Question 1

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.

Accepted Answer

(iii). - (iii) They have thin walls, dense cytoplasm and large prominent nucleus. - The chapter describes meristematic cells as small, with thin cell walls, a large and prominent nucleus, and dense cytoplasm containing many organelles — precisely the equipment for repeated division. - The cells are also tightly packed with little or no intercellular space, and these features together are what allow continuous and rapid cell division. - (i) is wrong — thick walls belong to sclerenchyma, whose cells are lignified and mostly dead, and dead cells do not divide. - (ii) is wrong — vacuoles are generally absent in meristematic cells; a large vacuole would leave too little cytoplasm and too few organelles for division. - (iv) is wrong — differentiation is what happens when a meristematic cell loses the ability to divide and turns into a permanent tissue; a differentiated cell is the opposite of a dividing one.

Question 2

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. Xylem fibre Tracheid Xylem parenchyma Vessel Phloem parenchyma Sieve tube Sieve pore Companion cell (b) phloem Phloem Epidermal tissue Epidermal tissue Xylem

Accepted Answer

- Coconut husk fibres are made of sclerenchyma, while coriander leaf stalks are made of collenchyma (with parenchyma). - Sclerenchyma cells have thick walls due to deposition of lignin, which makes them hard and strong, and most of these cells are dead. - A dead, lignified, rigid wall cannot give way, so the fibre resists bending and finally snaps — hard and brittle. - The chapter places coconut husk here itself, alongside walnut shell, as a hard covering made of sclerenchyma. - Collenchyma cells are living, with their corners unevenly thickened by pectin — a chemical the chapter compares to rubber for the flexibility it gives. - That uneven, unlignified thickening supports the stalk yet still lets it bend without breaking, so the coriander stalk stays soft and flexible. - Same job (support), two different materials: lignin buys strength at the cost of flexibility; pectin buys flexibility at the cost of strength.

Question 3

The red colour of blood is due to haemoglobin, an iron-rich protein in the Red Blood Cells (RBCs). RBCs live for about 4 months and are replaced regularly.

Accepted Answer

- Blood is red because of haemoglobin, an iron-rich protein carried inside the Red Blood Cells (RBCs). - RBCs live for about 4 months and are then replaced regularly by newly made ones, so the supply is continuously renewed. - This is why red blood oozes out of even a small cut on the skin. - Blood is a connective tissue — it connects the parts of the body by transporting nutrients, gases and hormones. - Its matrix is watery: plasma makes up 55 % of the total volume, and the formed elements — RBCs, WBCs and platelets — the remaining 45 %.

Question 4

If a plant is unable to transport food from leaves to roots which tissue is malfunctioning? (i) Xylem (ii) Phloem (iii) Epidermis (iv) Sclerenchyma

Accepted Answer

- Phloem — option (ii). - The chapter separates the two conducting tissues by cargo in its opening pages: "xylem transports water and minerals, while phloem transports food." Food travelling from leaves down to roots is therefore a phloem job. - Section 3.2.4(iii), Conducting tissues, names the cells that do it. Phloem "consists of sieve tubes, companion cells, phloem parenchyma and phloem fibres", and "Sieve tubes transport food from leaves to other parts of the plant." The roots are among those "other parts", so a plant that cannot move food from leaves to roots has sieve tubes of the phloem that are not working. - Why not (i) Xylem: the same section says xylem "transports water and minerals from the roots to other parts of the plant" — the wrong cargo, and the opposite direction to the one in the question. - Why not (iii) Epidermis: the chapter files the epidermis under "(i) Protective tissue". It is "the outermost layer of the plant body", "a tightly packed, single layer of flat and rectangular cells" that "protects all parts of the plants". The jobs listed for it there are protection by the cuticle, absorption through root hair, and gaseous exchange and transpiration through stomata — never food transport. It is not one of the conducting tissues at all. - Why not (iv) Sclerenchyma: it is listed as a simple permanent (supporting) tissue with "thick walls… due to deposition of lignin", of which "Most of these cells are dead". It supplies hardness and strength — coconut husk, walnut shell — not conduction. - At a Glance states it once more: "Complex permanent tissues include xylem and phloem that transport water and food respectively to all parts of the plant." - The book's printed Answer Key gives (iii) Epidermis, which does not agree with Section 3.2.4 or with the At a Glance summary. Both of those passages assign food transport from the leaves to the phloem's sieve tubes, and both classify the epidermis as a protective tissue with no conducting role, so the chapter's own text settles it the other way: the answer is (ii) Phloem, and the key entry should be treated as an error.

