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NCERT Class 9 Science Tissues in Action: Exercise Solutions

Step-by-step working for every question of End-of-chapter exercises in NCERT's Class 9 Science book, chapter “Tissues in Action”, written by Shishya. Each question is in our own short words; open the NCERT chapter for the exact wording and figures.

1. Exercises Q1

   Meristematic cells divide again and again. Which property lets them? (i) thick walls for protection (ii) large vacuoles storing nutrients (iii) thin walls, dense cytoplasm and a large prominent nucleus (iv) they are functionally differentiated

   1. Meristematic cells are small and tightly packed with little intercellular space.
   2. They possess thin cell walls, dense cytoplasm, and a large prominent nucleus.
   3. Vacuoles are generally absent in these cells.
   4. These specific structural features allow for continuous and rapid cell division.

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

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2. Exercises Q2

   A plant cannot move food from its leaves to its roots. Which tissue is failing? (i) xylem (ii) phloem (iii) epidermis (iv) sclerenchyma

   1. The question asks which tissue is failing if a plant cannot move food from leaves to roots.
   2. According to the chapter, phloem is the conducting tissue responsible for transporting food from leaves to other parts of the plant.
   3. Xylem transports water and minerals, while epidermis and sclerenchyma provide protection and support, not food transport.

   Answer: (ii) phloem

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3. Exercises Q3

   Why is the epithelium lining an animal's internal organs usually only one or a few cells thick? (i) to store food (ii) for maximum strength (iii) for quick exchange of materials across it (iv) to reduce friction

   1. The chapter describes a specific type of epithelial tissue that lines blood vessels.
   2. This tissue is described as a single layer of thin, flat cells.
   3. Its main function is to help in the rapid diffusion of liquids and gases.
   4. Being thin allows materials to pass through quickly for exchange.

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

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4. Exercises Q4

   Compare a straight-leg jump (knees and ankles kept stiff) with a normal jump (knees and ankles bent): how do the ankle, knee and hip positions differ?

   Uses a figure printed in the NCERT book — open the chapter above to see it.

   1. Straight-leg jump: the ankles and knees stay stiff and almost straight, so the hips also barely bend; the jump is low and the landing feels jarring.
   2. Normal jump: before take-off the ankles, knees and hips all bend, and then they straighten quickly to push the body up.
   3. On landing in a normal jump the ankles, knees and hips bend again, which cushions the impact.
   4. Bending at these joints lets the leg muscles pull on the bones through a larger movement, so the normal jump goes higher and is safer.

   Answer: In the straight-leg jump the ankle, knee and hip stay nearly straight; in the normal jump all three bend and then straighten, giving a stronger push and a softer landing.

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5. Exercises Q5

   Which type of joint works when you bend your knees and ankles? (i) ball and socket (ii) hinge (iii) pivot

   1. (i) The knee joint allows bending and straightening in one direction, similar to a door hinge.
   2. (ii) The ankle joint also functions as a hinge, permitting movement in a single plane.
   3. (iii) Ball and socket joints allow multi-directional movement, while pivot joints allow rotation, neither of which matches the knee or ankle action.

   Answer: (ii) hinge

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6. Exercises Q6

   Assertion-reason (options: (i) both true, R explains A (ii) both true, R does not explain A (iii) A true, R false (iv) A false, R true). A: epithelium suits gas exchange in the lungs; R: it has many layers of tall cells that slow diffusion. B: cardiac muscle contracts continuously without tiring; R: its cells have many mitochondria and a rich blood supply. C: tendons join bone to bone and allow joint movement; R: tendons are tough connective tissue passing force from muscle to bone. D: a hinge joint moves mainly in one plane; R: its bone ends let it slide in all directions.

