Secondary 4 Combined Science Biology Ecology Quiz

Secondary 4 Combined Science Biology Quiz - Ecology (Answer Key)

Total Marks: 40
Topic: Ecology

Section A Answers (1–10)

1. [1 mark]
Answer: Any one abiotic component e.g. water, sunlight, temperature, dissolved oxygen, soil.
Teaching note: Abiotic means non-living. A pond ecosystem includes water (abiotic) and fish (biotic).
Common mistake: Naming a living organism (e.g., fish) → not abiotic.

2. [1 mark]
Answer: Photosynthesis.
Teaching note: Producers (plants/algae) use sunlight in photosynthesis to make glucose, capturing solar energy.

3. [1 mark]
Answer: A food chain is a linear sequence showing how energy and nutrients pass from producer to successive consumers.
Teaching note: E.g., grass → grasshopper → frog. It shows feeding relationships.

4. [1 mark]
Answer: Primary consumer (or herbivore).
Teaching note: Grasshopper eats grass (producer), so it is first-level consumer.

5. [2 marks]
Answer: (a) Bacteria / fungi; role: break down dead organic matter into simple nutrients. (b) Earthworm / mushroom; role: decompose and recycle nutrients to soil.
Marking: 1 mark each example+role.
Teaching note: Decomposers return carbon and minerals to the cycle.

6. [1 mark]
Answer: Carbon dioxide ($CO_2$).
Teaching note: Respiration in decomposers: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + energy$.

7. [2 marks]
Answer: Bioaccumulation causes toxin concentration to increase at each trophic level (1). Top predators eat many prey and accumulate highest dose (1).
Teaching note: e.g., DDT in eagles causes thin eggshells.

8. [1 mark]
Answer: Deforestation / urbanisation / pollution / overfishing.
Teaching note: These destroy habitats.

9. [2 marks]
Answer: $6CO_2 + 6H_2O \xrightarrow{light, chlorophyll} C_6H_{12}O_6 + 6O_2$
Marking: 1 for reactants, 1 for products correct.
Teaching note: Glucose stores energy; oxygen is by-product.

10. [2 marks]
Answer: Rainforest has stable warmth, high rainfall, more niches (1); desert has extreme drought and temperature limiting life (1).
Teaching note: Biodiversity = variety of species.

Section B Answers (11–15)

11. [3 marks]
(a) [1] grass
(b) [1] 2 (grasshopper, mouse)
(c) [1] frog or snake
Teaching note: Producer makes own food. Primary consumers eat producer. Secondary eat primary.

12. [3 marks]
(a) [1] Habitat A (forest)
(b) [2] Forest has more layers/plants providing more habitats and food; field is open with less variety.
Marking: 1 for reason linked to structure, 1 for example.

13. [3 marks]
(a) [1] 12:00
(b) [2] Daylight drives photosynthesis in pond plants releasing $O_2$ (1); at night respiration uses $O_2$ lowering it (1).
Teaching note: Net oxygen = photosynthesis − respiration.

14. [2 marks]
(a) Reduces transpiration → less rainfall
(b) Increases runoff → less infiltration
Marking: 1 each.

15. [3 marks]
(a) [1] Pyramid drawn with base 1200, mid 180, top 25.
(b) [2] Energy lost as heat at each transfer (10% rule) (1); less biomass supported at higher levels (1).

Section C Answers (16–20)

16. [4 marks]
Answer: Sunlight → producers via photosynthesis (1) → primary consumers eat producers (1) → secondary/carnivore eats primary (1) → energy lost as heat at each step (1).
Teaching note: Only ~10% transferred; rest lost.

17. [4 marks]
Answer: Nitrogen gas fixed by rhizobium/lightning to nitrates (1); plants absorb nitrates (1); animals eat plants (1); decomposers return ammonia, nitrifying bacteria convert to nitrates (1).
Teaching note: Denitrifiers return $N_2$ to air.

18. [4 marks]
Answer: Fertilisers add nitrates → algal bloom (1) → blocks light, algae die (1) → decomposers multiply using $O_2$ (1) → fish suffocate (1).

19. [4 marks]
Answer: (1) Protected reserves e.g. national park stops habitat loss (2 marks: method+example). (2) Breeding programmes e.g. captive pandas (2 marks).
Marking: 2 per method with example.

20. [4 marks]
Answer: Effect 1: Small fish increase (no tuna predation) (1) → zooplankton decrease (1). Effect 2: Humans shift to more mussels/crab (1) → mussel/crab decline (1).
Teaching note: Trophic cascade from removing top predator.