Chapter 5

THE FUNDAMENTAL UNIT OF LIFE

While examining a thin slice of cork, Robert avoid air bubbles while putting the
Hooke saw that the cork resembled the cover slip with the help of a mounting
structure of a honeycomb consisting of many needle. Ask your teacher for help. We
have prepared a temporary mount of
little compartments. Cork is a substance
onion peel. We can observe this slide
which comes from the bark of a tree. This under low power followed by high
was in the year 1665 when Hooke made this powers of a compound microscope.
chance observation through a self-designed
microscope. Robert Hooke called these boxes Eyepiece
cells. Cell is a Latin word for ‘a little room’.
This may seem to be a very small and
insignificant incident but it is very important
Coarse adjustment
in the history of science. This was the very first
Body tube
time that someone had observed that living
Fine adjustment
things appear to consist of separate units. The
Arm
use of the word ‘cell’ to describe these units is
Clip Objective lens
being used till this day in biology. Microscope slide
Let us find out about cells. Stage
Swivel
Condenser
5.1 What are Living Organisms Mirror

Made Up of? Base

Activity ______________ 5.1 Fig. 5.1: Compound microscope

• Let us take a small piece from an onion What do we observe as we look through
bulb. With the help of a pair of forceps,
the lens? Can we draw the structures that
we can peel of f the skin (called
we are able to see through the microscope,
epidermis) from the concave side (inner
layer) of the onion. This layer can be on an observation sheet? Does it look like
put immediately in a watch-glass Fig. 5.2?
containing water. This will prevent the
peel from getting folded or getting dry.
What do we do with this peel?
• Let us take a glass slide, put a drop of Nucleus
water on it and transfer a small piece
of the peel from the watch glass to the Cells
slide. Make sure that the peel is
perfectly flat on the slide. A thin camel
hair paintbrush might be necessary to
help transfer the peel. Now we put a
drop of safranin solution on this piece
followed by a cover slip. Take care to Fig. 5.2: Cells of an onion peel

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 We can try preparing temporary mounts Chlamydomonas, Paramoecium and bacteria.
of peels of onions of different sizes. What do These organisms are called unicellular
we observe? Do we see similar structures or organisms (uni = single). On the other hand,
different structures? many cells group together in a single body
and assume different functions in it to form
What are these structures?
various body parts in multicellular organisms
These structures look similar to each other. (multi = many) such as some fungi, plants
Together they form a big structure like an and animals. Can we find out names of some
onion bulb! We find from this activity that more unicellular organisms?
onion bulbs of different sizes have similar Every multi-cellular organism has come
small structures visible under a microscope. from a single cell. How? Cells divide to
The cells of the onion peel will all look the produce cells of their own kind. All cells thus
same, regardless of the size of the onion they come from pre-existing cells.
came from.
These small structures that we see are Activity ______________ 5.2
the basic building units of the onion bulb.
• We can try preparing temporary
These structures are called cells. Not only
mounts of leaf peels, tip of roots of
onions, but all organisms that we observe onion or even peels of onions of different
around are made up of cells. However, there sizes.
are also single cells that live on their own. • After performing the above activity, let
us see what the answers to the following
Cells were first discovered by questions would be:
Robert Hooke in 1665. He observed (a) Do all cells look alike in terms of
the cells in a cork slice with the help shape and size?
(b) Do all cells look alike in structure?
of a primitive microscope.
(c) Could we find differences among
Leeuwenhoek (1674), with the cells from different parts of a plant
improved microscope, discovered the body?
free living cells in pond water for the (d) What similarities could we find?
first time. It was Robert Brown in
1831 who discovered the nucleus in Some organisms can also have cells of
More to know

the cell. Purkinje in 1839 coined the different kinds. Look at the following picture.
ter m ‘protoplasm’ for the fluid It depicts some cells from the human body.
substance of the cell. The cell theory,
that all the plants and animals are
composed of cells and that the cell is
the basic unit of life, was presented
by two biologists, Schleiden (1838)
and Schwann (1839). The cell theory
was further expanded by Virchow Blood
(1855) by suggesting that all cells cells
Nerve Cell
Smooth
arise from pre-existing cells. With the muscle
discovery of the electron microscope cell
in 1940, it was possible to observe and
understand the complex structure of
the cell and its various organelles. Bone
Fat cell
cell
The invention of magnifying lenses led to
the discovery of the microscopic world. It is
Ovum Sperm
now known that a single cell may constitute
a whole organism as in Amoeba, Fig. 5.3: Various cells from the human body

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 The shape and size of cells are related to every cell; plasma membrane, nucleus and
the specific function they perform. Some cells cytoplasm. All activities inside the cell and
like Amoeba have changing shapes. In some interactions of the cell with its environment
cases the cell shape could be more or less are possible due to these features. Let us see
fixed and peculiar for a particular type of cell; how.
for example, nerve cells have a typical shape.
Each living cell has the capacity to 5.2.1 P LASMA MEMBRANE OR CELL
perform certain basic functions that are
MEMBRANE
characteristic of all living forms. How does
a living cell perform these basic functions? This is the outermost covering of the cell that
We know that there is a division of labour in separates the contents of the cell from its
multicellular organisms such as human external environment. The plasma membrane
beings. This means that different parts of allows or permits the entry and exit of some
the human body perform different functions. materials in and out of the cell. It also
The human body has a heart to pump blood, prevents movement of some other materials.
a stomach to digest food and so on. Similarly, The cell membrane, therefore, is called a
division of labour is also seen within a single selectively permeable membrane.
cell. In fact, each such cell has got certain How does the movement of substances
specific components within it known as cell take place into the cell? How do substances
organelles. Each kind of cell organelle move out of the cell?
performs a special function, such as making Some substances like carbon dioxide or
new material in the cell, clearing up the oxygen can move across the cell membrane
waste material from the cell and so on. A by a process called diffusion. We have studied
cell is able to live and perfor m all its the process of diffusion in earlier chapters.
functions because of these organelles. These We saw that there is spontaneous movement
organelles together constitute the basic unit of a substance from a region of high
called the cell. It is interesting that all cells concentration to a region where its
are found to have the same organelles, no concentration is low.
matter what their function is or what Something similar to this happens in cells
organism they are found in. when, for example, some substance like CO2
(which is cellular waste and requires to be
uestions

Q
excreted out by the cell) accumulates in high
concentrations inside the cell. In the cell’s
1. Who discovered cells, and how?
2. Why is the cell called the external environment, the concentration of
structural and functional unit of CO2 is low as compared to that inside the
life? cell. As soon as there is a difference of
concentration of CO2 inside and outside a cell,
CO2 moves out of the cell, from a region of
high concentration, to a region of low
concentration outside the cell by the process
5.2 What is a Cell Made Up of? of diffusion. Similarly, O2 enters the cell by
What is the Structural the process of diffusion when the level or
concentration of O2 inside the cell decreases.
Organisation of a Cell? Thus, diffusion plays an important role in
We saw above that the cell has special gaseous exchange between the cells as well
components called organelles. How is a cell as the cell and its external environment.
organised? Water also obeys the law of diffusion. The
If we study a cell under a microscope, we movement of water molecules through such a
would come across three features in almost selectively permeable membrane is called Osmosis
.
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osmosis. The movement of water across the Activity ______________ 5.3
plasma membrane is also affected by the amount
of substance dissolved in water. Thus, osmosis Osmosis with an egg
is the passage of water from a region of high (a) Remove the shell of an egg by dissolving
it in dilute hydrochloric acid. The shell
water concentration through a selectively
is mostly calcium carbonate. A thin
permeable membrane to a region of low water outer skin now encloses the egg. Put
concentration till equilibrium is reached. the egg in pure water and observe after
What will happen if we put an animal cell 5 minutes. What do we observe?
or a plant cell into a solution of sugar or salt The egg swells because water passes
in water? into it by osmosis.
One of the following three things could (b) Place a similar de-shelled egg in a
concentrated salt solution and observe
happen:
for 5 minutes. The egg shrinks. Why?
1. If the medium surrounding the cell has Water passes out of the egg solution
a higher water concentration than the into the salt solution because the salt
cell, meaning that the outside solution solution is more concentrated.
is very dilute, the cell will gain water
We can also try a similar activity with dried
by osmosis. Such a solution is known
raisins or apricots.
as a hypotonic solution.
Water molecules are free to pass Activity ______________ 5.4
across the cell membrane in both
directions, but more water will come • Put dried raisins or apricots in plain
into the cell than will leave. The net water and leave them for some time.
Then place them into a concentrated
(overall) result is that water enters the
solution of sugar or salt. You will
cell. The cell is likely to swell up. observe the following:
2. If the medium has exactly the same (a) Each gains water and swells
water concentration as the cell, there when placed in water.
will be no net movement of water (b) However, when placed in the
across the cell membrane. Such a concentrated solution it loses
solution is known as an isotonic water, and consequently shrinks.
solution. Unicellular freshwater organisms and
Water crosses the cell membrane most plant cells tend to gain water through
in both directions, but the amount osmosis. Absorption of water by plant roots
going in is the same as the amount is also an example of osmosis.
going out, so there is no overall Thus, diffusion is important in exhange
movement of water. The cell will stay of gases and water in the life of a cell. In
the same size. additions to this, the cell also obtains
3. If the medium has a lower nutrition from its environment. Different
concentration of water than the cell, molecules move in and out of the cell
meaning that it is a very concentrated through a type of transport requiring use
solution, the cell will lose water by of energy.
osmosis. Such a solution is known as The plasma membrane is flexible and is
a hypertonic solution. made up of organic molecules called lipids
and proteins. However, we can observe the
Again, water crosses the cell
structure of the plasma membrane only
membrane in both directions, but this
through an electron microscope.
time more water leaves the cell than The flexibility of the cell membrane also
enters it. Therefore the cell will shrink. enables the cell to engulf in food and other
Thus, osmosis is a special case of diffusion material from its external environment. Such
through a selectively permeable membrane. processes are known as endocytosis. Amoeba
Now let us try out the following activity: acquires its food through such processes.

