

inhibition

Figure 8.33: Enzyme inhibitors

Competitive

inhibitor

interferes with

active site of

enzyme so

substrate Substrate

cannot bind

Enzyme

(a) Competitive inhibition

Substrate

Enzyme

Noncompetitve

inhibitor

changes shape of

enzyme so it cannot

bind to substrate

(b) Noncompetitive inhibition

Figure 8.34: Action of Enzyme

inhibitors

8.6.10 Competitive Inhibitor

Molecules that resemble the shape of the

substrate and may compete to occupy

the active site of enzyme are known as

competitive inhibitors. For Example: the

enzyme that catalyses the reaction between

carbon di oxide and the CO 2 acceptor

molecule in photosynthesis, known

as ribulose biphosphate carboxylase

oxygenase (RUBISCO) is competitively

inhibited by oxygen/carbon-di-oxide in

the chloroplast. The competitive inhibitor

is malonate for succinic dehydrogenase

(Figure 8.34).

8.6.11 Non-competitive Inhibitors

There are certain inhibitors which may

be unlike the substrate molecule but still

combines with the enzyme. This either

blocks the attachment of the substrate

to active site or change the shape so that

it is unable to accept the substrate. For

example the effect of the amino acids

alanine on the enzyme pyruvate kinase in

the final step of glycolysis.

Certain non-reversible/irreversible

inhibitors bind tightly and permanently

to an enzyme and destroy its catalytic

properties entirely. These could also be

termed as poisons. Example – cyanide

ions which blocks cytochrome oxidase

in terminal oxidation in cell aerobic

respiration, the nerve gas sarin blocks a

neurotransmitter in synapse transmission.

8.6.12 Allosteric Enzymes

They modify enzyme activity by causing

a reversible change in the structure of the

enzyme active site. This in turn affects

the ability of the substrate to bind to the

enzyme. Such compounds are called

294

---

allosteric inhibitors. Eg. The enzyme

hexokinase which catalysis glucose to

glucose-6 phosphate in glycolysis is

inhibited by glucose 6 phosphate. This is an

example for feedback allosteric inhibitor.

8.6.13 End Product Inhibition

(Negative Feedback Inhibition)

When the end product of a metabolic

pathway begins to accumulate, it may act

as an allosteric inhibitor of the enzyme

controlling the first step of the pathway.

Thus the product starts to switch off

its own production as it builds up.

The process is self – regulatory. As the

product is used up, its production is

switched on once again. This is called

end-product inhibition (Figure 8.35).

txt

2nd

End

product

txt

Enzyme1

Enzyme2

Enzyme3

txt

Figure 8.35: Negative feedback inhibition of enzyme

8.6.14 Enzyme Cofactors

Many enzymes require non-protein components

called cofactors for their efficient activity.

Cofactors may vary from simple inorganic ions

to complex organic molecules. They are of three

types: inorganic ions, prosthetic groups and

coenzymes (Figure 8.36).

• Holoenzyme – active enzyme with its

non protein component.

Cofactor

Catalytic site

Holoenzyme

Coenzyme

Apoenzyme

Figure 8.36: Enzyme components

• Apoenzyme – the inactive enzyme

without its non protein component.

• Inorganic ions help to increase the rate of

reaction catalysed by enzymes. Example:

Salivary amylase activity is increased in

the presence of chloride ions.

• Prosthetic groups are organic

molecules that assist in catalytic

function of an enzyme. Flavin adenine

dinucleotide (FAD) contains riboflavin

(vit B2), the function of which is to

accept hydrogen. ‘Haem’ is an ironcontaining

prosthetic group with an

iron atom at its centre.

• Coenzymes are organic compounds

which act as cofactors but do not

remain attached to the enzyme.

The essential chemical components

of many coenzymes are vitamins.

Eg. NAD, NADP, Coenzyme A, ATP

295

---

Ribozyme – Non

Protein Enzyme

A Ribozyme, also

called as catalytic

RNA; is a ribonucleic acid that acts as

enzyme. It is found in ribosomes.

8.6.15 Nomenclature of Enzymes

Most of the enzymes have a name based

on their substrate with the ending –ase.

For example lactase hydrolyses lactose

and amylase hydrolyses amylose. Other

enzymes like renin, trypsin do not depict

any relation with their function.

8.6.16 Classification of Enzymes

Enzymes are classified into six groups based on their mode of action.

Enzymes Mode of

action

Oxidoreductase Oxidation

and

reduction

(redox)

reactions

Transferase

Hydrolases

Isomerase

Transfer

a group

of atoms

from one

molecule to

another

Hydrolysis

of substrate

by addition

of water

molecule

Control the

conversion

of one

isomer to

another by

transferring

a group

of atoms

from one

molecule to

another

General scheme of reaction

296

Example

A red + B ox A ox + B red Dehydrogenase

A – B + C A + C – B Transaminase,

phosphotransferase

A – B + H 2 O

A – H + B – OH Digestive enzymes

A – B – C A – C – B Isomerase

(Continued)

---

Lyase

Ligase

Enzymes

Mode of

action

Break

chemical

bond without

addition of

water

Formation of

new chemical

bonds using

ATP as a

source of

energy

General scheme of reaction Example

A – B A + B Decarboxylase

A + B + ATP A – B + ADP + Pi DNA ligase

Telomerase – A

Ribonucleo Protein

Telomere protects

the end of the chromosome

from damage. Telomerase

is a ribonucleo protein also called as

terminal transferase.

8.6.17 Uses of Enzymes

Enzyme Source Application

Bacterial Bacillus Biological

protease

detergents

Bacterial

glucose

isomerase

Fungal

lactase

Bacillus

Kluyveromyces

Fructose

syrup

manufacture

Breaking

down of

lactose to

glucose and

galactose

Amylases Aspergillus Removal

of starch in

woven cloth

production

8.7 Nucleic Acids

As we know DNA and RNA are the

two kinds of nucleic acids. These were

originally isolated from cell nucleus. They

are present in all known cells and viruses

with special coded genetic programme

with detailed and specific instructions for

each organism heredity.

Friedrich Miescher

was the first to isolate a

non-protein substance

in nuclei of pus cells

and named it as ‘Nuclein’.

DNA and RNA are polymers of

monomers called nucleotides, each

of which is composed of a nitrogen

base, a pentose sugar and a phosphate.

A purine or a pyrimidine and a ribose or

deoxyribose sugar is called nucleoside.

A nitrogenous base is linked to pentose

sugar through n-glycosidic linkage and

forms a nucleoside. When a phosphate

group is attached to a nucleoside it is

called a nucleotide. The nitrogen base is a

297

---

heterocyclic compound that can be either

a purine (two rings) or a pyrimidine

(one ring). There are 2 types of purines –

adenine (A) and guanine (G) and 3 types

of pyrimidines – cytosine (C), thymine

(T) and uracil (U) (Figure 8.38).