Question 5

Platelets help in blood clotting at the site of the injury.

Accepted Answer

- Blood clots because of platelets, which act at the site of the injury. - Table 3.3 pairs the everyday experience — red blood oozing from a small cut — with the observation that a clot forms after some time, and the question "What causes blood to clot?" - The clot plugs the cut so that bleeding stops and germs cannot get in through the wound. - Platelets are one of the formed elements of blood, which together make up 45 % of its volume; the rest is plasma.

Question 6

Ground tissue system: This forms the main body of a plant between the dermal and conducting tissues. It includes parenchyma, collenchyma and sclerenchyma.

Accepted Answer

- A thick cuticle helps a desert plant because the waxy layer of cutin is water-proof and cuts down water loss; it harms an underwater plant because that same layer seals off the exchange of gases, water and minerals across its surface. - In a desert, water is the scarcest resource. The chapter states that in plants living in very dry habitats the epidermis may be covered by a thick layer of cuticle to reduce water loss by transpiration through the stomata. - The cuticle also shields the desert plant from mechanical injury, from invasion by parasites, and from the extreme heat and light of its habitat — all of which the epidermis is there to resist. - Underwater, the plant is surrounded by water on every side, so there is nothing to conserve — a thick cuticle solves a problem the plant does not have. - Worse, an aquatic plant takes in dissolved CO 2, O 2, water and minerals over its whole body surface; a thick waxy seal blocks that uptake and starves it of the gases needed for photosynthesis and respiration. - A thick opaque layer also cuts the light reaching the photosynthesising cells beneath the epidermis. - So the same structure is an adaptation in one habitat and a handicap in the other — structure is useful only in relation to the surroundings it must work in.

Question 7

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.

Accepted Answer

- To allow quick exchange of materials across them — option (iii). - Table 3.2 pairs each epithelial structure with the function it serves, and its first row is exactly this case: function "Exchange: Helps in rapid diffusion of liquids and gases"; structure "Single layer of thin, flat cells"; location "Lining of the tissue in the blood vessels and lungs". A single thin layer keeps the diffusion path short, which is what makes the exchange rapid. - The last row of the same table makes the same pairing for the gut: function "Absorption: Efficient uptake of nutrients, water, etc."; structure "Single layer of tall, pillar-like cells"; location "Lining of small intestine". Again a single layer wherever the tissue's job is moving material across itself. - Section 3.3.1 gives the general statement: epithelial tissue "lines the internal organs, such as the mouth, lungs, blood vessels and intestine" and "helps in the absorption, secretion and movement of substances." - Why not (ii) To provide maximum strength: Table 3.2 answers that with a different row. Where the body needs protection "from mechanical injury, friction and entry of microbes", the epithelium is "Many layers of cells; the outer cells are flat and tightly packed", located in "Skin, mouth and oesophagus". In this chapter strength comes from many layers — the opposite of the one-or-few-cell thickness the question asks about. - Why not (iv) To reduce friction: friction appears in that same many-layered protection row, not in either of the thin, single-layer rows. - Why not (i) To store food efficiently: storage is not among the five functions Table 3.2 lists for epithelium — they are exchange, protection, secretion, sensory functions and absorption. - The book's printed Answer Key gives (ii) To provide maximum strength, which does not agree with Table 3.2. In that table maximum strength belongs to the "Many layers of cells" protective epithelium of skin, mouth and oesophagus, while the one-cell-thick lining of blood vessels and lungs is set against "rapid diffusion of liquids and gases". The chapter's own table therefore settles it the other way: the answer is (iii), and the key entry should be treated as an error.

Question 8

During exercise or running, muscles need more oxygen, so breathing becomes faster and blood flow increases (face appears red).

Accepted Answer

- You breathe faster while running because the muscles need more oxygen, and your face turns red because the blood flow increases. - Working muscles use up oxygen quickly, so the breathing rate rises to take in more air. - The rib cage makes this possible: the ribs are joined to the spine at the back and to the sternum in front by flexible cartilage, letting the cage expand and contract so air moves in and out of the lungs. - The nervous tissue is in charge of the adjustment — during exercise the brain signals the heart to beat faster to meet the body's increased oxygen demand. - More blood flowing through the vessels close to the skin of the face is what makes it look red.

Question 9

Vascular tissue system: This consists of conducting tissues — xylem and phloem.

