NCERT Class 9 Science Chapter 3 Tissues in Action

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NCERT Class 9 Science Chapter 3 Tissues in Action

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Tissues in Action

Chapter – 3

Pause And Ponder

1. 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.

Ans: Coconut husk fibres are hard and brittle because they contain sclerenchyma tissue with thick, lignified cell walls. In contrast, coriander leaf stalks are soft and flexible because they contain collenchyma tissue, which has unevenly thickened cell walls and provides flexibility.

Pause And Ponder

1. 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?

Ans: A thick cuticle reduces water loss by transpiration, which helps desert plants survive. However, in underwater plants, a thick cuticle would reduce the absorption of water and dissolved gases, making it disadvantageous.

2. 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?

Ans: The dead xylem cells form continuous tubes that carry water upward, while the living cells of the leaves create a pulling force through transpiration. This transpiration pull keeps water moving against gravity.

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

Ans: Without stomata, the plant would not be able to exchange gases or carry out transpiration properly. As a result, photosynthesis, respiration, and water transport would be affected, and the plant may eventually die.

Pause And Ponder

1. 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?

Ans: 

Joint	Type of Movement
Shoulder joint	Ball and socket joint – movement in all directions
Hip joint	Ball and socket joint – movement in all directions
Elbow joint	Hinge joint – bending and straightening
Knee joint	Hinge joint – bending and straightening
Wrist joint	Gliding joint – sliding and limited movement
Ankle joint	Hinge joint – up and down movement
Neck joint	Pivot joint – turning the head from side to side

Revise, Reflect, Refine

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.

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

2. If a plant is unable to transport food from leaves to roots which tissue is malfunctioning?

(i) Xylem.

(ii) Phloem.

(iii) Epidermis.

(iv) Sclerenchyma.

Ans: (ii) Phloem.

3. 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.

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

4. 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?

Ans: During a straight-leg jump where you keep your knees and ankles stiff, the hinge joints in your knees and the joints in your ankles do not bend. In a normal jump, you naturally bend your knees and ankles, allowing the hinge joints to move, which provides flexibility and helps cushion the ends of the bones for shock absorption when you land.

5. Which type of joint is involved when you bend your knees and ankles?

(i) Ball and socket.

(ii) Hinge.

(iii) Pivot.

Ans: (ii) Hinge.

6. 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.

Ans: A. (iii) (A) is true, but (R) is false. (Epithelium in the lungs consists of a single layer of thin, flat cells to help in the rapid diffusion of gases, not multiple layers of tall cells.)

B. (i) Both (A) and (R) are true, and (R) is the correct explanation of (A). (Cardiac muscles work tirelessly and rhythmically, enabling the heart to beat throughout life without fatigue.)

C. (iv) (A) is false, but (R) is true. (Tendons connect muscles to bones, while ligaments are the ones that connect bone to bone.)

D. (iii) (A) is true, but (R) is false. (A hinge joint bends and straightens in one direction only, like a door hinge, and does not allow sliding in all directions.)

7. 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.

Table 3.7 Data related to the age of a tree, and corresponding increase in the diameter of stem and number of annual rings.

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

(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?

Ans:

(i) Interpretation: As the age of the tree increases, the diameter of the stem also increases steadily over time

(ii) Relation: The diameter of the teak tree increases proportionally with the number of annual rings formed

(iii) Responsible Tissue: The lateral meristem is responsible for the increase in the girth (diameter) of the stem. It is located along the circumference of stems, arranged in a ring where it produces new cells inside and outside in a concentric manner

8. 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?

Ans: Functions hampered: The tree loses its protective outer layer, which usually prevents water loss, protects against mechanical injury, and blocks the entry of harmful microorganisms and parasites.

(ii) Which plant tissue would be affected by further damage to the tree trunk even after debarking?

Ans: Tissue affected by further damage: The complex permanent tissues lying just beneath the bark, specifically the phloem and potentially the xylem, would be affected.

