Secondary 3 Biology Plant Biology Quiz

Secondary 3 Biology Quiz - Plant Biology (Answer Key)

Total Marks: 40

Section A

1. B [1]
Plant cells have a rigid cell wall made of cellulose; animal cells do not. Mitochondria, ribosomes, and nuclei are present in both.

2. To carry out photosynthesis / trap light energy. [1]
Chloroplasts contain chlorophyll which absorbs light for photosynthesis.

3. Guard cells [1]
Guard cells change shape to open or close the stoma.

4. B [1]
Osmosis is the movement of water from a region of high water potential (soil) to low water potential (root hair cell) through a partially permeable membrane.

5. Phloem [1]
Phloem transports sucrose and amino acids from leaves to other parts.

6. Carbon dioxide [1]
CO₂ is taken in through stomata for photosynthesis.

7. B [1]
Concentrated salt solution has lower water potential than the cell; water leaves by osmosis, causing plasmolysis.

8. Carbon dioxide + water → glucose + oxygen [2]
(1 mark for reactants, 1 mark for products; sunlight/chlorophyll may be stated above arrow but not required for mark)
Teaching note: Balance not required at Sec 3; full equation: $6CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6 + 6O_2$.

9. C [1]
Palisade mesophyll is near the upper surface to receive most light and has many chloroplasts.

10. Long hair-like projection / large surface area / thin wall. [1]
Increases surface area for absorption of water and minerals.

Section B

11. (a) Palisade mesophyll [1]
(b) Allow diffusion of gases (CO₂ and O₂) and water vapour. [1]
Teaching: Air spaces increase surface area for gas exchange.

12. [3]
Trend: Water loss increases as wind speed increases (1 mark).
Explanation: Wind removes water vapour from around the leaf, lowering humidity and increasing the concentration gradient for evaporation from stomata (1 mark). This speeds up transpiration (1 mark).
Marking: 1 for trend, 2 for reasoned explanation.

13. (a) To block light from reaching the covered part (control variable). [1]
(b) Blue-black [1]; shows starch is present, proving photosynthesis occurred where light was available [1].
Teaching: Iodine turns blue-black with starch.

14. [2]

• Xylem: dead cells, transports water/minerals upward, no companion cells.
• Phloem: living cells, transports food, has companion cells.
  (1 mark each difference; accept any two valid)

15. Rate stays constant / plateaus [1]. Limiting factor: CO₂ concentration or temperature [1].
Teaching: At saturation, light no longer limits; another factor does.

Section C

16. [4]

• Long projection increases surface area for absorption (1)
• Thin wall shortens diffusion distance (1)
• Water enters by osmosis down water potential gradient (1)
• Mineral ions absorbed by active transport using ATP (1)
  Teaching: Root hair is an extension of epidermal cell.

17. [4]
Soil → root hair cell (osmosis) (1) → cortex (via symplast/apoplast) (1) → xylem (1) → stem xylem → leaf xylem (1).
Teaching: Xylem vessels are continuous tubes.

18. (a) Rate rises from 10 to 30 °C then falls at 40 and sharply at 50 °C. [2] (1 for rise, 1 for fall)
(b) At 50 °C enzymes for photosynthesis denature / membrane damage reduces function. [2]

19. [4]

• Transpiration: loss of water vapour from leaves, passive, via xylem (2)
• Translocation: transport of organic food, active, via phloem (2)
  Teaching: Different tissues, different energy use.

20. [6]

• Stomata allow CO₂ in and O₂ out for photosynthesis (2)
• Open in light for gas exchange, close in dark (1)
• Low water: guard cells lose turgor, stomata close to reduce water loss (2)
• This limits photosynthesis but conserves water (1)
  Marking descriptors: 2 for role, 2 for response to low water, 2 for linking.