Accepted Answer

- Water rises because the dead cells of the xylem form open, unblocked pipes while the living cells of the leaf pull the water up by transpiration — the plant does not push water from below, it is sucked up from the top. - Tracheids and vessels are tubular and thick-walled and lose their living contents. Joined end to end, they make a continuous hollow tube running from root to leaf with no cytoplasm or nucleus in the way — being dead is exactly what makes them good pipes. - Their thick, lignified walls stop the tube from collapsing while the water inside it is under tension, and the chapter notes that xylem also gives strength to the plant. - At the top, the living epidermal cells of the leaf carry pores called stomata, through which water escapes as vapour. This evaporation is transpiration. - The chapter states the link directly: transpiration helps in water transportation by creating a transpiration pull in the xylem. - Every water molecule that leaves at the leaf drags the column behind it, so the loss of water at the top is what lifts fresh water at the bottom, against gravity, without any pump. - At the other end, living root hairs — projections of the root epidermal cells — increase the surface area for absorbing water and minerals and keep the column supplied. - So it is a partnership: dead cells supply the plumbing, living cells supply the force.

Question 10

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?

Accepted Answer

- In the straight-leg jump all three joints stay nearly straight the whole time; in the normal jump all three bend first and then straighten together. - Straight-leg jump. The knee stays locked straight before, during and after take-off, the hip stays extended with the trunk upright, and only the ankle can push. With one small joint doing all the work the jump is low, and on landing the stiff leg has nothing left to bend, so the shock passes straight up through the bones as a hard jolt. - Normal jump — the crouch. The ankle bends forward, the knee bends, and the hip bends so the body leans slightly forward. All three joints are flexed at the same time. - Normal jump — take-off. The three straighten in quick succession — hip, then knee, then ankle — each adding to the push, so the jump is far higher. - Normal jump — landing. The sequence reverses: ankle, knee and hip bend again and absorb the shock gradually, so the landing is soft. - Why the joints behave differently. The knee is a hinge joint and can only bend and straighten in one plane; the hip is a ball and socket joint, so it can also swing sideways and rotate as the body leans. - What actually does the bending. The chapter is explicit that joints allow movement but cannot move the bones on their own — muscles contract and pull on the bones through tendons, and the movement appears at the joint.

Question 11

White Blood Cells (WBCs) collect at infected areas, causing pus formation and inflammation (causing redness and swelling, and possible pus formation at the infected area). WBC Platelets RBCs

Accepted Answer

- An infected patch of skin turns red and swollen because White Blood Cells (WBCs) collect there. - WBCs gather at the infected area to fight the germs; this gives inflammation — the redness and the slight swelling — and possibly pus. - Fever may go with it, as the body responds to the infection. - WBCs are one of the formed elements of blood, alongside RBCs and platelets, which together make up 45 % of blood volume. - Note how the three formed elements divide the labour: RBCs carry oxygen, platelets seal wounds, WBCs fight infection — division of labour inside a single tissue.

Question 12

What do you think will happen if there were no stomata in the epidermis of the stem or leaves? 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? Many such questions can be asked but the answers lie in the diversity of animal tissues, which are specially adapted to perform different functions. It is interesting to understand how the structure of an animal tissue suits its specific function. Let us explore different kinds of animal tissues. Each tissue performs a specific function. 3.3.1 Epithelial tissues — Structure and functions Epithelial tissue forms the outer covering of the body (skin) and also lines the internal organs, such as the mouth, lungs, blood vessels and intestine. It is composed of closely packed cells with very little space between them.

Accepted Answer

- The plant would starve and then wilt — with no stomata there is neither gaseous exchange nor transpiration. - No CO 2 could enter the leaf, so photosynthesis would stop and the plant could not synthesise its food. - The O 2 produced in photosynthesis could not leave, and the O 2 needed for respiration could not enter through the leaf or stem surface. - With no transpiration there would be no transpiration pull, so water and minerals absorbed by the roots could not be lifted through the xylem to the top of a tall plant. - The chapter also credits transpiration with the elimination of wastes from the plant body — that route would be closed too. - The one gain would be almost no water loss, which is why plants of dry habitats reduce their exposure with a thick cuticle rather than losing stomata altogether. - On balance the loss far outweighs the gain: a plant sealed against water loss is also sealed against carbon dioxide, and it cannot feed itself.

Question 13

Compare your findings with those of your classmates and calculate the class average. Discuss why do bone and muscle mass differ between individuals, and how do they contribute to the overall body weight? 3.4.1 The musculoskeletal system in action Activity 3.5: Let us observe Move different parts of your body and observe what movement(s) it can make. Body Complete parts rotation Elbow No Shoulder Knee Neck Fingers Toes Wrist 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? The difference is due to the types of joints present. A joint is a junction between two or more bones. Joints allow movement but they cannot move the bones on their own. So, what actually causes the bones to move?

