Key
ideas u All living things have seven characteristics: reproduction, nutrition, respiration, growth, excretion, movement and sensitivity. u Living organisms are classified into groups according to how closely related they are. Each species of organism is given a unique two-word Latin name called a binomial. The first word of the binomial is the genus and the second word is the species. u Vertebrates are classified into five classes: fish, amphibians, reptiles, birds and mammals. They each have their own distinctive set of features. For example, amphibians have a smooth skin, fish and reptiles have scales, birds have feathers and scales, and mammals have hair. u Arthropods are invertebrates with jointed legs and segmented bodies. They can be further classified into arachnids, myriapods, insects and crustaceans. u Annelids are worms with segmented bodies but no legs. u Nematodes are worms with unsegmented bodies.
u Molluscs have unsegmented bodies, and often have a shell. u
Bacteria are single-celled organisms whose cells do not have nuclei.
u Fungi include moulds, mushrooms and toadstools. They have cells with cell walls but do not photosynthesise. u Viruses are not generally considered to be alive at all. They are not made of cells and cannot carry out any of the characteristics of living things on their own. u Flowering plants can be classified into monocotyledonous plants and dicotyledonous plants. Monocots have seeds with one cotyledon, and their leaves often have parallel veins. Dicots have seeds with two cotyledons, and their leaves generally have branching veins. u A dichotomous key is a set of paired contrasting descriptions which lead you through to the identification of an unknown organism.
Revision Key
ideasquestions 1
A student investigating an ecosystem found six different species of animals living there. The table shows some of their characteristics.
a b c d e
species
backbone
present
body
covering
jointed
legs
present
A
no
hard shell
no
B
yes
hair
yes
C
no
tough skeleton
yes
D
yes
scales
no
E
yes
smooth skin
yes
F
yes
scales
yes
To which kingdom do all these organisms belong? Which organism could be a mollusc? Which two organisms are reptiles? Name the class to which organism E belongs. State one other characteristic you would expect to see in organism B.
12
IGCSE
Biology
2 Three species of tree have the following binomials: Carpodiptera africana Commiphora africana Commiphora angolensis Which two of these species do biologists consider to be most closely related? Explain your answer. 3
Construct a dichotomous key to help someone to identify
fi
ve
of
your
teachers.
Try
to
meet
these
criteria: each pair of characteristics describes one contrasting feature – for example, ‘has dark hair’ versus ‘has brown hair’ (not ‘has dark hair’ versus ‘has a long nose’) l each
person
could
be
identifi
ed
without
having
to
compare them with another person – for example ‘is more than 1.8 m tall’ versus ‘is less than 1.8 m tall’ (not ‘is tall’ or ‘is short’) l contains no more than four pairs of points. l
When you
have
fi
nished,
swap
your
key
with
someone
else to check if it works. If it does not, then make adjustments to it before handing it in to be marked.
S
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