🌿 Tissues in Action
Based on official NCERT solution PDF
(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.
(i) Xylem (ii) Phloem (iii) Epidermis (iv) Sclerenchyma
(i) To store food efficiently. (ii) To provide maximum strength. (iii) To allow quick exchange of materials across them. (iv) To reduce friction.
| Body Part | Straight-Leg Jump | Normal Jump |
|---|---|---|
| Ankle | Stiff | Bent |
| Knee | Straight | Bent |
| Hip | Slight movement | Flexible bending |
| Shock Absorption | Very low | High |
| Comfort | Less | More |
(i) Ball and socket (ii) Hinge (iii) Pivot
(i) Both (A) and (R) true & (R) correct explanation. (ii) Both true but (R) not correct explanation. (iii) (A) true, (R) false. (iv) (A) false, (R) 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.
Answer: (iii) Assertion true, Reason false.
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 true and Reason is 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 false, Reason true. (Tendons connect muscle to bone; 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 true, Reason false.
Data: Age (yr): 5, 10, 20, 25, 30, 40 ; DBH (cm): 4, 8, 24, 28, 32, 40 ; Annual rings: 5, 10, 20, 25, 30, 40.
| Age (years) | Diameter (cm) | Annual rings |
|---|---|---|
| 5 | 4 | 5 |
| 10 | 8 | 10 |
| 20 | 24 | 20 |
| 25 | 28 | 25 |
| 30 | 32 | 30 |
| 40 | 40 | 40 |
(i) Analysis: The diameter of teak tree increases with age. In early years (5–10 years) increase is slow; after 10 years diameter increases more rapidly, showing active growth phase.
(ii) Relation: Direct relationship between diameter and number of annual rings. As number of rings increases, diameter also increases → greater rings = larger stem diameter.
(iii) Specialised tissue for girth: Lateral meristem (cambium). It is located along sides of stem, forming a ring-like structure.
(i) Transport of food (photosynthates) from leaves to roots is hampered.
(ii) Phloem tissue would be affected by further damage to trunk even after debarking.
(iii) If tissues beneath bark (cambium & xylem) are severely damaged, nutrient and water transport stops, and tree may die.
(iv) Assumption: bark contains phloem. If assumption changed (e.g., bark mostly dead tissue in some trees), then damage effect might differ, but generally phloem is in inner bark.
Tissue responsible: Collenchyma – provides mechanical support and flexibility due to living cells with uneven thickenings.
Impact if replaced by sclerenchyma: Sclerenchyma cells are dead, thick, lignified, and rigid. The sapling would lose flexibility, become brittle, and break easily in strong winds.
(i) Why type 'B' grew but type 'A' didn't? Type 'B' cuttings contained nodes with buds (meristematic tissue) which have actively dividing cells capable of developing new shoots. Type 'A' cuttings lacked nodes/buds, so no regeneration.
(ii) Difference in type 'B' compared to 'A': Presence of nodes with buds (meristematic zones) in type 'B' vs. their absence in type 'A'.
(iii) Observation / measurement to determine effect: Sprouting of new shoots from nodes after 2–3 weeks. Measurement: number of cuttings that developed visible buds/shoots, shoot length, or sprouting percentage.
(iv) Parameters kept same for fair comparison: Same soil type, watering schedule, light exposure, temperature, cutting size/length, planting depth, and time duration.
Explanation: Rohan's statement is partially correct, but Rajiv's argument is more accurate. Simple tissues (parenchyma, collenchyma, sclerenchyma) have similar cell types working together. However, complex tissues like xylem and phloem consist of different kinds of cells (tracheids, vessels, fibres, parenchyma in xylem; sieve tubes, companion cells, fibres in phloem). They are dissimilar in structure but cooperate to perform a common function (transport). Hence a broader definition: "group of cells that work together to perform a specific function."
Tissue: Sclerenchyma – cells are dead, thick-walled, and heavily lignified, providing hardness, rigidity, and durability.
Why not parenchyma: Parenchyma cells are living, thin-walled, soft, and loosely packed; they lack lignin. Their functions are storage, photosynthesis, and repair, not mechanical strength. Without lignin they cannot provide toughness or resistance to wear.
Correct view: Statement is incorrect. Meristematic tissues are found in three locations: Apical meristem (tips – length growth), Lateral meristem (cambium – girth increase), and Intercalary meristem (nodes/grass bases – regrowth).
Question Neha can ask: “If meristems are only at tips, how does the stem increase in thickness or how does grass regrow after being cut from the top?”
(i) Plant cell will have a larger vacuole (typically a large central vacuole occupying up to 90% of cell volume).
Reason: Plant vacuole stores water, nutrients, wastes, and provides turgor pressure for structural support. Animal cells have small temporary vacuoles (or none) and do not require turgor pressure.
(ii) Assumptions: Both cells are typical eukaryotic cells under normal conditions; plant cell is not specialized for a different function (like storage reduction); and no extreme water stress conditions.
Critical questions:
- Do some plant tissues perform multiple functions instead of just one?
- Can a tissue that mainly performs one function also assist in other roles (e.g., storage + support)?
- Are there tissues that both provide mechanical strength and store food?
- Do transport tissues (xylem/phloem) also provide structural support?
- Can the same tissue type behave differently based on location?
Examples:
- Parenchyma: Mainly storage, but also performs photosynthesis (chlorenchyma) and buoyancy (aerenchyma).
- Collenchyma: Support + flexibility, also helps in growth of young stems.
- Sclerenchyma: Strength and protection (e.g., seed coat, husk).
- Xylem: Water transport + mechanical support.
Thus statement is not fully correct; many plant tissues serve more than one function.