NCERT Solutions Class 9 Science Chapter 3 Tissues in Action

F R E E S T U D Y M AT E R I A L F O R E V E R Y S T U D E N T

CLASS 9 · SCIENCE

NCERT Solutions

Chapter 3: Tissues in Action

NCERT Textbook — Exploration

BOOK PAGES SECTIONS QUESTIONS MEDIUM

28 – 47 20 52 English

Solutions, notes, sample papers & more at 63 pages

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

CLASS 9 · SCIENCE · EXPLORATION

NCERT Solutions — Chapter 3: Tissues in Action
A single fertilised cell divides again and again and ends up as skin, bone, muscle, nerve, xylem and phloem.
Tissues in Action follows that story — how groups of similar cells specialise, why plant and animal tissues
took different paths, and how muscles, bones and joints work together to move you.

TEXTBOOK BOOK PAGES

Exploration (Class 9) 28 – 47

SECTIONS QUESTIONS

20 52

MEDIUM

English

Think It Over — Page 28
Chapter opener

THINK IT OVER

Q1 How is the study of cells and tissues significant for understanding the life processes
and human welfare?

Because every life process finally happens inside a cell, and no single cell in a large body can do
all of them at once.
A unicellular organism like Amoeba manages everything — nutrition, respiration, excretion,
movement — with one cell. In a multicellular body that is impossible, so cells of one kind group
into a tissue and take up one job. Studying tissues therefore tells us where each life process is
carried out and why that particular structure suits it:

Muscle tissue → movement, because its cells are long fibres that can contract.
Nervous tissue → control and coordination, because a neuron has a long axon that carries a
message far.
Xylem → water transport, because its cells are dead, hollow tubes with no cross-walls to
block flow.
Phloem → food transport, because its sieve tubes are living and are loaded by companion
cells.

Page 1 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Why it matters for human welfare: if you know the normal structure of a tissue,
you can tell what has gone wrong when it fails, and sometimes repair it. Bone-
marrow stem cells are transplanted to treat leukaemia and thalassaemia. Plant
tissue culture, which began with F. C. Steward showing in 1958 that a single carrot
phloem cell can regenerate a whole plant, now gives us disease-free planting
material and improved crops. Sipra Guha Mukherjee and S. C. Maheshwari raised a
complete plant from anther culture, a technique still used in crop improvement.

Tip: remember the hierarchy in one line — cells → tissue → organ → organ system
→ organism. Each level exists because it makes the division of labour finer.

Q2 How are tissues in plants and animals different, and why?

They differ because plants and animals live in different ways — plants stay fixed and make their
own food, animals move about and take food in.

POINT PLANT TISSUES ANIMAL TISSUES

Support Cell walls give rigidity; sclerenchyma and lignin No cell wall, so cells change shape
form the woody skeleton. The plant is held easily. Support comes from a living
upright by dead tissue. skeleton of bone and cartilage.

Growth Growth is restricted to meristems and Growth is spread over the whole body
continues all life. A tree adds girth every year. and mostly stops at maturity.

Nutrition Tissues for photosynthesis (chlorenchyma-type Tissues for digestion and absorption
parenchyma) — food is made inside. (epithelium of the gut) — food is taken
in from outside.

Transport Xylem and phloem — largely non-motile tubes; Blood — a fluid connective tissue
xylem is dead. pumped by cardiac muscle.

Energy Many supporting cells are dead, so they cost Nearly all cells are living and must be
cost nothing to maintain. supplied constantly.

Why it happens: an animal must be able to bend, run and change shape, so it
cannot afford a rigid wall around every cell; it pays instead with a living skeleton and
a constant food supply. A plant does not move, so it can spend cheap dead lignified
cells on support and keep growing from its tips all its life.

Page 2 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Q3 How is the division of labour at various levels of organisation in multicellular
organisms correlated with their structure and function?

At every level, the structure is shaped by the one job that level has to do — and each higher
level exists to combine jobs that a lower level cannot combine.

LEVEL STRUCTURE FUNCTION IT MAKES
POSSIBLE

Cell A neuron is drawn out into a long axon Carries a signal over a long
distance

Tissue Many muscle fibres bundled and lying parallel Their small individual pulls add up
to a large force

Organ The heart — cardiac muscle + epithelium + Pumps blood rhythmically for a
connective tissue + nerves lifetime

Organ Musculoskeletal system — bones, muscles, Posture, locomotion, protection
system tendons, ligaments, cartilage, joints of delicate organs

Organism All systems working under nervous control A complete, coordinated life

The same logic runs through the plant: epidermal cells are flat and waxy (protection),
parenchyma cells are thin-walled with spaces (storage and gas diffusion), xylem vessels are
hollow tubes (conduction) — and together they form the dermal, ground and vascular tissue
systems of the whole plant body.

Why division of labour raises efficiency: a cell that does only one job can be built
entirely for that job. A parenchyma cell that only stores food does not need thick
walls; a sclerenchyma cell that only gives strength does not even need to stay alive.
Specialisation removes the compromises that a jack-of-all-trades cell like Amoeba is
forced to make.

Activity 3.1: Let us design experiments — Page 29

Page 3 of 63

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Class 9 Science Chapter 3 Tissues in Action
a g l AglaSem · NCERT Solutions

3.2.1 Apical meristem — How do plants grow in length?
co m
em.
m as
ACTIVITY

.co a g l
a s em trend do you observe in the data you recorded in Table 3.1? Are your
gl
What
a
Q1
observations similar to those presented in the graphical representation (Fig. 3.2)?
What do you infer?

co m
m .
Table 3.1: Experimental data — length of onion root (cm) from the base of the bulb.
ag
l a se
EXPERIMENTAL ag DAY
DAY DAY DAY DAY DAY DAY
JARS 1 2 3 4 5 6 7

co m
em.
A

Bco
m g l as
. a
a sem
agl
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6
Jar A
5.5
se m
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Jar B
5
a
Length of roots (cm) from

4.5

m
the base of the bulb

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4

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3.5
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a g l
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a 2
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1
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ase
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0.5

0 2 3 4 5 6 7
Days
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ase
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Fig. 3.2, page 30 — growth of onion roots, the graph printed with Activity 3.1.

. a g
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ase
agl c
m .
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co agl
The roots in Jar A keep getting longer day after day; the roots in Jar B grow at the same rate until

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e
their tips are cut, and then they stop completely.

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a
These are the readings printed in Fig. 3.2 of the book (length of root in cm from the base of the
bulb):

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m .
m as e
.co


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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

DAY 1 2 3 4 5 6 7

Jar A (uncut) 0.25 0.8 1.8 2.9 3.8 4.9 5.8

Jar B (tip cut) 0.25 0.7 1.6 2.6 → 1.6 1.6 1.6 1.6

6 Jar A

5
Root length (cm)

4

3

2 Jar B — tip cut, growth stops

1

0
1 2 3 4 5 6 7
Days

Growth of onion roots, redrawn from the readings in Fig. 3.2. The dashed drop is the 1 cm of root tip
removed.

Now work out the rates:

Growth rate = (change in length) ÷ (time taken)

Jar A, day 1 → day 7 = (5.8 cm − 0.25 cm) ÷ 6 days = 5.55 cm ÷ 6 days ≈ 0.93 cm day⁻¹

Jar B, before cutting (day 1 → day 4) = (2.6 cm − 0.25 cm) ÷ 3 days = 2.35 cm ÷ 3 days ≈

0.78 cm day⁻¹

Length removed by the cut = 2.6 cm − 1.6 cm = 1.0 cm (matches the 1 cm cut in step 5)

Jar B, after cutting (day 4 → day 7) = (1.6 cm − 1.6 cm) ÷ 3 days = 0 cm day⁻¹

Inference: a root grows only from its tip. Remove the tip and the whole root stops elongating,
even though the rest of the root is alive and healthy.

Page 5 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Why it happens: the tip holds the root apical meristem — small cells with thin
walls, dense cytoplasm, a large nucleus and no vacuole, which divide continuously.
You saw these very cells in mitosis in an onion root tip in Chapter 2. Cutting the tip
removes the only dividing cells; the cells left behind have already differentiated into
permanent tissue and cannot divide. The shoot tip has the same kind of meristem,
which is why a plant also grows in height from its tip.

Check it yourself: Jar A is the control. Everything — same water, same light, same
bulbs — is kept identical, and only the tip is cut in Jar B. That is what lets you say the
tip, and nothing else, caused the difference.

In-text Questions — Page 30
3.2.2 Lateral meristem — How do plants grow in girth?

Q1 What causes this increase in girth?

A ring of actively dividing cells inside the stem — the lateral meristem.
These cells are arranged in a cylinder running along the length of the stem. When they divide,
the new cells are added inside and outside the ring in a concentric manner, so the stem
thickens from within while keeping its round shape.

Why it shows up as rings: the meristem divides fast in a favourable year (plenty of
water, warmth) and slowly in an unfavourable one. Fast growth gives a wide band of
large, thin-walled cells; slow growth gives a narrow band of small, thick-walled cells.
One wide band + one narrow band = one annual growth ring (Fig. 3.4). Counting
the rings gives the age of the tree, and their widths are a record of the climate the
tree lived through.

Did you know? This is why dicot stems get thicker every year but a grass or a palm
stem does not — they have no lateral meristem.

In-text Questions — Page 31

Page 6 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

3.2.3 Intercalary meristem; characteristics of meristematic tissue

Q1 What do you think happens to the growth of the plant if the tip of a young stem is
cut?

The stem stops growing in length, but the plant does not stop growing — new branches come
out from the nodes (Fig. 3.5).
Read it as two separate meristems being affected differently:

The shoot apical meristem is at the tip. Cut it off and there is nothing left to add cells to the
top, so height stops increasing.
The intercalary meristem, at the base of the internode just above the node, is untouched. It
goes on dividing, so lateral buds at the nodes sprout into new branches.

Why gardeners use this: when a hedge is trimmed, every cut shoot loses its apex
and pushes out several side branches instead of one long one. Many branches close
together is exactly what makes a hedge look bushy. Grass behaves the same way
after mowing or grazing (Fig. 3.6): its intercalary meristem sits low down at the
nodes, below the level of a grazing animal's mouth, so the blade regrows from the
base.

Try This: pinch off the growing tip of a tulsi or coriander plant at home and watch
for a week. You will get a shorter, bushier plant with more leaves — the same trick,
called pinching or pruning.

Q2 Why do you think that the cell of meristematic tissues lack vacuoles?

Because a large vacuole would take up the space and the resources that a rapidly dividing cell
needs for dividing.

A big central vacuole is mostly water; it pushes the cytoplasm into a thin layer against the
wall. A meristematic cell instead keeps its cytoplasm dense and full of organelles —
ribosomes, mitochondria, ER — because it must constantly build new proteins, new
membranes and new cell walls.
Division needs energy. The mitochondria supplying that energy must sit in cytoplasm, not be
squeezed out by a vacuole.
A vacuole makes a cell large. Meristematic cells stay small, so the nucleus is large relative to
the cytoplasm and can control the cell easily through repeated divisions.