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 Activity ______________ 5.5 What do we infer from this activity? It
appears that only living cells, and not dead
• Find out about electron microscopes cells, are able to absorb water by osmosis.
from resources in the school library or
Cell walls permit the cells of plants, fungi
through the internet. Discuss it with
your teacher. and bacteria to withstand very dilute
(hypotonic) external media without bursting.
In such media the cells tend to take up water
uestions

Q
by osmosis. The cell swells, building up
1. How do substances like CO2 and pressure against the cell wall. The wall exerts
water move in and out of the cell? an equal pressure against the swollen cell.
Discuss. Because of their walls, such cells can
2. Why is the plasma membrane withstand much greater changes in the
called a selectively permeable
surrounding medium than animal cells.
membrane?

5.2.3 NUCLEUS
5.2.2 CELL WALL
Remember the temporary mount of onion peel
Plant cells, in addition to the plasma we prepared? We had put iodine solution on
membrane, have another rigid outer covering the peel. Why? What would we see if we tried
called the cell wall. The cell wall lies outside observing the peel without putting the iodine
the plasma membrane. The plant cell wall is
solution? Try it and see what the difference
mainly composed of cellulose. Cellulose is a
is. Further, when we put iodine solution on
complex substance and provides structural
strength to plants. the peel, did each cell get evenly coloured?
When a living plant cell loses water According to their chemical composition
through osmosis there is shrinkage or dif ferent regions of cells get coloured
contraction of the contents of the cell away differentially. Some regions appear darker
from the cell wall. This phenomenon is known than other regions. Apart from iodine solution
as plasmolysis. We can observe this we could also use safranin solution or
phenomenon by performing the following methylene blue solution to stain the cells.
activity: We have observed cells from an onion; let
us now observe cells from our own body.
Activity ______________ 5.6
• Mount the peel of a Rhoeo leaf in water Activity ______________ 5.7
on a slide and examine cells under
the high power of a microscope. Note • Let us take a glass slide with a drop of
the small green granules, called water on it. Using an ice-cream spoon
chloroplasts. They contain a green gently scrape the inside surface of the
substance called chlorophyll. Put a cheek. Does any material get stuck on
strong solution of sugar or salt on the the spoon? With the help of a needle
mounted leaf on the slide. Wait for a we can transfer this material and
minute and observe under a spread it evenly on the glass slide kept
microscope. What do we see? ready for this. To colour the material
• Now place some Rhoeo leaves in boiling
we can put a drop of methylene blue
water for a few minutes. This kills the
solution on it. Now the material is ready
cells. Then mount one leaf on a slide
and observe it under a microscope. Put for observation under microscope. Do
a strong solution of sugar or salt on not forget to put a cover-slip on it!
the mounted leaf on the slide. Wait for • What do we observe? What is the shape
a minute and observe it again. What of the cells we see? Draw it on the
do we find? Did plasmolysis occur now? observation sheet.

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 • Was there a darkly coloured, spherical present in eukaryotic cells. Many of the
or oval, dot-like structure near the functions of such organelles are also
centre of each cell? This structure is performed by poorly organised parts of the
called nucleus. Were there similar cytoplasm (see section 5.2.4). The chlorophyll
structures in onion peel cells? in photosynthetic prokaryotic bacteria is
The nucleus has a double layered covering associated with membranous vesicles (bag
called nuclear membrane. The nuclear like structures) but not with plastids as in
membrane has pores which allow the transfer eukaryotic cells (see section 5.2.5).
of material from inside the nucleus to its
outside, that is, to the cytoplasm (which we
will talk about in section 5.2.4). Ribosomes
Plasma
The nucleus contains chromosomes, membrane

which are visible as rod-shaped structures

only when the cell is about to divide. Cell wall
Chromosomes contain infor mation for
inheritance of characters from parents to next Nucleoid
generation in the form of DNA (Deoxyribo
Nucleic Acid) molecules. Chromosomes are
composed of DNA and protein. DNA molecules
contain the information necessary for
constructing and organising cells. Functional Fig. 5.4: Prokaryotic cell
segments of DNA are called genes. In a cell
which is not dividing, this DNA is present as
part of chromatin material. Chromatin
5.2.4 CYTOPLASM
material is visible as entangled mass of thread
like structures. Whenever the cell is about to When we look at the temporary mounts of
divide, the chromatin material gets organised onion peel as well as human cheek cells, we
into chromosomes. can see a large region of each cell enclosed
The nucleus plays a central role in cellular by the cell membrane. This region takes up
reproduction, the process by which a single very little stain. It is called the cytoplasm.
cell divides and forms two new cells. It also The cytoplasm is the fluid content inside the
plays a crucial part, along with the plasma membrane. It also contains many
environment, in determining the way the cell specialised cell organelles. Each of these
will develop and what form it will exhibit at organelles performs a specific function for the
maturity, by directing the chemical activities cell.
of the cell. Cell organelles are enclosed by
In some organisms like bacteria, the membranes. In prokaryotes, beside the
nuclear region of the cell may be poorly absence of a defined nuclear region, the
defined due to the absence of a nuclear membrane-bound cell organelles are also
membrane. Such an undefined nuclear region absent. On the other hand, the eukaryotic
containing only nucleic acids is called a cells have nuclear membrane as well as
nucleoid. Such organisms, whose cells lack membrane-enclosed organelles.
a nuclear membrane, are called prokaryotes The significance of membranes can be
(Pro = primitive or primary; karyote ≈ karyon illustrated with the example of viruses.
= nucleus). Organisms with cells having a Viruses lack any membranes and hence do
nuclear membrane are called eukaryotes. not show characteristics of life until they enter
Prokaryotic cells (see Fig. 5.4) also lack a living body and use its cell machinery to
most of the other cytoplasmic organelles multiply.

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 uestion 5.2.5 (i) ENDOPLASMIC RETICULUM (ER)

Q 1. Fill in the gaps in the following

table illustrating differences
between prokaryotic and
eukaryotic cells.

Prokaryotic Cell Eukaryotic Cell

The endoplasmic reticulum (ER) is a large
network of membrane-bound tubes and
sheets. It looks like long tubules or round or
oblong bags (vesicles). The ER membrane is
similar in structure to the plasma membrane.
There are two types of ER– rough endoplasmic
reticulum (RER) and smooth endoplasmic
reticulum (SER). RER looks rough under a
1. Size : generally 1. Size: generally microscope because it has particles called
small ( 1-10 µm) large ( 5-100 µm) ribosomes attached to its surface. The
1 µm = 10–6 m ribosomes, which are present in all active
cells, are the sites of protein manufacture.
2. Nuclear region: 2. Nuclear region: The manufactured proteins are then sent to
_______________ well defined and various places in the cell depending on need,
_______________ surrounded by a using the ER. The SER helps in the
and known as__ nuclear membrane manufacture of fat molecules, or lipids,
important for cell function. Some of these
3. Chromosome: 3. More than one proteins and lipids help in building the cell
single chromosome membrane. This pr ocess is known as
membrane biogenesis. Some other proteins
4. Membrane-bound 4. _______________ and lipids function as enzymes and
cell organelles _______________ hormones. Although the ER varies greatly in
absent _______________ appearance in different cells, it always forms a
network system.

5.2.5 CELL ORGANELLES

Every cell has a membrane around it to keep
its own contents separate from the external
environment. Large and complex cells,
including cells from multicellular organisms,
need a lot of chemical activities to support
their complicated structure and function. To
keep these activities of different kinds
separate from each other, these cells use
membrane-bound little structures (or
‘organelles’) within themselves. This is one of
the features of the eukaryotic cells that
distinguish them from prokaryotic cells. Some
of these organelles are visible only with an
electron microscope. Fig. 5.5: Animal cell
We have talked about the nucleus in a
previous section. Some important examples Thus, one function of the ER is to serve as
of cell organelles which we will discuss now channels for the transport of materials
are: endoplasmic reticulum, Golgi apparatus, (especially proteins) between various regions
lysosomes, mitochondria and plastids. They of the cytoplasm or between the cytoplasm
are important because they carry out some and the nucleus. The ER also functions as a
very crucial functions in cells. cytoplasmic framework providing a surface
for some of the biochemical
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for some of the biochemical activities of the
Camillo Golgi was born at
cell. In the liver cells of the group of animals
Corteno near Brescia in
called vertebrates (see Chapter 7), SER plays
1843. He studied
a crucial role in detoxifying many poisons and
medicine at the University
drugs.
of Pavia. After graduating
in 1865, he continued to
work in Pavia at the
Hospital of St. Matteo. At
that time most of his
investigations were
concerned with the nervous system, In 1872
he accepted the post of Chief Medical Officer
at the Hospital for the Chronically Sick at
Abbiategrasso. He first started his
investigations into the nervous system in a
little kitchen of this hospital, which he had
converted into a laboratory. However, the
work of greatest importance, which Golgi
carried out was a revolutionary method of
staining individual nerve and cell structures.
This method is referred to as the ‘black
reaction’. This method uses a weak solution
of silver nitrate and is particularly valuable
in tracing the processes and most delicate
ramifications of cells. All through his life,
he continued to work on these lines,
modifying and improving this technique.
Fig. 5.6: Plant cell Golgi received the highest honours and
awards in recognition of his work. He shared
the Nobel prize in 1906 with Santiago
5.2.5 (ii) GOLGI APPARATUS Ramony Cajal for their work on the structure
of the nervous system.
The Golgi apparatus, first described by
Camillo Golgi, consists of a system of
membrane-bound vesicles (flattened sacs)
5.2.5 (iii) LYSOSOMES
arranged approximately parallel to each other
in stacks called cisterns. These membranes Structurally, lysosomes are membrane-bound
often have connections with the membranes sacs filled with digestive enzymes. These
of ER and therefore constitute another portion enzymes are made by RER. Lysosomes are a
of a complex cellular membrane system. kind of waste disposal system of the cell. These
The material synthesised near the ER is help to keep the cell clean by digesting any
packaged and dispatched to various targets foreign material as well as worn-out cell
organelles. Foreign materials entering the cell,
inside and outside the cell through the Golgi
such as bacteria or food, as well as old
apparatus. Its functions include the storage,
organelles end up in the lysosomes, which
modification and packaging of products in break complex substances into simpler
vesicles. In some cases, complex sugars may substances. Lysosomes are able to do this
be made from simple sugars in the Golgi because they contain powerful digestive
apparatus. The Golgi apparatus is also enzymes capable of breaking down all organic
involved in the formation of lysosomes [see material. During the disturbance in cellular
5.2.5 (iii)]. metabolism, for example, when the cell gets