Figure 8.37: Position of DNA in the cell

Figure 8.38: Structure of nucleic acid component

298

---

A characteristic feature that differentiates

DNA from RNA is that DNA contains

nitrogen bases such as Adenine, guanine,

thymine (5-methyl uracil) and cytosine

and the RNA contains nitrogen bases such

as adenine, guanine, cytosine and uracil

instead of thymine. The nitrogen base

is covalently bonded to the sugar ribose

in RNA and to deoxyribose (ribose with

one oxygen removed from C 2 ) in DNA.

Phosphate group is a derivative of (PO 4

3-

)

phosphoric acid, and forms phosphodiester

linkages with sugar molecule (Figure 8.39).

8.7.1 Formation of Dinucleotide and

Polynucleotide

Two nucleotides join to form

dinucleotide that are linked through 3′-5′

phosphodiester linkage by condensation

between phosphate groups of one with

sugar of other. This is repeated many

times to make polynucleotide.

Nucleoside

It is a combination of

base and sugar.

Examples

Adenosine = Adenine

+ Ribose

Guanosine = Guanine

+ Ribose

Cytidine = Cytosine

+ Ribose

Deoxythymidine

= Thymine +

Deoxyribose

Nucleotide

It is a combination

of nucleoside and

phosphoric acid.

Examples

Adenylic acid =

Adenosine +

Phosphoric acid

Guanylic acid =

Guanosine +

Phosphoric acid

Cytidylic acid =

Cytidine +

Phosphoric acid

Uridylic acid =

Uridine +

Phosphoric acid

Figure 8.39: Basic component of DNA

and RNA

8.7.2 Structure of DNA

Watson and Crick shared the Nobel Prize

in 1962 for their discovery, along with

Maurice Wilkins, who had produced the

crystallographic data supporting the model.

Rosalind Franklin (1920–1958) had earlier

produced the first clear crystallographic

evidence for a helical structure. James

Watson and Francis Crick (Figure 8.40) of

Cavendish laboratory in Cambridge built

a scale model of double helical structure of

DNA which is the most prevalent form of

DNA, the B-DNA. This is the secondary

structure of DNA.

Figure 8.40: Watson and Crick

As proposed by James Watson and

Francis Crick, DNA consists of right

handed double helix with 2 helical

polynucleotide chains that are coiled

around a common axis to form right

299

---

handed B form of DNA. The coils are

held together by hydrogen bonds which

occur between complementary pairs of

nitrogenous bases. The sugar is called

2′-deoxyribose because there is no

hydroxyl at position 2′. Adenine and

thiamine base pairs has two hydrogen

bonds while guanine and cytosine base

pairs have three hydrogen bonds.

Chargaff ’s Rule:

• A = T; G ≡ C

• A + G = T + C

• A : T = G : C = 1

As published by Erwin Chargaff in 1949,

a purine pairs with pyrimidine and vice

versa. Adenine (A) always pairs with

Thymine (T) by double bond and Guanine

(G) always pairs with Cytosine (C) by

triple bond.

Figure 8.41:

Rosalind franklin

Figure 8.42:

Erwin Chargaff

In 1950s, Maurice

Wilkins and Rosalind

Franklin of Kings

College, London

studied the X-ray crystallography and

revealed experimental data on the

structure of DNA

8.7.3 Features of DNA

• If one strand runs in the 5′-3′ direction,

the other runs in 3′-5′ direction and

thus are antiparallel (they run in

opposite direction). The 5′ end has the

phosphate group and 3’end has the OH

group.

• The angle at which the two sugars

protrude from the base pairs is about

120°, for the narrow angle and 240°

for the wide angle. The narrow angle

between the sugars generates a minor

groove and the large angle on the other

edge generates major groove.

• Each base is 0.34 nm apart and a

complete turn of the helix comprises

3.4 nm or 10 base pairs per turn in the

predominant B form of DNA.

• DNA helical structure has a diameter

of 20 A° and a pitch of about 34 A°.

X-ray crystal study of DNA takes a

stack of about 10 bp to go completely

around the helix (360°).

• Thermodynamic stability of the helix

and specificity of base pairing includes

(i) the hydrogen bonds between the

complementary bases of the double

helix (ii) stacking interaction between

bases tend to stack about each other

perpendicular to the direction of

helical axis. Electron cloud interactions

(∏ – ∏) between the bases in the helical

stacks contribute to the stability of the

double helix.

• The phosphodiester linkages gives an

inherent polarity to the DNA helix.

They form strong covalent bonds,

gives the strength and stability to the

polynucleotide chain (Figure 8.43).

300

---

Blue bands - Two

sugar-phosphate

chains

Complementary

base parings:

A=T and C G

The two chains run in

opposite direction

5’

3’

5’

3’

T

A

C

G

G

C

A

T

G

C

T

A

T

A

A

T

o

3.4A

breaking the entire structure. Whereas

in paranemic coiling the two strands

simply lie alongside one another,

making them easier to pull apart.

• Based on the helix and the distance between

each turns, the DNA is of three forms – A

DNA, B DNA and Z DNA (Figure 8.43) .

3’

5’

T

C

G

C

A

G

Minor Groove

C

A

T

A

T

A

G

T

Major Groove

o

3.4A

G

C

A

5’ 3’

o

20A

Figure 8.43: Structure of DNA

• Plectonemic coiling - the two strands

of the DNA are wrapped around each

other in a helix, making it impossible

to simply move them apart without

Figure 8.44: Forms of DNA

Feature B-DNA A-DNA Z-DNA

Type of helix Right-handed Right-handed Left-handed

Helical diameter (nm) 2.37 2.55 1.84

Rise per base pair (nm) 0.34 0.29 0.37

Distance per complete turn

3.4 3.2 4.5

(pitch) (nm)

Number of base pairs per

10 11 12

complete turn

Topology of major groove Wide, deep Narrow, deep Flat

Topology of minor groove Narrow, shallow Broad, shallow Narrow, deep

8.7.4 Ribonucleic Acid (RNA)

Ribonucleic acid (RNA) is a polymeric

molecule essential in various biological

roles in coding, decoding, regulation

and expression of genes. RNA is

single stranded and is unstable when

compared to DNA (Figure 8.45).

Figure 8.45: Structure of RNA

301

---

8.7.5 Types of RNA

• mRNA (messenger RNA):

Single stranded, carries a copy

of instructions for assembling

amino acids into proteins. It is

very unstable and comprises 5%

of total RNA polymer. Prokaryotic

mRNA (Polycistronic) carry coding

sequences for many polypeptides.

Eukaryotic mRNA (Monocistronic)

contains information for only one

polypeptide.

• tRNA (transfer RNA): Translates the

code from mRNA and transfers amino

acids to the ribosome to build proteins.

It is highly folded into an elaborate 3D

structure and comprises about 15% of

total RNA. It is also called as soluble

RNA.

• rRNA (ribosomal RNA): Single

stranded, metabolically stable, make

up the two subunits of ribosomes.