Page 7 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Why it happens: a vacuole is a storage and support structure — useful in a
permanent cell that has finished dividing and now stores food or keeps the cell
turgid. Vacuoles therefore appear later, when a meristematic cell differentiates into
parenchyma. Being vacuole-free is not an accident; it is part of the same package as
thin walls, dense cytoplasm, a large nucleus and no intercellular space — all of it
built for continuous, rapid division.

In-text Questions — Page 32
3.2.4 Permanent tissues; protective and supporting tissues

Q1 What do you observe? Are all the cells similar in shape and size? How many
different types of tissues can you identify? What differences do you notice among
them? What might be the reason for the presence of different types of cells and
tissues?

No — in the T.S. of the sunflower stem (Fig. 3.7) the cells are clearly not all alike, and you can
pick out several distinct tissues arranged in a definite order from outside inwards.

MOVING INWARDS WHAT THE CELLS LOOK LIKE WHAT IT IS DOING

Cuticle + epidermis (with epidermal One layer of flat, rectangular, Protection; checks water
hair) tightly packed cells under a waxy loss
film

Collenchyma Living cells, corners thickened Flexible support just under
the skin

Parenchyma / ground tissue Large, thin-walled, loosely packed Storage, photosynthesis,
with air spaces packing

Sclerenchyma cap Small cells with very thick, Hard mechanical strength
lignified walls; mostly dead

Vascular bundle — phloem outside, Phloem: living sieve tubes. Xylem: Food transport, girth
lateral meristem in the middle, xylem wide, thick-walled dead tubes growth, water transport
inside

The reason: one cell shape cannot do five jobs. A cell that conducts water must be hollow and
dead; a cell that stores food must be alive and roomy; a cell that gives strength must be thick-
walled. So the stem is built as a set of specialised tissues, each with the shape its job requires —
division of labour once again.

Page 8 of 63

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Class 9 Science Chapter 3 Tissues in Action
a g l AglaSem · NCERT Solutions

co m
m.
Tip: permanent tissues are of two kinds — simple (one cell type: parenchyma,

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com phloem). l
collenchyma, sclerenchyma) and complex (more than one cell type working
together:.xylem, a g
a s em
agl

co m
ag
What protects plants from mechanical injury, water loss, harmful microorganisms
.
Q2

e m
as
and extreme environmental conditions?

a g l

The epidermis — the single, outermost layer of flat, rectangular, tightly packed cells that covers
co m
every part of the plant body — together with the waxy cuticle of cutin laid over it.
e m.
c o m g l as
. a
s em
THREAT
a
HOW THE EPIDERMIS DEALS WITH IT

aglMechanical injury Cells are tightly packed with no gaps, and the cuticle forms a tough outer film

m a s
.co agl
Water loss Cutin is waxy and waterproof; in dry habitats the cuticle is laid down thicker still

se m
l a
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Microbes and An unbroken layer with no intercellular spaces gives no entry route; the cuticle
parasites resists invasion

Extreme conditions
co m
Epidermal hair traps a still layer of air and reduces heating and drying

m .
o m l a se
.c g
The epidermis is not only a barrier — it is also modified for two jobs the plant cannot do

m a
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without:

g l a
a In the root, epidermal cells grow out as root hair, which greatly increase the surface area for
absorbing water and minerals from the soil.
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com
In the leaf, the epidermis carries pores called stomata, through which gases are exchanged
g l a
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ase
and water vapour escapes as transpiration.

agl
Why transpiration is useful, not just a leak: water evaporating from the leaf
creates a transpiration pull in the xylem, and this pull is what lifts water all the way
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up a tall tree. Transpiration also helps the plant get rid of wastes.
m l as
m .co a g
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ag
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Q3 What keeps a plant upright? Why does a fresh twig bend but a dry twig break? Why
are seed coats hard and how do aquatic plants float?
s e m
m a
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l a se
ag by the three simple permanent tissues — parenchyma,
All four questions are answered
collenchyma and sclerenchyma — and by which of them is present where.

co m
m .
m as e
.co


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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

OBSERVATION TISSUE RESPONSIBLE THE STRUCTURAL REASON

A plant stands Sclerenchyma (plus turgid Lignin makes the walls rigid, so the stem resists
upright parenchyma in soft herbs) bending under its own weight

A fresh twig bends Collenchyma Living cells with pectin-thickened corners —
pectin behaves like rubber, so the wall gives and
springs back

A dry twig snaps Sclerenchyma The cells are dead and lignified; with the water
gone there is no give at all, so the wall cracks
instead of bending

Seed coats are hard Sclerenchyma Layers of dead, thick-walled lignified cells — the
same tissue as in coconut husk and walnut shell

Aquatic plants float Specialised parenchyma Large air-filled spaces between the loosely
packed cells lower the average density of the
plant below that of water

Why the difference between bending and breaking matters: a young stem in a
storm must deform and recover — that is a job for collenchyma, which is strong but
flexible. An old trunk must not deform at all — that is a job for sclerenchyma, which
is strong but brittle. Plants use both, in different places and at different ages.

In-text Questions — Page 33
(iii) Conducting tissues — Complex permanent tissues

Q1 How does water reach the leaves of tall trees? How does food prepared in leaves
reach other parts of the plant?

Water goes up through the xylem; food comes out of the leaves through the phloem. Both are
complex permanent tissues, made of more than one type of cell working together.

Page 10 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

XYLEM PHLOEM

Cells Tracheids, vessels, xylem fibres, xylem Sieve tubes, companion cells, phloem
present parenchyma parenchyma, phloem fibres

Living or Mostly dead and sclerenchymatous; xylem Mostly living
dead parenchyma is the only living component

Carries Water and minerals, root → rest of the plant Food, leaves → rest of the plant

Also does Gives strength to the plant Phloem parenchyma stores food,
resin, tannins and latex

Water upwards. Tracheids and vessels are tubular and thick-walled, and being dead they are
hollow — an unbroken pipe from root to leaf. Water evaporates from the leaf through the
stomata (transpiration); this pulls on the continuous column of water in the xylem, and the
whole column is dragged upwards. The thick lignified walls stop the tube from collapsing under
that pull.
Food outwards. Sieve tube cells are long and tubular, joined end to end by perforated walls so
that the contents of one flow into the next. Each sieve tube is looked after by a companion cell,
a specialised parenchyma cell whose main job is to monitor the loading and unloading of sugars
into and out of the sieve tube. Phloem fibres, being sclerenchymatous, hold the soft sieve tubes
in place.

Why xylem can afford to be dead but phloem cannot: water moves down a pull
created outside the tissue, so xylem only has to be an open, strong pipe — no living
machinery needed. Food, however, has to be actively pushed in at the leaf and taken
out at the root or fruit, and that costs energy. Only a living cell can spend energy, so
phloem stays alive.

Pause and Ponder — Page 33
Simple permanent tissues

PAUSE AND PONDER

Q1 You may have noticed that fibres of coconut husk are hard and brittle, whereas the
leaf stalks of coriander are soft and flexible. Find out the reason.

Different tissues: the coconut husk is sclerenchyma, the coriander leaf stalk is collenchyma (with
parenchyma).

Page 11 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

COCONUT HUSK FIBRE CORIANDER LEAF STALK

Tissue Sclerenchyma Collenchyma + parenchyma

Wall Uniformly thick, heavily deposited with lignin Thin, thickened only at the corners with
pectin

Living? Mostly dead at maturity Living, with cytoplasm and a vacuole

Behaviour Hard, strong, brittle — resists a pull but snaps Soft, flexible — bends and springs back
if bent far

Why the chemistry decides the feel: lignin is a rigid, waterproof polymer that locks
the cellulose fibres of the wall in place. Once it is deposited, the wall cannot stretch,
so the cell dies and the fibre becomes stiff and brittle. Pectin, in contrast, is soft and
gel-like — the book compares it to rubber — so a collenchyma wall can deform and
recover. Deposit lignin and you get a coir mat; deposit pectin and you get a stalk that
bends in the wind.

Did you know? This is exactly why coir is used for ropes, mats and mattress filling —
it is dead, lignified, rot-resistant and holds its shape, while a coriander stalk wilts
within hours of being plucked because its support depended on living, turgid cells.

Pause and Ponder — Page 34
Epidermis, xylem and stomata

PAUSE AND PONDER

Q2 Why do you think that a thick cuticle on the outer wall of epidermis is
advantageous for a plant living in the desert but disadvantageous for a plant living
underwater?

Because the cuticle blocks the movement of water and gases — and a desert plant needs that
block, while a submerged plant is killed by it.
In the desert. Water is the limiting factor. A thick waxy cuticle:

cuts down evaporation from the epidermal surface, so transpiration is restricted almost
entirely to the stomata, which the plant can close;
reflects some sunlight and reduces heating;
protects against abrasion by blowing sand and against parasites.

Page 12 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Underwater. Water is never in short supply, so there is nothing to conserve — and the cuticle
now only does harm:

A submerged plant absorbs water, minerals, dissolved CO₂ and O₂ directly through its
whole surface, because there is no transpiration pull to drive a root-to-leaf stream. A
waterproof cuticle would seal off that entire absorbing surface.
Gases diffuse about 10 000 times more slowly in water than in air, so the plant is already
short of CO₂ and O₂. Adding a diffusion barrier would starve it further.

Why it happens: a structure is never good or bad on its own — it is good only for a
particular environment. The cuticle costs the plant its gas and water exchange
across the surface and buys it water conservation. In the desert that trade is worth
making; underwater the plant pays the cost and gains nothing. That is why
submerged leaves have a very thin cuticle or none at all, and usually no stomata
either.

Q3 Once water is absorbed by plant roots, it has to travel against gravity through
xylem. How do the ‘dead’ cells of the xylem work together with the living cells of
leaves at the top to keep the water moving?

The dead cells supply the pipe; the living cells of the leaf supply the pull. Neither works without
the other.

Page 13 of 63

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Class 9 Science Chapter 3 Tissues in Action
a g l AglaSem · NCERT Solutions

co m
se m.
m l a
Water vapour
m .co out ofag
se Leaf (living cells) stomata
g l a
a = transpiration

co m
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g l as
a Xylem: dead,
hollow, lignified
. c om
tubes — no cross em
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Unbroken
glaa
walls, no cytoplasm
a s emwater column
agl pulled upward

m a s
m .co agl
l a se
g
a Root hair

. com
m a s em to the root.
.co agl
The living leaf pulls; the dead xylem is the pipe that carries the pull down

a s emby step:
gl
Step
a
m
1. In the leaf, living mesophyll cells lose water vapour through the stomata — transpiration.

a se
com g l
2. Losing water makes those cells draw water from the nearest xylem vessel.

m . a
s e
3. Water molecules stick to one another (cohesion), so the column of water in the xylem does
not break. Pulling at the topla
g
therefore pulls the whole column.
a
4. This tension — the transpiration pull — is transmitted right down to the root, where water

m
enters through the root hair and replaces what was lost.