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lysosome single membrane

Ribosomes no membrane
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damaged, lysosomes may burst and the In plant cells vacuoles are full of cell sap
enzymes digest their own cell. Therefore, and provide turgidity and rigidity to the cell.
lysosomes are also known as the ‘suicide bags’ Many substances of importance in the life of
of a cell. the plant cell are stored in vacuoles. These
include amino acids, sugars, various organic
5.2.5 (iv) MITOCHONDRIA acids and some proteins. In single-celled
organisms like Amoeba, the food vacuole
Mitochondria are known as the powerhouses
contains the food items that the Amoeba has
of the cell. Mitochondria have two membrane
consumed. In some unicellular organisms,
coverings. The outer membrane is porous
specialised vacuoles also play important roles
while the inner membrane is deeply folded.
in expelling excess water and some wastes
These folds increase surface area for ATP-
from the cell.
generating chemical reactions. The energy
required for various chemical activities needed
uestions

Q
for life is released by mitochondria in the form
of ATP (Adenosine triphopshate) molecules.
ATP is known as the energy currency of the 1. Can you name the two
cell. The body uses energy stored in ATP for organelles we have studied that
making new chemical compounds and for contain their own genetic
mechanical work. material?
Mitochondria are strange organelles in the 2. If the organisation of a cell is
sense that they have their own DNA and destroyed due to some physical
ribosomes. Therefore, mitochondria are able or chemical influence, what will
to make some of their own proteins. happen?
3. Why are lysosomes known as
5.2.5 (V) PLASTIDS suicide bags?
Plastids are present only in plant cells. There 4. Where are proteins synthesised
are two types of plastids – chromoplasts inside the cell?
(coloured plastids) and leucoplasts (white or
colourless plastids). Chromoplasts containing Each cell thus acquires its structure and
the pigment chlorophyll are known as ability to function because of the organisation
chloroplasts. Chloroplasts are important for of its membrane and organelles in specific
photosynthesis in plants. Chloroplasts also ways. The cell thus has a basic structural
contain various yellow or orange pigments in organisation. This helps the cells to perform
addition to chlorophyll. Leucoplasts are functions like respiration, obtaining nutrition,
primarily organelles in which materials such and clearing of waste material, or forming new
as starch, oils and protein granules are stored. proteins.
The internal organisation of the Chloroplast Thus, the cell is the fundamental structural
consists of numerous membrane layers unit of living organisms. It is also the basic
embedded in a material called the stroma. These functional unit of life.
are similar to mitochondria in external Cell Division
structure. Like the mitochondria, plastids also
have their own DNA and ribosomes. New cells are formed in organisms in order to
Animal grow, to replace old, dead and injured cells,
cell
5.2.5 (vi) VACUOLES and to form gametes required for reproduction.
The process by which new cells are made is
Vacuoles are storage sacs for solid or liquid called cell division. There are two main types
contents. Vacuoles are small sized in animal of cell division: mitosis and meiosis.
cells while plant cells have very large vacuoles. The process of cell division by which most
The central vacuole of some plant cells may of the cells divide for growth is called mitosis.
occupy 50-90% of the cell volume. In this process, each cell called mother cell

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 Fig. 5.7: Mitosis Fig. 5.8: Meiosis

divides to form two identical daughter cells offspring. They divide by a different process
(Fig. 5.7). The daughter cells have the same called meiosis which involves two consecutive
number of chromosomes as mother cell. It divisions. When a cell divides by meiosis it
helps in growth and repair of tissues in produces four new cells instead of just two (Fig.
organisms. 5.8). The new cells only have half the number
Specific cells of reproductive organs or of chromosomes than that of the mother cells.
tissues in animals and plants divide to form Can you think as to why the chromosome
gametes, which after fertilisation give rise to number has reduced to half in daughter cells?

What
you have
learnt
• The fundamental organisational unit of life is the cell.
• Cells are enclosed by a plasma membrane composed of lipids
and proteins.
• The cell membrane is an active part of the cell. It regulates
the movement of materials between the ordered interior of
the cell and the outer environment.
• In plant cells, a cell wall composed mainly of cellulose is
located outside the cell membrane.
• The presence of the cell wall enables the cells of plants,
fungi and bacteria to exist in hypotonic media without
bursting.
• The nucleus in eukaryotes is separated from the cytoplasm
by double-layered membrane and it directs the life processes
of the cell.
• The ER functions both as a passageway for intracellular
transport and as a manufacturing surface.
• The Golgi apparatus consists of stacks of membrane-bound
vesicles that function in the storage, modification and
packaging of substances manufactured in the cell.
• Most plant cells have large membranous organelles called
plastids, which are of two types – chromoplasts and
leucoplasts.

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 • Chromoplasts that contain chlorophyll are called
chloroplasts and they perform photosynthesis.
• The primary function of leucoplasts is storage.
• Most mature plant cells have a large central vacuole that
helps to maintain the turgidity of the cell and stores
important substances including wastes.
• Prokaryotic cells have no membrane-bound organelles, their
chromosomes are composed of only nucleic acid, and they
have only very small ribosomes as organelles.
• Cells in organisms divide for growth of body, for repalcing
dead cells, and for forming gametes for reproduction.

Exercises
1. Make a comparison and write down ways in which plant
cells are different from animal cells.
2. How is a prokaryotic cell different from a eukaryotic cell?
3. What would happen if the plasma membrane ruptures or
breaks down?
4. What would happen to the life of a cell if there was no Golgi
apparatus?
5. Which organelle is known as the powerhouse of the cell? Why?
6. Where do the lipids and proteins constituting the cell
membrane get synthesised?
7. How does an Amoeba obtain its food?
8. What is osmosis?
9. Carry out the following osmosis experiment:
Take four peeled potato halves and scoos each one out to
make potato cups. One of these potato cups should be made
from a boiled potato. Put each potato cup in a trough
containing water. Now,
(a) Keep cup A empty
(b) Put one teaspoon sugar in cup B
(c) Put one teaspoon salt in cup C
(d) Put one teaspoon sugar in the boiled potato cup D.
Keep these for two hours. Then observe the four potato cups
and answer the following:
(i) Explain why water gathers in the hollowed portion of
B and C.
(ii) Why is potato A necessary for this experiment?
(iii) Explain why water does not gather in the hollowed out
portions of A and D.
10. Which type of cell division is required for growth and repair
of body and which type is involved in formation of gametes?

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Chapter 6
TISSUES
From the last chapter, we recall that all living There are noticeable differences between
organisms are made of cells. In unicellular the two. Plants are stationary or fixed – they
organisms, a single cell performs all basic don’t move. Since they have to be upright, they
functions. For example, in Amoeba, a single have a large quantity of supportive tissue. The
cell carries out movement, intake of food, supportive tissue generally has dead cells.
gaseous exchange and excretion. But in multi- Animals on the other hand move around
cellular organisms there are millions of cells. in search of food, mates and shelter. They
Most of these cells are specialised to carry out
consume more energy as compared to plants.
specific functions. Each specialised function
Most of the tissues they contain are living.
is taken up by a different group of cells. Since
Another difference between animals and
these cells carry out only a particular function,
they do it very efficiently. In human beings, plants is in the pattern of growth. The growth
muscle cells contract and relax to cause in plants is limited to certain regions, while this
movement, nerve cells carry messages, blood is not so in animals. There are some tissues in
flows to transport oxygen, food, hormones and plants that divide throughout their life. These
waste material and so on. In plants, vascular tissues are localised in certain regions. Based
tissues conduct food and water from one part on the dividing capacity of the tissues, various
of the plant to other parts. So, multi-cellular plant tissues can be classified as growing or
organisms show division of labour. Cells meristematic tissue and permanent tissue. Cell
specialising in one function are often grouped growth in animals is more uniform. So, there
together in the body. This means that a is no such demarcation of dividing and non-
particular function is carried out by a cluster dividing regions in animals.
of cells at a definite place in the body. This
The structural organisation of organs and
cluster of cells, called a tissue, is arranged and
organ systems is far more specialised and
designed so as to give the highest possible
localised in complex animals than even in very
efficiency of function. Blood, phloem and
muscle are all examples of tissues. complex plants. This fundamental difference
A group of cells that are similar in structure reflects the different modes of life pursued by
and/or work together to achieve a particular these two major groups of organisms,
function forms a tissue. particularly in their different feeding methods.
Also, they are differently adapted for a
6.1 Are Plants and Animals Made sedentary existence on one hand (plants) and
active locomotion on the other (animals),
of Same Types of Tissues? contributing to this difference in organ system
Let us compare their structure and functions. design.
Do plants and animals have the same It is with reference to these complex animal
structure? Do they both perform similar and plant bodies that we will now talk about
functions? the concept of tissues in some detail.