It constitutes 80% of the total RNA.

It is a polymer with varied length

from 120–3000 nucleotides and gives

ribosomes their shape. Genes for rRNA

are highly conserved and employed for

phylogenetic studies (Figure 8.46).

Messenger RNA (mRNA)

Ribosomal RNA (rRNA)

Figure 8.46: Types of RNA

Transfer RNA (tRNA)

Summary

Cells are composed of water, inorganic

compounds and organic molecules.

The biomolecules of the cells include

carbohydrates, lipids, proteins, enzymes

and nucleic acids.

Carbohydrates include simple

sugars (monosaccharides) and

polysaccharides. Polysaccharide serve

as storage forms of sugar and structural

components of cell.

Lipids are the principle components

of cell membrane, and they serve

as energy storage and signalling

molecules.

Proteins are polymers of 20 different

amino acids, each of which has a

distinct side chain with specific

chemical properties. Each protein has

a unique aminoacid sequence which

determines its 3D structure.

Nucleic acids are the principle

information molecules of the cell. Both

DNA and RNA are polymers of purine

and pyrimidine nucleotides. Hydrogen

bonding between complementary base

pairs allows nucleic acids to direct

their self replication.

302

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Evaluation

1. The most basic amino acid is

a. Arginine

b. Histidine

c. Glycine

d. Glutamine

2. An example of feedback inhibition is

a. Cyanide action on cytochrome

b. Sulpha drug on folic acid

synthesiser bacteria

c. Allosteric inhibition of hexokinase

by glucose-6-phosphate

d. The inhibition of succinic

dehydrogenase by malonate

3. Enzymes that catalyse interconversion

of optical, geometrical or positional

isomers are

a. Ligases

b. Lyases

c. Hydrolases

d. Isomerases

4. Proteins perform many physiological

functions. For example some functions

as enzymes. One of the following

represents an additional function that

some proteins discharge:

a. Antibiotics

b. Pigment conferring colour to skin

c. Pigments making colours of

flowers

d. Hormones

5. Given below is the diagrammatic

representation of one of the categories

of small molecular weight organic

compounds in the living tissues.

Identify the category shown & one

blank component “ X” in it

HOH 2 C

OH

O

X

OH

Category

Compound

Cholesterol Guanine

Amino acid NH 2

Nucleotide

Adenine

Nucleoside Uracil

6. Distinguish between nitrogenous

base and a base found in inorganic

chemistry.

7. What are the factors affecting the rate

of enzyme reaction?

8. Briefly outline the classification of

enzymes

9. Write the characteristic feature of

DNA

10. Explain the structure and function of

different types of RNA

303

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ICT Corner

ENZYMES

Bio Catalyst

Steps

• Scan the QR code

• Click Enzymatic

• Start a new game

• Select yes if you using touch screen mobile / tablet

• Tap or click here

• Click experiments

Activity

• Move the slide to change temperature

• Go to next concept

• Try Quiz after experiments

Step 1

Step 3

URL:

Step 2

Step 4

https://www.biomanbio.com/HTML5GamesandLabs/LifeChemgames/lifechem.html

* Pictures are indicative only

304

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References

Unit 1: Diversity of Living World

1. Alexopoulos, C.J. and Mims, C.W., 1985. Introductory Mycology (3 rd Edition)Wiley

Eastern Limited.

2. Alison M.Smith, George Coupland, Liam Dolan, Nicholas Harberd, Jonathan Jones,

Cathie Martin, Robert Sablowski and Abigail Amey (2012) Plant biology, Garland

Science Taylor and Francis Group, LLC.

3. Bryce Kendrick, 2000. The Fifth Kingdom, Focus Publishing R. Pullins Company,

Newburyport.

4. Dubey, R.C. and Maheswari, D.K. 2010. A Text Book of Microbiology, S. Chand

&Company Ltd., New Delhi.

5. Dutta, A.C. 1999, Botany for Degree Students, Oxford University Press. Calcutta.J.

6. Landecker, E.M. 1996, Fundamentals of Fungi (4 th edition) Prentice Hall, Upper Saddle

River, New Jersey 07458.

7. Parihar, N.S. 1987, An Introduction to Embryophyta Volume 1 Bryophyta, Central

Book Depot, Allahabad.

8. Raven, P.H.,Evert, R.F. and Eichhorn, S.E. Biology of Plants (5 th edition) 1992. Worth

Publishers, New York,10003.

9. Singh, V., Pande,P.C. and Jishain,D.K., 2010, A Text Book of Botany, Rastogi

Publications, Meerut, India.

10. Taylor, D.J. Green, N.P.O and Stout, G.W. Biological Science (3rd Edition) 2005

Cambridge University Press, UK.

11. Van den Hoek, and Jah C. Mann, D.G and Jahns, H.M 2012. Algae An introduction to

phycology, Cambridge University Press.

12. Willis, K.J. and McElwain, J.C. 2005. The Evolution of Plants, Oxford University Press,

New Delhi.

13. Webster, J. and Weber, R. 2011. Introduction to fungi. Cambridge University Press,UK.

Unit 2: Plant Morphology and Taxonomy of Angiosperm

1. Bhattacharyya. B, 2005 – Systematic Botany, Narosa Publishing House Pvt. Ltd.

2. Gurcharan Singh, 2016. Plant Systematics 3rd Edition Oxford & IBH Publishing

Company Private Ltd.

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cataloging –in-Publication Data.

4. Anupam Dikshit, M.O. Siddiqui, Ashutosh pathak, Taxonomy of Angiosperms. Basic

Concepts, Molecular aspects and Future Prospects.

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Plant Species of The World, Special Edition January 2018.

6. Radford E. Albert. Fundamentals of plant systematics - Harper international edition

305

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Unit 3: Cell Biology and Biomolecules

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CBS Publishers. Second Edition.

2. Alison M. Smith, George Coupland, Liam, Dolan, Nicholas Harberd, Jonathan

Jones, Cathie Martin, Robert Sablowski and Abigail Amey. 2010. Plant Biology.

Garland Science. Taylor and Francis Group LLC.

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Edition.

4. Geoffrey M. Cooper and Robert E. Hausman. 2009. The Cell, Molecular Edition.

Sinauer Associates Inc. Fifth Edition.

5. James Watson, Tania A. Baker, Stephen P. Bell, Alexander Gann, Michael Levine

and Richard Losick. 2017. Molecular Biology of the gene. Pearson India Services Pvt.

Ltd. Seventh Edition.

6. Joanne Willey, Linda Sherwood and Chris Woolverton. 2011. Prescott’s Microbiology.

McGraw Hill companies Inc. Eighth edition

7. Linda E. Graham, James M. Graham and Lee W. Wilcox. 2006. Plant Biology. Pearson

Education Inc. Second edition.

8. Michael J. Pelczer, Chan E. C and Noel R. Kreg. 2016. Microbiology. McGraw Hill

Education Pvt. Ltd. Fifth Edition.