(iii) Which function of the tree would be hampered if the tissues beneath the bark were severely damaged?

Ans: Function hampered if tissues beneath are damaged: The transportation of food from the leaves to other parts of the plant (performed by phloem) and the transport of water and minerals from the roots (performed by xylem) would be severely hampered.

(iv) What assumptions are you making to answer the questions above? How would the answer change if your assumptions are also changed?

Ans: Assumptions: The main assumption is that the elephant only stripped the outer protective bark and did not severely destroy the deeper vascular tissues (phloem and xylem). If we assume the damage was deep enough to destroy the phloem entirely, the tree would starve and die because food transport would be completely cut off.

9. 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.

Ans: The tissue responsible for this flexibility is collenchyma, which provides support and allows parts of the plant to bend without breaking. If it were replaced by sclerenchyma, the stem would become hard, strong, and rigid due to the thick, lignified walls of sclerenchyma cells. As a result, the stem would lose its flexibility and would likely snap or break during strong monsoon winds rather than bending.

10. 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?

Ans: Type ‘B’ cuttings sprouted because they likely contained the nodes of the stem, whereas Type ‘A’ cuttings did not.

(ii) What difference was present in type ‘B’ compared to type ‘A’?

Ans: Type ‘B’ contained intercalary meristems, which are located at the nodes and allow plants to regenerate and sprout new branches, while Type ‘A’ lacked these meristems.

(iii) What observation or measurement was made to determine whether this change had an effect?

Ans: The sprouting and development of new branches or shoots from the cuttings after a few weeks.

(iv) What parameters should be kept the same for both types of cuttings to ensure a fair comparison?

Ans: Environmental conditions such as sunlight, air, water, and the nutrient medium (soil) should be kept exactly the same for a fair comparison.

11. 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. 

Ans: Rajiv is correct. A “simple permanent tissue” (like parenchyma, collenchyma, and sclerenchyma) is composed of only one type of similar cells. However, a “complex permanent tissue” (like xylem and phloem) is composed of different types of cells working together as a single unit to perform a specific function (for example, xylem consists of tracheids, vessels, parenchyma, and fibres).

12. 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.

Ans: Sclerenchyma tissue has the structural features suitable for providing this tough strength, as its cells have thick walls due to the deposition of lignin, making them hard and strong. Living parenchyma could not serve this purpose because its cells have thin walls, are loosely packed, and are primarily adapted for storing food and performing photosynthesis, rather than providing mechanical strength.

13. 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?

Ans: Vibha’s statement is incorrect. Meristematic cells are not located only at the root and shoot apices. Besides apical meristems, there are also intercalary meristems (found at the bases of leaves or internodes, especially in grasses) and lateral meristems (such as cambium, found along the sides of stems and roots).

To help Vibha understand, Neha can ask:

“If meristematic cells are present only at the root and shoot apices, then how does the stem increase in thickness and how do grasses regrow after being cut?”

This question will help Vibha realize that meristematic tissues are also present in other regions of the plant, such as lateral and intercalary meristems.

14. A plant cell and an animal cell are of the same size.

(i) Which cell will have a larger vacuole? Give reasons.

Ans: Plant cells generally have larger vacuoles.

(ii) What assumptions are you making to answer the question above?

Ans: We are assuming that we are comparing a mature permanent plant tissue cell with an animal cell. If we were looking at a meristematic plant cell, the comparison would fail because vacuoles are generally absent in actively dividing meristematic tissues.

15. 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?

Ans: The statement that each plant tissue performs only one specific function is incorrect because many tissues serve multiple roles. To critically examine this, you could ask whether the epidermis only provides protection or if the parenchyma is solely meant for storing food. For example, while the main job of the epidermis is to protect the plant, it also forms root hairs in the roots to absorb water and minerals, and contains stomata in the leaves for gaseous exchange and transpiration. Similarly, although parenchyma primarily stores food, it also performs photosynthesis in the green parts of the plant and creates air spaces in aquatic plants to help them float.