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A Level H1 Biology Ecology Quiz
Free A Level H1 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 H1 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 (1–10).
- Section B: Data and figure interpretation (11–15).
- Section C: Extended response and application (16–20).
- Write your answers in the spaces provided. Show working where required.
Section A: Short Structured Questions (1–10)
1. Define the term ecosystem. [2]
2. State one abiotic factor and one biotic factor that can affect the population size of a freshwater fish species. [2]
Abiotic: ___________________________
Biotic: ___________________________
3. With reference to energy flow in a food chain, explain why the amount of energy available to tertiary consumers is less than that available to primary consumers. [3]
4. Name the process by which nitrogen gas from the atmosphere is converted into ammonia by bacteria. [1]
5. State two characteristics of a stable climax community. [2]
(i) ___________________________
(ii) ___________________________
6. Describe the difference between a population and a community. [2]
7. The table below shows the number of individuals of two species in a grassland plot.
| Species | Number of individuals |
|---|---|
| Grass (producer) | 1200 |
| Beetle (primary consumer) | 300 |
Calculate the producer-to-primary-consumer ratio. [2]
Ratio = ___________ : ___________
8. State the term used to describe the role of a species within its habitat, including its use of resources and relationships with other species. [1]
9. Explain how deforestation can lead to an increase in atmospheric carbon dioxide concentration. [2]
10. Give one example of a greenhouse gas and state how it contributes to global warming. [2]
Gas: ___________________________
Contribution: ___________________________
Section B: Data and Figure Interpretation (11–15)
11. The graph below shows the change in population size of a rabbit population over 20 years in a closed grassland ecosystem.
Image pending generation: graph for Q11.
(a) Describe the pattern of population change from year 0 to year 8. [2]
(b) Suggest one biotic factor that could cause the decline after year 16. [1]
(a) ___________________________________________________________
(b) ___________________________________________________________
12. With reference to Fig. Q12 below, identify the trophic level of organism X and explain your answer. [2]
Image pending generation: diagram for Q12.
13. A student measured the oxygen concentration (mg/L) at two depths in a pond at midday:
| Depth | Oxygen concentration (mg/L) |
|---|---|
| Surface | 9.2 |
| 3 m depth | 4.1 |
Calculate the percentage decrease in oxygen concentration from surface to 3 m depth. [2]
% decrease = ___________ %
14. The figure shows a carbon cycle diagram with labelled boxes: atmosphere (CO₂), plant (photosynthesis), animal (respiration), decomposer, fossil fuels.
Image pending generation: diagram for Q14.
State two processes by which carbon moves from the biosphere to the atmosphere. [2]
(i) ___________________________
(ii) ___________________________
15. The table shows species richness in two ecosystems.
| Ecosystem | Number of plant species | Number of animal species |
|---|---|---|
| Forest A | 45 | 78 |
| Field B | 12 | 20 |
Calculate the total species richness for Forest A. [1]
Total = ___________
Section C: Extended Response and Application (16–20)
16. Explain how climate change can affect the distribution of the mosquito Aedes aegypti and the spread of mosquito-borne diseases in Singapore. [4]
17. A pond ecosystem receives untreated sewage. Describe the likely ecological consequences for the pond over a period of 4 weeks, with reference to nutrient enrichment and oxygen levels. [4]
18. With reference to the nitrogen cycle, describe the roles of decomposers and nitrifying bacteria. [3]
19. The graph shows mean temperature anomaly (°C) from 1980 to 2020 for Singapore.
Image pending generation: graph for Q19.
Using the graph, describe the trend and suggest how this may affect local biodiversity. [3]
20. Evaluate the use of biological control (introducing a natural predator) compared with chemical pesticide use to manage an invasive insect pest in a tropical crop ecosystem. [4]
Answers
A-Level Biology H1 Quiz - Ecology: Answer Key
Total Marks: 40
Topic: Ecology
Section A Answers (1–10)
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 community of organisms, 1 mark for interaction with abiotic environment.
Teaching note: Ecosystem includes both biotic (plants, animals, microbes) and abiotic (soil, water, climate) parts linked by energy flow and nutrient cycles.
2. [2 marks]
Abiotic: e.g., water temperature / dissolved oxygen / pH.