9. Suzanne Bell and Keith Morris. 2010. An Introduction to microscopy. CRC Press Taylor

and Francis group.

10. Taylor D. J., Green N. P. O and Stout G. W. Biological Science. Cambridege University

Press. Third Edition.

11. Thomas D. Pollard and William C. Earnshaw. 2008. Cell Biology. Saunders Elseviers.

Second Edition.

306

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Glossary

Acetyl CoA

Active site

Akinetes

Aleurone

Anamorph

Anisogamy

Apogamy

Apospory

Balausto

Basal body

Biosphere

Buffer

Carcinogen

Chemotaxonomy

Clades

Cladistics

Codon

Coenocytic condition

Dalton

Endosperm

Endospore

Eusporangiate

Fossil

Gametophyte

Genome

Germ

Small, water-soluble metabolite comprising an acetyl group

linked to coenzyme A (CoA).

Region of an enzyme molecule where the substrate binds

and undergoes a catalyzed reaction.

Thick walled, dormant, non motile asexual spores.

Outer layer of the endosperm

Asexual or imperfect state of fungi

Fusion of morphologically and physiologically dissimilar

gametes

Formation of sporophyte from the gametophytic tissue

without the fusion of gametes.

Development of the gametophyte from the sporophyte

without the formation of spores

Fleshy in dehiscent fruit

Structure at the base of cilia and flagella from which

microtubules forming the axoneme radiate

The region of earth on which life exist

A solution of the acid and base form of a compound that

undergoes little change in pH when small quantities of

strong acid or base are added.

Any chemical or physical agent that can cause cancer when

cells or organism s are exposed to it.

Classification based on the biochemical constituents of

plants

Group of species comprising common ancestor and its

descendants

Methodology used to classify organisms into monophyletic

group

Sequence of three nucleotides in DNA or mRNA that specifies

a particular amino acid during protein synthesis; also called

triplet

Aseptate, multinucleate condition

Unit of molecular mass approximately equal to the mass of a

hydrogen atom (1.66 × 10−24 g)

Nutritive tissue for the embryo

Thick walled, resting spores

Sporangium formed from a group of initials

The remains or impression of plant or animal of the past

geological age

The haploid plant body

Complete set of genes in an organism

Protein rich embryo

307

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Heterospory

Karyogamy

Karyotype

Km

Leptosporangiate

Merosity

Microgreens

Monograph

Monosulcate

Mycobank

Nucleoid

Oogamy

Parthenocarphy

Pendulous

Petrifaction

pH

Phylogeny

Pistillode

Plasmogamy

Pluriocular

Prophage

Protologue

Rachilla

Sporophyte

Teloemorph

Thallospores

Triplicate

X-Ray crystallography

Zoospore

Zygospore

Production of spores of different sizes: megaspores and

microspores

Fusion of nucleus

Number, sizes, and shapes of the entire set of metaphase

chromosomes of a eukaryotic cell.

A parameter that describes the affinity of an enzyme for its

substrate and equals the substrate concentration that yields

the half-maximal reaction rate;

Sporangium formed from a single initial

Number of parts per whorls

Young vegetable greens add flavour in culinary

Complete account of a taxon of any rank

Pollen grain with single furrow or pores

Online database documenting new mycological names

Genetic material of bacterium

Fusion of morphologically and physiologically dissimilar

gametes

Fruit developed without fertilization

Hanging downward loosely or freely (like catkin)

A process of fossil formation through infiltration of

minerals over a long period

A measure of the acidity or alkalinity of a solution defined

as the negative logarithm of the hydrogen ion concentration

in moles per liter

Evolution of group of organisms

Sterile pistil

Fusion of cytoplasm

An ovary with two or more locus

The integrated phage DNA with host DNA

Set of information associated with the scientific name of

a taxon at its first valid publication containing the entire

original material regarding the taxon

Central axis of a spikelet

Diploid plant body

Sexual or perfect state of the fungi

Asedual spores formed due to the fragmentation of hyphae

Pollen grain with three furrows or pores

Most commonly used technique for determining the threedimensional

structure of macromolecules (particularly

proteins and nucleic acids) by passing x-rays

Motile, asexual spores

Thick walled diploid resting spores

308

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English – Tamil Terminology

Acropetal succession (arrangement)

Aggregatte fruit

Akinetes

Anamorph

Anisogamy

Anthrophytes

Apogamy

Apospory

Arbitary marker

Basipetal succession

Biosphere

Buttress root

Centrifugal

Centripetal

Cladogram

Coenocytic

Conjugation

Cotyledons

Dry dehiscent fruit

Dry indehiscent fruit

Embryo

Endosperm

Endospores

Eukaryote

Eusporangiate

Fossil

Funicle

Gametophyte

Gene marker

Genome

Geocarpic fruit

Geophytes

Gynobasic

Heterospory

Homeostasis

Hydrochory

Indeterminate

Irritability

Isogamy

Karyogamy

Karyokinesis

Leaf primodium

Legume / Pod

நுனி நோக்கிய வரிசை

திரள்கனி

உறக்்க ்கராவித்து

பாலிலாநிலை

சமமறற ந்கமீட்களின் இணைவு

பூக்கும் தாவரங்களின் முன்நனோடிகள்

பாலிணைவின்மை

குன்றலிலலோ வித்துத்தன்மை

தன்னிசசையான குறிபபோன்

அடி நோக்கிய வரிசை

உயிரக்ந்கோளம்

பலச்க நவர

மையம் விலகியது

மையம் நோக்கியது

கிளை வரைபடம்

பலஉட்கரு நிலை

இணைவு

விதையிலைகள்

உலர வெடி்கனி

உலர வெடியோக்்கனி

்கரு

்கருவூண்திசு

அ்கவித்துகள்

உண்மை உட்கரு உயிரி

உண்மை வித்த்கத்தன்சம

தொல்லுயிரெசைம்

சூல்காம்பு

ந்கமீட்டக தாவரம்

மரபணு குறிபபோன்

மரபணுத் வதோகுபபு

புவிபுதை ்கனி/நிலத்த்கத்துக் ்கனி

நிலத்த்கத்துத் தூண்நைர தாவரம்

சூறசப அடி சூல்கத்தண்டு

மோறறு வித்த்கத்தன்சம

சமசசீர நிலை

நீரமூலம் பரவுதல

வரம்பறற வளரசசி

உறுத்துைரசசி

ஒத்த ந்கமீட்களின் இணைவு

உட்கரு இணைவு

்கோரிநயோச்கனசிஸ்

இசலத்நதோறறுவி

விதைபசப

309

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Leptosporangiate

Maturation promoting factor (MPF)