Meristem:- dense cytoplasm, thin cell

wall, large nuclei and absence of vacuoles.
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Q
• From the above observations, answer
uestions the following questions:
1. What is a tissue? 1. Which of the two onions has longer
2. What is the utility of tissues in roots? Why?
2. Do the roots continue growing
multi-cellular organisms?
even after we have removed their
tips?
3. Why would the tips stop growing
in jar 2 after we cut them?
6.2 Plant Tissues
The growth of plants occurs only in certain
6.2.1 MERISTEMATIC TISSUE specific regions. This is because the dividing
tissue, also known as meristematic tissue, is
located only at these points. Depending on
the region where they are present,
meristematic tissues are classified as apical,
lateral and intercalary (Fig. 6.2). New cells
produced by meristem are initially like those
of meristem itself, but as they grow and
mature, their characteristics slowly change and
they become differentiated as components of
other tissues.

Apical meristem

Jar 1 Jar 2

Fig. 6.1: Growth of roots in onion bulbs

Intercalary meristem
Activity ______________ 6.1
• Take two glass jars and fill them with
water.
• Now, take two onion bulbs and place
one on each jar, as shown in
Fig. 6.1.
• Observe the growth of roots in both
the bulbs for a few days.
• Measure the length of roots on day 1,
2 and 3.
• On day 4, cut the root tips of the onion
bulb in jar 2 by about 1 cm. After this, Lateral meristem (Cambium
observe the growth of roots in both the )
jars and measure their lengths each
day for five more days and record the
observations in tables, like the table Fig. 6.2: Location of meristematic tissue in plant body
below: Apical meristem is present at the growing
tips of stems and roots and increases the
Length Day 1 Day 2 Day 3 Day 4 Day 5 length of the stem and the root. The girth of
the stem or root increases due to lateral
Jar 1
meristem (cambium). Intercalary meristem
Jar 2 seen in some plants is located near the node.

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 Prominent - large

Cells of meristematic tissue are very active, 3. Can we think of reasons why there
they have dense cytoplasm, thin cellulose walls would be so many types of cells?
and prominent nuclei. They lack vacuoles. Can • We can also try to cut sections of plant
we think why they would lack vacuoles? (You roots. We can even try cutting sections
might want to refer to the functions of vacuoles of root and stem of different plants.
in the chapter on cells.)
6.2.2 (i) SIMPLE PERMANENT TISSUE
6.2.2 PERMANENT TISSUE A few layers of cells beneath the epidermis are
What happens to the cells formed by generally simple permanent tissue.
meristematic tissue? They take up a specific Parenchyma is the most common simple
role and lose the ability to divide. As a result, permanent tissue. It consists of relatively
they form a permanent tissue. This process unspecialised cells with thin cell walls. They
of taking up a permanent shape, size, and a are living cells. They are usually loosely
function is called differentiation. Differentiation arranged, thus large spaces between cells
leads to the development of various types of (intercellular spaces) are found in this tissue
permanent tissues. (Fig. 6.4 a). This tissue generally stores food.

Cuticle
Epidermis
Collenchyma
Parenchyma

Phloem

Xylem
Vascular bundle

Fig. 6.3: Section of a stem

Activity ______________ 6.2 In some situations, it contains chlorophyll and

performs photosynthesis, and then it is called
• Take a plant stem and with the help chlorenchyma. In aquatic plants, large air
of your teacher cut into very thin slices cavities are present in parenchyma to help
or sections. them float. Such a parenchyma type is called
• Now, stain the slices with safranin. aerenchyma.
Place one neatly cut section on a slide, The flexibility in plants is due to another
and put a drop of glycerine. permanent tissue, collenchyma. It allows
• Cover with a cover-slip and observe bending of various parts of a plant like tendrils
under a microscope. Observe the and stems of climbers without breaking. It
various types of cells and their also provides mechanical support. We can find
arrangement. Compare it with Fig. 6.3.
this tissue in leaf stalks below the epidermis.
• Now, answer the following on the
The cells of this tissue are living, elongated
basis of your observation:
1. Are all cells similar in structure?
and irregularly thickened at the
2. How many types of cells can corners. There is very little intercellular space
be seen? (Fig. 6.4 b).

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 Intercellular spaces
Wall thickenings
Nucleus
Thick lignified
Vacuole walls Narrow lumen
Cell wall
Lignified
thick wall

a Parenchyma
b Collenchyma c (i) c (ii)

Fig. 6.4: Various types of simple tissues: (a) Parenchyma (b) Collenchyma (c) Sclerenchyma (i) transverse section,
(ii) longitudinal section.

Yet another type of permanent tissue is

sclerenchyma. It is the tissue which makes the
plant hard and stiff. We have seen the husk of
a coconut. It is made of sclerenchymatous
tissue. The cells of this tissue are dead. They
are long and narrow as the walls are thickened Guard
due to lignin. Often these walls are so thick cells

that there is no internal space inside the cell Stoma

(Fig. 6.4 c). This tissue is present in stems,
Epidermal
around vascular bundles, in the veins of leaves cell
Guard
and in the hard covering of seeds and nuts. It cell
provides strength to the plant parts. (a) (b)

Activity ______________ 6.3

Fig. 6.5: Guard cells and epidermal cells: (a) lateral
• Take a freshly plucked leaf of Rhoeo. view, (b) surface view
• Stretch and break it by applying
pressure. parts of the plant often secrete a waxy, water-
• While breaking it, keep it stretched resistant layer on their outer surface. This aids
gently so that some peel or skin
in protection against loss of water, mechanical
projects out from the cut.
• Remove this peel and put it in a petri
injury and invasion by parasitic fungi. Since
dish filled with water. it has a protective role to play, cells of
• Add a few drops of safranin. epidermal tissue form a continuous layer
• Wait for a couple of minutes and then without intercellular spaces. Most epidermal
transfer it onto a slide. Gently place cells are relatively flat. Often their outer and
a cover slip over it. side walls are thicker than the inner wall.
• Observe under microscope. We can observe small pores here and
What you observe is the outermost layer there in the epidermis of the leaf. These pores
of cells, called epidermis. The epidermis is are called stomata (Fig. 6.5). Stomata are
usually made of a single layer of cells. In some enclosed by two kidney-shaped cells
plants living in very dry habitats, the epidermis called guard cells. They are necessary for
may be thicker since protection against water exchanging gases with the atmosphere.
loss is critical. The entire surface of a plant has Transpiration (loss of water in the form of
an outer covering epidermis. It protects all the water vapour) also takes place through
parts of the plant. Epidermal cells on the aerial stomata.

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 is a distinctive feature of the complex plants,
Recall which gas is required for
photosynthesis. one that has made possible their survival in
Find out the role of transpiration in plants. the terrestrial environment. In Fig. 6.3 showing
a section of stem, can you see different types
Epidermal cells of the roots, whose function of cells in the vascular bundle?
is water absorption, commonly bear long hair- Xylem consists of tracheids, vessels, xylem
like parts that greatly increase the total parenchyma (Fig. 6.7 a,b,c) and xylem fibres.
absorptive surface area. Tracheids and vessels have thick walls, and
In some plants like desert plants, many are dead cells when mature. Tracheids
epidermis has a thick waxy coating of cutin and vessels are tubular structures. This allows
(chemical substance with waterproof quality) them to transport water and minerals
on its outer surface. Can we think of a reason vertically. The parenchyma stores food. Xylem
for this? fibres are mainly supportive in function.
Is the outer layer of a branch of a tree Phloem is made up of five types of cells:
different from the outer layer of a young stem? sieve cells, sieve tubes, companion cells,
As plants grow older, the outer protective phloem fibres and the phloem parenchyma
tissue undergoes certain changes. A strip of [Fig. 6.7 (d)]. Sieve tubes are tubular cells with
secondary meristem located in the cortex forms perforated walls. Phloem transports food from
layers of cells which constitute the cork. Cells leaves to other parts of the plant. Except
of cork are dead and compactly arranged phloem fibres, other phloem cells are living cells.
without intercellular spaces (Fig. 6.6). They
also have a substance called suberin in their
walls that makes them impervious to gases
and water. Nucleus
Cork cells Ruptured epidermis
Pit

Pits
Cytoplasm

(a) Tracheid (b) Vessel (c) Xylem parenchyma

Fig. 6.6: Protective tissue

6.2.2 (ii) COMPLEX PERMANENT TISSUE Sieve plate

Sieve tube
The different types of tissues we have discussed
until now are all made of one type of cells,
which look like each other. Such tissues are Phloem
called simple permanent tissue. Yet another parenchyma
type of permanent tissue is complex tissue.
Companion cell
Complex tissues are made of more than one
type of cells. All these cells coordinate to
perform a common function. Xylem and
phloem are examples of such complex tissues.
They are both conducting tissues and (d) Section of phloem
constitute a vascular bundle. Vascular tissue Fig. 6.7: Types of complex tissue

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 uestions

Q
During breathing we inhale oxygen. Where
does this oxygen go? It is absorbed in the lungs
1. Name types of simple tissues. and then is transported to all the body cells
2. Where is apical meristem found? through blood. Why would cells need oxygen?
3. Which tissue makes up the husk The functions of mitochondria we studied
of coconut? earlier provide a clue to this question. Blood
4. What are the constituents of flows and carries various substances from one
phloem? part of the body to the other. For example, it
carries oxygen and food to all cells. It also
collects wastes from all parts of the body and
6.3 Animal Tissues carries them to the liver and kidney for
disposal.
When we breathe we can actually feel the Blood and muscles are both examples of
movement of our chest. How do these body tissues found in our body. On the basis of the
parts move? For this we have specialised cells functions they perform we can think of different
called muscle cells (Fig. 6.8). The contraction types of animal tissues, such as epithelial
and relaxation of these cells result in tissue, connective tissue, muscular tissue and
movement. nervous tissue. Blood is a type of connective
tissue, and muscle forms muscular tissue.