. co
se m
Why the tube must be dead: tracheids and vessels lose their cytoplasm and their end walls at

o m l a
g tends to collapse the tube
.cthick and lignified, which is essential — a column under tension
maturity, so a vessel is a continuous open pipe with nothing inside to obstruct flow. Their walls
m a
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are
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inwards, and only a stiff lignified wall can resist that.

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m ase
.co


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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

The key idea: the energy for lifting water does not come from the plant at all — it
comes from the Sun, which evaporates water at the leaf. The plant simply provides a
strong, unbroken pipe and a wet surface at the top. That is why water can be lifted
tens of metres up a tall tree with no pump anywhere in the system.

Q4 What do you think will happen if there were no stomata in the epidermis of the
stem or leaves?

The plant would seal itself in: gas exchange would nearly stop, transpiration would stop, and
with it the upward pull that carries water and minerals to the leaves.

PROCESS WHAT GOES WRONG WITHOUT CONSEQUENCE
STOMATA

Photosynthesis CO₂ cannot get in through the waxy Food production falls sharply; the plant
cuticle starves

Respiration O₂ cannot enter, CO₂ cannot leave Cells cannot release energy efficiently

Transpiration No water vapour escapes No transpiration pull — the xylem column is
not dragged upwards

Mineral Water no longer streams from root to Minerals dissolved in that stream never
supply leaf reach the leaves

Temperature No evaporative cooling from the leaf Leaves overheat in the sun and enzymes are
surface damaged

Waste removal Wastes normally eliminated with Wastes accumulate in the plant body
transpired water stay behind

Why plants keep stomata even though they lose water through them: a stoma
is a controlled hole. Every gain the plant makes — CO₂ in, cooling, the transpiration
pull — depends on that hole being open, and every gram of water lost is the price.
The plant manages the trade-off by opening and closing the stomata, which is far
better than not having them at all. A plant with no stomata is like a house with no
doors or windows: nothing enters, nothing leaves, nothing works.

Page 15 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Did you know? Some desert plants come close to this: they keep their stomata shut
all day and open them only at night, when the air is cool and moist, so that they lose
the least water for the CO₂ they take in.

In-text Questions — Page 34
3.3 Animal Tissues

Q1 Now think, which tissue helps you move? Which tissue enables you to sense heat or
cold? Which tissue allows oxygen to enter the blood? Which tissue holds the body
together so that the skin does not fall off?

Four different questions, four different animal tissues — and in every case the structure of the
tissue is the answer.

ACTION TISSUE WHY THAT STRUCTURE WORKS

Clench and open Muscular Long cylindrical muscle fibres lie parallel and can contract; skeletal
your fist tissue muscle is attached to bone by tendons, so its pull becomes
movement at a joint

Touch something Nervous Receptors in the skin pass the signal to a neuron; the dendrites
warm or cold tissue receive it and the long axon carries it to the brain within
milliseconds

Take a deep breath Epithelial The lining of the lung and of a blood vessel is a single layer of thin,
tissue flat cells, so the diffusion path for O₂ into the blood is as short as it
can be

Skin stays Connective Cells embedded in a matrix bind skin to the tissues beneath; the
attached tissue same family of tissues also joins muscle to bone (tendon) and bone
to bone (ligament)

Blinking your eyes uses all four at once — nervous tissue triggers it, muscular tissue moves the
eyelid, epithelium covers it, connective tissue holds it in place.

Why animals need four kinds: an animal body has to cover surfaces, hold parts
together, move, and coordinate. No single tissue design can do all four, so animal
tissues fall into exactly these four groups — epithelial, connective, muscular and
nervous.

Page 16 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Activity 3.2: Let us understand further — Page 36
3.3.2 How are various parts connected in our body?

ACTIVITY

Q1 Recall everyday experiences given in the first column of Table 3.3. Write your
observations and questions in your notebook. Compare your observations with the
observations given in Table 3.3.
Table 3.3: Your experiences, observations and questions from daily life

EXPERIENCES OBSERVATIONS QUESTIONS

When you get a small cut Red blood oozes out from the cut. A clot What causes blood
on your skin is formed after some time. to clot?

When you get a skin The area turns red and perhaps slightly
infection swollen. You may have a fever.

When you exercise or run You breathe faster. Your face may turn
red.

Here is the completed Table 3.3, with the observations the book gives and the questions each
one should make you ask.

EXPERIENCE OBSERVATION QUESTION IT RAISES

When you get a small Red blood oozes out from the cut. A What causes blood to clot?
cut on your skin clot is formed after some time.

When you get a skin The area turns red and perhaps What makes the infected area red and
infection slightly swollen. You may have a swollen — which blood cells collect there?
fever.

When you exercise or You breathe faster. Your face may Why does the body need more oxygen
run turn red. during exercise, and how does blood
deliver it faster?

All three experiences point to the same tissue: blood, a connective tissue in which cells float in a
fluid matrix called plasma.

Page 17 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

COMPONENT SHARE OF JOB
BLOOD

Plasma 55% of total Fluid matrix — carries cells, nutrients,
volume hormones and wastes

Formed elements — RBCs, WBCs, 45% of total Oxygen transport, defence, clotting
platelets volume

For an adult with about 5 L of blood:

Volume of plasma = 55% of 5 L = (55 ÷ 100) × 5 L = 2.75 L

Volume of formed elements = 45% of 5 L = (45 ÷ 100) × 5 L = 2.25 L

Why blood counts as a connective tissue: a connective tissue is defined by its
matrix — cells scattered in a non-living ground substance. In bone that matrix is
hard and rigid because calcium and phosphorus compounds are deposited in it; in
blood it is watery and jelly-like. Same design, completely different consistency, and
therefore completely different jobs.

Q2 What causes blood to clot?

Platelets — the smallest of the formed elements — collect at the site of the injury and start the
clot that seals it.
What happens at a cut, in order:

1. The vessel wall is torn and blood escapes.
2. Platelets reach the injured spot and stick to the torn edges and to one another, forming a
temporary plug.
3. They set off the chemical reactions of clotting, which lay down a mesh of fibres across the
wound.
4. Blood cells are trapped in that mesh; the mass hardens and bleeding stops.

Page 18 of 63

as e
Class 9 Science Chapter 3 Tissues in Action
a g l AglaSem · NCERT Solutions

co m
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Why the other observations follow the same logic:

m as e
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Redness of blood — haemoglobin, an iron-rich protein inside the RBCs. RBCs live
a l
a s em
for about 4 months and are replaced regularly.

a gl Redness and swelling of an infected patch, and pus — WBCs collect at the
infected area to fight the microbes, causing inflammation and pus formation.

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Faster breathing and a flushed face while running — the muscles need more
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Did you know? An RBC lasting about 4 months means roughly 120 days of service,
em.
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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Connective tissues

ACTIVITY

Q1 Perform the actions given in Table 3.4. Record your experiences and compare them
with the experiences given in Table 3.4. Study their functions and identify the
connective tissues (Fig. 3.12).
Table 3.4: Connective tissues

ACTION EXPERIENCE FUNCTION IDENTIFIED
CONNECTIVE
TISSUE

Touch your elbow A hard and rigid structure
gently

Press and fold your A soft and flexible
ear, or gently press structure that retains its
your nose and stop shape again

Touch your forearm Movement is felt in the
muscles and wiggle forearm even though the
your fingers fingers are far away

Sit on a chair and The joint does not go
move your leg upwards beyond a limit
till your knee allows

Plasma WBC
Collar bone
(55% of total
volume)
Platelets
Tendon
Formed elements
(45% of total
volume) Cartilage
RBCs

Long bone
Ligament

Kneecap

(a) Components of blood (b) Types of bones (c) Arrangement of tissues at a joint

Fig. 3.12, page 36 — redrawn sketch of the book’s illustration: (a) components of blood,
(b) types of bones, (c) arrangement of tissues at a joint.

Page 20 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Here is Table 3.4 completed. Each action lets you feel one connective tissue through your own
skin.

ACTION EXPERIENCE FUNCTION CONNECTIVE
TISSUE

Touch your elbow A hard and rigid structure Gives strength, support and Bone
gently protection

Press and fold your A soft and flexible Provides flexibility and Cartilage
ear, or gently press structure that retains its cushions the ends of bones
your nose and stop shape again for shock absorption

Touch your forearm Movement is felt in the Connects muscle to bone, Tendon
muscles and wiggle forearm even though the and thus brings about
your fingers fingers are far away movement

Sit on a chair and The joint does not go Connects bone to bone, Ligament
move your leg beyond a limit provides stability, limits
upwards till your movement and helps prevent
knee allows dislocation

Reading the results. The difference you feel between the elbow and the ear is a difference in
the matrix:

Bone matrix: rigid, containing calcium and phosphorus compounds → hard, strong,

protective

Cartilage matrix: soft and jelly-like → flexible, springs back, absorbs shock

Why you feel your forearm move when you wiggle a finger: the muscles that
move your fingers are not in your hand at all — they lie in the forearm, and they act
on the finger bones through long tendons that run across the wrist. The tendon is
tough, rope-like connective tissue: when the forearm muscle contracts, the tendon
transmits that force all the way to the finger. Putting the bulky muscle in the forearm
keeps the hand slim and precise.

Why your knee stops at a limit: ligaments join bone to bone across the joint. They
are strong but only slightly stretchable, so they allow the joint its normal range and
then hold — preventing the bones from being pulled out of place (dislocation).

Page 21 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Tip: remember it as tendon = muscle to bone, ligament = links bone to bone.

In-text Questions — Page 37
3.3.3 Can we control movement in our body?

Q1 Are there involuntary movements in the body?

Yes — a great many. Movement of food along the intestine and the beating of the heart go on
without any conscious control at all.

SKELETAL MUSCLE SMOOTH MUSCLE CARDIAC MUSCLE

Control Voluntary Involuntary Involuntary

Shape of Long, cylindrical, unbranched Spindle-shaped Cylindrical and branched
cell

Nuclei Many (multinucleate) One One

Striations Striated — clear light and Absent Faint
dark bands

Where Attached to the skeleton Stomach, intestine and Only in the heart
other organs

Typical Running, writing, lifting — Slow, continuous Tireless, rhythmic beating
work strong, fast, tires quickly movements such as for a whole lifetime
digestion

Why the heart never tires: cardiac muscle cells are branched and joined end to
end, so a wave of contraction spreads through the whole heart as one unit. They
also carry a very large number of mitochondria and receive an abundant blood
supply, so ATP is produced as fast as it is used and no oxygen debt builds up.
Skeletal muscle, by contrast, can outrun its oxygen supply — which is why your legs
ache after a sprint but your heart does not.

Page 22 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Tip: muscles never act on their own. Voluntary and involuntary muscles alike take
their instructions from nervous tissue — during exercise the brain signals the heart
to beat faster to meet the body's higher oxygen demand.

Activity 3.4: Let us investigate — Page 39
3.4 The Musculoskeletal System

ACTIVITY

Q1 What percentage of total body weight comes from bones and muscles?