Merosity

Metabolism

Middle Lamella

Monograph

Multiple fruit

Mycobank

Nuclear envelope

Nuclear organizer

Nucleoid

Oogamy

Pendulous

Pericarp

Petrification

Pili or Fimbriae

Pistillode

Plasmogamy

Plumule

Plurilocular

Polymorphism

Primary adapter

Probe

Prokaryote

Prophage

Rachilla

Radicle

Restriction site

Seed

Seed coat

Serotaxonomy

Sporophyte

Synaptonemal complex

Systematics

Tandem repeat

Taxon

Telomorph

Thallospores

Transduction

Transformation

True fruit

Zoospore

Zygospore

மெலி வித்த்கத்தன்சம

முதிரசசியை ஊக்்கபபடுத்தும் ்கோரணி

எண்ணிக்ச்க அமைவு

வளரசிதைமாறறம்

இடைமென் அடுக்கு

தனிக்்கடடுரை

கூடடுக்்கனி

பூஞசை வஙகி

நியூக்ளியர உறை

நியுக்ளிநயோலோர அமைப்பான்கள

உட்கரு ஒத்த அசமபபு

முடசட ்கருவுறுதல

தொங்குகின்ற

்கனி உறை

்கலலோதல

நுண் சிலும்புகள்

மலடடு சூல்கம்

சைட்டோபிளாச இணைவு

முளைக்குருத்து

பலலசற சூறசப

பலபடிவுடமை

முதன்மை மோறறி

ஆய்வி

தொல்லுட்கரு உயிரி

ஃபாஜ் முன்நனோடி

சிறு்கதிரின் மையஅசசு

முளை நவர

வரையறு தளம்

விதை

விதை உறை

ஊநீர வச்கபபோடடியல

வித்த்கத்தோவரம்

சைனோபடினிமல வதோகுதி

முறைபபோடடு தாவரவியல

ஒருசெயல நி்கழும் மாறிகள்

வச்கபபோடடுத் வதோகுதி

போலநிலை

உடல வித்துகள்

மரபணு ஊடு்கடத்தல

மரபணு மாறறம்

வமய்க்்கனி

இயஙகு வித்து

உறக்்க ்கருமுடசட

310

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Competitive Examination Questions

Unit – 1 Diversity of Living World

1. Which of the following are found in

extreme saline conditions? (NEET-

2017)

a. Archaebacteria

b. Eubacteria

c. Cyanobacteria

d. Mycobacteria

2. Select the mismatch (NEET – 2017)

a. Frankia Alnus

b. Rhodospirillum Mycorrhiza

c. Anabaena Nitrogen fixer

d. Rhizobium Alfalfa

3. Which among the following are the

smallest living cells, known without a

definite cell wall, pathogenic to plants as

well as animals and can survive without

oxygen? (NEET – 2017)

a. Bacillus b. Pseudomonas

c. Mycoplasma d. Nostoc

4. Read the following statements ( A to E ) and

select the option with all correct statements

(AIPMT – 2015)

A. Mosses and Lichens are the first

organisms to colonise a bare rock.

B. Selaginella is a homosporous

pteridophyte.

C. Coralloid roots in Cycas have VAM.

D. Main plant body in bryophytes

is gametophytic, whereas in

pteridophytes it is sporophytic.

E. In gymnosperms, male and female

gametophytes are present within

sporangia located on sporophyte.

a. B, C and E

b. A, C and D

c. B, C and D

d. A, D and E

5. An example of colonial alga is (NEET –

2017)

a. Chlorella b. Volvox

c. Ulothrix d. Spirogyra

6. Five kingdom system of classification

suggested by R.H. Whittaker is not

based on (AIPMT – 2014)

a. Presence or absence of a well

defined nucleus

b. Mode of reproduction

c. Mode of nutrition

d. Complexity of body organisation

7. Mycorrhizae are the example of (NEET

– 2017)

` a. Fungitasis c. Amensalism

b. Antibiosis d. Mutualism

8. Which of the following shows coiled

RNA strand and capsomeres? (AIPMT

– 2014)

a. Polio virus

b. Tobacco mosaic virus

c. Measles virus

d. Retrovirus

9. Viroids differ from viruses in having :

(NEET – 2017)

a. DNA molecules with protein coat

b. DNA molecules without protein coat

c. RNA molecules with protein coat

d. RNA molecules without protein coat

10. Select the mismatch (NEET – 2017)

a. Pinus — Dioecious

b. Cycas — Dioecious

c. Salvinia — Heterosporous

d. Equisetum — Homosporous

311

---

11. Life cycle of Ectocarpus and Fucus

respectively are (NEET – 2017)

a. Haplontic, Diplontic

b. Diplontic, Haplodiplontic

c. Haplodiplontic, Diplontic

d. Haplodiplontic, Halplontic

12. Zygote meiosis is characterisitic of

(NEET – 2017)

a. Marchantia b. Fucus

c. Funaria d. Chlamydomonas

13. Which of the following is correctly

matched for the product produced by

them? (NEET – 2017)

a. Acetobacter acetic : Antibiotics

b. Methanobacterium : Lactic acid

c. Penicillium notatum : Acetic acid

d. Saccharomyces cerevisiae : Ethanol

14. Which of the following components

provides sticky character to the bacterial

cell? (NEET – 2017)

a. Cell wall b. Nuclear membrane

c. Plasma membrane d. Glycocalyx

15. Which of the following statements is

wrong for viroids? (NEET – 2016)

a. They lack a protein coat

b. They are smaller than viruses

c. They causes infections

d. Their RNA is a high molecular weight

16. In bryophytes and pteridophytes,

transport of male gametes require

(NEET – 2016)

a. Wind b. Insects

c. Birds d. Water

17. How many organisms in the list below are

autotrophs? (AIPMT Mains 2012)

Lactobacillus, Nostoc, Chara, Nitrosomonas,

Nitrobacter, Streptomyces, Saccharomyces,

Trypanosoma, Porphyra, Wolffia

a. Four b. Five

c. Six d. Three

18. Which of the following would appear as

the pioneer organisms on bare rocks?

(NEET – 2016)

a. Lichens b. Liverworts

c. Mosses d. Green algae

19. Monoecious plant of Chara shows

occurrence of (NEET-2013)

a. Stamen and carpel on the same plant

b. Upper antheridium and lower

oogonium on the same plant

c. Upper oogonium and lower

antheridium on the same plant

d. Antheridiophore and archegoniophore

on the same plant

20. Read the following five statement (A-

E) and answer as asked next to them

(AIPMT Prelims – 2012)

a. In Equisetum, the female gametophyte

is retained on the parent sporophyte

b. In Ginkgo, male gametophyte is not

independent

c. The sporophyte in Riccia is more

developed than that in Polytrichum

d. Sexual reproduction in Volvox is

isogamous

e. The spores of slime moulds lack cell

walls

How many of the above statement are

correct? (AIPMT Prelims – 2012)

a. Two b. Three

c. Four d. One

21 One of the major components of cell

wall of most fungi is (NEET – 2016)

a. Chitin b. Peptidoglycan

c. Cellulose d. Hemicellulose

312

---

22. Which one of the following statements

is wrong? (NEET – 2016)

a. Cyanobacteria are also called bluegreen

algae

b. Golden algae are also called desmids

c. Eubacteria are also called false

bacteria

d. Phycomycetes are also called algal

fungi

23. Flagellated male gametes are present

in all the three of which one of the

following sets? (AIPMT Prelims –

2007

a. Riccia, Dryopteris and Cycas

b. Anthoceros, Funaria and Spirogyra

c. Zygnema, Saprolegnia and Hydrilla

d. Fucus, Marsilea and Calotropis

24. Ectophloic siphonostele is found in

(AIPMT Prelims – 2005)

a. Adiantum and Cucurbitaceae

b. Osmunda and Equisetum

c. Marsilea and Botrychium

d. Dicksonia and maiden hair fern

25. Which part of the tobacco plant is

infected by Meloidogyne incognita?