6.3.1 EPITHELIAL TISSUE

The covering or protective tissues in the animal

body are epithelial tissues. Epithelium covers
most organs and cavities within the body. It
also forms a barrier to keep different body
systems separate. The skin, the lining of the
mouth, the lining of blood vessels, lung alveoli
and kidney tubules are all made of epithelial
tissue. Epithelial tissue cells are tightly packed
and form a continuous sheet. They have only
a small amount of cementing material between
them and almost no intercellular spaces.
Obviously, anything entering or leaving the
body must cross at least one layer of
epithelium. As a result, the permeability of the
cells of various epithelia play an important role
in regulating the exchange of materials
between the body and the external
environment and also between different parts
of the body. Regardless of the type, all
Smooth muscle fibres
epithelium is usually separated from the
underlying tissue by an extracellular fibrous
basement membrane.
Nucleus Different epithelia (Fig. 6.9) show differing
Smooth muscle fibre structures that correlate with their unique
functions. For example, in cells lining blood
(Cell)
vessels or lung alveoli, where transportation
of substances occurs through a selectively
Fig. 6.8: Location of muscle fibres permeable surface, there is a simple flat kind

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of epithelium. This is called the simple of skin). Simple squamous epithelial cells are
squamous epithelium (squama means scale extremely thin and flat and form a delicate
lining. The oesophagus and the lining of the
mouth are also covered with squamous
epithelium. The skin, which protects the body,
is also made of squamous epithelium. Skin
epithelial cells are arranged in many layers to
(a) Squamous prevent wear and tear. Since they are arranged
in a pattern of layers, the epithelium is called
stratified squamous epithelium.
Where absorption and secretion occur, as
in the inner lining of the intestine, tall epithelial
cells are present. This columnar (meaning
‘pillar-like’) epithelium facilitates movement
across the epithelial barrier. In the respiratory
tract, the columnar epithelial tissue also has
cilia, which are hair-like projections on the
outer surfaces of epithelial cells. These cilia can
move, and their movement pushes the mucus
forward to clear it. This type of epithelium is
thus ciliated columnar epithelium.
Cuboidal epithelium (with cube-shaped
cells) forms the lining of kidney tubules and
ducts of salivary glands, where it provides
(b) Stratified squamous mechanical support. Epithelial cells often
acquire additional specialisation as gland cells,
which can secrete substances at the epithelial
surface. Sometimes a portion of the epithelial
tissue folds inward, and a multicellular gland
is formed. This is glandular epithelium.

6.3.2 CONNECTIVE TISSUE

Blood is a type of connective tissue. Why would
it be called ‘connective’ tissue? A clue is
(c) Cuboidal
provided in the introduction of this chapter!
Now, let us look at this type of tissue in some
more detail. The cells of connective tissue are
loosely spaced and embedded in an
intercellular matrix (Fig. 6.10). The matrix may
be jelly like, fluid, dense or rigid. The nature
of matrix differs in concordance with the
function of the particular connective tissue.

Activity 6.4
(d) Columnar (Ciliated) Take a drop of blood on a slide and
observe different cells present in it
Fig. 6.9: Different types of epithelial tissues under a microscope.

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 Cytoplasm
Blood has a fluid (liquid) matrix called
Nucleus plasma, in which red blood corpuscles (RBCs),
white blood corpuscles (WBCs) and platelets
Neutrophil Eosinophil Basophil
are suspended. The plasma contains proteins,
Different white (polynuclear
leucocyte)
salts and hormones. Blood flows and
blood corpuscles
transports gases, digested food, hormones
and waste materials to different parts of the
body.
Bone is another example of a connective
Lymphocyte Monocyte Platelets
(a) tissue. It forms the framework that supports
Haversian canal the body. It also anchors the muscles and
(contains blood vessels
Chondrocyte
supports the main organs of the body. It is a
and nerve fibres) strong and nonflexible tissue (what would be
Hyaline matrix
the advantage of these properties for bone
functions?). Bone cells are embedded in a
hard matrix that is composed of calcium and
phosphorus compounds.
Canaliculus (contains (c) Two bones can be connected to each other
slender process of bone
cell or osteocyte) by another type of connective tissue called the
(b)
ligament. This tissue is very elastic. It has
Red blood
corpuscle
considerable strength. Ligaments contain
very little matrix and connect bones with
Reticular fibre Fibroblast bones. Tendons connect muscles to bones and
are another type of connective tissue. Tendons
are fibrous tissue with great strength but
limited flexibility.
Another type of connective tissue,
cartilage, has widely spaced cells. The solid
matrix is composed of proteins and sugars.
Macrophage
Cartilage smoothens bone surfaces at joints
and is also present in the nose, ear, trachea
Collagen fibre and larynx. We can fold the cartilage of the ears,
Mast cell Plasma cell
(d)
but we cannot bend the bones in our arms.
Nucleus Think of how the two tissues are different!
Fat droplet
Areolar connective tissue is found between
the skin and muscles, around blood vessels
and nerves and in the bone marrow. It fills
the space inside the organs, supports internal
organs and helps in repair of tissues.
Where are fats stored in our body? Fat-
storing adipose tissue is found below the skin
and between internal organs. The cells of this
tissue are filled with fat globules. Storage of
fats also lets it act as an insulator.
Adipocyte
(e) 6.3.3 MUSCULAR TISSUE

Fig. 6.10: Types of connective tissues: (a) types of blood Muscular tissue consists of elongated cells,
cells, (b) compact bone, (c) hyaline cartilage, also called muscle fibres. This tissue is
(d) areolar tissue, (e) adipose tissue responsible for movement in our body.

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Muscles contain special proteins called [Fig. 6.11(a)]. These muscles are also called
contractile proteins, which contract and relax skeletal muscles as they are mostly attached
to cause movement. to bones and help in body movement. Under
Nuclei
the microscope, these muscles show alternate
light and dark bands or striations when
Striations stained appropriately. As a result, they are
also called striated muscles. The cells of this
tissue are long, cylindrical, unbranched and
multinucleate (having many nuclei).
(a) Striated muscle
The movement of food in the alimentary
canal or the contraction and relaxation of blood
Spindle shaped vessels are involuntary movements. We cannot
muscle cell really start them or stop them simply by
wanting to do so! Smooth muscles [Fig.
6.11(b)] or involuntary muscles control such
movements. They are also found in the iris of
the eye, in ureters and in the bronchi of the
lungs. The cells are long with pointed ends
(spindle-shaped) and uninucleate (having a
single nucleus). They are also called unstriated
muscles – why would they be called that?
Nucleus
Smooth muscle The muscles of the heart show rhythmic
(b)
contraction and relaxation throughout life.
These involuntary muscles are called cardiac
muscles [Fig. 6.11(c)]. Heart muscle cells are
cylindrical, branched and uninucleate.
Striations
Activity 6.5
Compare the structures of different
types of muscular tissues. Note down
their shape, number of nuclei and
Nuclei position of nuclei within the cell in
the Table 6.1.

Table 6.1:

Features Striated Smooth Cardiac

Shape
Number of nuclei
(c) cardiac muscle
Position of nuclei
Fig. 6.11: Types of muscles fibres: (a) striated muscle,
(b) smooth muscle, (c) cardiac muscle
6.3.4 NERVOUS TISSUE
We can move some muscles by conscious
will. Muscles present in our limbs move when All cells possess the ability to respond to
we want them to, and stop when we so decide. stimuli. However, cells of the nervous tissue
Such muscles are called voluntary muscles are highly specialised for being stimulated and

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then transmitting the stimulus very rapidly (processes) called dendrites. An individual
from one place to another within the body. The nerve cell may be up to a metre long. Many
brain, spinal cord and nerves are all composed nerve fibres bound together by connective
of the nervous tissue. The cells of this tissue tissue make up a nerve.
are called nerve cells or neurons. A neuron The signal that passes along the nerve fibre
consists of a cell body with a nucleus and is called a nerve impulse. Nerve impulses allow
cytoplasm, from which long thin hair-like us to move our muscles when we want to. The
parts arise (Fig. 6.12). Usually each neuron functional combination of nerve and muscle
has a single long part (process), called the tissue is fundamental to most animals. This
axon, and many short, branched parts combination enables animals to move rapidly
in response to stimuli.
Nucleus

uestions

Q
Dendrite

1. Name the tissue responsible for

movement in our body.
Axon
Nerve ending
2. What does a neuron look like?
3. Give three features of cardiac
muscles.
Cell body
4. What are the functions of
Fig. 6.12: Neuron-unit of nervous tissue areolar tissue?

What
you have
learnt
• Tissue is a group of cells similar in structure and function.
• Plant tissues are of two main types – meristematic and
permanent.
• Meristematic tissue is the dividing tissue present in the
growing regions of the plant.
• Permanent tissues are derived from meristematic tissue once
they lose the ability to divide. They are classified as simple
and complex tissues.
• Parenchyma, collenchyma and sclerenchyma are three types
of simple tissues. Xylem and phloem are types of complex
tissues.
• Animal tissues can be epithelial, connective, muscular and
nervous tissue.
• Depending on shape and function, epithelial tissue is
classified as squamous, cuboidal, columnar, ciliated and
glandular.

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 • The different types of connective tissues in our body include
areolar tissue, adipose tissue, bone, tendon, ligament,
cartilage and blood.
• Striated, unstriated and cardiac are three types of muscle
tissues.
• Nervous tissue is made of neurons that receive and conduct
impulses.