Bones make up about 12 – 15 per cent of an adult's body weight; muscle makes up about 40 –
50 per cent in adult males and about 30 – 40 per cent in adult females. Together, well over half
your weight is musculoskeletal.
Worked example for a student weighing 50 kg (use your own reading from the weighing scale
in step 1):

Weight of a part = total body weight × (percentage ÷ 100)

Bone (12 – 15%): lower estimate = 50 kg × 12/100 = 6.0 kg

upper estimate = 50 kg × 15/100 = 7.5 kg

Muscle, adult male (40 – 50%) = 50 kg × 40/100 to 50 kg × 50/100 = 20 kg to 25 kg

Muscle, adult female (30 – 40%) = 50 kg × 30/100 to 50 kg × 40/100 = 15 kg to 20 kg

Bone + muscle (male figures) = 6.0 kg + 20 kg = 26 kg to 7.5 kg + 25 kg = 32.5 kg

As a fraction of body weight = 26 ÷ 50 = 0.52 to 32.5 ÷ 50 = 0.65, i.e. 52% – 65% of total

body weight

Page 23 of 63

as e
Class 9 Science Chapter 3 Tissues in Action
a g l AglaSem · NCERT Solutions

co m
m.
Check it yourself: to get the class average, add every student's estimated bone

m
weight and divide by the number of students —
o l a se
g of students).
.c bone weight = (sum of all bone weights in kg) ÷ (number
a
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class average
se same for muscle.
Doathe
l
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Why the answer is a range and not a single number: the percentages are
.
m depends on age, gender, body
s e
averages for a population. Your own value

a g
composition and even ethnicity, sola the honest answer is an interval, not one figure.
That is also why step 2 asks you to look up values for an Indian body type rather
than use a number from anywhere in the world.
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Discuss why do bone and muscle mass differ between individuals, and how do they
g
Q2
a contribute to the overall body weight?

m a s
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a s em
gl on the person:
Why they differ. Bone and muscle are living tissues that are constantly being built up and
broken down, and the balance a
depends

m
Age — bone mass builds up through childhood and adolescence, peaks in early adulthood,

. co
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and slowly declines later.

o m l a se
Gender — adult males on average carry more muscle (40 – 50%) than adult females (30 –
.c a g
m
se Physical activity — muscles and bones respond to load. A kabaddi player or a farmer who
40%).

a
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Nutrition — protein is needed to build muscle; calcium, phosphorus and vitamin D are
se m
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.
needed for the bone matrix. A poor diet lowers both.
m a
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agl
Body size and composition — a taller, heavier frame carries a bigger skeleton; a person
with more fat has a lower percentage of muscle even at the same weight.
Health — illness, immobility and hormonal changes reduce both.

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How they contribute to body weight. Bone is dense because its matrix is loaded with calcium

m a s
and phosphorus compounds; muscle is bulky because it is the largestemsingle tissue in the body.
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Bone (12 – 15%) + muscle (30 – 50%) = roughly 42% to 65% of total body weight
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The rest is fat, skin, blood, organs and body fluids.
m .
as e
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com
m .
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.co


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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Why this matters: a change in weight is not the same thing as a change in health.
Two students of the same weight can have very different amounts of muscle and
bone. Regular exercise, correct posture, proper nutrition and yoga increase the
muscle and bone share — which keeps bones strong, joints flexible and the body
protected from stiffness — even if the reading on the weighing scale hardly moves.

Activity 3.5: Let us observe — Page 39
3.4.1 The musculoskeletal system in action

ACTIVITY

Q1 Move different parts of your body and observe what movement(s) it can make.

Here is Table 3.5 filled in. The book gives the elbow row (No, No, Yes) as your model; the rest
follow from the type of joint at each place.

Page 25 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

BODY COMPLETE PARTIAL BENDING TURNING, SIDE- JOINT
PART ROTATION ROTATION RAISING, UP-
DOWN OR ANY
OTHER MOVEMENT

Elbow No No Yes Only bending and Hinge
straightening, in one
plane

Shoulder Yes Yes Yes Forward, backward, Ball and
sideways and circular socket

Knee No No Yes Bending and Hinge
straightening only;
kneecap protects it

Neck No Yes Yes Side-to-side turning Pivot
(‘no’), nodding up and
down

Fingers No No Yes Bending at each joint; Hinge
the thumb base also
swings

Toes No No Yes Bending up and down Hinge
(that is what you feel
in the tendon at the
heel)

Wrist No Yes Yes Up-down, side-to-side Gliding joint
and a small circling between
movement many small
bones

Why the answers are not all the same: the movement a part can make is decided
by the shape of the bone ends at the joint. A rounded head sitting in a shallow
socket (shoulder) can swing in every direction. A cylinder held in a curved notch
(elbow, knee) can only swing in one plane, like a door on its hinge. A peg turning in a
ring (neck) can only rotate. Bones fused edge to edge (skull) cannot move at all.
Structure fixes function here just as it does in a tissue.

Tip: a joint by itself cannot move anything. Muscles pull on the bones through
tendons; the joint only decides which way that pull is allowed to move the bone.

Page 26 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

In-text Questions — Page 39
3.4.1 The musculoskeletal system in action

Q1 You may have noticed that some parts of our body can move easily in many
directions, while others move only in a single direction. Why does this happen?

Because the type of joint is different at different places, and a joint is simply the junction
between two or more bones shaped in a particular way.

JOINT HOW THE BONES FIT MOVEMENT ALLOWED EXAMPLE

Ball and Rounded top of one bone sits in a Forward, backward, Shoulder, hip
socket shallow hollow of the other sideways and circular

Hinge Bone ends shaped so they swing Bending and Elbow, knee (protected
in one plane only, like a door straightening in one by the kneecap)
hinge direction

Pivot One bone turns within a ring Rotation — side to side, Skull on the backbone
formed by another like a doorknob (neck)

Fixed Flat bones joined edge to edge None Bones of the skull

Why the body does not simply use ball-and-socket joints everywhere: freedom
of movement is bought at the cost of stability. A shoulder can swing anywhere, and
it is also the joint most easily dislocated. A knee has to carry your whole body
weight, so it is built to move in one plane and to refuse every other direction — the
ligaments see to that. And where nothing must move at all, as around the brain, the
joints are fixed so the skull stays a rigid protective case even while you run and
jump.

Q2 So, what actually causes the bones to move?

The muscles do — by contracting and pulling the bones through tendons. Joints only permit
movement; they cannot produce it.
The chain of events, in order:

Page 27 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

1. The nervous system sends an impulse to the muscle. (The musculoskeletal system works
under the control of the nervous system.)
2. The muscle contracts — it gets shorter and thicker.
3. The tendon, a tough flexible band joining the muscle to the bone, transmits that pulling
force to the bone.
4. The bone turns about the joint, and the joint decides the direction and the limit of that turn.
5. The ligaments holding bone to bone stop the movement going past a safe limit; the
cartilage at the bone ends cushions the contact.

Why muscles can only pull, never push: a muscle produces force only by
shortening. So to bend a joint one way and straighten it back, the body needs
muscles on both sides of the bone that pull in turn — one contracts while the other
relaxes. That is why muscles are almost always arranged in pairs across a joint.

Pause and Ponder — Page 40
3.5 Types of Joints

PAUSE AND PONDER

Q5 Look at the picture given below (Fig. 3.17). Carefully observe the various poses of
classical and folk dances of India. Can you identify which joints are involved? Also,
what type of movement each joint allows?

1 2 3 4 5 6 7 8 9

Fig. 3.17, page 40 — redrawn sketch of the nine dance poses printed in the book; the
original is a colour illustration of classical and folk dancers.

Almost every joint in the body appears somewhere in Fig. 3.17. Look at what each dancer is
doing and name the joint by the movement, not by the pose.

Page 28 of 63

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Class 9 Science Chapter 3 Tissues in Action
a g l AglaSem · NCERT Solutions

co m
m.
WHAT YOU CAN SEE IN JOINT TYPE MOVEMENT IT ALLOWS

as e
com
THE POSES INVOLVED

. a g l
e m
asout sideways, circled
Arms raised above the head, Shoulder Ball and Forward, backward, sideways and

a g l
swung socket circular movement of the whole arm

One leg lifted to the side and Hip Ball and Free movement of the thigh in all
m
.co ag
swung out (as in the first and socket directions

sem
second poses)

a
Elbow bent sharply to hold a Elbow agl Hinge Bending and straightening the forearm
mudra near the shoulder in one plane

co m
e m.
Deep araimandi knee bend, Knee Hinge Bending and straightening the leg; the

m l as
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kneecap protects the joint
g
weight on a bent knee

em a
a s
gltoes pointed, heel struck on the
Standing on the ball of the foot, Ankle and toe Hinge Up-and-down movement of the foot; the

a floor joints tendon at the heel transmits the pull

m a s
Skull on the

em
.co Pivot Rotation of the head, side to side like a
agl
Head turned side to side, the
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classic greeva movement

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Fingers held in precise mudras Finger joints Hinge Bending of each finger segment; the

m
muscles are in the forearm and pull
through long tendons
. co
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Skull itself, holding its shape Bones of the Fixed No movement — the brain, eyes and

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through jump skull ears stay

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Why classical dance is such a good demonstration: a dance pose holds a joint at
se m
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.
the extreme of its range, so the limit set by the joint's shape becomes obvious. The
m a
ase
arm can be raised straight overhead — a ball and socket allows that. The knee

a gl
cannot bend backwards no matter how the dancer moves — a hinge forbids it. And
nothing is possible without muscles pulling on bones through tendons while
ligaments keep the bones in place.
co m
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o m l a se
ag list the joints you are
.cTry This: stand in one of the poses and, without moving,
m holding bent. Then try the same pose with your knees locked straight — you will find
l a se
ag
.c
you cannot balance, because the small adjustments of the ankle and knee are what
keep you upright.
s e m
m a
e m . co agl
g l as
Think as a Scientist — Page 42
a

co m
m .
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.co


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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

From one cell to an organism: Totipotency

THINK AS A SCIENTIST

Q(a) What do you conclude about the characteristics of phloem cells of carrot?

That a mature carrot phloem cell is totipotent — although it has already differentiated into a
food-conducting cell, it still carries the complete set of instructions to build an entire plant, and
it can be made to use them again.
Steward's 1958 experiment shows this in three steps:

Mature phloem cell → dedifferentiation (regains the ability to divide)

→ divides into an undifferentiated mass of unspecialised cells

→ redifferentiation into root, shoot and finally a complete carrot plant

So the characteristics are: the cell is living (a dead xylem cell could never do this), it has retained
its full nucleus and complete genetic information, and its differentiated state is reversible
given the right nutrients, hormones and conditions.

Why this was so surprising: until then, differentiation looked like a one-way street
— once a cell became a phloem cell, that was the end of the story. Steward showed
the street runs both ways in plants. A single carrot cell can do what a zygote does:
divide and differentiate into an entire organism.

Q(b) In which of the three combinations would you obtain the highest and lowest
biomass? What could be the possible reason(s) for this observation?

