NCERT Textbook: Diversity in Living Organisms | General Science(Prelims) by IRS Divey Sethi - UPSC PDF Download

 Page 1


Have you ever thought of the multitude of
life-forms that surround us? Each organism
is different from the other to a lesser or greater
extent. For instance, consider yourself and a
friend.
• Are you both of the same height?
• Does your nose look exactly like your
friend’s nose?
• Is your hand-span the same as your
friend’s?
However, if we were to compare ourselves
and our friends with a monkey, what would
we say? Obviously, we and our friends have
a lot in common when we compare ourselves
with a monkey. But suppose we were to add
a cow to the comparison? We would then
think that the monkey has a lot more in
common with us than with the cow.
Activity ______________7.1
• We have heard of ‘desi’ cows and Jersey
cows.
• Does a desi cow look like a Jersey cow?
• Do all desi cows look alike?
• Will we be able to identify a Jersey cow
in a crowd of desi cows that don’t look
like each other?
• What is the basis of our identification?
In this activity, we had to decide which
characteristics were more important in
forming the desired category. Hence, we were
also deciding which characteristics could be
ignored.
Now, think of all the different forms in
which life occurs on earth. On one hand we
have microscopic bacteria of a few micrometre
in size. While on the other hand we have blue
whale and red wood trees of California
of approximate sizes of 30 metres and
100 metres respectively. Some pine trees live
for thousands of years while insects like
mosquitoes die within a few days. Life also
ranges from colourless or even transparent
worms to brightly coloured birds and flowers.
This bewildering variety of life around us
has evolved on the earth over millions of
years. However, we do not have more than a
tiny fraction of this time to try and
understand all these living organisms, so we
cannot look at them one by one. Instead, we
look for similarities among the organisms,
which will allow us to put them into different
classes and then study different classes or
groups as a whole.
In order to make relevant groups to study
the variety of life forms, we need to decide
which characteristics decide more
fundamental differences among organisms.
This would create the main broad groups of
organisms. Within these groups, smaller sub-
groups will be decided by less important
characteristics.
uestions
1. Why do we classify organisms?
2. Give three examples of the range
of variations that you see in life-
forms around you.
7.1 What is the Basis of
Classification?
Attempts at classifying living things into
groups have been made since time
immemorial. Greek thinker Aristotle classified
animals according to whether they lived on
Q
7
D D D D DIVERSITY IVERSITY IVERSITY IVERSITY IVERSITY     IN IN IN IN IN L L L L LIVING IVING IVING IVING IVING O O O O ORGANISMS RGANISMS RGANISMS RGANISMS RGANISMS
Chapter
2022-23
Page 2


Have you ever thought of the multitude of
life-forms that surround us? Each organism
is different from the other to a lesser or greater
extent. For instance, consider yourself and a
friend.
• Are you both of the same height?
• Does your nose look exactly like your
friend’s nose?
• Is your hand-span the same as your
friend’s?
However, if we were to compare ourselves
and our friends with a monkey, what would
we say? Obviously, we and our friends have
a lot in common when we compare ourselves
with a monkey. But suppose we were to add
a cow to the comparison? We would then
think that the monkey has a lot more in
common with us than with the cow.
Activity ______________7.1
• We have heard of ‘desi’ cows and Jersey
cows.
• Does a desi cow look like a Jersey cow?
• Do all desi cows look alike?
• Will we be able to identify a Jersey cow
in a crowd of desi cows that don’t look
like each other?
• What is the basis of our identification?
In this activity, we had to decide which
characteristics were more important in
forming the desired category. Hence, we were
also deciding which characteristics could be
ignored.
Now, think of all the different forms in
which life occurs on earth. On one hand we
have microscopic bacteria of a few micrometre
in size. While on the other hand we have blue
whale and red wood trees of California
of approximate sizes of 30 metres and
100 metres respectively. Some pine trees live
for thousands of years while insects like
mosquitoes die within a few days. Life also
ranges from colourless or even transparent
worms to brightly coloured birds and flowers.
This bewildering variety of life around us
has evolved on the earth over millions of
years. However, we do not have more than a
tiny fraction of this time to try and
understand all these living organisms, so we
cannot look at them one by one. Instead, we
look for similarities among the organisms,
which will allow us to put them into different
classes and then study different classes or
groups as a whole.
In order to make relevant groups to study
the variety of life forms, we need to decide
which characteristics decide more
fundamental differences among organisms.
This would create the main broad groups of
organisms. Within these groups, smaller sub-
groups will be decided by less important
characteristics.
uestions
1. Why do we classify organisms?
2. Give three examples of the range
of variations that you see in life-
forms around you.
7.1 What is the Basis of
Classification?
