Tissues in Action - Chapter 3 Class 9 Exploration

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.
Thin walls
Dense
cytoplasm
Large prominent
nucleus
Thick walls /
large vacuole —
cannot divide
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The correct option is
(iii) They have thin walls, dense cytoplasm and large prominent nucleus.
These features let the cells divide quickly and continuously. Thick walls, large vacuoles or being differentiated would all stop a cell from dividing.
Why Meristematic Cells Divide Fast
Thin walls
Nothing stiff to stop division.
↓
Dense cytoplasm, large nucleus
Ready to make new cells.
↓
Answer: (iii)
Back to: 3.2 Tissues for Growth in Plants

If a plant is unable to transport food from leaves to roots, which tissue is malfunctioning?
(i) Xylem (ii) Phloem (iii) Epidermis (iv) Sclerenchyma
Phloem —
carries food
(blocked X)
Food cannot
reach the roots
Xylem —
carries water
(working)
Malfunctioning
tissue = phloem
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The correct option is
(ii) Phloem.
Phloem carries food from the leaves to the rest of the plant. If food cannot reach the roots, the phloem is not working. Xylem carries water, not food.
Which Tissue Failed?
Food moves leaves → roots
This is the job of phloem.
↓
Food is not reaching the roots
So the phloem is not working.
↓
Answer: (ii) Phloem
Back to: 3.2.4 Permanent tissues

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.
Thin, single-layer lining
Materials diffuse
across quickly
_) Nutrients
Found in lungs
and blood vessels
Thick wall —
exchange is slow X
Nutrients
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The correct option is
(iii) To allow quick exchange of materials across them.
A thin lining lets gases and liquids diffuse across quickly, which is why the lining of the lungs and blood vessels is just one cell thick.
Why the Lining Is Thin
One or a few cells thick
A very short distance to cross.
↓
Gases and liquids diffuse across quickly
As in lungs and blood vessels.
↓
Answer: (iii) Quick exchange of materials
Back to: 3.3.1 Epithelial tissues — Structure and functions

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?
Straight-leg
jump — joints
stiff and straight
Hard landing
(shock not
absorbed)
Normal jump —
ankle, knee, hip
bend
Soft landing
(shock absorbed)
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In the straight-leg jump the ankle, knee and hip stay stiff and almost straight, so the joints hardly bend and the landing feels hard.
In the normal jump the ankle, knee and hip all bend, letting the hinge joints fold and the ball-and-socket hip flex. This bending softens the landing and absorbs the shock.
Straight-Leg Jump vs Normal Jump
Straight-leg jump
Ankle, knee and hip stay stiff; the landing feels hard.
↓
Normal jump
Hinge joints fold and the hip flexes.
↓
Bending the joints absorbs the shock
Back to: 3.5 Types of Joints

Which type of joint is involved when you bend your knees and ankles?
(i) Ball and socket (ii) Hinge (iii) Pivot
Knee — hinge joint
Bends in one
direction only
Works like a
door hinge
Ankle — hinge joint
Bends in one
direction only
Works like a
door hinge
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The correct option is
(ii) Hinge.
The knee and ankle bend in one direction, like a door hinge, so they are hinge joints.
Which Joint Bends?
Knee and ankle
They bend in one direction only.
↓
Like the hinge of a door
So they are hinge joints.
↓
Answer: (ii) Hinge
Back to: 3.5.2 Hinge joint

In each case (A, B, C, D), choose: (i) Both A and R true, R is correct explanation of A; (ii) Both true, R not the correct explanation; (iii) A true, R false; (iv) A false, R 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.
lung epithelium
is thin, not many
tall layers
cardiac muscle:
many mitochondria,
rich blood supply
tendon joins
muscle to bone
(not bone to bone)
hinge joint
moves in one
plane only
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A → (iv)
A is false, R is true... actually the assertion is false (lung epithelium is a single thin layer, not multiple tall layers) and the reason as stated is also false, so the gas-exchange epithelium is thin. Best fit: A is false. The reason describes the wrong structure, so
(iv)
does not fit perfectly; the assertion is false because lung epithelium is thin and single-layered.
B → (i)
Both true and the reason correctly explains it: many mitochondria and a rich blood supply give cardiac muscle the energy and oxygen to work without tiring.
C → (iv)
The assertion is false (tendons connect muscle to bone, not bone to bone), but the reason is true (tendons are tough connective tissue that transmits force from muscle to bone).
D → (iii)
The assertion is true (a hinge joint moves in one plane), but the reason is false (hinge bones do not slide in all directions).
Assertion and Reason
Check the assertion
Is the statement itself true?
↓
Check the reason
Is it true, and does it explain the assertion?
↓
Then pick the matching option for A, B, C and D
Back to: 3.3 Animal Tissues