Accepted Answer

- Bones and muscles together make up roughly half of the body's weight — bone about 12 - 15 % for all adults, and muscle about 40 - 50 % in adult males and 30 - 40 % in adult females. - Worked example for a student of 50 kg, taking bone = 13.5 % and muscle = 35 %: - bone mass = 50 × 13.5/100 = 6.75 kg - muscle mass = 50 × 35/100 = 17.5 kg - together = 6.75 + 17.5 = 24.25 kg, i.e. 24.25/50 × 100 = 48.5 % of the total body weight - Why they differ between individuals — the chapter names three reasons: age, gender and body composition; it adds that the percentages may also vary by ethnicity or body type. - Level of physical activity and nutrition matter too: the chapter says correct posture, proper nutrition, regular exercise and yoga keep bones strong and muscles fit, so two people of the same weight can carry very different bone and muscle mass. - How they contribute to body weight — the skeleton is the rigid framework and the muscles are the tissue that pulls on it, so between them they account for the single largest share of body weight; fat, organs and body fluids make up the rest. - Expect the class average to sit near these figures, with the boys' muscle percentage higher than the girls' and the bone percentage similar for everyone.

Question 14

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

Accepted Answer

- Hinge joint — option (ii). - Section 3.5.2 names the knee outright: "the elbow bends and straightens in one direction only like a door hinge… This type of joint is called a hinge joint. A similar hinge joint is present in the knee, where a small bone called the kneecap protects the joint." Bending your knee is precisely the movement that section is describing. - Why not (iii) Pivot: Section 3.5.3 gives the pivot joint a different action in a different place — the skull is "connected to the backbone through a pivot joint, which allows the head to move side to side like a doorknob turning in its socket." That is a turn about an axis, not a bend, and it sits at the neck. - Why not (i) Ball and socket: Section 3.5.1 places it at the shoulder, where "the rounded top of the upper arm bone fits into a shallow hollow of the shoulder bone", and the joint "allows forward, backwards, sideways and circular movements." The knee has no such freedom — recording that contrast is the point of Table 3.5, whose worked Elbow row reads Complete rotation: No, Partial rotation: No, Bending: Yes. - On the ankle — this is reasoning, not chapter content. The chapter never classifies the ankle: it is not one of the body parts listed in Table 3.5 (Elbow, Shoulder, Knee, Neck, Fingers, Toes, Wrist), and none of Sections 3.5.1–3.5.4 mentions it. Applying the chapter's own definition, pointing the toes down and up is bending in one direction only rather than rotating, which fits the hinge description and not the pivot's side-to-side turn. Treat that as an inference from the chapter's criteria, not as a statement the book makes. - The book's printed Answer Key gives (iii) Pivot, which does not agree with Sections 3.5.2 and 3.5.3. Section 3.5.2 says in so many words that a hinge joint "is present in the knee", and Section 3.5.3 assigns the pivot joint to the skull-and-backbone connection at the neck, so the chapter's own text settles it the other way: the answer is (ii) Hinge, and the key entry should be treated as an error.

Question 15

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? 40 Exploration Grade 9

Accepted Answer

- The dance poses between them use all four joint types the chapter names — ball and socket, hinge, pivot, and (unmoving) fixed. - Shoulder — ball and socket joint. The rounded top of the upper arm bone sits in a shallow hollow of the shoulder bone, so the raised, spread and circling arms of almost every pose can move forward, backwards, sideways and in circles. This is the freest joint in the body and the reason arm positions carry so much of the expression. - Hip — ball and socket joint. Gives the turned-out, sideways and circular leg movements of the classic half-sitting stance. - Elbow — hinge joint. Bends and straightens the forearm in one direction only, like a door hinge — used whenever the arm is folded in or extended out. - Knee — hinge joint. Bends and straightens in one plane for the deep bent-knee stance; the kneecap, a small bone, protects the joint while it is loaded. - Ankle — hinge-type movement. Up-and-down movement of the foot for the flat-footed stamping of the footwork. - Neck — pivot joint. The skull is connected to the backbone by a pivot joint, letting the head move side to side like a doorknob turning in its socket — the signature head movement of Indian classical dance. - Wrist and fingers. Bending and partial rotation shape the hand gestures. - Backbone. Not a single joint but a column of vertebrae with a cartilage disc between each pair, cushioning them and allowing the torso to bend and twist without injuring the spinal cord. - Skull — fixed joints. Its flat bones stay locked together throughout, keeping the brain safe however vigorously the body moves. - In every case the joint only permits the movement; the chapter is explicit that joints cannot move bones on their own — muscles contract and pull on the bones through tendons, and the movement appears at the joint.