(NEET – 2016)

a. Flower b. Leaf

c. Stem d. Root

26. Select the correct statement (NEET –

2016)

a. Gymnosperms are both homosporous

and heterosporous

b Salvinia, Ginkgo and Pinus all are

gymnosperms

c. Sequoia is one of the tallest trees

d. The leaves of gymnosperms are not

well adapted to extremes of climate

27. Seed formation without fertilization in

flowering plants involves the process of

(NEET – 2016)

a. Sporulation

b. Budding

c. Somatic hybridization

d. Apomixis

28. Chrysophytes, Euglenoids, Dinoflagellates

and Slime moulds are included in the

kingdom (NEET – 2016)

a. Animalia b, Monera

c. Protista d. Fungi

29. The primitive prokaryotes responsible

for the production of biogas from the

dung of ruminant animals, include the

(NEET – 2016)

a. Halophiles b. Thermoacidophiles

c. Methanogens d. Eubacteria

Unit – 2 Plant Morphology and

Taxonomy of Angiosperm

1. Leaves become modified into spines in

[AIPMT-2015]

a. Silk Cotton b. Opuntia

c. Pea d. Onion

2. Keel is the characteristic feature of flower

of [AIPMT-2015]

a. Tomato b. Tulip

c. Indigofera d. Aloe

3. Perigynous flowers are found in

[AIPMT-2015]

a. Rose b. Guava

c. Cucumber d. China rose

4. Which one of the following statements is

correct [AIPMT-2014]

a. The seed in grasses is not endospermic

b. Mango is a parthenocarpic fruit

313

---

c. A proteinaceous aleurone layer is

present in maize grain

d. A sterile pistil is called a staminode

5. An example of edible underground stem

is [AIPMT-2014]

a. Carrot b. Groundnut

c. Sweet potato d. Potato

6. Placenta and pericarp are both edible

portions in [AIPMT-2014]

a. Apple b. Banana

c. Tomato d. Potato

7. When the margins of sepals or petals

overlap one another without any

particular direction, the condition is

termed as [AIPMT-2014]

a. Vexillary b. Imbricate

c. Twisted d. Valvate

8. An aggregate fruit is one which develops

from [AIPMT-2014]

a. Multicarpellary syncarpous gynoecium

b. Multicarpellary apocarpous

gynoecium

c. Complete inflorescence

d. Multicarpellary superior ovary

9. Non-albuminous seed is produced in

[AIPMT-2014]

a. Maize b. Castor

c. Wheat d. Pea

10. Seed coat is not thin, membranous in

[NEET-2013]

a. Coconut b. Groundnut

c. Gram d. Maize

11. In china rose the flower are [NEET-2013]

a. Actinomorphic. Epigynous with

valvate aestivation

b. Zygomorphic, hypogynous with

imbricate aestivation

c. Zygomorphic, epigynous with

twisted aestivation

d. Actinomorphic, hypogynous with

twisted aestivation

12. Placentation in tomato and lemon is

[AIPMT Prelims-2012]

a. Marginal b. Axile

c. Parietal d. Free central

13. Vexillary aestivation is characteristic of

the family [AIPMT Prelims-2012]

a. Solanaceae b. Brassicaceae

c. Fabaceae d. Asteraceae

14. Phyllode is present in [AIPMT

Prelims-2012]

a. Australian Acacia b. Opuntia

c. Asparagus d. Euphorbia

15. How many plants in the list given below

have composite fruits that develop from

an inflorescence? Walnut, poppy, radish,

pineapple, apple, tomato. [AIPMT

Prelims-2012]

a. Two b. Three

c. Four d. Five

16. Cymose inflorescence is present in

[AIPMT Prelims-2012]

a. Trifolium b. Brassica

c. Solanum d. Sesbania

17. Which one of the following organism

is correctly matched with its three

characteristics? [AIPMT Mains -2012]

a. Pea : C3 pathway, Endospermic seed,

Vexillary aestivation

b. Tomato : Twisted aestivation, Axile

placentation, Berry

c. Onion: Bulb, Imbricate aestivation,

Axile placentation

d. Maize : C3 pathway, Closed

vascular bundles, scutellum

314

---

18. How many plants in the list given below

have marginal placentation?

Mustard, Gram, Tulip, Asparagus, Arhar,

sun hemp, Chilli, Colchicine, Onion,

Moong, Pea, Tobacco, Lupin [AIPMT

Mains -2012]

a. Four b. Five

c. Six d. Three

19. The Eyes of the potato tuber are

[AIPMT Prelims-2011]

a. Axillary buds b. Root buds

c. Flower buds d. Shoot buds

20. Which one of the following statements is

correct? [AIPMT Prelims-2011]

a. Flower of tulip is a modified shoot

b. In tomato, fruit is a capsule

c. Seeds of orchids have oil – rich

endosperm

d. Placentation in primrose is basal

21. A drup develops in [AIPMT

Prelims-2011]

a. Tomato b. Mango

c. Wheat d. Pea

Unit 3 Cell biology and Biomolecules

1. Who invented electron microscope?

(2010 AIIMS, 2008 JIPMER)

a. Janssen b. Edison

c. Knoll and Ruska d. Landsteiner

2. Specific proteins responsible for the flow

of materials and information into the cell

are called (2009 AIIMS)

a. Membrane receptors

b. carrier proteins

c. integeral proteins

d. none of these

3. Omnis-cellula-e-cellula was given by

(2007 AIIMS)

a. Virchow b. Hooke

c. Leeuwenhoek d. Robert Brown

4. Which of the following is responsible for

the mechanical support, protein synthesis

and enzyme transport (2007 AIIMS)

a. cell membrane

b. mitochondria

c. dictyosomes

d. endoplasmic reticulum

5. Genes present in the cytoplasm of

eukaryotic cells are found in (2006

AIIMS)

a. mitochondria and inherited via egg

cytoplasm

b. lysosomes and peroxisomes

c. Golgi bodies and smooth endoplasmic

reticulum

d. Plastids inherited via male gametes

6. In which one the following would you

expect to find glyoxysomes(2005 AIIMS)

