Class 09 Biology - Tissues in Action - Exercises

Questions and Answers

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. Answer: (iii) They have thin walls, dense cytoplasm and large prominent nucleus. (These features support active metabolism and frequent cell division).

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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 Answer: (ii) Phloem. (Phloem is the complex permanent tissue responsible for the translocation of food).

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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. Answer: (iii) To allow quick exchange of materials across them (such as oxygen, nutrients, and waste products).

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

Answer: In a straight-leg jump, the ankles, knees, and hips remain stiff and extended, providing no shock absorption or additional power from bending. In a normal jump, these joints bend significantly (flexion) to store energy and then straighten rapidly (extension) to provide upward thrust, and they bend again upon landing to absorb the impact.

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

(i) Ball and socket (ii) Hinge (iii) Pivot Answer: (ii) Hinge. (The knee and ankle primarily move in one plane, similar to a door hinge).

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6. Assertion (A) and Reason (R) Analysis:

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) (A) is true, but (R) is false. (The lung epithelium is a single layer of thin, flat cells to facilitate rapid 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. Answer: (i) Both (A) and (R) are true, and (R) is the correct explanation of (A).

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) (A) is false, but (R) is true. (Ligaments connect bone to bone; Tendons connect 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. Answer: (iii) (A) is true, but (R) is false. (Hinge joints are shaped to restrict movement to one plane).

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7. Annual Rings and Tree Age:

(i) Interpretation of the graph? Answer: The diameter of the stem increases linearly with time, and the number of annual rings perfectly matches the age of the tree (1 ring per year). (ii) Relation between diameter and annual rings? Answer: As more annual rings are added by the lateral meristem each year, the diameter (girth) of the tree increases. (iii) Responsible tissue and location? Answer: Lateral meristem (also called cambium), located in a ring-like arrangement within the stem.

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8. Elephant debarking a tree:

(i) Which functions are hampered? Answer: Protection against pathogens/water loss (dermal function) and transport of food (as the phloem is located just beneath the bark). (ii) Which tissue affected by further damage? Answer: The xylem (for water transport) and the vascular cambium (responsible for secondary growth). (iii) Functions hampered if tissues beneath bark are damaged? Answer: Upward transport of water/minerals (xylem) and the ability to grow in girth (cambium).

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9. Bending sapling and Sclerenchyma:

Answer: Collenchyma is responsible for the flexibility and mechanical strength in young stems. If replaced by sclerenchyma, the stem would become extremely rigid and brittle; instead of bending during winds, it would likely snap and break.

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10. Sugarcane Cuttings:

(i) Why did Type B grow but not Type A? Answer: Type B cuttings likely contained nodes with axillary buds (meristematic tissue), which are necessary for sprouting. Type A cuttings were likely internodal sections lacking these buds. (ii) What difference was present? Answer: The presence of meristematic cells in the buds of Type B. (iii) Observation? Answer: Sprouting of new shoots and root development. (iv) Parameters for fair comparison? Answer: Same amount of water, light, temperature, soil quality, and depth of planting.

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11. Simple vs. Complex Tissues Discussion:

Answer: Simple tissues (like parenchyma) are composed of only one type of cell that is structurally and functionally similar. Complex tissues (like xylem and phloem) are composed of more than one type of cell (e.g., vessels, tracheids, fibers, parenchyma in xylem) that work together as a unit to perform a common function.

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12. Coconut Husk and Parenchyma:

Answer: Coconut husk is made of sclerenchyma fibers, which have thick, lignified walls that provide extreme mechanical strength and durability. Parenchyma cells are thin-walled and usually living; they are designed for metabolic activities and storage, not for providing the heavy-duty structural support required by the husk.

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13. Meristematic Locations:

Answer: Vibha's statement is incomplete. While meristems are at apices (Apical meristem), they also exist as Lateral meristems (for girth) and Intercalary meristems (at the base of leaves or nodes). Neha could ask: "What about the tissue that makes the stem thicker, or allows grass to grow back after being mowed?"

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14. Vacuole comparison:

(i) Which has a larger vacuole? Answer: The plant cell will have a much larger central vacuole. It stores cell sap and maintains turgor pressure, keeping the cell firm. (ii) Assumptions? Answer: We assume the plant cell is a mature, differentiated cell and the animal cell is a typical somatic cell.

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15. "Each plant tissue performs only one specific function" - Critically examine.

Answer: This statement is often incorrect. For example, parenchyma can perform photosynthesis (chlorenchyma), store food, and provide buoyancy (aerenchyma). Xylem provides both water conduction and mechanical support. Questions to ask: "Does a tissue's role change during the plant's life?" or "Can one tissue type have different specialized forms?"