Question 16

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.

Accepted Answer

A (iii) B (i) C (iv) D (iii). - A — (iii): (A) is true, but (R) is false. - Assertion true: Table 3.2 places a single layer of thin, flat cells in the lining of the lungs precisely because it helps rapid diffusion of liquids and gases. - Reason false on two counts: that lining is one cell thick, not multiple layers of tall cells; and its thinness speeds diffusion rather than slowing it. Multiple layers of tall cells describe the protective and absorptive epithelia instead. - B — (i): both true, and (R) is the correct explanation of (A). - Assertion true: the chapter says cardiac muscles work tirelessly and rhythmically, enabling the heart to beat throughout life without fatigue. - Reason true and genuinely explanatory: many mitochondria mean a steady supply of energy, and an abundant blood supply keeps delivering the oxygen and nutrients needed to make it — so the muscle never runs an energy debt, which is exactly why it does not tire. - C — (iv): (A) is false, but (R) is true. - Assertion false: tendons connect muscle to bone; it is ligaments that connect bone to bone, and Table 3.4 sets the two out side by side. - Reason true, and it is the chapter's own sentence: when a muscle contracts, the tendon transmits this force to the bone, resulting in movement at a joint. Note that the reason quietly states the correct fact that the assertion gets wrong. - D — (iii): (A) is true, but (R) is false. - Assertion true: §3.5.2 says a hinge joint bends and straightens in one direction only, like a door hinge — the elbow and the knee. - Reason false: bone ends shaped to allow sliding in all directions would give a ball and socket joint. The hinge shape is what restricts movement to one plane, so the reason describes the opposite of what a hinge does.

Question 17

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. increase in the diameter of stem and number of annual rings S. No. 1. 2. 3. 4. 5. 6. (i) Analyse the graph in terms of the diameter of the stem over time and share the interpretation. (ii) What is the relation between the diameter of the teak tree to the annual rings formed? (iii) Which specialised tissue is responsible for the girth of the stem and where is it located?

Accepted Answer

- The graph to draw. One graph carrying two plotted lines against the same axes. - x-axis: Age of the teak tree (years), scaled 0 to 40 in steps of 5. - y-axis: Diameter (cm) and Number of annual rings, scaled 0 to 40 in steps of 5 — both quantities happen to share the same range, so one scale serves both. - Line 1 — DBH (cm): plot (5,4), (10,8), (20,24), (25,28), (30,32), (40,40) and join the points. - Line 2 — Number of annual rings: plot (5,5), (10,10), (20,20), (25,25), (30,30), (40,40) and join the points. This comes out as a perfectly straight line through the origin at 45^°. - Mark each plotted point clearly, use a different symbol or line style for the two lines, and add a key naming them. (i) Interpretation of the diameter curve - The diameter increases steadily throughout — the teak tree never stops thickening, because its lateral meristem keeps dividing year after year. - Average rate over the whole record: (40 - 4)/(40 - 5) = 36/35 ≈ 1.03 cm per year. - The rate is not uniform, interval by interval: - 5 → 10 yr: 8-4/5 = 0.8 cm/yr - 10 → 20 yr: 24-8/10 = 1.6 cm/yr - 20 → 25 yr: 28-24/5 = 0.8 cm/yr - 25 → 30 yr: 32-28/5 = 0.8 cm/yr - 30 → 40 yr: 40-32/10 = 0.8 cm/yr - So the curve is steepest between years 10 and 20, where girth grows at twice the rate of every other stretch, and settles back to a steady 0.8 cm/yr after that. - This matches the chapter's account of annual rings: some are wide and some narrow, reflecting favourable or unfavourable growth conditions in that year. The years 10 - 20 were the favourable ones for this tree. (ii) Relation between diameter and annual rings - The number of annual rings equals the age in years exactly — 5, 10, 20, 25, 30, 40 rings at 5, 10, 20, 25, 30, 40 years — so one ring is laid down each year, and counting rings gives the tree's age. - Diameter and ring count rise together: the more rings, the greater the diameter. Each ring is one year's fresh layer of cells added to the girth. - The relation is close to proportional but not exactly so, because rings differ in width: 4/5 = 0.8 cm per ring at age 5, 24/20 = 1.2 cm per ring at age 20, and 40/40 = 1.0 cm per ring at age 40. - Practical use: from a cut trunk, ring count gives the age and ring widths give the climate record of the years the tree grew through. (iii) The tissue responsible for girth - The lateral meristem. - It is a meristematic tissue of actively dividing cells arranged in a ring along the circumference of the stem — visible in the T.S. of the sunflower stem in Fig. 3.7, lying between the phloem outside and the xylem inside. - It divides and produces new cells both inside and outside in concentric layers, and that is what increases the diameter of the stem.

