O Level Biology Ecology Quiz

O-Level Biology Quiz - Ecology: Answer Key

Total Marks: 40
Topic: Ecology (O-Level 6093, Theme III: Organisms and their Environment)

Section A: Multiple Choice

1. B [1]
A community is all the living organisms of different species living in a habitat. A is the environment, C is a population, D is abiotic surroundings.
Teaching note: Remember habitat = place, population = one species, community = many species together.

2. C [1]
Photosynthesis by plants/algae uses CO₂ + H₂O → glucose + O₂, removing CO₂. Respiration, combustion, decomposition release CO₂.
Teaching note: Carbon cycle: photosynthesis is the main removal process.

3. B [1]
Herbivore feeds only on plants. Carnivore eats animals, omnivore both, decomposer breaks down dead matter.

4. C [1]
Biotic = living. Fungal infection is caused by a living organism. Others are abiotic (non-living).

5. B [1]
Arrows show energy flow from producer → consumer. Not animal movement.

Section B: Structured

6. [2]
Definition: The natural environment where an organism lives. [1]
It provides food, shelter, and conditions for survival. [1]
Marking: 1 for "place where organism lives", 1 for mention of resources/conditions.

7. [2]
Any two: (i) salinity of water [1] (ii) oxygen level in soil [1] (also accepted: temperature, tidal range, soil type).
Note: Must be abiotic (non-living).

8. [2]
Decomposers break down dead organisms and waste. [1] They release nutrients (e.g., nitrates) back into soil for plants. [1]
Teaching note: Without decomposers, nutrients locked in dead matter.

9. [2]
Phytoplankton → zooplankton → small fish → large fish. [2 for full chain, 1 if partial]
Marking: Correct order of all four = 2 marks.

10. [2]
Any two: (i) stability against environmental change [1] (ii) provides variety of resources/food webs [1] (also: medicinal sources, ecological balance).

Section C: Data Interpretation

11. [3]

• Rabbit population increases first, then fox population follows after a delay. [1]
• When foxes increase, they eat more rabbits so rabbit numbers fall. [1]
• Then fox numbers fall due to less food, allowing rabbits to recover. [1]
  Marking descriptors: Predator-prey cycle with lag = 3 marks.

12. [3]

• Not all ingested food is absorbed; some lost as faeces. [1]
• Energy lost as heat from respiration. [1]
• Some used for life processes, not passed on. [1]
  Teaching note: ~10% transferred, rest lost (second law of thermodynamics).

13. [3]

• Decomposers (bacteria/fungi) respire and break down waste. [1]
• Carbon released as CO₂, mass reduces. [1]
• Water also lost by evaporation/transpiration of microbes. [1]

14. [3]
Working: Efficiency = (energy at grasshopper / energy at grass) × 100 [1]
= (1000 / 10000) × 100 [1]
= 10% [1]
Answer: 10%

15. [4]

• Nitrogen gas (N₂) fixed by lightning or bacteria (Rhizobium in roots, Azotobacter in soil). [1+1]
• Converted to ammonia/nitrates. [1]
• Plants absorb nitrates via roots for proteins. [1]
  Marking: 4 points = 4 marks.

16. [4]
(i) Loss of habitat → species decline/displacement. [2: statement + explain]
(ii) Soil erosion / reduced water retention → downstream flooding. [2]
Accepted alternatives: reduced biodiversity, carbon release.

17. [4]
Example web: Algae → tadpole → dragonfly larva; Water lily → tadpole → fish; Dead leaves → bacteria (decomposer). [1 per correct link, max 4]
Must use diagram labels.

18. [3]

• Population: one species in area, e.g., all rattan palms. [1+1 example]
• Community: all species, e.g., palms + monkeys + insects. [1]
  Marking: Definition diff + example each.

19. [4]
(i) Global warming → habitat shift / coral bleaching. [2]
(ii) Ocean acidification → shellfish decline. [2]
Any two consequences with explanation.

20. [5]
Why increasing: [2] protected area, more prey, anti-poaching.
Evaluate healthy: [3] rising count suggests good habitat & breeding; but need other species data; single species not full ecosystem health.
Marking: 2 for reasons, 3 for balanced evaluation with caveat.