Plot a graph between the age of a tree (in years) on the x-axis and the diameter of the tree (in cm) along with the number of annual rings formed over time on the y-axis, using the data given in the Table 3.7.
S. No.
Age of the teak tree (Years)
DBH (Diameter at Breast Height) of tree (cm)
Number of annual rings formed
1.
5
4
5
2.
10
8
10
3.
20
24
20
4.
25
28
25
5.
30
32
30
6.
40
40
40
Y-axis: diameter (cm)
and number of rings
Diameter rises
with age
Number of rings
= age of tree
X-axis: age of
tree (years)
10
Age of teak tree (years)
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What the graph of the teak tree shows
Age of the tree (years)
DBH (cm)
Annual rings formed
What this tells us
5
4
5
Rings = age, right from the start
10
8
10
Diameter has doubled in 5 years
20
24
20
The fastest growth in girth
25
28
25
Growth in girth begins to slow
30
32
30
Steady, slower thickening
40
40
40
Rings still equal the age exactly
(i) The graph rises steadily: as the tree gets older, its diameter increases. So the stem keeps growing thicker over time.
(ii) The number of annual rings equals the age in years, and the diameter grows along with it — so more rings mean a thicker, older tree.
(iii) The lateral meristem is responsible for the girth of the stem. It lies in a ring along the stem.
Reading the Teak Tree Graph
Age increases
The diameter increases steadily.
↓
Annual rings
Their number equals the age in years.
↓
More rings and a wider trunk both mean an older tree
Back to: 3.2.2 Lateral meristem — How do plants grow in girth?

A tree was severely debarked by an elephant (bark is rich in nutrients). (i) Which function(s) are hampered by debarking? (ii) Which plant tissue is affected by further damage to the trunk? (iii) Which function is hampered if the tissues beneath the bark are damaged? (iv) What assumptions are you making?
Bark removed
by elephant
Phloem (in bark)
damaged — food
transport stops
Xylem (deeper
wood) — water
transport
Deeper damage
stops water
transport too
sh
Sere V
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(i) Debarking damages the phloem in the bark, so the transport of food from leaves to roots is hampered.
(ii) Further damage to the trunk would affect the xylem, which lies deeper in the wood.
(iii) If the xylem beneath the bark is damaged, the transport of water and minerals up the tree is hampered, and the tree may dry out.
(iv) We assume the bark holds the phloem and that the elephant removed only the outer layers. If deeper layers were also removed, water transport would fail too and the tree could die.
Debarked Tree
Bark is damaged
The phloem in the bark is destroyed.
↓
Food cannot move leaves → roots
Deeper damage would also harm the xylem.
↓
Transport of food stops first, then water
Back to: 3.2.4 Permanent tissues

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 —
flexible, thick corners
Stem bends
without breaking /
Sclerenchyma —
hard, thick walls
Stem would be
brittle and snap X
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The flexibility is given by
collenchyma
, whose living cells have thick, pectin-rich corners that bend without breaking.
If collenchyma were replaced by sclerenchyma, the stem would become hard and stiff. In strong winds it could not bend, so it would be brittle and might snap instead of swaying.
Why the Sapling Bends
Collenchyma
Living cells with pectin-rich corners bend without breaking.
↓
If replaced by sclerenchyma
Lignified cells make the stem hard and stiff.
↓
A stiff stem could snap in strong winds
Back to: 3.2.4 Permanent tissues