Highest biomass: combination 2 — light present, air present, liquid medium + nutrients (20%
increase).
Lowest biomass: combinations 1 and 3, where the fresh weight actually reduced below the
starting weight.

Page 30 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

# LIGHT AIR MEDIUM CHANGE IN WHAT WAS MISSING
FRESH WEIGHT

1 ✓ ✗ Solid + reduced No air — no oxygen for respiration; a
nutrients solid medium also limits contact with
nutrients

2 ✓ ✓ Liquid + 20% increased Nothing — all three factors present
nutrients

3 ✗ ✓ Liquid + reduced No light
nutrients

Now put a number on the growth. The cultures were started from 2-mg fragments (Fig. 3.19):

Increase in fresh weight = initial weight × (percentage increase ÷ 100)

= 2 mg × (20 ÷ 100) = 0.4 mg

Final fresh weight = 2 mg + 0.4 mg = 2.4 mg

For combinations 1 and 3 the change is negative, so the final weight is less than 2 mg.

Reasons. Only combination 2 gives the cells everything at once:

Air supplies oxygen for aerobic respiration. Without it (combination 1) the cells cannot
release enough energy to divide, and they consume their own stored food — so fresh weight
falls.
Light is needed for photosynthesis and also as a signal for growth and greening. Without it
(combination 3) the cells keep respiring but make nothing, so again the stored material is
used up.
A liquid medium surrounds every cell with nutrients and lets the culture be stirred, which is
how single cells shear off into suspension in the first place. A solid medium touches only one
face of the tissue.

Why the weight goes down and not merely stops rising: a living cell must respire
whether or not it is growing. If it cannot take in or make food, it oxidises its own
reserves, and the fresh weight of the culture drops below where it started.

Page 31 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Q(c) Will you get the same results if you culture animal cells instead of carrot cells?

No. Animal cells can be grown in culture, but a differentiated animal cell will not regenerate a
whole animal the way a carrot phloem cell regenerates a whole plant.

CARROT (PLANT) CELLS ANIMAL CELLS

Totipotency of a Retained — can dedifferentiate and Lost in almost all body cells once
mature cell redifferentiate they have differentiated

What grows in An unorganised mass of cells that then Usually only a sheet of the same cell
culture forms root, shoot and a whole plant type — a tissue, not an organism

Cell wall Present; helps the mass hold together Absent; cells depend on attachment
and take shape and on signals from neighbours

Cells that can still Practically any living parenchyma or Only special stem cells, such as
form many types phloem cell those in bone marrow

Why the difference: an animal's body plan is laid down early in development and its
cells then commit permanently to one fate; they also depend on precise positions,
blood supply and signals from surrounding tissues that a dish cannot reproduce. A
plant, being fixed in one place, must be able to repair and replace any part it loses —
so it keeps that flexibility in ordinary body cells all its life.

Did you know? Animal stem cells are the exception that proves the rule. Bone
marrow stem cells can still divide and make new blood cells, which is why they are
transplanted from a healthy donor to patients with leukaemia or thalassaemia.

Q(d) Think and mention any two commercial applications of the study above.

Two clear ones:

1. Micropropagation — mass production of identical, disease-free planting material. A few
grams of tissue from one superior plant can be cultured to raise thousands of plantlets in a
small laboratory space, at any time of year, all genetically identical to the parent. This is how
banana, sugarcane, potato and orchid planting material is produced commercially.

Page 32 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

2. Industrial production of plant chemicals. Cultured cells can be grown in large vessels to
make valuable phytochemicals — medicines, pigments, flavours — without growing,
harvesting and destroying whole plants, and without depending on the season.

Two more worth knowing:

Crop improvement through genetic engineering. Scientists studied how the bacterium
Agrobacterium tumefaciens, which causes crown gall disease, transfers its genetic material
into plant cells. That knowledge, combined with tissue culture, now lets useful genes be
introduced into crops to produce improved and disease-resistant varieties.
Haploid plants from anther culture, the line of work of Sipra Guha Mukherjee and S. C.
Maheshwari, which speeds up the breeding of new varieties.

Why totipotency is the key to all of them: every one of these applications depends
on the same single fact — that a mature plant cell can be persuaded to become a
whole plant again. Without that, a cultured cell would only ever give you more cells
of the same kind.

Revise, Reflect, Refine — Page 44
End-of-chapter questions

REVISE, REFLECT, REFINE

Q1 Meristematic tissues divide repeatedly. What property of their cells allows them to
do this? (i) They have thick walls for protection. (ii) They contain large vacuoles that
store nutrients. (iii) They have thin walls, dense cytoplasm and large prominent
nucleus. (iv) They are functionally differentiated cells.

(iii) They have thin walls, dense cytoplasm and large prominent nucleus.

Page 33 of 63

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Class 9 Science Chapter 3 Tissues in Action
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co m
m.
Why this is the right set: each feature is directly useful for division —

m as e
.co g l
Thin walls — the wall can be stretched and a new wall laid down quickly between
a
a s em
the daughter cells. A thick lignified wall would make that impossible.

a gl Dense cytoplasm with many organelles — ribosomes to make protein,
mitochondria to supply the energy, ER and Golgi to build new membranes and
wall material.
. c om ag
Large prominent nucleus — the DNA
s e m has to be copied before every division, and
a control the cell efficiently.
a large nucleus in a small cell lcan
ag
Add to these: vacuoles absent and the cells tightly packed with little or no
intercellular space.
co m
se m.
o m l a
g is dead and cannot
m .c are wrong: (i) thick walls belong to sclerenchyma, which
Why the others
a
l a se (ii) large vacuoles are a feature of mature parenchyma; they would push the cytoplasm
divide.

agaside. (iv) a cell that has already differentiated has lost the power to divide — that is what
differentiation means.
m a s
em
.co agl
a s
Q2 agl food from leaves to roots which tissue is
If a plant is unable to transport
malfunctioning? (i) Xylem (ii) Phloem (iii) Epidermis (iv) Sclerenchyma

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m
(ii) Phloem.

l a se is made in the leaves and has to travel downwards to the roots, which cannot
g
Food
a photosynthesise. That job belongs to the sieve tubes of the phloem, helped by companion cells
that load and unload the sugars.
se m
com g l a
m . a
ase
agl
Why not the others: xylem carries water and minerals upwards from the root, not
food downwards. The epidermis is a protective covering. Sclerenchyma is dead,
thick-walled supporting tissue and conducts nothing.

co m
m .
o m l a se
.ceverywhere, food. Question 8 in this set (the debarkedagtree) is the same idea seen
Tip: remember the direction — xylem: root → leaf, water. Phloem: leaf →

se m
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a
from the outside.

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g l as
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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Q3 Why are the epithelial tissues that line an animal’s internal organs usually only one
or a few cells thick? (i) To store food efficiently. (ii) To provide maximum strength.
(iii) To allow quick exchange of materials across them. (iv) To reduce friction.

(iii) To allow quick exchange of materials across them.

Why thinness matters so much: substances cross an epithelium by diffusion, and
the rate of diffusion falls as the distance to be crossed increases. A single layer of
thin, flat cells gives the shortest possible path, so oxygen from the air in the lungs
reaches the blood almost instantly, and digested food crosses the intestinal lining
quickly. Table 3.2 makes the link exactly: the exchange epithelium of blood vessels
and lungs is a single layer of thin, flat cells.

Why the others are wrong: storing food is not an epithelial job. Where strength is needed the
epithelium is not thin at all — the skin, mouth and oesophagus have many layers of tightly
packed cells (Table 3.2), which is precisely why they cannot be used for exchange. Reducing
friction is done by secretions such as mucus, not by being thin.

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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Q4 You can perform these two jumps (Fig. 3.21): Straight-leg jump — keep knees and
ankles stiff. Normal jump — bend knees and ankles naturally. How did your ankle,
knee and hip positions differ between the two jumps?

(a) (b)
Fig. 3.21, page 44 — redrawn sketch of the two starting positions shown in the book.

In the normal jump all three joints bend deeply before take-off and bend again on landing; in
the straight-leg jump they stay almost locked, and you jump much lower and land with a jolt.

JOINT STRAIGHT-LEG JUMP NORMAL JUMP

Ankle Held stiff; almost no bending, only a Bends and then straightens forcefully, pushing
small push from the toes the foot down against the ground

Knee Locked straight; the hinge joint is not Bends deeply into a crouch, then straightens hard
used at all to drive the body up

Hip Stays upright, trunk nearly vertical Bends forward as the body lowers, then extends
as you rise

Result Low jump, hard landing, jarring felt in Higher jump, soft controlled landing
the legs and spine

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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Why bending makes such a difference: a muscle produces force only while it
shortens. Crouching first stretches the muscles of the thigh and calf, so each has a
longer distance over which to pull and can do more work on the body. Three joints
working in sequence — hip, then knee, then ankle — add their pushes together. On
landing, the same joints bend to spread the impact over a longer time, and the
cartilage at the bone ends absorbs the shock. With the joints locked, the whole
impact is passed straight up the bones to the spine in an instant, which is why the
landing hurts.

Check it yourself: this is why an athlete is coached to land softly on bent knees, and
why the same crouch appears in kabaddi, kho-kho and in the araimandi stance of
classical dance.

Q5 Which type of joint is involved when you bend your knees and ankles? (i) Ball and
socket (ii) Hinge (iii) Pivot

(ii) Hinge.
The knee and the ankle both bend and straighten in one direction only, like a door turning on its
hinge. At the knee a small bone, the kneecap, sits in front of the joint and protects it.

Why a hinge and not a ball and socket: the knee and the ankle carry your whole
body weight, and every landing sends a large force up through them. A hinge allows
movement in a single plane and refuses all other directions, which is exactly what
keeps the leg stable under load. A ball and socket joint, like the shoulder, buys
freedom of movement at the cost of stability — useful for an arm, dangerous for a
leg.

(iii) Pivot is wrong — a pivot joint allows rotation, as when you shake your head to say ‘no’.

Page 37 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Q6 In each of the following cases (A, B, C and D), choose the correct option as given
below: (i) Both (A) and (R) are true, and (R) is the correct explanation of (A). (ii) Both
(A) and (R) are true, but (R) is not the correct explanation of (A). (iii) (A) is true, but
(R) is false. (iv) (A) is false, but (R) is true. A. Assertion: Epithelium is well-suited for
gas exchange in the lungs. Reason: It consists of multiple layers of tall cells that
slow down diffusion. B. Assertion: Cardiac muscle can contract continuously
without fatigue. Reason: Cardiac muscle cells have a high number of mitochondria
and an abundant blood supply. C. Assertion: Tendons connect bone to bone and
allow joint movement. Reason: Tendons are made of tough connective tissue that
transmits force from muscle to bone. D. Assertion: In a hinge joint, movement
occurs primarily in one plane. Reason: The bone ends are shaped to allow sliding in
all directions.