Exercises
1. Define the term “tissue”.
2. How many types of elements together make up the xylem
tissue? Name them.
3. How are simple tissues different from complex tissues in
plants?
4. Differentiate between parenchyma, collenchyma and
sclerenchyma on the basis of their cell wall.
5. What are the functions of the stomata?
6. Diagrammatically show the difference between the three
types of muscle fibres.
7. What is the specific function of the cardiac muscle?
8. Differentiate between striated, unstriated and cardiac
muscles on the basis of their structure and site/location in
the body.
9. Draw a labelled diagram of a neuron.
10. Name the following.
(a) Tissue that forms the inner lining of our mouth.
(b) Tissue that connects muscle to bone in humans.
(c) Tissue that transports food in plants.
(d) Tissue that stores fat in our body.
(e) Connective tissue with a fluid matrix.
(f) Tissue present in the brain.
11. Identify the type of tissue in the following: skin, bark of
tree, bone, lining of kidney tubule, vascular bundle.

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 12. Name the regions in which parenchyma tissue is present.
13. What is the role of epidermis in plants?
14. How does the cork act as a protective tissue?
15. Complete the following chart:

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Chapter 7
DIVERSITY IN LIVING ORGANISMS
Have you ever thought of the multitude of for thousands of years while insects like
life-forms that surround us? Each organism mosquitoes die within a few days. Life also
is different from the other to a lesser or greater ranges from colourless or even transparent
extent. For instance, consider yourself and a worms to brightly coloured birds and flowers.
friend. This bewildering variety of life around us
• Are you both of the same height? has evolved on the earth over millions of
• Does your nose look exactly like your years. However, we do not have more than a
friend’s nose? tiny fraction of this time to try and
• Is your hand-span the same as your understand all these living organisms, so we
friend’s? cannot look at them one by one. Instead, we
However, if we were to compare ourselves look for similarities among the organisms,
and our friends with a monkey, what would which will allow us to put them into different
we say? Obviously, we and our friends have classes and then study different classes or
a lot in common when we compare ourselves groups as a whole.
with a monkey. But suppose we were to add In order to make relevant groups to study
a cow to the comparison? We would then the variety of life forms, we need to decide
think that the monkey has a lot more in which characteristics decide more
common with us than with the cow. fundamental differences among organisms.
This would create the main broad groups of
Activity ______________ 7.1 organisms. Within these groups, smaller sub-
• We have heard of ‘desi’ cows and Jersey groups will be decided by less important
cows. characteristics.
• Does a desi cow look like a Jersey cow?
Do all desi cows look alike?
•
uestions

Q
• Will we be able to identify a Jersey cow
in a crowd of desi cows that don’t look 1. Why do we classify organisms?
like each other? 2. Give three examples of the range
• What is the basis of our identification? of variations that you see in life-
In this activity, we had to decide which forms around you.
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 7.1 What is the Basis of
which life occurs on earth. On one hand we Classification?
have microscopic bacteria of a few micrometre
in size. While on the other hand we have blue Attempts at classifying living things into
whale and red wood trees of California groups have been made since time
of approximate sizes of 30 metres and immemorial. Greek thinker Aristotle classified
100 metres respectively. Some pine trees live animals according to whether they lived on

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land, in water or in the air. This is a very of mutually related characteristics to be used
simple way of looking at life, but misleading for classification.
too. For example, animals that live in the sea Now-a-days, we look at many inter-related
include corals, whales, octopuses, starfish characteristics starting from the nature of the
and sharks. We can immediately see that cell in order to classify all living organisms.
these are very different from each other in What are some concrete examples of such
numerous ways. In fact, habitat is the only characteristics used for a hierarchical
point they share in common. This is not an classification?
appropriate way of making groups of • A eukaryotic cell has membrane-bound
organisms to study and think about. organelles, including a nucleus, which
We therefore need to decide which allow cellular processes to be carried out
characteristics to be used as the basis for efficiently in isolation from each other.
making the broadest divisions. Then we will Therefore, organisms which do not have
have to pick the next set of characteristics a clearly demarcated nucleus and other
for making sub-groups within these divisions. organelles would need to have their
This process of classification within each biochemical pathways organised in very
group can then continue using new different ways. This would have an effect
characteristics each time.
on every aspect of cell design. Further,
Before we go on, we need to think about
nucleated cells would have the capacity
what is meant by ‘characteristics’. When we
to participate in making a multicellular
are trying to classify a diverse group of
organism because they can take up
organisms, we need to find ways in which
specialised functions. Therefore, nucleus
some of them are similar enough to be
can be a basic characteristic of
thought of together. These ‘ways’, in fact, are
classification.
details of appearance or behaviour, in other
words, form and function. • Do the cells occur singly or are they
What we mean by a characteristic is a grouped together and do they live as an
particular feature or a particular function. That indivisible group? Cells that group
most of us have five fingers on each hand is together to form a single organism use
thus a characteristic. That we can run, but the the principle of division of labour. In such
banyan tree cannot, is also a characteristic. a body design, all cells would not be
Now, to understand how some identical. Instead, groups of cells will
characteristics are decided as being more carry out specialised functions. This
fundamental than others, let us consider how makes a very basic distinction in the
a stone wall is built. The stones used will have body designs of organisms. As a result,
different shapes and sizes. The stones at the an Amoeba and a worm are very different
top of the wall would not influence the choice in their body design.
of stones that come below them. On the other • Do organisms produce their own food
hand, the shapes and sizes of stones in the through the process of photosynthesis?
lowermost layer will decide the shape and size Being able to produce one’s own
of the next layer and so on. food versus having to get food from
The stones in the lowermost layer are like outside would make very different
the characteristics that decide the broadest body designs.
divisions among living organisms. They are • Of the organisms that perform
independent of any other characteristics in photosynthesis (plants), what is the level
their effects on the form and function of the of organisation of their body?
organism. The characteristics in the next level • Of the animals, how does the individual’s
would be dependent on the previous one and body develop and organise its different
would decide the variety in the next level. In parts, and what are the specialised
this way, we can build up a whole hierarchy organs found for different functions?

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 We can see that, even in these few questions When we connect this idea of evolution to
that we have asked, a hierarchy is developing. classification, we will find some groups of
The characteristics of body design used for organisms which have ancient body designs
classification of plants will be very different that have not changed very much. We will
from those important for classifying animals. also find other groups of organisms that have
This is because the basic designs are different, acquired their particular body designs
based on the need to make their own food relatively recently. Those in the first group
(plants), or acquire it (animals). Therefore, are frequently referred to as ‘primitive’ or ‘lower’
these design features (having a skeleton, for organisms, while those in the second group
example) are to be used to make sub-groups, are called ‘advanced’ or ‘higher’ organisms. In
rather than making broad groups. reality, these terms are not quite correct since
they do not properly relate to the differences.
uestions

Q
All that we can say is that some are ‘older’
organisms, while some are ‘younger’
1. Which do you think is a more basic organisms. Since there is a possibility that
characteristic for classifying complexity in design will increase over
organisms? evolutionary time, it may not be wrong to say
(a) the place where they live. that older organisms are simpler, while
(b) the kind of cells they are younger organisms are more complex.
made of. Why?
2. What is the primary characteristic
on which the broad division of Biodiversity means the diversity of life
organisms is made? forms. It is a word commonly used to
3. On what bases are plants and refer to the variety of life forms found
animals put into different in a particular region. Diverse life forms
categories? share the environment, and are
affected by each other too. As a result,
a stable community of different species
7.2 Classification and Evolution comes into existence. Humans have
All living things are identified and categorised played their own part in recent times
on the basis of their body design in form and in changing the balance of such
function. Some characteristics are likely to communities. Of course, the diversity
make more wide-ranging changes in body in such communities is affected by
More to know

design than others. There is a role of time in particular characteristics of land,

this as well. So, once a certain body design water, climate and so on. Rough
comes into existence, it will shape the effects estimates state that there are about ten
of all other subsequent design changes, million species on the planet, although
simply because it already exists. In other we actually know only one or two
words, characteristics that came into millions of them. The warm and humid
existence earlier are likely to be more basic tropical regions of the earth, between
than characteristics that have come into the tropic of Cancer and the tropic of
existence later. Capricorn, are rich in diversity of plant
This means that the classification of life and animal life. This is called the region
forms will be closely related to their evolution. of megadiversity. Of the biodiversity
What is evolution? Most life forms that we on the planet, more than half is
see today have arisen by an accumulation of concentrated in a few countries —
changes in body design that allow the Brazil, Colombia, Ecuador, Peru,
organism possessing them to survive better. Mexico, Zaire, Madagascar,
Charles Darwin first described this idea of Australia, China, India, Indonesia and
evolution in 1859 in his book, The Origin of Malaysia.
Species.

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 uestions 7.3.1 MONERA

Q 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-

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
Groups organisms in this group can be either by
synthesising their own food (autotrophic) or
Biologists, such as Ernst Haeckel (1894), getting it fr om the environment
Robert Whittaker (1969) and Carl Woese (heterotrophic). This group includes bacteria,
(1977) have tried to classify all living blue-green algae or cyanobacteria, and
organisms into broad categories, called mycoplasma. Some examples are shown
kingdoms. The classification Whittaker in Fig. 7.1.
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 Resting
Archaea) and Eubacteria (or Bacteria) is also spore
in use.
Further classification is done by naming Bacteria
the sub-groups at various levels as given in
the following scheme:
Kingdom
Phylum (for animals) / Division (for plants)
Heterocyst
Class
Order Anabaena
Family
Genus
Species Fig. 7.1: Monera
Thus, by separating organisms on the
basis of a hierarchy of characteristics into 7.3.2 PROTISTA
smaller and smaller groups, we arrive at the
This group includes many kinds of unicellular
basic unit of classification, which is a eukaryotic organisms. Some of these
‘species’. So what organisms can be said to organisms use appendages, such as hair-like
belong to the same species? Broadly, a species cilia or whip-like flagella for moving around.
includes all organisms that are similar Their mode of nutrition can be autotrophic
enough to breed and perpetuate. or heterotrophic. Examples are unicellular
The important characteristics of the five algae, diatoms and protozoans (see Fig. 7.2
kingdoms of Whittaker are as follows: for examples).