a. Endosperm of wheat

b. endosperm of castor

c. Palisade cells in leaf

d. Root hairs

7. A quantosome is present in (JIPMER 2012)

a. Mitochondria b. Chloroplast

c. Golgi bodies d. ER

8. In mitochondria the enzyme cytochrome

oxidase is present in (2012 JIPMER)

a. Outer mitochondrial membrane

b. inner mitochondrial membrane

c. Stroma d. Grana

9. Which organelle is present in higher

number in secretory cell (2008 JIPMER)

a. Mitochondria b. Chloroplast

c. Nucleus d. Dictyosomes

10. Major site for the synthesis of lipids

(2013 NEET)

a. Rough ER b. smooth ER

c. Centriole d. Lysosome

315

---

11. Golgi complex plays a major role in.

(2013 NEET)

a. post translational modification of

proteins and glycosidation of lipids

b. translation of proteins

c. Transcription of proteins

d. Synthesis of lipid

12. Main arena of various types of activities

of a cell is (2010 AIPMT)

a. Nucleus b. Mitochondria

c. Cytoplasm d. Chloroplast

13. The thylakoids in chloroplast are

arranged in (2005 JIPMER)

a. regular rings b. linear array

c. diagonal direction d. stacked discs

17. The main organelle involved in

modification and routing of newly

synthesised protein to their destinations

is (AIPMT 2005)

a. Mitochondria

b. Glyoxysomes

c. Spherosomes

d. Endoplasmic reticulum

18. Algae have cell wall made up of (AIPMT

2010)

a. Cellulose, galactans and mannans

b. Cellulose, chitin and glucan

c. Cellulose, Mannan and peptidoglycan

d. Muramic acid and galactans

14. Sequences of which of the following

is used to know the phylogeny (2002

JIPMER)

a. mRNA b. rRNA c. tRNA d. Hn RNA

15. Structures between two adjacent cells

which is an effective transport pathway-

(2010 AIPMT)

a. Plasmodesmata

b. Middle lamella

c. Secondary wall layer

d. Primary wall layer

16. In active transport carrier proteins are

used, which use energy in the form of

ATP to

a. transport molecules against

concentration gradient of cell wall

b. transport molecules along

concentration gradient of cell

membrane

c. transport molecules against

concentration gradient of cell

membrane

d. transport molecules along

concentration gradient of cell wall

316

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BOTANICAL NAMES AND COMMON NAMES

S.No Botanical name Common name Tamil name

1 Abrus precatorius Crab’s eye குன்றிமணி

2 Acacia nilotica Babul tree ்கருவேலம்

3 Acalypha indica Indian Acalypha குபசபநமனி

4 Achyranthes aspera Chaff flower நாயுருவி

5 Albizia lebbeck Indian siris வோச்க

6 Allium cepa Onion வெங்காயம்

7 Allium sativum Garlic வெளசளபபூண்டு

8 Aloe vera Indian aloe நைோறறுக்்கறறோசை

9 Alstonia scholaris Devilwood ஏழிலைபபோசல

10 Amorphophallus

Elephant foot yam ்கருணைக் கிைஙகு

paeoniifolius

11 Argemone mexicana Mexican poppy குடிநயோடடிப பூண்டு

12 Areca catechu Betel nut பாக்கு / ்கமுகு

13 Avicennia marina White mangrove வெளசள

அலையோறறி

14 Azadirachta indica Neem வேம்பு

15 Beta vulgaris Beetroot பீடருட

16 Bombax ceiba White Silk cotton இலவம் பஞசு

17 Bambosa bambos Bamboo மூஙகில

18 Borassus flabellifer Palmyra palm பனை

19 Bougainvillea Paper flower ்கோகிதபபூ

20 Brassica juncea Mustard ்கடுகு

21 Brassica oleracea var. Cauliflower

்கோலிஃபிளவர

botrytis

22 Brassica oleracea var. Cabbage

முடசடக்ந்கோசு

capitata

23 Caesalpinia pulcherrima Peacock flower மயிறவ்கோன்சற

24 Calotropis gigantea Giant milkweed எருக்கு

25 Canna indica Canna ்கலவோசை

26 Carica papaya Papaya பபபோளி

27 Cassia auriculata Avaram ஆவாரை

28 Cassia fistula Indian laburnum வ்கோன்சற

29 Casuarina equisetifolia Whistling pine சவுக்கு

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30 Ceiba pentandra Red silk cotton செவ்விலவ மரம்

31 Centella asiatica Indian penny wort வலலோசர

32 Chrysanthemum indicum Chrysanthemum சாமந்தி

33 Cinnamomum zeylanicum Cinnamon படசட

34 Cocos nucifera Coconut தென்னை

35 Coffea arabica Coffee plant ்கோஃபி தாவரம்

36 Colocasia esculenta Cocoyam சேனைக் கிைஙகு

37 Coriandrum sativum. Coriander வ்கோத்துமலலி

38 Corypha umbraculifera Talipot palm தாழிபபசன

39 Couroupita guianensis Cannonball tree ோ்கலிங்கமரம்

40 Crotalaria retusa Rattle weed கிலுகிலுபசப

41 Cucumis sativus Cucumber வெளளரி

42 Curcuma amada Mango ginger மா இஞசி

43 Cuscuta reflexa Dodder plant அம்மையோர கூந்தல

44 Daucus carota Carrot ்கோரட

45 Delonix regia Gulmohar,flame tree. செம்மயிறவ்கோன்சற.

46 Dioscorea bulbifera Potato yam வ்கோடிக்கிைஙகு

47 Dolichos biflorus Horsegram வ்கோளளு

48 Eugenia jambolana Jamun நாவல

49 Ficus benghalensis Banyan. ஆலமரம்

50 Ficus carica Common fig சீமை அத்தி

51 Ficus racemosa Indian fig அத்தி

52 Ficus religiosa Peepal. அரச மரம்

53 Gloriosa superba Malabar glory lilly செங்கோந்தள

54 Gossypium herbaceum Cotton பருத்தி

55 Hibiscus rosa-sinensis Shoe flower, China rose. செம்பருத்தி

56 Hiptage benghalensis Clustered hiptage மாதவிக்வ்கோடி

57 Hordeum vulgare. Barley போரலி

58 Jasminum officinale Jasmine மலலிச்க

59 Mangifera indica Mango மா

60 Mimosa pudica Touch me not plant வதோடடோறசுருஙகி

61 Mitrogyna parvifolia Kadamb ்கடம்பு

62 Moringa oleifera Drumstick முருங்கை

63 Murraya koenigii Curry leaf ்கறிவேப்பிலை

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64 Musa paradisiaca Banana வாழை