CASE ASSERTION REASON ANSWER

A True False (iii)

B True True and explains A (i)

C False True (iv)

D True False (iii)

A — (iii). The assertion is right: the lung lining is superb for gas exchange. The reason is the
exact opposite of the truth. Table 3.2 says the exchange epithelium is a single layer of thin, flat
cells, which makes the diffusion path as short as possible. Multiple layers of tall cells would slow
diffusion down, so that arrangement is found where protection is needed — skin, mouth,
oesophagus.
B — (i). Cardiac muscle really does work rhythmically for a lifetime without fatigue, and the
reason given is exactly why. Fatigue sets in when a muscle uses ATP faster than it can make it. A
large number of mitochondria means a high rate of aerobic ATP production; an abundant blood
supply keeps delivering the oxygen and glucose that those mitochondria need and removes the
wastes. Supply therefore keeps pace with demand and no oxygen debt builds up.
C — (iv). The assertion is false: ligaments connect bone to bone. Tendons connect muscle to
bone. The reason, taken on its own, is a correct statement — tendons are tough connective
tissue and they transmit the force of a contracting muscle to a bone.
D — (iii). The assertion is true: a hinge joint moves in one plane, as the elbow and knee do. The
reason is false; bone ends shaped for sliding in all directions describe a ball and socket joint, not
a hinge. In fact it contradicts the assertion.

Page 38 of 63

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Class 9 Science Chapter 3 Tissues in Action
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co m
m.
Tip for assertion–reason questions: judge the assertion and the reason separately

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first, and only then ask whether the reason explains the assertion. In C the reason is
o g if you read them
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together.

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Plot a graph between the age of a m
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tree (in years) on the x-axis and the diameter of
anumber of annual rings formed over time on the y-
Q7

agl
the tree (in cm) along with the
axis, using the data given in the Table 3.7. (i) Analyse the graph in terms of the

m
diameter of the stem over time and share the interpretation. (ii) What is the
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relation between the diameter of the teak tree to the annual rings formed? (iii)

o m l a se
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a se Table 3.7: Data related to the age of a teak tree, and corresponding increase in the
agl diameter of stem and number of annual rings

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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

40

30 steep stretch,
DBH (cm) / rings

10–20 years

20

DBH (cm)

10 Annual rings

0
0 10 20 30 40
Age of the teak tree (years)

Both curves rise with age. The rings line is perfectly straight (one ring a year); the DBH line has a
steep patch between 10 and 20 years.

(i) Diameter over time. The diameter increases steadily throughout — the tree never stops
thickening. But the rate is not the same every year:

Rate of increase in diameter = (change in DBH) ÷ (change in age)

5 → 10 years: (8 − 4) cm ÷ (10 − 5) years = 4 cm ÷ 5 years = 0.8 cm year⁻¹

10 → 20 years: (24 − 8) cm ÷ 10 years = 16 cm ÷ 10 years = 1.6 cm year⁻¹

20 → 25 years: (28 − 24) cm ÷ 5 years = 0.8 cm year⁻¹

25 → 30 years: (32 − 28) cm ÷ 5 years = 0.8 cm year⁻¹

30 → 40 years: (40 − 32) cm ÷ 10 years = 8 cm ÷ 10 years = 0.8 cm year⁻¹

Average over the whole record = (40 − 4) cm ÷ (40 − 5) years = 36 ÷ 35 ≈ 1.03 cm year⁻¹

Interpretation: the young tree (10 – 20 years) grew in girth twice as fast as at any other stage
— 1.6 cm year⁻¹ against 0.8 cm year⁻¹. That decade was clearly a stretch of favourable
conditions, and the lateral meristem was most active then. After 20 years the rate settles back to

Page 40 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

a steady 0.8 cm year⁻¹.
(ii) Diameter and annual rings. Rings and age are related exactly one-to-one — 5 years/5
rings, 20 years/20 rings, 40 years/40 rings — because one ring is formed each year. So
diameter increases with the number of rings, but not in strict proportion:

Diameter added per ring = DBH ÷ number of rings

At 5 rings: 4 ÷ 5 = 0.80 cm per ring At 20 rings: 24 ÷ 20 = 1.20 cm per ring

At 25 rings: 28 ÷ 25 = 1.12 cm per ring At 40 rings: 40 ÷ 40 = 1.00 cm per ring

Mean radial width of one ring at 40 years = (40 ÷ 2) cm ÷ 40 rings = 20 ÷ 40 = 0.5 cm = 5

mm

So the relation is: more rings → larger diameter, and the number of rings gives the age.
Wide rings mark favourable years and narrow rings unfavourable ones, which is why the
diameter-per-ring figure is not constant.
(iii) The tissue. The lateral meristem. It is located as a ring of actively dividing cells inside the
stem, running along its circumference. Its cells divide and add new cells both inwards and
outwards in a concentric manner, so the stem grows in diameter and lays down one annual ring
each year.

Did you know? Because each ring records one year's conditions, scientists read old
timber the way you read a diary — the widths tell them about droughts and good
rainfall years long before any weather records were kept.

Page 41 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Q8 In a forest, it was observed that one of the trees was severely debarked by an
elephant to meet its food requirements, as the bark is a rich source of nutrients
(Fig. 3.22). Based on your learning, answer the following: (i) Which function(s) of the
tree is/are hampered by debarking? (ii) Which plant tissue would be affected by
further damage to the tree trunk even after debarking? (iii) Which function of the
tree would be hampered if the tissues beneath the bark were severely damaged?
(iv) What assumptions are you making to answer the questions above? How would
the answer change if your assumptions are also changed?

Tree trunk

Bark stripped off

Elephant

Fig. 3.22, page 45 — redrawn sketch of the photograph: an elephant stripping bark from
a tree trunk.

Work outwards-in. The bark is the outermost protective layer; just beneath it lie the phloem and
the lateral meristem; deepest of all is the xylem.
(i) Functions hampered by debarking.

Protection is lost. The bark is made of dead, compactly arranged cork cells containing a
substance that makes them impermeable to water and gases. Strip it and the trunk is open
to water loss, to fungi, bacteria and insects, and to mechanical injury.
Food transport is interrupted. The phloem lies immediately under the bark, so it is usually
torn away with it. Sugars made in the leaves can then no longer reach the roots.
Girth growth stops at that patch, because the lateral meristem sits just inside the phloem
and is damaged too.

(ii) Tissue affected by further damage to the trunk. Going deeper, the next tissues to be
destroyed are the lateral meristem (cork cambium and the cambium of the vascular bundle)
and then the xylem. Xylem damage is the most serious of all, because xylem also gives the

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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

trunk its mechanical strength.
(iii) Function hampered if the tissues beneath the bark are severely damaged. The upward
transport of water and minerals from the roots to the leaves, since that is the xylem's job —
and with it the tree's mechanical strength, so the trunk may snap in a storm. If the phloem is
completely ringed all round, the roots are cut off from their food supply, they starve, they stop
absorbing water and minerals, and the whole tree eventually dies even though its leaves are
untouched.
(iv) Assumptions, and what changes if they are altered.

ASSUMPTION MADE IF THE ASSUMPTION CHANGES…

The debarking goes all the way round If only a patch on one side is stripped, phloem on the other side
the trunk (ringing) still carries food down and the tree usually survives and heals over
the wound

The damage reaches the phloem and If only the dead outer cork is scraped off, the tree loses protection
cambium, not just the outer dead cork but keeps transporting food and can regenerate new cork from
the cork cambium

The tree is a dicot with secondary A monocot such as a palm or bamboo has no cork cambium and
growth and continuous bark no ring of phloem beneath a bark, so the same injury has a quite
different effect

Xylem is still intact If the xylem is also cut through, the leaves stop receiving water
and wilt within days — much faster than death by starvation of the
roots

The injury is not re-infected and the If fungi enter the exposed wood, decay spreads and even a partly
season is favourable debarked tree may die

Why the direction of transport decides everything: phloem carries food
downwards from leaves to roots, so a complete ring of damage starves the roots but
not the leaves. Xylem carries water upwards, so damaging it kills the leaves first.
Which tissue is cut tells you which end of the tree dies first.

Q9 Aamrapali observed that a young mango sapling’s stem bends flexibly during
monsoon winds and does not break. Which tissue is responsible for this flexibility?
Predict and provide your explanation of the impact if the existing tissue was
replaced by sclerenchyma.

Collenchyma is responsible for the flexibility.

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Class 9 Science Chapter 3 Tissues in Action
a g l AglaSem · NCERT Solutions

Collenchyma consists of living cells whose walls are unevenly thickened at the corners by the
co m
deposition of pectin — a chemical the book compares to rubber. The extra material at the
e m.
m
cowind g
corners gives strength, while the thin regions in between let the wall deform. So the stem can
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as replaced by sclerenchyma:
bend under the and spring back when the gust passes.

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COLLENCHYMA (PRESENT) SCLERENCHYMA (HYPOTHETICAL)
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a s
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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Q10 Sohan designed an experiment for the regeneration of sugarcane, where he used
cuttings to grow sugarcane. He used two types of cuttings, type ‘A’ and type ‘B’ (Fig.
3.23). After a few weeks, type ‘B’ cuttings sprouted and developed into sugarcane
plants, whereas the type ‘A’ cuttings did not sprout. (i) Why were the type ‘B’
cuttings able to grow as sugarcane but type ‘A’ could not? (ii) What difference was
present in type ‘B’ compared to type ‘A’? (iii) What observation or measurement
was made to determine whether this change had an effect? (iv) What parameters
should be kept the same for both types of cuttings to ensure a fair comparison?

(A) (B)

Fig. 3.23, page 46 — redrawn sketch of the two sugarcane cuttings photographed in the
book.

Look carefully at Fig. 3.23. Cutting (A) is a smooth length of stem taken from between two
nodes — a plain internode. Cutting (B) carries a node: you can see the swollen ring with a bud
on it and the beginnings of root growth.
(i) Why B grew and A did not. Sprouting needs cells that can still divide. A node carries a bud
(dormant shoot apical meristem) and the intercalary meristem at the base of the internode
just above it. Cutting B has these, so it can produce a new shoot and roots. Cutting A is made

Page 45 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

entirely of permanent tissue — parenchyma, sclerenchyma, xylem and phloem — every cell of
which has lost the ability to divide. It can stay alive for a while, but it has no growing point, so it
never sprouts.
(ii) The difference. The presence of a node with a bud (and its meristematic tissue) in B; A is an
internode with no node and no bud.
(iii) What was observed or measured. Whether or not a shoot appeared, and then how much.
In practice you would record:

number of cuttings that sprouted out of the total planted (percentage sprouting);
the number of days taken for the first shoot to appear;
the length of the new shoot in cm, measured at fixed intervals;
the number of roots formed and their length in cm.

Sprouting percentage = (number of cuttings that sprouted ÷ total cuttings planted) × 100

Example: if 18 of 20 type-B cuttings sprouted, sprouting = (18 ÷ 20) × 100 = 90%

If 0 of 20 type-A cuttings sprouted, sprouting = 0%

(iv) Parameters to keep the same so that only the presence of a node differs:

the same variety of sugarcane, from the same parent plant;
the same length and thickness of each cutting, and cuttings of the same age;
the same soil, the same pot size, the same depth and orientation of planting;
the same amount and frequency of watering;
the same temperature, sunlight and humidity — plant them side by side;
the same number of cuttings of each type, so the percentages are comparable, and the
same observation dates.

