Tissues in Action
1. Meristematic tissues divide repeatedly. What property of their cells allows them to do this?
Correct Option: (iii) They have thin walls, dense cytoplasm and large prominent nucleus.
Explanation: Meristematic cells are actively dividing cells. They have a dense cytoplasm, prominent nuclei, and thin cellulose cell walls because they do not need thick protective walls or large vacuoles yet, allowing for rapid metabolic activity and division.
2. If a plant is unable to transport food from leaves to roots which tissue is malfunctioning?
Correct Option: (ii) Phloem.
Explanation: Phloem is the specialized plant vascular tissue responsible for the translocation (transport) of food and organic nutrients prepared by the leaves to other parts of the plant, including the roots.
3. Why are the epithelial tissues that line an animal’s internal organs usually only one or a few cells thick?
Correct Option: (iii) To allow quick exchange of materials across them.
Explanation: A thin layer minimizes the diffusion distance, enabling efficient and rapid exchange of gases, nutrients, and waste products across the tissue (such as in the alveoli of the lungs).
4. You can perform these two jumps (Fig. 3.21): Straight-leg jump vs. Normal jump. How did your ankle, knee and hip positions differ between the two jumps?
Difference in Positions:
Straight-leg Jump: The ankles, knees, and hips are kept stiff, rigid, and nearly straight throughout the jump. This results in minimal shock absorption, transferring the impact force abruptly through the skeleton.
Normal Jump: The ankles, knees, and hips bend flexibly and naturally (flexion) prior to takeoff and upon landing. This acts as a shock absorber, compressing and extending smoothly to cushion the impact and generate efficient propulsion.
5. Which type of joint is involved when you bend your knees and ankles?
Correct Option: (ii) Hinge.
Explanation: The knee and ankle joints function primarily as hinge joints, allowing movement back and forth in a single plane.
6. Assertion-Reason Questions
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: (iv) (A) is false, but (R) is true. (Correction: The assertion is false because lung epithelium consists of a single thin layer of flat cells—simple squamous epithelium—to speed up diffusion, not multiple layers of tall cells).
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. (Correction: 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) (A) is true, but (R) is false. (Reason is false because hinge joint bone ends restrict movement to a single plane rather than allowing sliding in all directions).
7. Graph and Data Analysis (Table 3.7 – Teak Tree)
(i) Analysis of graph (Age vs. Diameter & Annual Rings):
As the age of the teak tree increases, both the diameter at breast height (DBH) and the number of annual rings increase proportionally in a linear or steady upward trend.
(ii) Relation between diameter and annual rings:
There is a direct positive correlation; generally, each year of growth adds one annual ring, which corresponds to the progressive increase in the stem’s diameter due to secondary growth.
(iii) Specialized tissue responsible for girth and its location:
Lateral meristems (specifically vascular cambium and cork cambium) are responsible for increasing the girth of the stem. They are located laterally in the cylindrical layers inside the stem and root.
8. Tree Debarking by an Elephant (Fig. 3.22)
(i) Functions hampered by debarking:
Transport of food (phloem transport) is disrupted, and protection against mechanical injury and pathogen entry is compromised.
(ii) Plant tissue affected by further damage:
The vascular cambium and the underlying secondary xylem (wood) would be affected.
(iii) Function hampered if tissues beneath the bark are damaged:
The upward transport of water and dissolved minerals from the roots to the leaves by the xylem would be severely hampered, eventually causing the tree to dry out and die.
(iv) Assumptions and changes:
- Assumption: It is assumed that the debarking was complete (girdling) around the entire circumference of the trunk.
- If changed: If only a partial strip of bark was removed, the tree might survive because lateral movement of nutrients can sometimes compensate, preventing immediate death.
9. Mango Sapling Flexibility
Tissue responsible: Collenchyma.
Impact if replaced by sclerenchyma:
Sclerenchyma is composed of dead, highly lignified, rigid cells that provide maximum stiffness and hardness. If collenchyma were replaced by sclerenchyma, the stem would lose its flexible, elastic nature and would snap or break easily under the strong mechanical stress of monsoon winds instead of bending.
10. Sugarcane Regeneration Experiment (Fig. 3.23)
(i) Why type ‘B’ grew while ‘A’ did not:
Type ‘B’ cuttings contained viable nodes/buds containing meristematic tissue, whereas type ‘A’ lacked the necessary nodes or buds required for sprouting.
(ii) Difference between ‘B’ and ‘A’:
Type ‘B’ includes growth nodes (buds), while type ‘A’ consists of internodal regions without buds.
(iii) Observation/Measurement made:
Measurement of shoot length, root development, and the percentage or time taken for successful sprouting.
(iv) Parameters to keep the same for a fair comparison:
Length and thickness of the cuttings, environmental conditions (temperature, sunlight, moisture/watering), soil type, and nutrient availability.
11. Simple vs. Complex Tissues Discussion (Rohan vs. Rajiv)
Explanation:
- Simple tissues (like parenchyma, collenchyma, and sclerenchyma) are composed of only one type of cell that look alike and perform a uniform function.
- Complex tissues (like xylem and phloem) are made of more than one type of cell working together as a functional unit. For example, xylem consists of tracheids, vessels, xylem parenchyma, and xylem fibres—different cells structurally, but they collectively coordinate to execute a single major function (water transport). Therefore, Rajiv’s counter-argument is correct.
12. Coconut Husk Fibres and Parenchyma
Tissue providing strength: Sclerenchyma (specifically thick-walled sclerenchymatous fibre cells containing lignin).
Why living parenchyma couldn’t serve the purpose:
Parenchyma cells have thin cellulose walls, large vacuoles, and are typically living cells specialized for food storage, photosynthesis, or packaging. They lack the mechanical rigidity, toughness, and waterproof lignin impregnation required to withstand heavy pulling and wear-and-tear characteristic of coconut husk mats.
13. Location of Meristematic Cells (Vibha vs. Neha)
Critique of the statement: Vibha’s statement is incorrect. While meristems are indeed located at root and shoot apices (apical meristems), they are also found in other regions, such as the lateral sides of stems and roots (lateral meristems/cambium) and at the base of leaves/internodes (intercalary meristems).
Question Neha can ask: “If meristematic cells are only at the tips, how do plant stems and trunks increase in thickness or how do grasses regrow after being grazed from the base?”
14. Vacuoles in Plant vs. Animal Cells
(i) Which cell will have a larger vacuole & reasons:
The plant cell will have a much larger central vacuole. Plant cells need large vacuoles to store water, maintain turgor pressure against the cell wall for structural rigidity, and store metabolic waste, whereas animal cells typically have many small, temporary vacuoles or none at all because they rely on other structural support systems.
(ii) Assumptions made:
It is assumed that both cells are mature, normal, and functioning under standard environmental conditions.
15. Critical Examination of Plant Tissue Functions
Questions to ask:
- Does any plant tissue perform more than one physiological role?
- Do cells within a single tissue undergo modifications to take on secondary functions?
Examples to use:
- Parenchyma: Primarily functions in food storage, but when it contains chloroplasts (chlorenchyma), it performs photosynthesis; in aquatic plants (aerenchyma), it provides buoyancy.
- Epidermis: Primarily protective, but specialized epidermal cells (guard cells) regulate gas exchange and transpiration.