Attempts at classifying living things into
groups have been made since time
immemorial. Greek thinker Aristotle classified
animals according to whether they lived on
Q
7
D D D D DIVERSITY IVERSITY IVERSITY IVERSITY IVERSITY     IN IN IN IN IN L L L L LIVING IVING IVING IVING IVING O O O O ORGANISMS RGANISMS RGANISMS RGANISMS RGANISMS
Chapter
2022-23
land, in water or in the air. This is a very
simple way of looking at life, but misleading
too. For example, animals that live in the sea
include corals, whales, octopuses, starfish
and sharks. We can immediately see that
these are very different from each other in
numerous ways. In fact, habitat is the only
point they share in common. This is not an
appropriate way of making groups of
organisms to study and think about.
We therefore need to decide which
characteristics to be used as the basis for
making the broadest divisions. Then we will
have to pick the next set of characteristics
for making sub-groups within these divisions.
This process of classification within each
group can then continue using new
characteristics each time.
Before we go on, we need to think about
what is meant by ‘characteristics’. When we
are trying to classify a diverse group of
organisms, we need to find ways in which
some of them are similar enough to be
thought of together. These ‘ways’, in fact, are
details of appearance or behaviour, in other
words, form and function.
What we mean by a characteristic is a
particular feature or a particular function. That
most of us have five fingers on each hand is
thus a characteristic. That we can run, but the
banyan tree cannot, is also a characteristic.
Now, to understand how some
characteristics are decided as being more
fundamental than others, let us consider how
a stone wall is built. The stones used will have
different shapes and sizes. The stones at the
top of the wall would not influence the choice
of stones that come below them. On the other
hand, the shapes and sizes of stones in the
lowermost layer will decide the shape and size
of the next layer and so on.
The stones in the lowermost layer are like
the characteristics that decide the broadest
divisions among living organisms. They are
independent of any other characteristics in
their effects on the form and function of the
organism. The characteristics in the next level
would be dependent on the previous one and
would decide the variety in the next level. In
this way, we can build up a whole hierarchy
of mutually related characteristics to be used
for classification.
Now-a-days, we look at many inter-related
characteristics starting from the nature of the
cell in order to classify all living organisms.
What are some concrete examples of such
characteristics used for a hierarchical
classification?
• A eukaryotic cell has membrane-bound
organelles, including a nucleus, which
allow cellular processes to be carried out
efficiently in isolation from each other.
Therefore, organisms which do not have
a clearly demarcated nucleus and other
organelles would need to have their
biochemical pathways organised in very
different ways. This would have an effect
on every aspect of cell design. Further,
nucleated cells would have the capacity
to participate in making a multicellular
organism because they can take up
specialised functions. Therefore, nucleus
can be a basic characteristic of
classification.
• Do the cells occur singly or are they
grouped together and do they live as an
indivisible group? Cells that group
together to form a single organism use
the principle of division of labour. In such
a body design, all cells would not be
identical. Instead, groups of cells will
carry out specialised functions. This
makes a very basic distinction in the
body designs of organisms. As a result,
an Amoeba and a worm are very different
in their body design.
• Do organisms produce their own food
through the process of photosynthesis?
Being able to produce one’s own
food versus having to get food from
outside would make very different
body designs.
• Of the organisms that perform
photosynthesis (plants), what is the level
of organisation of their body?
• Of the animals, how does the individual’s
body develop and organise its different
parts, and what are the specialised
organs found for different functions?
DIVERSITY IN LIVING ORGANISMS 81
2022-23
Page 3


Have you ever thought of the multitude of
life-forms that surround us? Each organism
is different from the other to a lesser or greater
extent. For instance, consider yourself and a
friend.
• Are you both of the same height?
• Does your nose look exactly like your
friend’s nose?
• Is your hand-span the same as your
friend’s?
However, if we were to compare ourselves
and our friends with a monkey, what would
we say? Obviously, we and our friends have
a lot in common when we compare ourselves
with a monkey. But suppose we were to add
a cow to the comparison? We would then
think that the monkey has a lot more in
common with us than with the cow.
Activity ______________7.1
• We have heard of ‘desi’ cows and Jersey
cows.
• Does a desi cow look like a Jersey cow?
• Do all desi cows look alike?
• Will we be able to identify a Jersey cow
in a crowd of desi cows that don’t look
like each other?
• What is the basis of our identification?
In this activity, we had to decide which
characteristics were more important in
forming the desired category. Hence, we were
also deciding which characteristics could be
ignored.
Now, think of all the different forms in
which life occurs on earth. On one hand we
have microscopic bacteria of a few micrometre
in size. While on the other hand we have blue
whale and red wood trees of California
of approximate sizes of 30 metres and
100 metres respectively. Some pine trees live
for thousands of years while insects like
mosquitoes die within a few days. Life also
ranges from colourless or even transparent
worms to brightly coloured birds and flowers.
This bewildering variety of life around us
has evolved on the earth over millions of
years. However, we do not have more than a
tiny fraction of this time to try and
understand all these living organisms, so we
cannot look at them one by one. Instead, we
look for similarities among the organisms,
which will allow us to put them into different
classes and then study different classes or
groups as a whole.