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?
Cutting A —
no node:
does not sprout X
Cutting B —
has a node
with a bud:
sprouts /
Node contains
meristematic tissue
Keep soil, water,
light the same
(fair test)
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(i) Type B grew because its cutting included a node with an intercalary or apical meristem, which can divide and form new shoots; type A had no such growing region.
(ii) Type B contained a node (with buds and meristematic tissue), while type A was a piece of internode without one.
(iii) The observation was that type B sprouted and grew into sugarcane plants while type A did not.
(iv) Soil, water, light, temperature and the size of the cuttings should be kept the same, so only the presence of a node differs.
Sugarcane Cuttings A and B
Type B had a node
The node carries buds and meristematic tissue.
↓
Type A had no node
No dividing region, so no new shoot.
↓
Only type B sprouted into a plant
Back to: 3.2.3 Intercalary meristem — How do plants grow after being cut?

Rohan says, "A tissue is a group of similar cells performing similar functions." Rajiv argues this is true for simple tissues but a little different for complex tissues. Provide your explanation.
Simple tissue
(parenchyma) —
cells all alike
Complex tissue
(xylem) —
many cell types
Vessels,
tracheids,
parenchyma
together
Different cells,
one shared
function
i
Different cells —
one job (transport)
All cells similar —
one job (storage)
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Rohan's statement fits
simple tissues
like parenchyma, where all the cells are of one kind doing one job.
Rajiv is right about
complex tissues
like xylem and phloem. These are made of more than one type of cell (for example, vessels, tracheids and parenchyma in xylem) working together for one overall function, transport. So they are still one tissue, but not all cells are alike.
Is a Tissue Always One Cell Type?
Simple tissue
Parenchyma — all cells of one kind.
↓
Complex tissue
Xylem and phloem — several cell types together.
↓
Both are tissues, so Rajiv’s point stands
Back to: 3.2.4 Permanent tissues

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.
Coconut husk /
coir mat —
needs strength
Sclerenchyma —
thick lignified walls Y
Parenchyma —
thin walls, soft X
Only sclerenchyma
gives lasting strength
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The strength comes from
sclerenchyma
, whose cells have thick walls hardened with lignin, making them tough and fibrous.
Living parenchyma has thin walls and is soft, with loosely packed cells that store food. It cannot bear strain or give the hard, lasting strength needed for mats, so it could not replace sclerenchyma.
Why Coconut Husk Is Tough
Sclerenchyma
Thick walls hardened with lignin — tough and fibrous.
↓
Parenchyma
Thin-walled, soft, loosely packed cells.
↓
Only sclerenchyma can bear the strain
Back to: 3.2.4 Permanent tissues

Vibha claims, "Meristematic cells are located only at the root and shoot apices." What do you think? What question could Neha ask to help her understand if the statement is incorrect?
Apical — at the
tips (this part is true)
Lateral — ring in
the stem (thickens
trunk)
Intercalary — at
the nodes (regrowth)
So meristems are
NOT only at the tips
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Vibha's statement is incorrect. Apical meristems are at the root and shoot tips, but there are also lateral meristems (which thicken the stem) and intercalary meristems (at the nodes of grasses).
Neha could ask: "If meristems are only at the tips, then how does a tree trunk grow thicker, and how does grass grow back after it is cut?" This points to the lateral and intercalary meristems.
Are Meristems Only at the Tips?
Apical meristem
At the root and shoot tips.
↓
Lateral and intercalary meristems
In the stem, and at the nodes of grasses.
↓
So Vibha’s statement is incorrect
Back to: 3.2.3 Intercalary meristem — How do plants grow after being cut?

A plant cell and an animal cell are the same size. (i) Which cell will have a larger vacuole? Give reasons. (ii) What assumptions are you making?
Plant cell — one
large central vacuole
Nucleus pushed
to the edge
Animal cell — small
or no vacuoles
Same size, but
plant cell's vacuole
is larger
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(i) The
plant cell
will have the larger vacuole. Plant cells usually have one big central vacuole that stores water and keeps the cell firm, while animal cells have only small vacuoles or none.
(ii) We assume both are mature, normal cells of the same type of plant and animal, and that the plant cell is not a special one (like a meristematic cell, which has hardly any vacuole).
Plant Cell vs Animal Cell
Plant cell
One big central vacuole storing water, keeping the cell firm.
↓
Animal cell
Only small vacuoles, or none.
↓
The plant cell has the larger vacuole
Back to: 3.1 Why are Plant and Animal Tissues Different?