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Some general biology textbook authors place the microscopic, unicellular green
algae (Division Chlorophyta) in the Kingdom Protista, and place the larger,
multicellular (macroscopic) green algae (Division Chlorophyta) in the Kingdom
Plantae.
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 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
Macronucleus
chitin. Examples are yeasts, molds and
Micronucleus
mushrooms (see Fig. 7.3 for examples).

Waste

Paramecium

Nucleus
Saccharomyces Penicillium Agaricus
(Yeast) (Mold) (Mushroom)

Fig. 7.3: Fungi

Some fungal species live in permanent lichens

Amoeba 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
Flagellum (long) coloured patches on the bark of trees.

7.3.4 PLANTAE
These are multicellular eukaryotes with cell
walls. They are autotrophs and use
Nucleus chlorophyll for photosynthesis. Thus, all
plants are included in this group. Since plants
Euglena
and animals are most visible forms of the
diversity of life around us, we will look at the
Fig. 7.2: Protozoa subgroups in this category later (section 7.4).

7.3.3 FUNGI 7.3.5 ANIMALIA

These are heterotrophic eukaryotic These include all organisms which are
organisms. Some of them use decaying organic multicellular eukaryotes without cell walls.
material as food and are therefore called They are heterotrophs. Again, we will look at
saprotrophs. Others require a living their subgroups a little later in section 7.5.

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 Fig. 7.4: The Five Kingdom classification

uestions 7.4 Plantae

Q 1. What is the criterion for

classification of organisms as
belonging to kingdom Monera or
Protista?
2. In which kingdom will you place
an organism which is single-
celled, eukaryotic
photosynthetic?
and

3. In the hierarchy of classification,

which grouping will have the
The first level of classification among plants
depends on whether the plant body has well-
differentiated, distinct parts. The next level of
classification is based on whether the
differentiated plant body has special tissues
for the transport of water and other
substances. Further classification looks at the
ability to bear seeds and whether the seeds
are enclosed within fruits.

smallest number of organisms 7.4.1 THALLOPHYTA

with maximum common
characteristics and which will Plants that do not have well-differentiated body
have the largest number of design fall in this group. The plants in this
organisms? group are commonly called algae. These plants

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are predominantly aquatic. Examples are 7.4.2 BRYOPHYTA
Spirogyra, Ulothrix, Cladophora, Ulva and
Chara (see Fig. 7.5). These are called the amphibians of the plant
kingdom. The plant body is commonly
differentiated to form stem and leaf-like
structures. However, there is no specialised
tissue for the conduction of water and other
substances from one part of the plant body
to another. Examples are moss (Funaria) and
Marchantia (see Fig. 7.6).
Ricky is a Funny Merchant.
Bro

Cladophora
Ulothrix

Cell-wall Riccia
Chloroplast
Pyrenoids
Nucleus
Cytoplasm

Ulva Marchantia Funaria

Spirogyra
Fig. 7.6: Some common bryophytes

7.4.3 PTERIDOPHYTA
In this group, the plant body is differentiated
into roots, stem and leaves and has
specialised tissue for the conduction of water
and other substances from one part of the
plant body to another. Some examples are
Marsilea, ferns and horse-tails (see Fig. 7.7).
The reproductive organs of plants in all
these three groups are very inconspicuous,
and they are therefore called ‘cryptogams’, or
‘those with hidden reproductive organs’.
Chara On the other hand, plants with well-
differentiated reproductive parts that
Fig. 7.5: Thallophyta – Algae ultimately make seeds are called
phanerogams.
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 ovary fruit

7.4.5 ANGIOSPERMS
Leaf
This word is made from two Greek words:
angio means covered and sperma– means
seed. These are also called flowering plants.
The seeds develop inside an ovary which is
modified to become a fruit. Plant embryos in
seeds have structures called cotyledons.
Cotyledons are called ‘seed leaves’ because in
Stem many instances they emerge and become
Root green when the seed germinates. The
angiosperms are divided into two groups on
Marsilea Fern the basis of the number of cotyledons present
Fig. 7.7: Pteridophyta in the seed. Plants with seeds having a single
cotyledon are called monocotyledonous or
phanerogams. Seeds are the result of sexual monocots. Plants with seeds having two
reproduction process. They consist of the cotyledons are called dicots (see Figs. 7.9
embryo along with stored food, which assists and 7.10).
for the initial growth of the embryo during
germination. This group is further classified,
based on whether the seeds are naked or
enclosed in fruits, giving us two groups:
gymnosperms and angiosperms.

7.4.4 GYMNOSPERMS
This term is derived from two Greek words:
gymno– means naked and sperma– means
seed. The plants of this group bear naked
seeds and are usually perennial, evergreen
and woody. Examples are pines and deodar
(see Fig. 7.8 for examples).

Fig. 7.9: Monocot Paphiodilum

Pinus Cycas
Fig. 7.8: Gymnosperms Fig. 7.10: Dicot Ipmoea
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 Fig. 7.11: Classification of plants

Activity ______________ 7.2 • How many petals are found in the

flower of these plants?
• Soak seeds of green gram, wheat, • Can you write down further
maize, peas and tamarind. Once they characteristics of monocots and dicots
become tender, try to split the seed. Do on the basis of these observations?
all the seeds break into two nearly
uestions

Q
equal halves?
• The seeds that do are the dicot seeds
and the seeds that don’t are the 1. Which division among plants has
monocot seeds. the simplest organisms?
• Now take a look at the roots, leaves and 2. How are pteridophytes different
flowers of these plants. from the phanerogams?
• Are the roots tap-roots or fibrous? 3. How do gymnosper ms and
• Do the leaves have parallel or reticulate angiosperms differ from each
venation? other?

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7.5 Animalia layers of cells: one makes up cells on the
outside of the body, and the other makes the
These are organisms which are eukaryotic, inner lining of the body. Some of these species
multicellular and heterotrophic. Their cells live in colonies (corals), while others have a
do not have cell-walls. Most animals are solitary like–span (Hydra). Jellyfish and sea
mobile. anemones are common examples (see
They are further classified based on the Fig. 7.13).
extent and type of the body design
differentiation found. Tentacles
Tentacles
Stinging cell
7.5.1 PORIFERA
The word Porifera means organisms with
holes. These are non-motile animals attached Mouth
to some solid support. There are holes or
‘pores’, all over the body. These lead to a canal
system that helps in circulating water
Epidermis
throughout the body to bring in food and Mesoglea
oxygen. These animals are covered with a Gastrodermis
hard outside layer or skeleton. The body Gastrovascular
design involves very minimal differentiation cavity
Sea anemone
and division into tissues. They are commonly
Foot
called sponges, and are mainly found in
Hydra
marine habitats. Some examples are shown
in Fig. 7.12.
Fig. 7.13: Coelenterata

7.5.3 PLATYHELMINTHES
The body of animals in this group is far more
complexly designed than in the two other
groups we have considered so far. The body
is bilaterally symmetrical, meaning that the
Euplectella Sycon left and the right halves of the body have the
same design. There are three layers of cells
from which differentiated tissues can be
made, which is why such animals are called
triploblastic. This allows outside and inside
body linings as well as some organs to be
made. There is thus some degree of tissue
Spongilla formation. However, there is no true internal
body cavity or coelom, in which well-
Fig. 7.12: Porifera developed organs can be accommodated. The
body is flattened dorsoventrally (meaning from
7.5.2 COELENTERATA (CNIDARIA) top to bottom), which is why these animals are
called flatworms. They are either free-living or
These are animals living in water. They show parasitic. Some examples are free-living
more body design differentiation. There is a animals like planarians, or parasitic animals
cavity in the body. The body is made of two like liverflukes (see Fig. 7.14 for examples).

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 Branched
7.5.5 ANNELIDA
Eyes gastrovascular
cavity
Annelid animals are also bilaterally
Scolex Sucker symmetrical and triploblastic, but in addition
Acetabulum Neck
they have a true body cavity. This allows true
organs to be packaged in the body structure.
There is, thus, extensive organ differentiation.
Pharynx
This differentiation occurs in a segmental
Mouth
and anus fashion, with the segments lined up one after
the other from head to tail. These animals
are found in a variety of habitats– fresh water,
Liverfluke Tape worm
Planaria marine water as well as land. Earthworms
and leeches are familiar examples (see
Fig. 7.16).
Fig. 7.14: Platyhelminthes

Tentacle
7.5.4 NEMATODA Palp

The nematode body is also bilaterally

symmetrical and triploblastic. However, the
body is cylindrical rather than flattened.
There are tissues, but no real organs,
although a sort of body cavity or a pseudo-
Parapodia Genital
coelom, is present. These are very familiar papillae
as parasitic worms causing diseases, such Anus
as the worms causing elephantiasis (filarial
worms) or the worms in the intestines
(roundworm or pinworms). Some examples
Parapodia
are shown in Fig. 7.15.

Nereis Earthworm Leech

Female

Fig. 7.16: Annelida

largest group of animals

7.5.6 ARTHROPODA
Male
This is probably the largest group of animals.
These animals are bilaterally symmetrical and
segmented. There is an open circulatory
system, and so the blood does not flow in well-
defined blood vessels. The coelomic cavity is
blood-filled. They have jointed legs (the word
‘arthropod’ means ‘jointed legs’). Some
Wuchereria
familiar examples are prawns, butterflies,
Ascaris
houseflies, spiders, scorpions and crabs (see
Fig. 7.15: Nematoda (Aschelminthes) Fig. 7.17).

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 7.5.8 ECHINODERMATA
In Greek, echinos means hedgehog (spiny
mammal), and derma means skin. Thus, these
are spiny skinned organisms. These are
Aranea(Spider)
exclusively free-living marine animals. They
Palaemon are triploblastic and have a coelomic cavity.
(Prawn) Palamnaeus They also have a peculiar water-driven tube
(Scorpion)
system that they use for moving around. They
have hard calcium carbonate structures that
Butterfly
they use as a skeleton. Examples are sea-stars
and sea urchins (see Fig. 7.19).