Why a fair test needs all this: the experiment claims that the node caused the
sprouting. That claim only holds if the node is the one thing that differs between the
two groups. If the type-B cuttings had also been thicker, or better watered, you could
not tell which factor did the work. Everything else is kept constant precisely so that
one variable is left free to be tested.

Did you know? Sugarcane, potato and sweet potato are all propagated
commercially in exactly this way — from stem pieces carrying buds — because it is
faster than seed and gives plants identical to the parent.

Page 46 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Q11 During the discussion in class, Rohan gives a statement that, “A tissue is a group of
similar cells performing similar functions”. But Rajiv counter argues that, “this is
true in case of simple tissues but little different in case of complex tissues”.
Provide your explanation in view of the discussion in class.

Rajiv is right, and Rohan's statement needs one word changed. A tissue is a group of cells that
work together for a common function — they need not all be the same kind of cell.

SIMPLE PERMANENT TISSUE COMPLEX PERMANENT
TISSUE

Cell types Only one kind of cell More than one kind of cell

Examples Parenchyma, collenchyma, sclerenchyma Xylem, phloem

How the work is Every cell does the same job — all parenchyma Different cells do different parts
shared cells store food of one job

Take xylem. It has four different cell types and only one purpose — moving water up the plant:

Tracheids and vessels — tubular, thick-walled and dead; they are the pipes.
Xylem fibres — sclerenchymatous; they give mechanical strength.
Xylem parenchyma — the only living component; it stores food.

Take phloem. Again four cell types, one purpose — moving food:

Sieve tubes — long, tubular, joined end to end by perforated walls; the channel itself.
Companion cells — specialised parenchyma cells that regulate the sieve tube and monitor
the loading and unloading of sugars.
Phloem parenchyma — stores food, resin, tannins and latex.
Phloem fibres — sclerenchymatous; they support the soft sieve tubes.

A better definition, covering both cases: a tissue is a group of cells that are organised together
and work as a unit to carry out a specific function — similar in structure in a simple tissue, of
several kinds in a complex tissue.

Why complex tissues had to evolve: conduction is not one job but several — an
open channel, strength to keep it from collapsing, storage, and regulation of what
enters and leaves. No single cell type can be hollow and dead and alive and
regulating at the same time. So the plant assembles several cell types into one
tissue. The same idea appears in animals: blood is a connective tissue made of RBCs,
WBCs, platelets and plasma, all serving transport and defence.

Page 47 of 63

Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Q12 Coconut husk fibres are used for mats which are tough and fibrous. Which tissue
has structural features suitable for providing this strength? Explain why living
parenchyma couldn’t serve the same purpose.

Sclerenchyma. Coconut husk fibre is sclerenchyma, and every one of its features is a strength
feature.

FEATURE OF SCLERENCHYMA WHAT IT GIVES THE MAT

Uniformly thick walls, heavily deposited Rigidity and resistance to being pulled apart or crushed
with lignin

Long, narrow, tapering cells packed end to Fibres that can be twisted into strong yarn and woven
end

Most cells are dead at maturity No water content to be lost, so the fibre keeps its shape and
strength when dry

Lignin is water-resistant The mat survives washing, damp floors and rain without
rotting quickly

Why living parenchyma could not do this:

Parenchyma cells have thin walls — there is almost no material to resist a pull. They tear
easily.
They are loosely packed with intercellular spaces, so the tissue is soft and spongy rather
than fibrous.
They are living and full of water. Their firmness comes from turgor, not from the wall. Dry
them out and they collapse and shrivel — a mat made of parenchyma would go limp the day
it was made.
Being alive, they would also need a food and water supply, and would rot and be attacked by
microbes as soon as they were cut off from the plant.

The key contrast: parenchyma is strong only while it is alive and full of water;
sclerenchyma is strong because its wall is thick and lignified, and it stays strong after
the cell dies. For anything that has to last outside the plant — coir rope, jute, a
walnut shell, a seed coat — you need the dead, lignified tissue.

Page 48 of 63

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Class 9 Science Chapter 3 Tissues in Action
a g l AglaSem · NCERT Solutions

co m
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Vibha claims to her friend Neha that, “Meristematic cells are located only at the
se
Q13

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root and shoot apices”. What do you think about this statement? What question
g
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can Neha a is incorrect?

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The statement is incorrect. Apical meristem is only one of three kinds. Meristematic cells are
. co ag
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base of internodes (intercalary meristem).
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Questions Neha can ask Vibha — each one points at a fact her claimm .
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1..c“If
a goflaa tree get thicker every
a sem year, and what forms the annual growth rings we count to find its age?”
agl c
.
2. “When a lawn is mowed, the shoot tips of every blade of grass are cut off. Why does the
grass grow back?”
s e m
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3. “After a hedge is trimmed, more branches appear and it turns bushy. Where are the new
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4. “In our own Activity 3.1,
bulb stayed alive and kept working. Which dividing cells were still present elsewhere?”

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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Any one of these forces the correct conclusion: apical meristem adds length at the tips, lateral
meristem adds girth along the stem, and intercalary meristem at the nodes lets grasses and
hedges regenerate after being cut.

Tip: a good counter-question does not just say “you are wrong”. It offers an everyday
observation that the wrong idea cannot account for, and lets the other person work
it out.

Q14 A plant cell and an animal cell are of the same size. (i) Which cell will have a larger
vacuole? Give reasons. (ii) What assumptions are you making to answer the
question above?

(i) The plant cell. A mature plant cell has one large central vacuole that can occupy most of the
cell volume, pushing the cytoplasm and the nucleus into a thin layer against the wall. An animal
cell has either no vacuole or only a few very small ones.
Reasons:

Turgor and support. A plant cell has a rigid cell wall. Filling the vacuole with water presses
the cytoplasm out against that wall and makes the cell firm — this turgor is what keeps a
soft herb upright. An animal cell has no wall, so a big water-filled vacuole would simply burst
it or distort its shape.
Storage. The plant makes its own food and stores water, food, pigments and wastes in the
vacuole. An animal takes in food as needed and removes wastes through blood and
excretory organs, so it has no need of a large storage sac.
Cheap growth. A plant cell enlarges mainly by taking in water into the vacuole rather than
by making new cytoplasm — a very economical way to grow.
Flexibility. An animal cell must change shape to move, divide and squeeze past neighbours;
a large vacuole would make it stiff.

(ii) Assumptions made:

Both cells are mature and differentiated, not dividing — a meristematic plant cell has no
vacuole at all, so if the plant cell were meristematic the answer could change.
The plant cell is a typical living parenchyma-type cell, not a dead cell such as a xylem vessel
or sclerenchyma fibre.
The animal cell is an ordinary body cell — not a specialised one such as a fat cell or a large
vacuolated secretory cell.
The plant cell is turgid (well supplied with water); a wilted cell has a shrunken vacuole.
“Same size” means the same total cell volume, so we are genuinely comparing the fraction of
that volume taken by the vacuole.

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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Why stating assumptions matters: the answer “plant cell” is only true for the
usual, mature case. Naming the assumptions shows exactly when the answer would
stop being true — and that is what separates a scientific answer from a memorised
one.

Q15 A textbook states, “Each plant tissue performs only one specific function”. What
questions would you ask to critically examine the correctness of this statement?
What examples of tissues would you take to find out the answers to these
questions?

The statement is an over-simplification. Specialisation makes one function dominant, but most
plant tissues do more than one job.
Questions worth asking:

1. Does any tissue in the chapter have more than one function listed for it?
2. Does the same tissue behave differently in different organs, or in different plants?
3. Does the function change with the age or the condition of the plant?
4. Can one function be carried out by more than one tissue — that is, is the mapping tissue →
function one-to-one at all?
5. If a tissue really did only one thing, what should we expect to see when it is damaged? Does
the plant lose only that one ability?

Examples that answer them:

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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

TISSUE FUNCTIONS IT ACTUALLY PERFORMS WHAT THAT SHOWS

Parenchyma Stores food; photosynthesises in the green parts; One tissue, at least four jobs
forms air spaces that let aquatic plants float; — and which one it does
packing tissue depends on where it is

Epidermis Protection; reduces water loss through the cuticle; The same tissue is a barrier
absorbs water and minerals as root hair; allows in one organ and an
gas exchange and transpiration through stomata absorbing surface in another

Xylem Transports water and minerals; also provides The book itself gives xylem
strength to the plant; xylem parenchyma stores two functions in the same
food sentence

Phloem Transports food; phloem parenchyma stores food, A complex tissue divides
resin, tannins and latex; phloem fibres give several functions among its
strength cell types

Lateral meristem Increases girth; also gives rise to cork cambium, A dividing tissue produces
which forms the protective bark protective tissue as well

Collenchyma and Both give mechanical support — one with Two different tissues share
sclerenchyma flexibility, the other with rigidity one function, so the mapping
is not one-to-one either way

Conclusion. A fairer statement would be: each plant tissue is specialised for a main function, but
many tissues perform additional functions as well, and one function may be shared by more than one
tissue. And the deepest counter-example is totipotency itself — a mature phloem cell, whose
"one function" is food transport, can be made to regenerate an entire carrot plant.

Tip: to test any sweeping statement in science, do not argue with it — look for a
single clear counter-example. Parenchyma alone is enough to disprove this one.

The Journey Beyond — Page 47

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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Project work

THE JOURNEY BEYOND

Q1 Visit a doctor and find out what happens in ligament rupture, cartilage rupture and
fracture of bones. How can we reduce the risk by changing our lifestyle and
nutritional balance?

How to do it: carry a written list of questions, note the doctor's answers in your own words, and
ask for one example each of an injury they commonly treat in young people. Record the tissue
involved, the symptom, the usual treatment and the recovery time.
Sample answer:

INJURY TISSUE WHAT HAPPENS WHY RECOVERY IS SLOW
INVOLVED OR FAST

Ligament Ligament — bone The tough band tears, so the Ligaments have a poor
rupture to bone joint loses stability and can move blood supply, so healing is
beyond its safe limit; there is slow; a badly torn one may
pain, swelling and a feeling that need surgery
the joint gives way

Cartilage Cartilage — cushion The soft, jelly-matrix pad tears; Cartilage has almost no
rupture at bone ends and the bone ends grind together, blood supply of its own, so it
between vertebrae causing pain and stiffness on heals very poorly and
movement damage is often permanent

Fracture of Bone — rigid matrix The bone cracks or breaks; Bone is richly supplied with
bone of calcium and severe pain, swelling and blood, so it heals
phosphorus inability to bear weight comparatively well once set
compounds — usually in 6 to 8 weeks

Reducing the risk:

Nutrition — calcium and phosphorus for the bone matrix (milk, curd, ragi, sesame, green
leafy vegetables), vitamin D from sunlight to absorb that calcium, and protein for muscle and
for the connective tissue of tendons and ligaments.
Regular exercise — loading a bone makes it lay down more matrix, and strong muscles
around a joint take load off the ligaments.
Warm up and stretch before games; most ligament tears happen on a cold, sudden twist.
Correct posture while sitting, studying and lifting; lift with the knees bent, not with a bent
back.
Yoga — research shows it improves flexibility, posture and breathing, reduces stress and
helps prevent lifestyle diseases. 21 June is observed every year as International Yoga Day.