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?
Parenchyma —
stores food AND
photosynthesises
“a
LINE
Epidermis —
protects AND helps
transpiration/absorption
One tissue can do
several jobs
So ‘only one function’
is too simple
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I would ask: "Does any single tissue do more than one job?" and "Can the same job be shared by more than one tissue?"
Examples: parenchyma both stores food and does photosynthesis in green parts, so it has more than one function. The epidermis protects and also helps in transpiration and absorption. These show the statement is too simple — one tissue can do several jobs.
Does One Tissue Do Only One Job?
Ask: can one tissue do many jobs?
Parenchyma stores food and photosynthesises.
↓
Ask: can one job be shared?
Support comes from collenchyma and sclerenchyma.
↓
So the statement is not fully correct
Back to: 3.2.4 Permanent tissues

Project 1
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?
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A ligament rupture is a torn band joining bone to bone; a cartilage rupture is damage to the cushioning at a joint; a fracture is a broken bone. Risk can be lowered with regular exercise to keep muscles and bones strong, a calcium- and vitamin-rich diet, proper warm-ups, and avoiding sudden overloading of joints.

Project 2
Sit with your feet flat on the floor. Place your fingers on the back of your ankle just above the heel. Point your toes down and up, and feel the tendon moving. Tendons withstand huge pulling forces — explore other tendons around different joints.
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As you point your toes, you can feel a thick cord (the Achilles tendon) tighten and move behind the ankle. It connects the calf muscle to the heel bone and transmits the pulling force that lifts the foot. Similar tendons can be felt at the wrist, behind the knee and at the elbow, each connecting a muscle to a bone.

Project 3
Reflect on any physical practice you are familiar with, such as yoga or kabaddi. How would it support bone and muscle health?
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Yoga stretches and holds the body in postures, which improves flexibility of joints, strengthens muscles and improves posture and breathing. Kabaddi involves running, holding and quick movements, which build muscle strength, stamina and strong bones. Both, done regularly, keep the musculoskeletal system fit and reduce stiffness.

Project 4
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?
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Pruning removes old shoots and encourages meristems to form fresh, bushy growth. Grafting joins a healthy shoot so its meristems and conducting tissues continue growth. Irrigation keeps xylem supplied with water so transport works. Crop rotation keeps the soil rich in minerals, so roots and conducting tissues stay healthy.

Project 5
Turn a nature walk into a research project. Observe different leaves and their adaptations for desert, moist or aquatic habitats. Consult an elder about leaves that stay fresh, repel water or deter insects, and their traditional uses.
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Desert leaves are often thick with a waxy cuticle to save water; aquatic leaves are thin with air spaces to float; moist-habitat leaves are broad. Elders may point to leaves used as plates or insect repellents. While learning tribal dance steps, note how the hinge joints (knees, elbows), the ball-and-socket joints (shoulders, hips) and the pivot joint (neck) all work together, and build a short drama showing these movements.

Project 6
Study various dance forms of different tribal communities across the country. Each student learn and experience at least five steps. Observe the joint movements involved in performing these steps and then develop a dance or drama on the concept of joint movements. Perform this at the school’s annual function so that students from different grades can learn from it.
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Pick dance forms such as Bihu, Ghoomar, Santhali or Bhangra and learn five steps of each. While practising, note which joints do the work: the
hinge joints
at the knees and elbows bend and straighten, the
ball-and-socket joints
at the shoulders and hips swing the limbs in circles, and the
pivot joint
in the neck turns the head side to side.
Build a short dance-drama in which each movement highlights one joint type, and present it at the annual function so younger students can see how joints make movement possible.
💭 The Quest Continues …
Will it be possible to obtain a complete animal from an animal cell like plants? If yes, what would be the advantages and challenges of this development?
It may become possible through advanced cloning and stem-cell methods. The advantages could be saving endangered animals and producing tissues for treatment; the challenges include the difficulty that most animal cells are not totipotent, plus serious ethical and safety concerns.