In order to make relevant groups to study
the variety of life forms, we need to decide
which characteristics decide more
fundamental differences among organisms.
This would create the main broad groups of
organisms. Within these groups, smaller sub-
groups will be decided by less important
characteristics.
uestions
1. Why do we classify organisms?
2. Give three examples of the range
of variations that you see in life-
forms around you.
7.1 What is the Basis of
Classification?
Attempts at classifying living things into
groups have been made since time
immemorial. Greek thinker Aristotle classified
animals according to whether they lived on
Q
7
D D D D DIVERSITY IVERSITY IVERSITY IVERSITY IVERSITY     IN IN IN IN IN L L L L LIVING IVING IVING IVING IVING O O O O ORGANISMS RGANISMS RGANISMS RGANISMS RGANISMS
Chapter
2022-23
land, in water or in the air. This is a very
simple way of looking at life, but misleading
too. For example, animals that live in the sea
include corals, whales, octopuses, starfish
and sharks. We can immediately see that
these are very different from each other in
numerous ways. In fact, habitat is the only
point they share in common. This is not an
appropriate way of making groups of
organisms to study and think about.
We therefore need to decide which
characteristics to be used as the basis for
making the broadest divisions. Then we will
have to pick the next set of characteristics
for making sub-groups within these divisions.
This process of classification within each
group can then continue using new
characteristics each time.
Before we go on, we need to think about
what is meant by ‘characteristics’. When we
are trying to classify a diverse group of
organisms, we need to find ways in which
some of them are similar enough to be
thought of together. These ‘ways’, in fact, are
details of appearance or behaviour, in other
words, form and function.
What we mean by a characteristic is a
particular feature or a particular function. That
most of us have five fingers on each hand is
thus a characteristic. That we can run, but the
banyan tree cannot, is also a characteristic.
Now, to understand how some
characteristics are decided as being more
fundamental than others, let us consider how
a stone wall is built. The stones used will have
different shapes and sizes. The stones at the
top of the wall would not influence the choice
of stones that come below them. On the other
hand, the shapes and sizes of stones in the
lowermost layer will decide the shape and size
of the next layer and so on.
The stones in the lowermost layer are like
the characteristics that decide the broadest
divisions among living organisms. They are
independent of any other characteristics in
their effects on the form and function of the
organism. The characteristics in the next level
would be dependent on the previous one and
would decide the variety in the next level. In
this way, we can build up a whole hierarchy
of mutually related characteristics to be used
for classification.
Now-a-days, we look at many inter-related
characteristics starting from the nature of the
cell in order to classify all living organisms.
What are some concrete examples of such
characteristics used for a hierarchical
classification?
• A eukaryotic cell has membrane-bound
organelles, including a nucleus, which
allow cellular processes to be carried out
efficiently in isolation from each other.
Therefore, organisms which do not have
a clearly demarcated nucleus and other
organelles would need to have their
biochemical pathways organised in very
different ways. This would have an effect
on every aspect of cell design. Further,
nucleated cells would have the capacity
to participate in making a multicellular
organism because they can take up
specialised functions. Therefore, nucleus
can be a basic characteristic of
classification.
• Do the cells occur singly or are they
grouped together and do they live as an
indivisible group? Cells that group
together to form a single organism use
the principle of division of labour. In such
a body design, all cells would not be
identical. Instead, groups of cells will
carry out specialised functions. This
makes a very basic distinction in the
body designs of organisms. As a result,
an Amoeba and a worm are very different
in their body design.
• Do organisms produce their own food
through the process of photosynthesis?
Being able to produce one’s own
food versus having to get food from
outside would make very different
body designs.
• Of the organisms that perform
photosynthesis (plants), what is the level
of organisation of their body?
• Of the animals, how does the individual’s
body develop and organise its different
parts, and what are the specialised
organs found for different functions?
DIVERSITY IN LIVING ORGANISMS 81
2022-23
SCIENCE 82
We can see that, even in these few questions
that we have asked, a hierarchy is developing.
The characteristics of body design used for
classification of plants will be very different
from those important for classifying animals.
This is because the basic designs are different,
based on the need to make their own food
(plants), or acquire it (animals). Therefore,
these design features (having a skeleton, for
example) are to be used to make sub-groups,
rather than making broad groups.
uestions
1. Which do you think is a more basic
characteristic for classifying
organisms?
(a) the place where they live.
(b) the kind of cells they are
made of. Why?
2. What is the primary characteristic
on which the broad division of
organisms is made?
3. On what bases are plants and
animals put into different
categories?
7.2 Classification and Evolution
All living things are identified and categorised
on the basis of their body design in form and
function. Some characteristics are likely to
make more wide-ranging changes in body
design than others. There is a role of time in
this as well. So, once a certain body design
comes into existence, it will shape the effects
of all other subsequent design changes,
simply because it already exists. In other
words, characteristics that came into
existence earlier are likely to be more basic
than characteristics that have come into
existence later.
This means that the classification of life
forms will be closely related to their evolution.
