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A Level H2 Biology Ecology Quiz

Free A Level H2 Biology Ecology quiz, HY3 Exam version, with questions, answers, and A Level-style practice for Singapore students.

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Questions

A-Level Biology H2 Quiz - Ecology

Name: ___________________________
Class: ___________________________
Date: ___________________________
Score: ___________ / 40

Duration: 60 minutes
Total Marks: 40
Topic: Ecology

Instructions:

Answer all 20 questions.
Section A: Short structured questions (1–8). Section B: Data and diagram interpretation (9–14). Section C: Extended response (15–20).
Use clear scientific terminology. Show workings for calculation questions.
Write your answers in the spaces provided.

Section A: Short Structured Questions (1–8) [16 marks]

1. Define the term ecosystem. [2]

2. State two abiotic components of a freshwater pond ecosystem. [2]
(i) ___________________________
(ii) ___________________________

3. Explain the difference between a food chain and a food web. [2]

4. What is meant by the term trophic level? [1]

5. A population of grasshoppers in a field has a carrying capacity of 1200. Explain what is meant by carrying capacity. [2]

6. Name the process by which nitrogen gas from the atmosphere is converted into ammonia by bacteria. [1]

7. State one human activity that increases the concentration of atmospheric carbon dioxide. [1]

8. Using the formula for species richness, explain what a higher value indicates about a community. [3]

Section B: Data and Diagram Interpretation (9–14) [14 marks]

9. The graph below shows the change in population size of two species, X and Y, in a closed habitat over 20 years.

Graph for Q9 (ALEVEL Biology H2)

Generated graph for Q9.

With reference to the graph, describe the relationship between the populations of X and Y. [3]

10. The table shows energy transfer at successive trophic levels in a grassland ecosystem.

Trophic level	Energy received (kJ m⁻² yr⁻¹)
Producers	50 000
Primary consumers	5 000
Secondary consumers	500

Calculate the percentage efficiency of energy transfer from producers to primary consumers. [2]
Working: ________________________________________________
Answer: ____________________

11. Explain why energy transfer between trophic levels is low (typically < 20%). [3]

12. The diagram shows a pond food web.

Diagram for Q12 (ALEVEL Biology H2)

Generated diagram for Q12.

Identify one organism that acts as a decomposer and state its role. [2]
Decomposer: ____________________
Role: ___________________________________________________

13. A student counted 40 daisies in a 1 m² quadrat. The field has an area of 800 m². Estimate the total daisy population. [2]
Working: ________________________________________________
Answer: ____________________

14. With reference to the nitrogen cycle, state the role of nitrifying bacteria. [2]

Section C: Extended Response (15–20) [10 marks]

15. Describe how succession occurs on a bare rock surface from pioneer to climax community. [4]

16. Explain how carbon is cycled between organisms and the atmosphere. [3]

17. A lake receives fertiliser runoff. Predict and explain the effect on dissolved oxygen concentration. [3]

18. Define biodiversity and state two reasons why high biodiversity increases ecosystem stability. [3]

19. Using a chi-squared test, a student compared observed and expected beetle counts in two habitats. Observed = [30, 10], Expected = [20, 20]. Given χ² = 10.0, critical value at p<0.05 = 3.84, state the conclusion. [2]
Conclusion: ________________________________________________

20. Suggest how climate change may alter species distribution in a tropical forest. [3]

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Answers

A-Level Biology H2 Quiz - Ecology: Answer Key

Total Marks: 40
Topic: Ecology

Section A Answers (1–8)

1. [2 marks]
Definition: An ecosystem is a community of living organisms (biotic components) interacting with each other and with their non-living (abiotic) environment in a particular area.
Marking: 1 mark for biotic community, 1 mark for abiotic interaction.
Teaching note: Ecosystem includes both parts and their exchanges of energy/matter.

2. [2 marks]
Any two: temperature, light intensity, dissolved oxygen, pH, salinity, water flow. [1+1]
Common mistake: Listing biotic items like fish.

3. [2 marks]
A food chain is a linear sequence of organisms showing who eats whom (1 mark). A food web is a network of interconnected food chains showing multiple feeding relationships (1 mark).
Teaching note: Webs are more realistic and show resilience.

4. [1 mark]
The position an organism occupies in a food chain, e.g. producer, primary consumer.

5. [2 marks]
Carrying capacity is the maximum population size that the environment can sustain indefinitely (1 mark) given available resources such as food, space, and water (1 mark).

6. [1 mark]
Nitrogen fixation.

7. [1 mark]
Burning fossil fuels / deforestation / cement production (any one).

8. [3 marks]
Species richness = number of different species in a community (1 mark). A higher value indicates greater variety of species (1 mark) and usually a more complex community (1 mark).
Teaching note: Do not confuse with abundance (individual count).

Section B Answers (9–14)

9. [3 marks]

Species Y (prey) fluctuates cyclically (1 mark).
Species X (predator) peaks ~2 years after Y (1 mark).
Predator population follows prey due to dependent consumption (1 mark).
From graph: lag visible at year 4 (Y peak) → year 6 (X peak).

10. [2 marks]
Efficiency = (5000 / 50000) × 100 = 10%
Working: 5000 ÷ 50000 = 0.1 → ×100 = 10%
Answer: 10% [2 marks for correct calc]

11. [3 marks]

Not all ingested food is absorbed; some lost as faeces (1).
Much energy lost as heat via respiration (1).
Some parts not consumed (e.g. bones) (1).

12. [2 marks]
Decomposer: Bacteria (1). Role: Break down dead organic matter/detritus, releasing nutrients to ecosystem (1).

13. [2 marks]
Density = 40 per m². Total = 40 × 800 = 32 000.
Working: 40 × 800 = 32 000
Answer: 32 000 daisies.

14. [2 marks]
Convert ammonia to nitrite then nitrate (1 mark) which plants absorb (1 mark).
Teaching note: Nitrosomonas and Nitrobacter are examples.

Section C Answers (15–20)

15. [4 marks]

Pioneer species (lichens/mosses) colonise bare rock, weather it (1).
Soil accumulates, grasses/herbs establish (1).
Shrubs then trees outcompete, increasing biomass (1).
Climax community stable with high diversity (1).

16. [3 marks]

CO₂ from atmosphere taken by photosynthesis into glucose (1).
Passed via food chains (1).
Returned by respiration, decay, combustion (1).

17. [3 marks]

Fertiliser causes algal bloom (1).
Algae die, decomposers respire using O₂ (1).
Dissolved O₂ falls, may kill fish (1).

18. [3 marks]
Biodiversity = variety of species/genes/ecosystems (1). Reasons: more niches → redundant functions (1); pests/disease less likely to wipe all (1).

19. [2 marks]
χ² = 10.0 > 3.84, reject null hypothesis (1). Significant difference in distribution between habitats (1).

20. [3 marks]

Rising temps shift species upslope/away (1).
Altered rainfall changes composition (1).
Some species local extinction if unable to migrate (1).