NCERT Textbook - Diversity in Living Organisms Class 9 Notes | EduRev

General Science for UPSC (Civil Services) Prelims

Created by: Divey Sethi

Class 9 : NCERT Textbook - Diversity in Living Organisms Class 9 Notes | EduRev

 Page 1


Have you ever thought of the multitude of
life-forms that surround us? Each organism
is different from all others 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 repectively. 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 7
7 7 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
Page 2


Have you ever thought of the multitude of
life-forms that surround us? Each organism
is different from all others 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 repectively. 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 7
7 7 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
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, their habitat is the
only point they share in common. This is no
good as a 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 form 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, this is
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
necessary.
• 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
Page 3


Have you ever thought of the multitude of
life-forms that surround us? Each organism
is different from all others 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 repectively. 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 7
7 7 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
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, their habitat is the
only point they share in common. This is no
good as a 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 form 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, this is
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
necessary.
• 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 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 first 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
of the planet, more than half is
concentrated in a few countries –
Brazil, Colombia, Ecuador, Peru,
Mexico, Zaire, Madagascar,
Australia, China, India, Indonesia and
Malaysia.
Page 4


Have you ever thought of the multitude of
life-forms that surround us? Each organism
is different from all others 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 repectively. 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 7
7 7 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
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, their habitat is the
only point they share in common. This is no
good as a 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 form 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, this is
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
necessary.
• 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 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 first 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
of the planet, more than half is
concentrated in a few countries –
Brazil, Colombia, Ecuador, Peru,
Mexico, Zaire, Madagascar,
Australia, China, India, Indonesia and
Malaysia.
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 (1959) 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).
Page 5


Have you ever thought of the multitude of
life-forms that surround us? Each organism
is different from all others 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 repectively. 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 7
7 7 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
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, their habitat is the
only point they share in common. This is no
good as a 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 form 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, this is
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
necessary.
• 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 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 first 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
of the planet, more than half is
concentrated in a few countries –
Brazil, Colombia, Ecuador, Peru,
Mexico, Zaire, Madagascar,
Australia, China, India, Indonesia and
Malaysia.
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 (1959) 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).
SCIENCE 84
to become multicellular organisms at certain
stages in their lives. They have cell-walls made
of a tough complex sugar called chitin.
Examples are yeast and mushrooms (see Fig.
7.3 for examples).
Water vacuole
Cilia
Macronucleus
Micronucleus
Oral groove
Cytosome
Food vacuole
Cytopyge
Waste
Flagellum (long)
Flagellum (short)
Eyespot
Photoreceptor
Contractile
vacuole
Chloroplast
Photoreceptor
Nucleolus
Nucleus
Ectoplasm
Endoplasm
Mitochondria
Nucleus
Crystals
Food vacuole
Contractile vacuole
Advancing
pseudopod
Paramecium
Amoeba
Euglena
Fig. 7.2: Protozoa
7.3.3 FUNGI
These are heterotrophic eukaryotic
organisms. They use decaying organic
material as food and are therefore called
saprophytes. Many of them have the capacity
Fig. 7.3: Fungi
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.
Penicillium
Agaricus
Aspergillus
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