What is evolution? Most life forms that we
see today have arisen by an accumulation of
changes in body design that allow the
organism possessing them to survive better.
Charles Darwin first described this idea of
evolution in 1859 in his book, The Origin of
Species.
When we connect this idea of evolution to
classification, we will find some groups of
organisms which have ancient body designs
that have not changed very much. We will
also find other groups of organisms that have
acquired their particular body designs
relatively recently. Those in the first group
are frequently referred to as ‘primitive’ or ‘lower’
organisms, while those in the second group
are called ‘advanced’ or ‘higher’ organisms. In
reality, these terms are not quite correct since
they do not properly relate to the differences.
All that we can say is that some are ‘older’
organisms, while some are ‘younger’
organisms. Since there is a possibility that
complexity in design will increase over
evolutionary time, it may not be wrong to say
that older organisms are simpler, while
younger organisms are more complex.
Q
More to know
Biodiversity means the diversity of life
forms. It is a word commonly used to
refer to the variety of life forms found
in a particular region. Diverse life forms
share the environment, and are
affected by each other too. As a result,
a stable community of different species
comes into existence. Humans have
played their own part in recent times
in changing the balance of such
communities.  Of course, the diversity
in such communities is affected by
particular characteristics of land,
water, climate and so on. Rough
estimates state that there are about ten
million species on the planet, although
we actually know only  one or two
millions of them. The warm and humid
tropical regions of the earth, between
the tropic of Cancer and the tropic of
Capricorn, are rich in diversity of plant
and animal life. This is called the region
of megadiversity. Of the biodiversity
on the planet, more than half is
concentrated in a few countries —
Brazil, Colombia, Ecuador, Peru,
Mexico, Zaire, Madagascar,
Australia, China, India, Indonesia and
Malaysia.
2022-23
Page 4


Have you ever thought of the multitude of
life-forms that surround us? Each organism
is different from the other to a lesser or greater
extent. For instance, consider yourself and a
friend.
• Are you both of the same height?
• Does your nose look exactly like your
friend’s nose?
• Is your hand-span the same as your
friend’s?
However, if we were to compare ourselves
and our friends with a monkey, what would
we say? Obviously, we and our friends have
a lot in common when we compare ourselves
with a monkey. But suppose we were to add
a cow to the comparison? We would then
think that the monkey has a lot more in
common with us than with the cow.
Activity ______________7.1
• We have heard of ‘desi’ cows and Jersey
cows.
• Does a desi cow look like a Jersey cow?
• Do all desi cows look alike?
• Will we be able to identify a Jersey cow
in a crowd of desi cows that don’t look
like each other?
• What is the basis of our identification?
In this activity, we had to decide which
characteristics were more important in
forming the desired category. Hence, we were
also deciding which characteristics could be
ignored.
Now, think of all the different forms in
which life occurs on earth. On one hand we
have microscopic bacteria of a few micrometre
in size. While on the other hand we have blue
whale and red wood trees of California
of approximate sizes of 30 metres and
100 metres respectively. Some pine trees live
for thousands of years while insects like
mosquitoes die within a few days. Life also
ranges from colourless or even transparent
worms to brightly coloured birds and flowers.
This bewildering variety of life around us
has evolved on the earth over millions of
years. However, we do not have more than a
tiny fraction of this time to try and
understand all these living organisms, so we
cannot look at them one by one. Instead, we
look for similarities among the organisms,
which will allow us to put them into different
classes and then study different classes or
groups as a whole.
In order to make relevant groups to study
the variety of life forms, we need to decide
which characteristics decide more
fundamental differences among organisms.
This would create the main broad groups of
organisms. Within these groups, smaller sub-
groups will be decided by less important
characteristics.
uestions
1. Why do we classify organisms?
2. Give three examples of the range
of variations that you see in life-
forms around you.
7.1 What is the Basis of
Classification?
Attempts at classifying living things into
groups have been made since time
immemorial. Greek thinker Aristotle classified
animals according to whether they lived on
Q
7
D D D D DIVERSITY IVERSITY IVERSITY IVERSITY IVERSITY     IN IN IN IN IN L L L L LIVING IVING IVING IVING IVING O O O O ORGANISMS RGANISMS RGANISMS RGANISMS RGANISMS
Chapter
2022-23
land, in water or in the air. This is a very
simple way of looking at life, but misleading
too. For example, animals that live in the sea
include corals, whales, octopuses, starfish
and sharks. We can immediately see that
these are very different from each other in
numerous ways. In fact, habitat is the only
point they share in common. This is not an
appropriate way of making groups of
organisms to study and think about.
We therefore need to decide which
characteristics to be used as the basis for
making the broadest divisions. Then we will
have to pick the next set of characteristics
for making sub-groups within these divisions.
This process of classification within each
group can then continue using new
characteristics each time.