Biotic: e.g., predation by larger fish / competition for food / parasite.
Marking: 1 mark each, acceptable relevant example.
Common mistake: Giving two abiotic factors only.
3. [3 marks]
Energy is lost at each trophic level mainly as heat from respiration (1), not all parts of organisms are consumed (1), and not all consumed material is assimilated (1). Thus tertiary consumers receive less than primary consumers.
Teaching note: Only ~10% of energy transfers between levels (ecological efficiency).
4. [1 mark]
Nitrogen fixation.
Note: Specifically biological nitrogen fixation by prokaryotes (e.g., Rhizobium).
5. [2 marks]
Any two: high species diversity / resistant to small disturbances / nutrient cycling balanced / dominated by climax species adapted to climate.
Marking: 1 mark each.
6. [2 marks]
A population is a group of individuals of the same species in an area (1). A community is all populations of different species living and interacting in an area (1).
7. [2 marks]
Ratio = 1200 : 300 = 4 : 1.
Working: Divide both by 300 → 4 : 1.
Marking: 1 mark for correct simplification, 1 for format.
8. [1 mark]
Niche.
9. [2 marks]
Trees remove CO₂ via photosynthesis (1); cutting them reduces CO₂ uptake and burning/decomposition releases stored CO₂ (1).
10. [2 marks]
Gas: e.g., CO₂ / methane (CH₄).
Contribution: traps infrared radiation in atmosphere, enhancing greenhouse effect and warming Earth.
Marking: 1 mark each.
Section B Answers (11–15)
11. [3 marks]
(a) [2] Population increased rapidly (exponentially) from 50 to 600 individuals between year 0 and 8, indicating a period of low limitation.
(b) [1] Predation increase / disease outbreak / food shortage.
Marking: (a) 1 for rise, 1 for magnitude/pattern; (b) 1 for valid biotic factor.
12. [2 marks]
X is a secondary consumer (1) because it eats the primary consumer (snail) and is eaten by tertiary consumer (snake) (1).
Teaching note: Trophic level from position in food web.
13. [2 marks]
% decrease = ((9.2 – 4.1) / 9.2) × 100 = (5.1 / 9.2) × 100 = 55.4% ≈ 55%.
Marking: 1 for correct subtraction and division, 1 for answer.
14. [2 marks]
(i) Respiration (by animals/plants)
(ii) Decomposition (by decomposers)
Also accept: combustion of fossil fuels (but that is from geosphere, still to atmosphere).
Marking: 1 each.
15. [1 mark]
Total = 45 + 78 = 123 species.
Section C Answers (16–20)
16. [4 marks]
Climate warming raises temperatures and humidity suitable for Aedes aegypti survival (1), expands its geographic range into previously cooler areas (1), increases breeding cycle speed and bite rate (1), leading to greater transmission of dengue/zika (1). In Singapore, warmer urban areas and rainfall variability create more breeding sites.
Marking descriptors: 4 pts as above; 2–3 for partial mechanism; 1 for only stating spread.
17. [4 marks]
Sewage adds nutrients (N, P) causing eutrophication (1). Algal bloom grows, then dies (1). Decomposers respire using O₂, depleting dissolved oxygen (1). Fish and aerobic organisms die, reducing biodiversity (1).
Teaching note: Nutrient enrichment → hypoxia → death.
18. [3 marks]
Decomposers break down dead organic matter, releasing ammonia (ammonification) (1). Nitrifying bacteria convert ammonia to nitrite then nitrate (nitrification) (1), making nitrogen available to plants (1).
Marking: 1 each step.
19. [3 marks]
Trend: temperature anomaly rose from 0.1°C (1980) to 1.0°C (2020), ~1°C increase (1). This warming can shift species ranges, cause coral bleaching, mismatch breeding times (1), reducing local biodiversity (1).
Marking: 1 description, 2 impact.
20. [4 marks]
Biological control: targets specific pest, less pollution, sustainable (1) but slow, risk of predator becoming invasive (1). Chemical pesticide: fast knock-down (1) but kills non-targets, bioaccumulation, resistance (1). Evaluation should weigh ecology vs efficacy.
Marking: 2 points each side or balanced 4-point argument.
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