O Level Biology Plant Biology Quiz

O-Level Biology Quiz - Plant Biology (Answer Key)

Total Marks: 40
Topic: Plant Biology (Syllabus 6093, Theme III)

Section A

1. C [1]
Chloroplasts are present in plant cells (site of photosynthesis) but absent in animal cells. Animal cells have membrane, nucleus, mitochondria.

2. B [1]
Osmosis is the movement of water across a partially permeable membrane from dilute to concentrated solution. Root hair absorbs soil water by osmosis.

3. B [1]
Carbon dioxide is taken in via stomata and used in photosynthesis to make glucose.

4. B [1]
Xylem transports water and dissolved mineral salts from roots upward to leaves. Phloem transports sugars.

5. A [1]
Guard cells flank stomata and change shape to open/close them, controlling gas exchange and water loss.

Section B

6. [2]

• Long projection / elongated shape → increases surface area for absorption [1]
• Thin wall / many mitochondria (for active transport) [1]
  (Mark any two correct adaptations.)

7. [2]
Mineral ion concentration in soil is usually lower than inside the root hair cell [1], so ions must move against the concentration gradient, which requires energy (ATP) from respiration — this is active transport, not diffusion (which is passive, down gradient) [1].

8. [3]
Soil → root hair cell (by osmosis) [1] → cortex → xylem vessel [1] → up the stem → leaf mesophyll [1].

9. [3]
Water moved out of the cell by osmosis [1] because the salt solution was more concentrated (lower water potential) than the cell sap [1]; the cell became plasmolysed (membrane pulled from wall) [1].

10. [2]
Carbon dioxide + water → glucose + oxygen [1]
(With light and chlorophyll) [1]
Equation: $6CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2$

11. [2]
Flat shape gives large surface area for diffusion of gases [1]; air spaces inside leaf allow gases to circulate to cells [1].

12. [2]

• Hollow (no cytoplasm) and dead → uninterrupted water column [1]
• Thickened with lignin / narrow → supports and prevents collapse [1]
  (Other: pits for sideways movement.)

13. [3]
Transpiration pulls water from leaves (evaporation from mesophyll) [1]; this creates tension in xylem [1]; continuous column drawn up from roots (transpiration pull / cohesion-tension) [1].

Section C

14. [2]
Palisade mesophyll [1]; contains most chloroplasts / columnar cells packed with chloroplasts for light absorption [1].

15. [3]
Higher light opens stomata and warms leaf, increasing evaporation → higher transpiration [1]; also more photosynthesis uses water [1]; at high light stomata may limit or humidity near leaf saturates so rate plateaus [1].

16. [3]
As distance increases, bubble rate decreases (inverse relationship) [1]; farther lamp = lower light intensity [1]; light is limiting photosynthesis so less oxygen produced (fewer bubbles) [1].

17. [2]
Root hairs are on mature epidermal cells behind tip [1]; tip has meristem (dividing cells) not yet differentiated for absorption [1].

18. [2]
Any two: temperature, humidity, air movement, light intensity, species/size of shoot [1 each].

19. [2]
Light-dependent: thylakoid / grana [1]; light-independent: stroma [1].

20. [3]
At 35°C enzymes (Rubisco) less efficient / begin to denature [1]; respiration increases more than photosynthesis using products [1]; so net rate lower despite high CO₂ [1].

Common mistakes to flag:

• Confusing xylem (water) with phloem (food).
• Writing diffusion for ion uptake (must be active).
• Plasmolysis described as bursting (that is animal cell lysis).
• Not stating "against gradient" in active transport.