Before we go on, we need to think about
what is meant by ‘characteristics’. When we
are trying to classify a diverse group of
organisms, we need to find ways in which
some of them are similar enough to be
thought of together. These ‘ways’, in fact, are
details of appearance or behaviour, in other
words, form and function.
What we mean by a characteristic is a
particular feature or a particular function. That
most of us have five fingers on each hand is
thus a characteristic. That we can run, but the
banyan tree cannot, is also a characteristic.
Now, to understand how some
characteristics are decided as being more
fundamental than others, let us consider how
a stone wall is built. The stones used will have
different shapes and sizes. The stones at the
top of the wall would not influence the choice
of stones that come below them. On the other
hand, the shapes and sizes of stones in the
lowermost layer will decide the shape and size
of the next layer and so on.
The stones in the lowermost layer are like
the characteristics that decide the broadest
divisions among living organisms. They are
independent of any other characteristics in
their effects on the form and function of the
organism. The characteristics in the next level
would be dependent on the previous one and
would decide the variety in the next level. In
this way, we can build up a whole hierarchy
of mutually related characteristics to be used
for classification.
Now-a-days, we look at many inter-related
characteristics starting from the nature of the
cell in order to classify all living organisms.
What are some concrete examples of such
characteristics used for a hierarchical
classification?
• A eukaryotic cell has membrane-bound
organelles, including a nucleus, which
allow cellular processes to be carried out
efficiently in isolation from each other.
Therefore, organisms which do not have
a clearly demarcated nucleus and other
organelles would need to have their
biochemical pathways organised in very
different ways. This would have an effect
on every aspect of cell design. Further,
nucleated cells would have the capacity
to participate in making a multicellular
organism because they can take up
specialised functions. Therefore, nucleus
can be a basic characteristic of
classification.
• Do the cells occur singly or are they
grouped together and do they live as an
indivisible group? Cells that group
together to form a single organism use
the principle of division of labour. In such
a body design, all cells would not be
identical. Instead, groups of cells will
carry out specialised functions. This
makes a very basic distinction in the
body designs of organisms. As a result,
an Amoeba and a worm are very different
in their body design.
• Do organisms produce their own food
through the process of photosynthesis?
Being able to produce one’s own
food versus having to get food from
outside would make very different
body designs.
• Of the organisms that perform
photosynthesis (plants), what is the level
of organisation of their body?
• Of the animals, how does the individual’s
body develop and organise its different
parts, and what are the specialised
organs found for different functions?
DIVERSITY IN LIVING ORGANISMS 81
2022-23
SCIENCE 82
We can see that, even in these few questions
that we have asked, a hierarchy is developing.
The characteristics of body design used for
classification of plants will be very different
from those important for classifying animals.
This is because the basic designs are different,
based on the need to make their own food
(plants), or acquire it (animals). Therefore,
these design features (having a skeleton, for
example) are to be used to make sub-groups,
rather than making broad groups.
uestions
1. Which do you think is a more basic
characteristic for classifying
organisms?
(a) the place where they live.
(b) the kind of cells they are
made of. Why?
2. What is the primary characteristic
on which the broad division of
organisms is made?
3. On what bases are plants and
animals put into different
categories?
7.2 Classification and Evolution
All living things are identified and categorised
on the basis of their body design in form and
function. Some characteristics are likely to
make more wide-ranging changes in body
design than others. There is a role of time in
this as well. So, once a certain body design
comes into existence, it will shape the effects
of all other subsequent design changes,
simply because it already exists. In other
words, characteristics that came into
existence earlier are likely to be more basic
than characteristics that have come into
existence later.
This means that the classification of life
forms will be closely related to their evolution.
What is evolution? Most life forms that we
see today have arisen by an accumulation of
changes in body design that allow the
organism possessing them to survive better.
Charles Darwin first described this idea of
evolution in 1859 in his book, The Origin of
Species.
When we connect this idea of evolution to
classification, we will find some groups of
organisms which have ancient body designs
that have not changed very much. We will
also find other groups of organisms that have
acquired their particular body designs
relatively recently. Those in the first group
are frequently referred to as ‘primitive’ or ‘lower’
organisms, while those in the second group
are called ‘advanced’ or ‘higher’ organisms. In
reality, these terms are not quite correct since
they do not properly relate to the differences.
All that we can say is that some are ‘older’
organisms, while some are ‘younger’
organisms. Since there is a possibility that
complexity in design will increase over
evolutionary time, it may not be wrong to say
that older organisms are simpler, while
younger organisms are more complex.
Q
More to know
Biodiversity means the diversity of life
forms. It is a word commonly used to
refer to the variety of life forms found
in a particular region. Diverse life forms
share the environment, and are
affected by each other too. As a result,
a stable community of different species
comes into existence. Humans have
played their own part in recent times
in changing the balance of such
communities.  Of course, the diversity
in such communities is affected by
particular characteristics of land,
water, climate and so on. Rough
estimates state that there are about ten
million species on the planet, although
we actually know only  one or two
millions of them. The warm and humid
tropical regions of the earth, between
the tropic of Cancer and the tropic of
Capricorn, are rich in diversity of plant
and animal life. This is called the region
of megadiversity. Of the biodiversity
on the planet, more than half is
concentrated in a few countries —
Brazil, Colombia, Ecuador, Peru,
Mexico, Zaire, Madagascar,
Australia, China, India, Indonesia and
Malaysia.