Question 18

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?

Accepted Answer

(i) Functions hampered by debarking - Protection and food transport are the two that fail first. - The bark is made of cork cells — dead, compactly arranged, and containing a substance that makes them impermeable to water and gases. Strip it and the trunk loses its shield against water loss, mechanical injury, harmful microorganisms and extreme environmental conditions. - Immediately beneath the bark lies the phloem. If it is torn away with the bark, food made in the leaves can no longer be carried down to the stem and the roots, and the roots begin to starve because they cannot photosynthesise for themselves. - The exposed wound is an open door for parasites and pathogens — the chapter notes that the cuticle and outer covering exist partly to prevent invasion by parasites. (ii) Tissue affected by further damage to the trunk - Working inwards from the surface, the order in Fig. 3.7 is epidermis/cork → ground tissue → phloem → lateral meristem → xylem. - So the phloem is hit next, and then the lateral meristem (cambium) just inside it. Deeper damage reaches the xylem. (iii) Function hampered if the tissues beneath the bark are severely damaged - Loss of phloem → transport of food from leaves to stem and roots stops completely; the roots starve. - Loss of lateral meristem → the tree can no longer grow in girth, cannot lay down new phloem, new xylem or new cork, and so cannot heal the wound or add another annual ring. - Loss of xylem → transport of water and minerals from roots to leaves stops, and the tree also loses the mechanical strength xylem provides. The leaves wilt, photosynthesis fails, and the tree dies. (iv) Assumptions, and how the answers would change - Assumed that the tree is a dicot with secondary growth, so it has bark, a cambium ring and annual rings at all. - Assumed that "bark" here means the dead cork layer together with the phloem just under it — that is, the elephant took conducting tissue and not merely the dead covering. - Assumed that the damage runs all the way round the trunk, not just across a patch. - Assumed the cambium underneath is still alive. - If only the dead cork was scraped off and phloem plus cambium survive, the tree loses protection alone. The cork cambium can divide and make fresh cork, and the tree recovers with a scar. - If the damage is a patch rather than a complete ring, food can still travel down through the intact phloem on the undamaged side, and the tree survives. - If it is a complete ring and the phloem is gone all round, the roots are permanently cut off from food. They starve and die, and the whole tree follows — even though the xylem is intact and the leaves stay green for a while, because water can still go up while food cannot come down.

Question 19

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.

Accepted Answer

- Collenchyma is the tissue responsible for the flexibility of the mango sapling's stem. - Its cells are living, with their corners unevenly thickened by pectin — a chemical the chapter compares to rubber for the flexibility it gives. - That combination supports the stem without making it rigid, which is precisely what the chapter credits collenchyma with: it allows parts of the plant like stems and tendrils to bend without breaking. - In a monsoon gust the stem gives way, lets the wind pass, and springs back. - If sclerenchyma replaced it, the stem would become stiff and brittle and would snap. - Sclerenchyma cells have thick walls due to deposition of lignin, making them hard and strong and forming the woody structure — and most of these cells are dead. - Hard is not the same as tough: a rigid rod cannot absorb the energy of a gust the way a flexible one can, so the force would go into breaking the stem instead of bending it. - Being dead and lignified, sclerenchyma also cannot stretch or elongate, so a young growing stem would lose the ability to extend and to recover its shape after being bent. - The chapter's own contrast makes the point in two familiar objects: coconut husk fibre (sclerenchyma) is hard and brittle, while a coriander leaf stalk (collenchyma) is soft and flexible. A sapling built like coconut husk would not survive a monsoon.

Question 20

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?