Page 53 of 63

as e
Class 9 Science Chapter 3 Tissues in Action
a g l AglaSem · NCERT Solutions

Proper footwear, safe playing surfaces, and enough rest between hard sessions.
co m
e m.
m l as
.co a g
a s em the following activity. (i) Sit with your feet flat on the floor. (ii) Place your
Perform
gl fingers on the back of your ankle just above the heel (Fig. 3.24). (iii) Point your toes
Q2

a down and up, and you will feel the tendon moving. Tendons are designed to

co m
withstand huge pulling forces. Try exploring other tendons in your body around the
different joints.
e m . ag
g l as
a

co m
em.
m l as
m .co a g
l a se
ag Back of the ankle,
just above the heel
m a s
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l a se
a g

co m floor
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m as e
.co a g l
a s em Fig. 3.24, page 47 — redrawn sketch: fingers placed on the back of the ankle, just above

agl the heel.

se m
com g l a
m . a
ase

a gl
What you will feel: a thick, firm cord under the skin just above the heel that tightens and slides
when you point your toes down, and slackens when you pull them up. That is the tendon joining
your calf muscle to the heel bone.
co m
m .
Other tendons you can find on yourself:
m as e
.co a g l
se m
g l a
a c
m .
m a s e
e m . co agl
g l as
a

co m
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m ase
.co


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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

WHERE TO PRESS WHAT TO DO TENDON CONNECTING

Back of the ankle, above the heel Point the toes down and up Calf muscle → heel bone

Back of the wrist Straighten and bend the fingers Forearm muscles → finger bones

Front of the elbow Bend the elbow against resistance Biceps → forearm bone

Just below the kneecap Straighten the knee while seated Thigh muscle → shin bone

Back of the knee, on either side Bend the knee Hamstring muscles → leg bones

Why tendons can take such large forces: a tendon is dense connective tissue
whose fibres all run in the same direction — the direction of the pull. Fibres lined up
along the line of force share the load evenly, which is exactly how a rope is made
strong. The heel tendon in particular has to carry several times your body weight
every time you push off to run or jump, so it is the thickest tendon in the body.

Check it yourself: notice that the muscle that moves your fingers is in the forearm,
not in the hand. Keeping the bulky muscle far away and transmitting its pull through
long tendons is what makes the hand slim enough for fine work — writing, playing
an instrument, holding a dance mudra.

Q3 Reflect on any of the physical practices you are familiar with, such as yoga, kabaddi,
etc. How would it support bone and muscle health?

How to answer: pick one practice you actually do, describe what the body does in it, and then
connect each movement to a tissue in this chapter — bone, muscle, tendon, ligament, cartilage.
Sample answer — kabaddi. A kabaddi raid combines sprinting, sudden stops, low crouches,
twisting escapes and grappling.

Bone. Running and jumping load the leg bones repeatedly. Bone responds to load by
depositing more of its calcium-and-phosphorus matrix, so the bones become denser and
stronger.
Muscle. Repeated powerful contraction thickens the skeletal muscle fibres, so the player
produces more force and tires less quickly.
Joints and ligaments. Constant changes of direction train the ligaments and the muscles
around the knee and ankle to hold the joint steady, which is the best protection against a
sprain.

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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Cartilage. Movement circulates the fluid around the joint and keeps the cartilage nourished
— it has no blood supply of its own.
Heart and lungs. Cardiac muscle works harder and the breathing rate rises, improving
oxygen delivery to every tissue.

Sample answer — yoga. Yoga, described in ancient Indian texts, includes physical postures,
breathing and meditation. Holding an asana keeps a muscle contracted without movement,
which builds endurance; the stretches slowly increase the range of a joint; weight-bearing
postures load the bones of the arms and spine; and the breathing practices improve the
expansion of the rib cage, which the flexible cartilage joining the ribs to the sternum makes
possible. Research shows yoga improves flexibility, posture and breathing, reduces stress and
helps prevent lifestyle diseases.

Tip: whatever practice you choose, write your answer as “this movement → this
tissue → this change”. That is what turns a description into a scientific explanation.

Q4 Reflect on any gardening methods you know, such as pruning, grafting, irrigation
or crop rotation. How does each practice support the healthy functioning of plant
tissues like meristems, conducting tissues or supporting tissues?

Each garden practice works on a particular tissue. Match the practice to the tissue and the
reason becomes obvious.

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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

PRACTICE TISSUE IT ACTS HOW IT HELPS
ON

Pruning / Apical and Removing the shoot tip takes away the apical meristem, so
trimming a intercalary the buds at the nodes are released and many side branches
hedge meristem sprout — the plant becomes bushier and flowers more

Taking stem Meristem at the Only a cutting that carries a node with a bud can regenerate
cuttings node — exactly the sugarcane result in Question 10

Grafting and Lateral meristem The two cut surfaces are matched so their cambium layers
budding (cambium) of stock touch; the dividing cells knit together and their xylem and
and scion phloem become continuous, so water and food flow across
the join

Irrigation Xylem, root hair and Keeps the soil moist so root hair can absorb water; maintains
parenchyma the unbroken water column in the xylem and the turgor of
parenchyma that keeps soft stems upright. Over-watering, on
the other hand, drives air out of the soil and suffocates the
roots

Mulching Root hair and Slows evaporation from the soil, so absorption by root hair
epidermis continues steadily and the plant is not forced to close its
stomata

Crop rotation All tissues — Restores nitrogen and minerals that the xylem must carry up.
and manuring through mineral Without nitrogen the plant cannot build protein for new
supply meristematic cells; without calcium it cannot build cell walls

Staking a young Collenchyma and Supports the stem while its own supporting tissues are still
plant sclerenchyma developing, so it does not break in wind

The common thread: gardening is applied plant anatomy. Every one of these
practices either protects a meristem, keeps a conducting tissue supplied and
unbroken, or takes some load off a supporting tissue.

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Class 9 Science Chapter 3 Tissues in Action AglaSem · NCERT Solutions

Q5 Turn a nature walk into a research project. (i) Observe different leaves and study
their adaptations for various environments, such as desert, very moist or aquatic
habitats. (ii) Consult an elder community resource persons about their knowledge
on different plant leaves, such as leaves that remain fresh for a long time, repel
water or deter insects. Find out their traditional uses, such as making plates,
preparing cooling wraps or functioning as insect repellents.

How to run it as a project: choose 8 – 10 plants growing in different situations near you. For
each, record the habitat, and note the thickness and feel of the leaf, how waxy the surface is,
whether it is hairy, and whether it is thin and floating or thick and fleshy. Press one leaf of each
as a specimen. Then interview an elder and record what the leaf is traditionally used for and
why.
Sample answer — part (i):

HABITAT EXAMPLE WHAT YOU OBSERVE TISSUE-LEVEL REASON

Desert / dry Aak, cactus, Thick, fleshy or reduced to Very thick cuticle over the epidermis
khejri, aloe spines; a shiny waxy cuts evaporation; water-storing
surface; often hairy; few parenchyma fills the fleshy leaf; hair
stomata, sunk into pits traps still air and slows water loss

Very moist / Colocasia Large, broad, thin, soft A thin cuticle and many stomata allow
shady (arbi), banana, leaves rapid transpiration; the large surface
ferns catches the little light available under
a canopy

Aquatic — Lotus, water Leaf floats, upper surface Stomata on the upper surface only;
floating hyacinth waxy and water-repellent, specialised parenchyma with large air
stalk spongy and light spaces gives buoyancy, which is
exactly how the book explains floating

Aquatic — Hydrilla, Thin, ribbon-like or finely Almost no cuticle and usually no
submerged Vallisneria divided leaves; no waxy stomata, because gases and minerals
shine are absorbed directly through the
whole surface (see Pause and Ponder
Q2)

Saline / Mangroves Thick, leathery, often Thick cuticle limits water loss even
coastal glossy leaves though water is all around, because
the water is salty and hard to absorb

Sample answer — part (ii), traditional uses: banana and palash leaves are used as pattal (leaf
plates) because they are large, waterproof and do not tear when hot food is served; banana
leaves also stay fresh for days. Betel and banana leaves are used as cooling wraps for fevers.
Neem and tulsi leaves are placed among stored grain and clothes as insect repellents. Turmeric

Page 58 of 63

as e
Class 9 Science Chapter 3 Tissues in Action
a g l AglaSem · NCERT Solutions

and neem leaves are used on skin infections. Ask your elder why that particular leaf, and you will
co m
usually find the answer is the waxy cuticle, the leaf's size and toughness, or a chemical stored in
e m.
m l as
.co g
its parenchyma.

em a
a s
gl record the local name, the botanical name if you can find it, the habitat and the
ause,
Tip:
and add your pressed leaf. That turns a walk into a proper piece of documented
fieldwork.
com
e m . ag
g l as
a
Q6 Study various dance forms of different tribal communities across the country. Each

c o m
.
student learn and experience at least five steps. Observe the joint movements

s e
involved in performing these steps and then develop a dance or dramam on the
. c
concept
a la function so that
om of joint movements. Perform this at the school’s annual
g
a s em
students from different grades can learn from it.

agl ANSWER

om a s
. c agl
How to build it: divide the class into groups, each taking one dance form. Learn five steps, then

s e
write down for each step which joints movem and what kind of joint each one is. Turn that table
into the script of the performance.la
ag
Sample answer — a movement analysis you can start from:

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m .
e
DANCE CHARACTERISTIC STEP JOINTS IN TYPE OF JOINT

m l as
.co g
ACTION

m (Assam)
eBihu a
a s
gl
Quick bending at the waist with Hip, vertebral Ball and socket; the cartilage

a rapid hip sways column discs between the vertebrae
allow bending and twisting
se m
com g l a
m .
Continuous spinning with the Shoulder, Ball and socket; hinge; pivot
a
se
Ghoomar

l a
(Rajasthan) arms circling overhead ankle, neck

Santhal / Jhumar
ag
Side-stepping in a line with Hip, knee, Ball and socket and hinge

m
linked arms and a swing of the shoulder

co
(Jharkhand)
body
m .
m a e
sBall
.co
Bhangra (Punjab) High jump with the arms Hip, knee,
ag l and socket; hinge — the

a s em thrown up ankle, crouch-and-drive of Question

agl shoulder 4

.c
Cheraw / bamboo Stepping in and out between Ankle, knee, Hinge — fast, precise, one
s e m
m a
.co agl
dance (Mizoram) clapping bamboo poles toe joints plane

sem
g l a
a
A workable script for the performance:

1. Open with a still tableau; a narrator names the four joint types.

co m
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m ase
.co


a g l Page 59 of 63