Pariplaneta
(Cockroach)

Musca
(House fly)
Scolopendra
(Centipede)

Fig. 7.17: Arthropoda

Antedon Holothuria
7.5.7 MOLLUSCA (feather star) (sea cucumber)

In the animals of this group, there is bilateral

symmetry. The coelomic cavity is reduced.
There is little segmentation. They have an
open circulatory system and kidney-like
organs for excretion. There is a foot that is
used for moving around. Examples are snails
and mussels (see Fig. 7.18).
Echinus (sea urchin) Asterias (sea-star)

Fig. 7.19: Echinodermata

7.5.9 PROTOCHORDATA
These animals are bilaterally symmetrical,
triploblastic and have a coelom. In addition,
they show a new feature of body design,
namely a notochord, at least at some stages
during their lives. The notochord is a long
Chiton
Octopus rod-like support structure (chord=string) that
runs along the back of the animal separating
the nervous tissue from the gut. It provides a
place for muscles to attach for ease of
movement. Protochordates may not have a
proper notochord present at all stages in their
Unio lives or for the entire length of the animal.
Pila Protochordates are marine animals. Examples
are Balanoglossus, Herdmania and
Fig. 7.18: Mollusca
Amphioxus (see Fig. 7.20).

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 scaleless. They are ectoparasites or borers of
Proboscis other vertebrates. Petromyzon (Lamprey) and
Myxine (Hagfish) are examples.
Collarette

Collar
7.5.10 (ii) PISCES
These are fish. They are exclusively aquatic
animals. Their skin is covered with scales/
Anus Branchial region plates. They obtain oxygen dissolved in water
by using gills. The body is streamlined, and a
Gill pores
muscular tail is used for movement. They are
Dorsally cold-blooded and their hearts have only two
Posthepatic curved chambers, unlike the four that humans have.
region genital wings
They lay eggs. We can think of many kinds of
fish, some with skeletons made entirely of
Middosrsal cartilage, such as sharks, and some with a
ridge
skeleton made of both bone and cartilage, such
Hepatic caeca as tuna or rohu [see examples in Figs. 7.22 (a)
and 7.22 (b)].
Hepatic region

Fig. 7.20: Protochordata: Balanoglossus

7.5.10 VERTEBRATA
Synchiropus splendidus Caulophyryne jordani
These animals have a true vertebral column (Mandarin fish) (Angler fish)
and internal skeleton, allowing a completely
different distribution of muscle attachment
points to be used for movement.
Vertebrates are bilaterally symmetrical,
triploblastic, coelomic and segmented, with
complex differentiation of body tissues and Pterois volitans
organs. All chordates possess the following (Lion fish)
features: Eye
(i) have a notochord Spiracle
(ii) have a dorsal nerve cord
(iii) are triploblastic
(iv) have paired gill pouches
(v) are coelomate.
Vertebrates are grouped into six classes. Pelvic fin
Dorsal fin
7.5.10 (i) CYCLOSTOMATA Tail
Caudal fin Sting ray
Cyclostomes are jawless vertebrates. They are
Electric ray (Torpedo)
characterised by having an elongated eel-like Dorsal fin
Tail
Eye
body, circular mouth, slimy skin and are

Mouth Gills
Pectoral Pelvic
fin fin
Scoliodon (Dog fish)
Fig. 7.21: A jawless vertebrate: Petromyzon Fig. 7.22 (a): Pisces

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Crocodile have 3 mammal Thecodont
character:- 4 chamber heart
Diaphragm

Eye
Head 7.5.10 (iv) REPTILIA
Nostril
Pectoral These animals are cold-blooded, have scales
Mouth fin and breathe through lungs. While most of
Caudal Pelvic
Pectoral Mouth Dorsal them have a three-chambered heart, crocodiles
fin Brood
fin fin have four heart chambers. They lay eggs with
fin pouch
Tail
tough coverings and do not need to lay their
Labeo rohita (Rohu)
Male Hippocampus eggs in water, unlike amphibians. Snakes,
(Sea horse) turtles, lizards and crocodiles fall in this
Wing like pectoral category (see Fig. 7.24).

Scales
Tail
Pelvic fin
Exocoetus (Flying fish) Turtle

Chameleon

Anabas (Climbing perch)

Poisonous teeth - Maxillary
Fig. 7.22 (b): Pisces

7.5.10 (iii) AMPHIBIA

These animals differ from the fish in the lack
of scales, in having mucus glands in the skin, King Cobra
and a three-chambered heart. Respiration is
through either gills or lungs. They lay eggs.
These animals are found both in water and on
land. Frogs, toads and salamanders are some
examples (see Fig. 7.23).

House wall lizard

(Hemidactylus)
Flying lizard (Draco)
Salamander
Toad
Fig. 7.24: Reptilia

7.5.10 (v) AVES

These are warm-blooded animals and have a
four-chambered heart. They lay eggs. There
Rana tigrina is an outside covering of feathers, and two
(Common frog)
Hyla (Tree frog)
forelimbs are modified for flight. They breathe
through lungs. All birds fall in this category
Fig. 7.23: Amphibia (see Fig. 7.25 for examples).

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 Whale

White Stork
(Ciconia ciconia) Rat

Human
Bat
Cat

Ostrich
(Struthio camelus)
Male Tufted Duck
(Aythya fuligula) Fig. 7.26: Mammalia

uestions

Pigeon
Sparrow Q 1. How do poriferan animals differ
from coelenterate animals?
2. How do annelid animals differ
from arthropods?
3. What are the differences between
amphibians and reptiles?
4. What are the differences between
animals belonging to the Aves
group and those in the mammalia
group?

Carolus Linnaeus (Karl

Crow von Linne) was born in
Sweden and was a doctor
by professsion. He was
Fig. 7.25: Aves (birds)
interested in the study of
plants. At the age of 22, he
7.5.10 (vi) MAMMALIA published his first paper on
plants. While serving as a
Mammals are warm-blooded animals with
personal physician of a Carolus Linnaeus
four-chambered hearts. They have mammary
wealthy government (1707-1778)
glands for the production of milk to nourish
official, he studied the diversity of plants
their young. Their skin has hairs as well as
in his employer’s garden. Later, he
sweat and oil glands. Most mammals familiar
published 14 papers and also brought out
to us produce live young ones. However, a
the famous book Systema Naturae from
few of them, like the platypus and the echidna
which all fundamental taxonomical
lay eggs, and some, like kangaroos give birth
researches have taken off. His system of
to very poorly developed young ones. Some
classification was a simple scheme for
examples are shown in Fig. 7.26.
arranging plants so as to be able to identify
The scheme of classification of animals is
them again.
shown in Fig. 7.27.

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 Fig. 7.27: Classification of animals

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7.6 Nomenclature the result of the process of classification
which puts it along with the organisms it is
Why is there a need for systematic naming of most related to. But when we actually name
living organisms? the species, we do not list out the whole
hierarchy of groups it belongs to. Instead, we
Activity ______________ 7.3 limit ourselves to writing the name of the genus
• Find out the names of the following and species of that particular organism. World
animals and plants in as many over, it has been agreed that both these names
languages as you can: will be used in Latin forms.
1. Tiger 2. Peacock 3. Ant Certain conventions are followed while
4. Neem 5. Lotus 6. Potato writing the scientific names:
As you might be able to appreciate, it 1. The name of the genus begins with a
would be difficult for people speaking or capital letter.
writing in different languages to know when 2. The name of the species begins with a
they are talking about the same organism. This small letter.
3. When printed, the scientific name is
problem was resolved by agreeing upon a
given in italics.
‘scientific’ name for organisms in the same
4. When written by hand, the genus name
manner that chemical symbols and formulae
and the species name have to be
for various substances are used the world over.
underlined separately.
The scientific name for an organism is thus
unique and can be used to identify it Activity ______________ 7.4
anywhere in the world.
The system of scientific naming or • Find out the scientific names of any
five common animals and plants. Do
nomenclature we use today was introduced
these names have anything in
by Carolus Linnaeus in the eighteenth common with the names you normally
century. The scientific name of an organism is use to identify them?

What
you have
learnt
• Classification helps us in exploring the diversity of life forms.
• The major characteristics considered for classifying all
organisms into five major kingdoms are:
(a) whether they are made of prokaryotic or eukaryotic cells
(b) whether the cells are living singly or organised into
multi-cellular and thus complex organisms
(c) whether the cells have a cell-wall and whether they
prepare their own food.
• All living organisms are divided on the above bases into five
kingdoms, namely Monera, Protista, Fungi, Plantae and
Animalia.
• The classification of life forms is related to their evolution.

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 • Plantae and Animalia are further divided into subdivisions
on the basis of increasing complexity of body organisation.
• Plants are divided into five groups: Thallophytes, Bryophytes,
Pteridophytes, Gymnosperms and Angiosperms.
• Animals are divided into ten groups: Porifera, Coelenterata,
Platyhelminthes, Nematoda, Annelida, Arthropoda, Mollusca,
Echinodermata, Protochordata and Vertebrata.
• The binomial nomenclature makes for a uniform way of
identification of the vast diversity of life around us.
• The binomial nomenclature is made up of two words – a generic
name and a specific name.

Exercises
1. What are the advantages of classifying organisms?
2. How would you choose between two characteristics to be used
for developing a hierarchy in classification?
3. Explain the basis for grouping organisms into five kingdoms.
4. What are the major divisions in the Plantae? What is the basis
for these divisions?
5. How are the criteria for deciding divisions in plants different
from the criteria for deciding the subgroups among animals?
6. Explain how animals in Vertebrata are classified into further
subgroups.

D IVERSITY IN L IVING O RGANISMS 97

2019-2020