   1. (i) Epithelium in the lungs is thin to allow gas exchange, so the reason claiming it has multiple layers of tall cells that slow diffusion is false.
   2. (ii) Cardiac muscle contracts continuously without fatigue, and the reason correctly explains this by citing its high mitochondria count and rich blood supply.
   3. (iii) The assertion that tendons connect bone to bone is false because they connect muscle to bone, while the reason correctly states they transmit force from muscle to bone.
   4. (iv) Hinge joints allow movement in one plane, so the assertion is true, but the reason is false because the bone ends do not allow sliding in all directions.

   Answer: A (iii); B (i); C (iv); D (iii)

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7. Exercises Q7

   Teak tree data (age in years: diameter at breast height in cm, annual rings): 5: 4, 5; 10: 8, 10; 20: 24, 20; 25: 28, 25; 30: 32, 30; 40: 40, 40. Plot diameter and number of rings against age. (i) Interpret how the diameter changes over time. (ii) How are diameter and annual rings related? (iii) Which tissue makes the stem thicker, and where is it?

   1. (i) The diameter of the teak tree increases as its age progresses, showing steady growth over time.
   2. (ii) The number of annual rings formed is equal to the age of the tree, and the diameter increases in relation to the number of rings.
   3. (iii) The lateral meristem (cambium) makes the stem thicker; it lies along the sides of the stem, running around its circumference.

   Answer: (i) Diameter grows steadily with age (from 4 cm at 5 years to 40 cm at 40 years); (ii) one annual ring forms each year, so more rings go with a larger diameter; (iii) the lateral meristem (cambium) along the sides of the stem increases its girth.

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8. Exercises Q8

   An elephant has stripped the bark off a tree to eat it. (i) Which functions of the tree suffer? (ii) Which tissue would be hit by further damage to the trunk? (iii) Which function suffers if the tissues under the bark are badly damaged? (iv) What assumptions did you make, and how would the answers change if they changed?

   Uses a figure printed in the NCERT book — open the chapter above to see it.

   1. (i) The removal of bark strips away the protective cork layer, exposing the inner tissues to water loss and damage.
   2. (ii) The vascular tissue system, specifically the phloem located just under the bark, is the tissue most likely to be hit by further damage to the trunk.
   3. (iii) If the tissues under the bark are badly damaged, the transport of food and nutrients from the leaves to the rest of the tree suffers.
   4. (iv) The assumption is that the elephant removed the outer bark but left the inner vascular tissues intact; if the damage extended deeper to the xylem, water transport would also fail.

   Answer: (i) Protection and water retention; (ii) Vascular tissue (phloem); (iii) Food transport; (iv) Assumption that only outer bark was removed, otherwise water transport would also be affected.

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9. Exercises Q9

   A young mango sapling's stem bends in monsoon winds without breaking. Which tissue gives this flexibility? Predict what would happen if it were replaced by sclerenchyma.

   1. Collenchyma tissue is responsible for the flexibility of the young mango sapling's stem.
   2. This tissue contains pectin, a chemical that provides flexibility similar to rubber.
   3. Collenchyma allows parts like stems to bend without breaking under stress.
   4. If replaced by sclerenchyma, the stem would become hard and strong due to lignin deposition.
   5. Sclerenchyma cells are dead and form a woody structure, making the stem brittle.
   6. The stem would likely break instead of bending when exposed to monsoon winds.

   Answer: Collenchyma provides flexibility; replacing it with sclerenchyma would make the stem hard, brittle, and prone to breaking.

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10. Exercises Q10

    Sohan planted two kinds of sugarcane cuttings: in Fig. 3.23 type A is a piece of stem between nodes and type B a piece with a node; B sprouted and A did not. (i) Why did B grow and A not? (ii) What was different in B? (iii) What observation showed the effect? (iv) What should be kept the same for a fair test?

    Uses a figure printed in the NCERT book — open the chapter above to see it.

