Class 9 - Chapter 3:Tissues in Action

Exercise Solution

1. Meristematic tissues divide repeatedly. What property of their cells allows them to do this?

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

Meristematic cells are actively dividing cells. They have thin cell walls, dense cytoplasm and a prominent nucleus, which help them divide continuously.

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

Answer: (ii) Phloem

Phloem transports prepared food from leaves to all parts of the plant. If food cannot reach the roots, the phloem tissue is not functioning properly.

3. Why are the epithelial tissues that line an animal's internal organs usually only one or a few cells thick?

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

Thin epithelial tissues help in rapid diffusion, absorption and exchange of gases, nutrients and wastes between cells and their surroundings.

4. How did your ankle, knee and hip positions differ between the two jumps?

Answer:

• Straight-leg jump: Ankles, knees and hips remain stiff and nearly straight.
• Normal jump: Ankles, knees and hips bend naturally before and during the jump.

Bending these joints allows muscles to generate greater force and makes jumping easier and higher.

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

Answer: (ii) Hinge joint

The knee and ankle joints allow movement mainly in one plane, like the opening and closing of a door. Therefore, they are hinge joints.

6. Assertion and Reason

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.

Answer: (iii) Assertion is true, but Reason is false.

The lung epithelium is made of thin squamous cells that promote rapid diffusion of gases.

B.

Assertion: Cardiac muscle can contract continuously without fatigue.

Reason: Cardiac muscle cells have a high number of mitochondria and abundant blood supply.

Answer: (i) Both Assertion and Reason are true, and Reason is the correct explanation.

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.

Answer: (iv) Assertion is false, but Reason is true.

Tendons connect muscle to bone, whereas ligaments connect bone 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.

Answer: (iii) Assertion is true, but Reason is false.

Sliding in all directions occurs in gliding joints, not hinge joints.

7. Teak Tree Data Analysis

(i) Analyse the graph in terms of the diameter of the stem over time.

Answer:

The diameter of the teak tree stem increases continuously with age. As the tree grows older, secondary growth causes the stem to become thicker. The graph shows a positive relationship between age and stem diameter.

(ii) What is the relation between the age of the teak tree and the annual rings formed?

Answer:

One annual ring is formed every year. Therefore:

Number of Annual Rings = Age of Tree (in years)

The number of annual rings increases directly with age.

(iii) Which specialised tissue is responsible for the girth of the stem and where is it located?

Answer:

The lateral meristem (cambium) is responsible for increasing the girth of the stem. It is located between the xylem and phloem tissues.

8. Debarking of a Tree

(i) Which function(s) of the tree is/are hampered by debarking?

Answer:

Debarking damages the phloem present in the bark. As a result, transport of food from leaves to other parts of the tree is hampered.

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

Answer:

Further damage may affect the cambium and eventually the xylem tissue inside the trunk.

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

Answer:

If the xylem and cambium are damaged, water and mineral transport, secondary growth and overall survival of the tree will be affected.

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

Answer:

The answers assume that the bark removed contains the phloem and that the damage is extensive. If only a small portion of bark is removed, the tree may recover. If deeper tissues such as cambium and xylem are also damaged, the effects become much more severe and may ultimately lead to the death of the tree.

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.

Answer:

The tissue responsible for flexibility in a young mango sapling is collenchyma. Collenchyma cells are living cells with unevenly thickened cell walls that provide both support and flexibility.

If collenchyma were replaced by sclerenchyma, the stem would become very hard and rigid because sclerenchyma cells have thick, lignified walls and are dead at maturity. The sapling would lose its flexibility and could break easily during strong winds.

10. Sugarcane Regeneration Experiment

(i) Why were the type 'B' cuttings able to grow as sugarcane but type 'A' could not?

Answer:

Type 'B' cuttings contained a node with a bud (meristematic tissue). The bud divided continuously and developed into a new sugarcane plant. Type 'A' cuttings lacked a viable bud and therefore could not sprout.

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

Answer:

Type 'B' had a node containing an active bud, whereas type 'A' did not have such a growing point.

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

Answer:

The observation was whether new shoots and roots developed from the cuttings. The number of sprouts and the growth of the plant were recorded.

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

Answer:

• Length of the cuttings
• Amount of water supplied
• Soil type
• Sunlight received
• Temperature
• Time period of observation

11. During the discussion in class, Rohan gives a statement that, “A tissue is a group of similar cells performing similar functions”. But Rajiv counters arguing 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.

Answer:

Rohan's statement is correct for simple tissues because they are made up of only one type of similar cells performing the same function. Examples are parenchyma, collenchyma and sclerenchyma.

Rajiv is also correct because complex tissues consist of different types of cells working together to perform a common function. For example, xylem contains tracheids, vessels, xylem fibres and xylem parenchyma, while phloem contains sieve tubes, companion cells, phloem fibres and phloem parenchyma.

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.

Answer:

The tissue responsible for the strength of coconut husk fibres is sclerenchyma.

Sclerenchyma cells have very thick, lignified cell walls which provide mechanical strength and rigidity.

Living parenchyma cells have thin cell walls and large intercellular spaces. They mainly function in storage and metabolic activities and therefore cannot provide the toughness and strength required for making mats.

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

Answer:

The statement is incorrect. Meristematic tissues are not found only at the root and shoot apices. They are also present as:

• Intercalary meristems at the bases of leaves and internodes.
• Lateral meristems (cambium) along the sides of stems and roots.

Neha may ask:

"If meristematic tissues occur only at root and shoot tips, then how does the girth of a stem increase during secondary growth?"

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

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

Answer:

The plant cell will have a larger vacuole.

Plant cells usually possess a large central vacuole that stores water, food and waste materials and helps maintain turgidity. Animal cells either have very small vacuoles or none at all.

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

Answer:

The assumption is that both cells are mature and healthy cells under normal conditions and belong to typical plant and animal 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?

Answer:

The statement is not completely correct because many plant tissues perform more than one function.

Questions to examine the statement:

• Does a tissue perform only one function throughout its life?
• Can a tissue provide both support and storage?
• Can a tissue transport materials and also store food?
• Do different cells within a tissue perform different functions?

Examples:

• Parenchyma: Storage, photosynthesis and healing.
• Collenchyma: Support and flexibility.
• Xylem: Water transport and mechanical support.
• Phloem: Food transport and storage.

Therefore, many plant tissues perform multiple related functions rather than only one specific function.