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O Level Biology Ecology Quiz
Free O Level Biology Ecology quiz, HY3 Exam version, with questions, answers, and O Level-style practice for Singapore students.
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Questions
O-Level Biology Quiz - Ecology
Name: ___________________________
Class: ___________________________
Date: ___________________________
Score: ___________ / 40
Duration: 50 minutes
Total Marks: 40
Instructions:
- Answer all 20 questions.
- Section A: Multiple-choice (1 mark each).
- Section B: Structured questions (2–3 marks each).
- Section C: Data interpretation and extended response (3–5 marks each).
- Write your answers in the spaces provided.
Section A: Multiple Choice (Questions 1–5)
1. Which of the following best describes a community in an ecosystem? [1]
A. All the physical factors in a habitat
B. All the living organisms of different species in a habitat
C. A single population of one species
D. The non-living surroundings of an organism
2. Which process removes carbon dioxide from the atmosphere? [1]
A. Respiration
B. Combustion
C. Photosynthesis
D. Decomposition
3. An organism that feeds only on plants is called a: [1]
A. Carnivore
B. Herbivore
C. Omnivore
D. Decomposer
4. Which of these is a biotic factor? [1]
A. Temperature
B. Soil pH
C. Fungal infection
D. Light intensity
5. In a food chain, the arrows represent: [1]
A. Movement of animals
B. Flow of energy
C. Direction of wind
D. Water cycle
Section B: Structured Questions (Questions 6–10)
6. Define the term habitat. [2]
7. State two abiotic factors that can affect the distribution of mangrove trees. [2]
(i) __________________________________________________________
(ii) _________________________________________________________
8. Explain why decomposers are important in a nutrient cycle. [2]
9. A pond contains phytoplankton, zooplankton, small fish and large fish.
Draw a simple food chain using these organisms in the correct order. [2]
10. Give two reasons why biodiversity is important in an ecosystem. [2]
(i) __________________________________________________________
(ii) __________________________________________________________
Section C: Data Interpretation and Extended Response (Questions 11–20)
11. The graph below shows the population sizes of foxes and rabbits in a forest over 10 years.
Image pending generation: graph for Q11.
Describe the relationship between the fox and rabbit populations. [3]
12. Explain how energy is lost between trophic levels. [3]
13. A student sets up a compost bin with garden waste. After 4 weeks, the mass of waste has decreased.
Explain the biological processes responsible for this decrease. [3]
14. The table shows the percentage of energy transferred at each stage in a grassland food chain.
| Stage | Energy (kJ/m²/yr) |
|---|---|
| Sunlight reaching grass | 100 000 |
| Grass (producer) | 10 000 |
| Grasshopper (primary consumer) | 1 000 |
| Frog (secondary consumer) | 100 |
Calculate the percentage efficiency of energy transfer from grass to grasshopper. Show your working. [3]
Working: ______________________________________________________
Answer: ______________________________________________________
15. Describe how nitrogen enters the living components of an ecosystem and becomes available to plants. [4]
16. A forested hillside is cleared for agriculture. Predict two effects this could have on the local ecosystem and explain each. [4]
(i) __________________________________________________________
(ii) _________________________________________________________
17. The diagram shows a pond ecosystem with labelled organisms.
Image pending generation: diagram for Q17.
Using the diagram, construct a food web with at least three links. [4]
18. Explain the difference between a population and a community, giving one example of each from a tropical rainforest. [3]
19. Human activities such as burning fossil fuels increase atmospheric carbon dioxide.
Describe two consequences of this increase for ecosystems. [4]
(i) __________________________________________________________
(ii) _________________________________________________________
20. A nature reserve uses camera traps to count leopards. The table shows counts over 3 years.
| Year | Estimated leopard count |
|---|---|
| 2022 | 18 |
| 2023 | 24 |
| 2024 | 30 |
Suggest why the population might be increasing and evaluate whether this indicates a healthy ecosystem. [5]
Answers
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.
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