Accepted Answer

(i) Why type B grew and type A did not - Type B contained a node; type A did not. - A node is the point on the stem where branches or leaves arise, and it carries a bud together with intercalary meristem, which the chapter locates at the base of the internode or just above the node. - Meristematic cells divide continuously, so the bud at the node can sprout into a new shoot, after which the cutting puts out roots and grows into a whole sugarcane plant. - Type A was cut from the internode — the part of the stem between two nodes. Its cells are permanent tissue: through differentiation they have lost the ability to divide, and a tissue that cannot divide cannot produce a new shoot. - This is the same principle as the hedge that grows bushy after trimming and the grass that grows back after mowing — the intercalary meristem at the nodes is what regenerates the plant. (ii) The difference present in type B - The presence of at least one node, with its bud and its intercalary meristematic tissue. - Type A had only internode tissue, entirely permanent and non-dividing. (iii) Observations and measurements made - Whether each cutting sprouted at all — a simple yes/no for every cutting. - The number of cuttings that sprouted out of the total in each group, e.g. 8/10 of type B against 0/10 of type A. - The number of days taken to sprout. - The number of shoots produced per cutting. - The length of each new shoot in cm, measured at fixed intervals over the few weeks. - Whether roots formed, and how many. (iv) Parameters to keep the same for a fair comparison - Everything except the one factor being tested — the presence of a node. - Same sugarcane variety, and cuttings taken from the same parent plant of the same age. - Same length and thickness of every cutting. - Equal numbers of cuttings in group A and group B. - Same soil or growing medium, same pot size, and the same depth and orientation of planting. - Same watering schedule, light, temperature and humidity for both groups. - Same period of observation, with both groups checked on the same days.

Question 21

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.

Accepted Answer

- Both are partly right, and Rajiv's correction is the one that matters: Rohan's definition fits simple tissues but breaks down for complex tissues. - Rohan is quoting the chapter's general definition correctly — a tissue is a group of cells, similar in structure, that work together to perform a specific function. - It holds for simple permanent tissues. Parenchyma, collenchyma and sclerenchyma are each made of only one type of cell, which is exactly what "simple" means in the chapter. - It holds for meristematic tissue too, and for animal tissues like muscle and epithelium. - It fails for complex permanent tissues, which the chapter defines as being made up of more than one type of cell working together. - Xylem contains tracheids, vessels, xylem parenchyma and xylem fibres — dead and living cells, tubular and fibrous, side by side. Tracheids and vessels are thick-walled tubes; the parenchyma is the only living component; the fibres are sclerenchymatous. Structurally they are not alike at all, yet all of them serve one job: conducting water and minerals, and giving strength. - Phloem contains sieve tubes, companion cells, phloem parenchyma and phloem fibres. Sieve tubes carry the food, companion cells regulate loading and unloading of sugars, parenchyma stores food, resin, tannins and latex, and fibres give strength. Four different cell types, one shared purpose. - So the accurate statement is: a tissue is a group of cells — similar or dissimilar in structure — that work together to perform a specific function. - It is the shared function, not identical structure, that makes a group of cells a tissue. Rohan has described the usual case; Rajiv has spotted the exception that forces the better definition.

Question 22

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.

Accepted Answer

- Sclerenchyma gives coir mats their strength. - Its cells have thick walls due to deposition of lignin, which makes them hard and strong and forms the woody structure of the plant. - The chapter names this exact use: sclerenchyma is found in stems, leaf veins, and the hard coverings of seeds and nuts, such as coconut husk and walnut shell. - Most sclerenchyma cells are dead, which is an advantage here — the fibre keeps its shape and strength after the husk is cut, beaten and dried, with nothing left inside that needs water or food. - The cells are long, narrow and tightly packed with no intercellular space, so they resist pulling and tearing along their length — which is what a mat is subjected to every day. - Living parenchyma could not do this job. - Parenchyma cells are thin-walled and unlignified, so they carry no reinforcement and crush or tear under any real load. - They are loosely packed with intercellular spaces, which makes the tissue soft and easily torn apart. - They are living and full of water and stored food — dried out for a mat they would shrink and collapse; kept moist they would rot. - Parenchyma's actual work is storage, photosynthesis in green parts, and forming air spaces that let aquatic plants float. None of that requires or produces mechanical toughness. - The general rule the chapter is teaching: lignified dead walls give strength, thin living walls give metabolic activity — no tissue gets both.

Question 23

Vibha claims to her friend Neha that, “Meristematic cells are located only at the root and shoot apices”. What do you think about this statement? What question can Neha ask Vibha to help her understand further if the statement is incorrect?