65 Nelumbo nucifera Indian lotus தாமரை

66 Neolamarckia cadamba Ven Kadambu வவண்்கடம்ப மரம்

67 Nerium oleander Oleander அரளி

68 Numphaea rubra Red Water lilly வைவ்வலலி

69 Nymphaea nouchali Blue water lilly நீல ஆம்பல

70 Nymphaea pubescens White water lilly வெளசள அலலி,

வய்தல

71 Ocimum sanctum Tulsi துளசி

72 Ocimum tenuiflorum Tulsi ்கருந்துளசி

73 Oryza sativa Paddy, Rice வல

74 Phaseolus vulgaris. Beans பீன்ஸ்

75 Physalis angulata Balloon cherry வைோடக்குத்தக்்கோளி

76 Piper nigrum Pepper மிளகு

77 Prosopis juliflora Honey mesquite சீசமக்்கருவேலம்

78 Raphanus sativus Radish முளளஙகி

79 Saraca indica Ashoka அநைோ்க மரம்

80 Solanum nigrum Black night shade மணித்தக்்கோளி

81 Solanum lycopersicum Tomato தக்்கோளி

82 Solanum melongena Brinjal ்கத்திரி

83 Solanum tuberosum Potato உருளை

84 Sorghum bicolor Sorghum நைோளம்

85 Theobroma cacao Cocoa tree வ்கோக்ந்கோ மரம்

86 Triticum aestivum Wheat ந்கோதுமை

87 Vitis vinifera Grapes திராடசை

88 Zea mays Maize, corn மக்்கோச்சோளம்

89 Zingiber officinale Ginger இஞசி

90 Zizyphus jujuba Jujube இலந்தை

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Botany - Class XI

List of Authors and Reviewers

Reviewers

Dr. K.V. Krishnamurthy,

Professor and Head (Rtd),

Bharathidasan University, Trichy

Dr. P. Ravichandran,

Associate Professor and Head,

Department of Botany, MS University, Tirunelveli

Dr. R. Ravindhran,

Associate Professor and Head,

Department of Plant Biology and Biotechnology,

Loyola College, Chennai.

Dr. M.P. Ramanujam,

Associate Professor of Botany

Kanchi Mamunivar Center for Post Graduate Studies

Pondichery

Academic Coordinators

K. Manjula,

Lecturer in Botany, DIET, Triplicane, Chennai.

J.Radhamani,

Lecturer in Botany, DIET, Kancheepuram.

Domain Experts

Dr. S.S. Rathinakumar,Principal (Rtd.),

Sri Subramania Swamy Government Arts College, Thiruthani.

Dr. D. Narashiman, Professor and Head (Rtd.),

Plant Biologly & BioTechnology, MCC College, Tambaram,

Kancheepuram.

Dr. Mujeera Fathima, Associate Professor of Botany,

Govt. Arts & Science College, Nandanam, Chennai.

Dr. K.P. Girivasan, Associate Professor of Botany,

Govt. Arts & Science College, Nandanam, Chennai.

Dr. C.V. Chitti Babu, Associate Professor of Botany,

Presidency College, Chennai.

Dr. Renu Edwin, Associate Professor of Botany,

Presidency College, Chennai.

Dr. D. Kandavel, Associate Professor of Botany,

Periyar EVR College, Trichy.

Dr. T. Sekar, Associate Professor of Botany,

Pachaiyappa's College, Chennai.

Dr. D. Kathiresan, Assosiate Professor of Botany,

Saraswathi Narayana College, Madurai.

Dr. S. Nagaraj, Assistant Professor of Botany,

University of Madras, Guindy Campus, Chennai.

Dr. M. Kumar, Assistant Professor of Botany,

MCC College, Tambaram, Kancheepuram.

Art and Design Team

Chief Co-ordinator and Creative Head

Srinivasan Natarajan

Graphics

Gopu Rasuvel,

Karthik kalaiarasu

Illustration

A. Jeyaseelan,

S.Gopu, Dr. N. Maheshkumar, Sathish,

N. Rajesh Kumar, Iyappan, Alagappan

Art Teachers,

Government of Tamil Nadu.

Students,

Government College of Fine Arts,

Chennai & Kumbakonam.

Layout

Winmac Solutions

In-House

QC - Gopu Rasuvel

- Karthik Kalaiarasu

- Tamilkumaran.C

Authors

P. Senthil, P.G. Assistant in Botany,

GBHSS, Uthangarai, Krishnagiri.

P. Saravanakumaran,

P.G. Assistant in Botany, GHSS, Koduvilarpatti, Theni.

Dr. N. Maheshkumar, Dist. Environmental Coordinator,

Chief Educational Office, Namakkal.

P. Anandhimala, P.G. Assistant in Botany,

GGHSS,Pochampalli, Krishnagiri.

Dr. P. Sivashankar,

P.G. Assistant in Botany, GGHSS, Nachiyar Koil. Thanjavur.

G. Muthu, P.G. Assistant in Botany,

GHSS (ADW) Achampatti, Madurai.

J. Mani, P.G. Assistant in Botany,

GHSS, R Gobinathampatti, Dharmapuri.

U. Kalirajan,P.G. Assistant in Botany,

ADWHSS, Meenambakkam, Kancheepuram.

G. Sathiyamoorthy,

PGTGHSS, Jayapuram, Vellore.

S.B. Amuthavalli, P.G. Assistant in Botany,

GHSS, Ottery (Extension), Vandalur, Kancheepuram.

S. Malar Vizhi,P.G. Assistant in Botany,

GHSS, Chenbagaramanputhoor, Kannyakumari.

G. Bagyalakshmi, P.G. Assistant in Botany,

GGHSS, Jalagandapuram, Salem.

M. Chelladurai,

P.G. Assistant in Botany, GGHSS, Samuthiram, Salem.

C. Kishore Kumar,

P.G. Assistant in Botany, GHSS, Thattaparai,Vellore.

M. Vijayalakshmi , P.G. Assistant in Botany,

Model School, Asthinapuram, Ariyalur.

M. Lakshmi, P.G. Assistant in Botany,

Sri Sankara Senior Secondary School, Adyar, Chennai.

M. Chamundeswari, P.G. Assistant in Botany,

Prince MHSS, Nanganallur, Kancheepuram.

Content Readers

Dr. T. S. Subha, Associate Professor in Botany,

Bharathi Women’s College, Chennai.

Dr. M. Pazhanisami,

Associate Professor in Botany,

Govt. Arts College, Nandanam, Chennai

Dr. G. Rajalakshmi, Assistant Professor in Botany,

Bharathi Women’s College, Chennai.

Dr. R. Kavitha, Assistant Professor in Botany,

Bharathi Women’s college, Chennai.

C. Natarajan,

P.G. Assistant in Botany, PAK Palanisamy HSS, Chennai.

ICT Coordinator

N. Rajesh Kumar, B.T. Assistant,

CCMAGGHSS, Coimbatore

This book has been printed on 80 G.S.M.

Elegant Maplitho paper.

Printed by offset at:

Co-ordination

Ramesh Munisamy

Typist

Pavithran, SCERT, Chennai

320