2022-23
DIVERSITY IN LIVING ORGANISMS 83
uestions
1. Which organisms are called
primitive and how are they
different from the so-called
advanced organisms?
2. Will advanced organisms be the
same as complex organisms?
Why?
7.3 The Hierarchy of Classification-
Groups
Biologists, such as Ernst Haeckel (1894),
Robert Whittaker (1969) and Carl Woese
(1977) have tried to classify all living
organisms into broad categories, called
kingdoms. The classification Whittaker
proposed has five kingdoms: Monera,
Protista, Fungi, Plantae and Animalia, and
is widely used. These groups are formed on
the basis of their cell structure, mode and
source of nutrition and body organisation.
The modification Woese introduced by
dividing the Monera into Archaebacteria (or
Archaea) and Eubacteria (or Bacteria) is also
in use.
Further classification is done by naming
the sub-groups at various levels as given in
the following scheme:
Kingdom
Phylum (for animals) / Division (for plants)
Class
Order
Family
Genus
Species
Thus, by separating organisms on the
basis of a hierarchy of characteristics into
smaller and smaller groups, we arrive at the
basic unit of classification, which is a
‘species’. So what organisms can be said to
belong to the same species? Broadly, a species
includes all organisms that are similar
enough to breed and perpetuate.
The important characteristics of the five
kingdoms of Whittaker are as follows:
7.3.1 MONERA
These organisms do not have a defined
nucleus or organelles, nor do any of them
show multi-cellular body designs. On the
other hand, they show diversity based on
many other characteristics. Some of them
have cell walls while some do not. Of course,
having or not having a cell wall has very
different effects on body design here from
having or not having a cell wall in multi-
cellular organisms. The mode of nutrition of
organisms in this group can be either by
synthesising their own food (autotrophic) or
getting it from the environment
(heterotrophic). This group includes bacteria,
blue-green algae or cyanobacteria, and
mycoplasma. Some examples are shown
in Fig. 7.1.
Q
Bacteria
Resting
spore
Heterocyst
Anabaena
Fig. 7.1: Monera
7.3.2 PROTISTA
This group includes many kinds of unicellular
eukaryotic organisms. Some of these
organisms use appendages, such as hair-like
cilia or whip-like flagella for moving around.
Their mode of nutrition can be autotrophic
or heterotrophic. Examples are unicellular
algae, diatoms and protozoans (see Fig. 7.2
for examples).
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Page 5


Have you ever thought of the multitude of
life-forms that surround us? Each organism
is different from the other to a lesser or greater
extent. For instance, consider yourself and a
friend.
• Are you both of the same height?
• Does your nose look exactly like your
friend’s nose?
• Is your hand-span the same as your
friend’s?
However, if we were to compare ourselves
and our friends with a monkey, what would
we say? Obviously, we and our friends have
a lot in common when we compare ourselves
with a monkey. But suppose we were to add
a cow to the comparison? We would then
think that the monkey has a lot more in
common with us than with the cow.
Activity ______________7.1
• We have heard of ‘desi’ cows and Jersey
cows.
• Does a desi cow look like a Jersey cow?
• Do all desi cows look alike?
• Will we be able to identify a Jersey cow
in a crowd of desi cows that don’t look
like each other?
• What is the basis of our identification?
In this activity, we had to decide which
characteristics were more important in
forming the desired category. Hence, we were
also deciding which characteristics could be
ignored.
Now, think of all the different forms in
which life occurs on earth. On one hand we
have microscopic bacteria of a few micrometre
in size. While on the other hand we have blue
whale and red wood trees of California
of approximate sizes of 30 metres and
100 metres respectively. Some pine trees live
for thousands of years while insects like
mosquitoes die within a few days. Life also
ranges from colourless or even transparent
worms to brightly coloured birds and flowers.
This bewildering variety of life around us
has evolved on the earth over millions of
years. However, we do not have more than a
tiny fraction of this time to try and
understand all these living organisms, so we
cannot look at them one by one. Instead, we
look for similarities among the organisms,
which will allow us to put them into different
classes and then study different classes or
groups as a whole.
In order to make relevant groups to study
the variety of life forms, we need to decide
which characteristics decide more
fundamental differences among organisms.
This would create the main broad groups of
organisms. Within these groups, smaller sub-
groups will be decided by less important
characteristics.
uestions
1. Why do we classify organisms?
2. Give three examples of the range
of variations that you see in life-
forms around you.
7.1 What is the Basis of
Classification?