Accepted Answer

- Vibha's statement is incorrect — she has described the apical meristem only, and the chapter names three kinds of meristematic tissue. - Apical meristem — at the root and shoot tips; increases the plant's length. This is the part Vibha has right, and it is what the onion experiment in Activity 3.1 demonstrates. - Lateral meristem — actively dividing cells arranged in a ring along the circumference of the stem; they divide inwards and outwards in concentric layers and increase the girth. Nowhere near a tip. - Intercalary meristem — at the base of the internode or just above the node; it is why grasses regrow after mowing or grazing and why a trimmed hedge turns bushy. - The chapter adds a fourth site in "Ready to Go Beyond": as a stem ages, some cells below the epidermis regain the ability to divide, act as lateral meristematic cells and form the cork cambium, which makes the bark. - Questions Neha can ask to help Vibha see the gap: - "If the dividing cells were only at the tips, how does a tree trunk get thicker every year and lay down annual rings?" - "A lawn is mowed, so the shoot tips have been cut off — why does the grass grow back?" - "Why does a hedge become bushier after trimming instead of simply stopping?" - "In Activity 3.1 we cut the root tips of Jar B and those roots stopped growing in length — but did that tell us anything about growth in girth?" - "Which meristem makes the bark of an old tree, and is it anywhere near a tip?" - Each of these points at a growth that Vibha's statement cannot explain, which is a better way of correcting her than simply naming the missing meristems.

Question 24

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?

Accepted Answer

(i) Which cell will have the larger vacuole - The plant cell. - A mature plant cell keeps one large central vacuole that occupies most of the cell's volume and stores cell sap, water and food. - Filled with water, the vacuole presses outwards and keeps the cell turgid — this is how a non-woody plant part stays firm and upright — and the rigid cell wall can withstand that pressure without the cell bursting. - An animal cell has no cell wall, only a flexible membrane. A large water-filled vacuole would push it out of shape or burst it, so animal cells have small vacuoles or none at all. - There is a functional reason as well: a plant cannot move to fetch food or walk away from its wastes, so it needs a large internal store; an animal ingests food and removes wastes continuously and does not. (ii) Assumptions being made - That both cells are mature, differentiated cells. Chapter 3 states that vacuoles are generally absent in meristematic cells — so if the plant cell were a dividing meristematic cell, it would have little or no vacuole and the answer could flip. - That the plant cell is a living cell such as parenchyma, not a dead sclerenchyma cell or an empty xylem vessel, which have no cell contents to speak of. - That both cells are normally hydrated; a wilted plant cell has a shrunken vacuole. - That "same size" means the same total cell volume, so the question is really about how that volume is divided between vacuole and cytoplasm. - That the animal cell is an ordinary body cell and not a specialised secretory or fat-storing cell.

Question 25

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?

Accepted Answer

- The statement is incorrect: most plant tissues perform several functions, and many single functions need more than one tissue. - Questions worth asking to test it: - "Can a single named tissue be shown doing two clearly different jobs?" - "Does the chapter's own description of any one tissue already list more than one function?" - "Does the same tissue do the same job in every organ — root, stem, leaf — and in every habitat?" - "Can any one function be completed by one tissue acting alone, or does it need partners?" - "Can a tissue's function change over the plant's life, or is it fixed once and for all?" - Tissues to test the questions on: - Parenchyma — mainly stores food, but also performs photosynthesis in the green parts of the plant, and in aquatic plants forms the air spaces that help them float. One tissue, three functions. - Xylem — transports water and minerals from the roots upward and provides strength to the plant; the chapter states both in the same paragraph. - Epidermis — protects against mechanical injury, water loss, harmful microorganisms and extreme conditions; its stomata carry out gaseous exchange, transpiration and elimination of wastes; its root hairs increase surface area for absorbing water and minerals. Protection, exchange, transport and absorption from one tissue. - Phloem — sieve tubes conduct food, phloem parenchyma stores food, resin, tannins and latex, and phloem fibres provide strength. - Sclerenchyma — gives mechanical strength in stems and leaf veins and forms the hard protective coverings of seeds and nuts. - Testing the other direction — lifting water to the top of a tall tree needs the xylem (the pipe), the root epidermis with its root hairs (absorption) and the leaf epidermis with its stomata (the transpiration pull). Three tissues, one function. - A tissue that changed its role — in F. C. Steward's experiment the phloem cells of carrot dedifferentiated, divided and redifferentiated into a whole plant, so even a specialised conducting cell is not locked to one function for ever. - Conclusion: tissues are specialised, which is not the same as single-purpose. The chapter's own definition is that a tissue performs "a specific function" — specific means characteristic, not solitary.

Revise, Reflect, Refine 3.1 (part 1 of 16)

Exercise 3.1