    1. (i) Type B cuttings contained a node which houses intercalary meristem, allowing new growth to occur.
    2. (ii) The key difference was that type B had a node while type A was just a stem piece between nodes.
    3. (iii) The observation was that type B cuttings sprouted and developed into new plants after a few weeks.
    4. (iv) Parameters like soil type, water amount, sunlight, and temperature should be kept identical for both cuttings.

    Answer: (i) B had a node with meristem; (ii) Presence of a node; (iii) B sprouted; (iv) Environmental conditions.

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11. Exercises Q11

    Rohan says a tissue is a group of similar cells doing similar work; Rajiv says that holds for simple tissues but not quite for complex tissues. Explain.

    1. Rohan is correct for simple permanent tissues because they consist of only one type of cell performing a similar function.
    2. Rajiv is correct for complex permanent tissues because they are made up of more than one type of cell.
    3. In complex tissues like xylem and phloem, different cells have different structures and perform specific roles to work together.
    4. For example, xylem contains tracheids, vessels, parenchyma, and fibres, while phloem has sieve tubes, companion cells, and other elements.
    5. Thus, complex tissues are groups of dissimilar cells that coordinate to perform a specific function rather than just similar cells doing similar work.

    Answer: Rohan's definition applies to simple tissues which have one cell type, while Rajiv is right that complex tissues contain multiple cell types with different functions working together.

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12. Exercises Q12

    Coconut husk fibre makes tough mats. Which tissue's structure gives this strength, and why could living parenchyma not do the same job?

    1. (i) Sclerenchyma is the tissue with structural features suitable for providing strength to coconut husk fibres.
    2. (i) Sclerenchyma cells have thick walls due to the deposition of lignin, which makes them hard and strong.
    3. (ii) Living parenchyma cells have thin walls and are loosely packed with intercellular spaces.
    4. (ii) Parenchyma is primarily used for storage and photosynthesis, lacking the rigid structure needed for tough mats.

    Answer: (i) Sclerenchyma; (ii) Parenchyma has thin walls and is not hard enough for strength.

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13. Exercises Q13

    Vibha says meristematic cells are found only at the root and shoot tips. Is she right? What question could Neha ask to help her see if it is wrong?

    1. Vibha's statement is incorrect because meristematic tissues are not limited to just the root and shoot tips.
    2. The chapter explains that plants have three types of meristems: apical, lateral, and intercalary.
    3. Lateral meristem is located along the circumference of stems to increase girth, while intercalary meristem is found at the base of plants like grasses.
    4. Neha can ask Vibha if she knows about lateral or intercalary meristems, which are also made of meristematic cells but located elsewhere.

    Answer: Vibha is wrong; Neha can ask about the presence of lateral or intercalary meristems in stems and grass bases.

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14. Exercises Q14

    A plant cell and an animal cell are the same size. (i) Which has the larger vacuole, and why? (ii) What assumptions are you making?

    1. (i) The plant cell will have the larger vacuole.
    2. (i) Plant cells store water and nutrients in a large central vacuole to maintain turgor pressure.
    3. (i) Animal cells typically have small, temporary vacuoles or none at all.
    4. (ii) We assume the plant cell is a mature, non-meristematic cell.
    5. (ii) We assume the animal cell is a typical somatic cell, not a specialized storage cell.

    Answer: (i) The plant cell has a larger vacuole because it stores water and maintains turgor; (ii) We assume the plant cell is mature and the animal cell is a standard somatic cell.

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15. Exercises Q15

    A statement says every plant tissue does only one specific job. What questions would you ask to test it, and which tissues would you use as examples?

    1. Ask if a single tissue can perform more than one function at the same time.
    2. Ask if the cells within a complex tissue have different roles that contribute to multiple functions.
    3. Use xylem as an example because it transports water and minerals while also providing strength to the plant.
    4. Use phloem as an example because it transports food and its parenchyma cells store food materials and resins.

    Answer: The statement is incorrect because tissues like xylem and phloem perform multiple functions such as conduction, support, and storage.

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