Attempts at classifying living things into
groups have been made since time
immemorial. Greek thinker Aristotle classified
animals according to whether they lived on
Q
7
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Chapter
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land, in water or in the air. This is a very
simple way of looking at life, but misleading
too. For example, animals that live in the sea
include corals, whales, octopuses, starfish
and sharks. We can immediately see that
these are very different from each other in
numerous ways. In fact, habitat is the only
point they share in common. This is not an
appropriate way of making groups of
organisms to study and think about.
We therefore need to decide which
characteristics to be used as the basis for
making the broadest divisions. Then we will
have to pick the next set of characteristics
for making sub-groups within these divisions.
This process of classification within each
group can then continue using new
characteristics each time.
Before we go on, we need to think about
what is meant by ‘characteristics’. When we
are trying to classify a diverse group of
organisms, we need to find ways in which
some of them are similar enough to be
thought of together. These ‘ways’, in fact, are
details of appearance or behaviour, in other
words, form and function.
What we mean by a characteristic is a
particular feature or a particular function. That
most of us have five fingers on each hand is
thus a characteristic. That we can run, but the
banyan tree cannot, is also a characteristic.
Now, to understand how some
characteristics are decided as being more
fundamental than others, let us consider how
a stone wall is built. The stones used will have
different shapes and sizes. The stones at the
top of the wall would not influence the choice
of stones that come below them. On the other
hand, the shapes and sizes of stones in the
lowermost layer will decide the shape and size
of the next layer and so on.
The stones in the lowermost layer are like
the characteristics that decide the broadest
divisions among living organisms. They are
independent of any other characteristics in
their effects on the form and function of the
organism. The characteristics in the next level
would be dependent on the previous one and
would decide the variety in the next level. In
this way, we can build up a whole hierarchy
of mutually related characteristics to be used
for classification.
Now-a-days, we look at many inter-related
characteristics starting from the nature of the
cell in order to classify all living organisms.
What are some concrete examples of such
characteristics used for a hierarchical
classification?
• A eukaryotic cell has membrane-bound
organelles, including a nucleus, which
allow cellular processes to be carried out
efficiently in isolation from each other.
Therefore, organisms which do not have
a clearly demarcated nucleus and other
organelles would need to have their
biochemical pathways organised in very
different ways. This would have an effect
on every aspect of cell design. Further,
nucleated cells would have the capacity
to participate in making a multicellular
organism because they can take up
specialised functions. Therefore, nucleus
can be a basic characteristic of
classification.
• Do the cells occur singly or are they
grouped together and do they live as an
indivisible group? Cells that group
together to form a single organism use
the principle of division of labour. In such
a body design, all cells would not be
identical. Instead, groups of cells will
carry out specialised functions. This
makes a very basic distinction in the
body designs of organisms. As a result,
an Amoeba and a worm are very different
in their body design.
• Do organisms produce their own food
through the process of photosynthesis?
Being able to produce one’s own
food versus having to get food from
outside would make very different
body designs.
• Of the organisms that perform
photosynthesis (plants), what is the level
of organisation of their body?
• Of the animals, how does the individual’s
body develop and organise its different
parts, and what are the specialised
organs found for different functions?
DIVERSITY IN LIVING ORGANISMS 81
2022-23
SCIENCE 82
We can see that, even in these few questions
that we have asked, a hierarchy is developing.
The characteristics of body design used for
classification of plants will be very different
from those important for classifying animals.
This is because the basic designs are different,
based on the need to make their own food
(plants), or acquire it (animals). Therefore,
these design features (having a skeleton, for
example) are to be used to make sub-groups,
rather than making broad groups.
uestions
1. Which do you think is a more basic
characteristic for classifying
organisms?
(a) the place where they live.
(b) the kind of cells they are
made of. Why?
2. What is the primary characteristic
on which the broad division of
organisms is made?
3. On what bases are plants and
animals put into different
categories?
7.2 Classification and Evolution
All living things are identified and categorised
on the basis of their body design in form and
function. Some characteristics are likely to
make more wide-ranging changes in body
design than others. There is a role of time in
this as well. So, once a certain body design
comes into existence, it will shape the effects
of all other subsequent design changes,
simply because it already exists. In other
words, characteristics that came into
existence earlier are likely to be more basic
than characteristics that have come into
existence later.
This means that the classification of life
forms will be closely related to their evolution.
What is evolution? Most life forms that we
see today have arisen by an accumulation of
changes in body design that allow the
organism possessing them to survive better.
Charles Darwin first described this idea of
evolution in 1859 in his book, The Origin of
Species.
When we connect this idea of evolution to
classification, we will find some groups of
organisms which have ancient body designs
that have not changed very much. We will
also find other groups of organisms that have
acquired their particular body designs
relatively recently. Those in the first group
are frequently referred to as ‘primitive’ or ‘lower’
organisms, while those in the second group
are called ‘advanced’ or ‘higher’ organisms. In
reality, these terms are not quite correct since
they do not properly relate to the differences.
All that we can say is that some are ‘older’
organisms, while some are ‘younger’
organisms. Since there is a possibility that
complexity in design will increase over
evolutionary time, it may not be wrong to say
that older organisms are simpler, while
younger organisms are more complex.
Q
More to know
Biodiversity means the diversity of life
forms. It is a word commonly used to
refer to the variety of life forms found
in a particular region. Diverse life forms
share the environment, and are
affected by each other too. As a result,
a stable community of different species
comes into existence. Humans have
played their own part in recent times
in changing the balance of such
communities.  Of course, the diversity
in such communities is affected by
particular characteristics of land,
water, climate and so on. Rough
estimates state that there are about ten
million species on the planet, although
we actually know only  one or two
millions of them. The warm and humid
tropical regions of the earth, between
the tropic of Cancer and the tropic of
Capricorn, are rich in diversity of plant
and animal life. This is called the region
of megadiversity. Of the biodiversity
on the planet, more than half is
concentrated in a few countries —
Brazil, Colombia, Ecuador, Peru,
Mexico, Zaire, Madagascar,
Australia, China, India, Indonesia and
Malaysia.
2022-23
DIVERSITY IN LIVING ORGANISMS 83
uestions
1. Which organisms are called
primitive and how are they
different from the so-called
advanced organisms?
2. Will advanced organisms be the
same as complex organisms?
Why?
7.3 The Hierarchy of Classification-
Groups
Biologists, such as Ernst Haeckel (1894),
Robert Whittaker (1969) and Carl Woese
(1977) have tried to classify all living
organisms into broad categories, called
kingdoms. The classification Whittaker
proposed has five kingdoms: Monera,
Protista, Fungi, Plantae and Animalia, and
is widely used. These groups are formed on
the basis of their cell structure, mode and
source of nutrition and body organisation.
The modification Woese introduced by
dividing the Monera into Archaebacteria (or
Archaea) and Eubacteria (or Bacteria) is also
in use.
Further classification is done by naming
the sub-groups at various levels as given in
the following scheme:
Kingdom
Phylum (for animals) / Division (for plants)
Class
Order
Family
Genus
Species
Thus, by separating organisms on the
basis of a hierarchy of characteristics into
smaller and smaller groups, we arrive at the
basic unit of classification, which is a
‘species’. So what organisms can be said to
belong to the same species? Broadly, a species
includes all organisms that are similar
enough to breed and perpetuate.
The important characteristics of the five
kingdoms of Whittaker are as follows:
7.3.1 MONERA
These organisms do not have a defined
nucleus or organelles, nor do any of them
show multi-cellular body designs. On the
other hand, they show diversity based on
many other characteristics. Some of them
have cell walls while some do not. Of course,
having or not having a cell wall has very
different effects on body design here from
having or not having a cell wall in multi-
cellular organisms. The mode of nutrition of
organisms in this group can be either by
synthesising their own food (autotrophic) or
getting it from the environment
(heterotrophic). This group includes bacteria,
blue-green algae or cyanobacteria, and
mycoplasma. Some examples are shown
in Fig. 7.1.
Q
Bacteria
Resting
spore
Heterocyst
Anabaena
Fig. 7.1: Monera
7.3.2 PROTISTA
This group includes many kinds of unicellular
eukaryotic organisms. Some of these
organisms use appendages, such as hair-like
cilia or whip-like flagella for moving around.
Their mode of nutrition can be autotrophic
or heterotrophic. Examples are unicellular
algae, diatoms and protozoans (see Fig. 7.2
for examples).
2022-23
SCIENCE 84
protoplasm of a host organism for food. They
are called parasites. Many of them have the
capacity to become multicellular organisms at
certain stages in their lives. They have cell-
walls made of a tough complex sugar called
chitin. Examples are yeasts, molds and
mushrooms (see Fig. 7.3 for examples).
Macronucleus
Micronucleus
Waste
Flagellum (long)
Nucleus
Nucleus
Paramecium
Amoeba
Euglena
Fig. 7.2: Protozoa
7.3.3 FUNGI
These are heterotrophic eukaryotic
organisms. Some of them use decaying organic
material as food and are therefore called
saprotrophs. Others require a living
Some fungal species live in permanent
mutually dependent relationships with blue-
green algae (or cyanobacteria). Such
relationships are called symbiotic. These
symbiobic life forms are called lichens. We have
all seen lichens as the slow-growing large
coloured patches on the bark of trees.
7.3.4 PLANTAE
These are multicellular eukaryotes with cell
walls. They are autotrophs and use
chlorophyll for photosynthesis. Thus, all
plants are included in this group. Since plants
and animals are most visible forms of the
diversity of life around us, we will look at the
subgroups in this category later (section 7.4).
7.3.5 ANIMALIA
These include all organisms which are
multicellular eukaryotes without cell walls.
They are heterotrophs. Again, we will look at
their subgroups a little later in section 7.5.
Fig. 7.3: Fungi
Agaricus
(Mushroom)
Penicillium
(Mold)
Saccharomyces
(Yeast)
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