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Secondary 4 Pure Biology Ecology Quiz
Free Exam-Derived Owl Alpha Secondary 4 Pure Biology Ecology quiz with questions and answers for Singapore students. This page is rendered as a direct URL so the questions and answers can be discovered without pressing in-page buttons.
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Questions
Secondary 4 Pure Biology Quiz - Ecology
Name: ___________________________
Class: ___________________________
Date: ___________________________
Score: ________ / 40
Duration: 45 minutes
Total Marks: 40
Instructions:
- Answer ALL questions.
- Write your answers in the spaces provided.
- The number of marks for each question or part-question is shown in brackets [ ].
- You may use a calculator where necessary.
- Diagrams are not drawn to scale unless stated.
Section A: Multiple Choice Questions (10 marks)
Questions 1–10: Choose the most accurate answer from the options A, B, C, or D. Each question carries 1 mark.
1. Which of the following is an abiotic factor in a freshwater pond ecosystem?
A. Algae
B. Dissolved oxygen
C. Water fleas
D. Aquatic plants
Answer: ___________
2. A group of organisms of the same species living in a defined area at the same time is best described as a
A. community.
B. population.
C. ecosystem.
D. habitat.
Answer: ___________
3. Which of the following correctly represents a simple food chain in a grassland ecosystem?
A. Grass → Grasshopper → Snake → Eagle
B. Eagle → Snake → Grasshopper → Grass
C. Grass → Snake → Grasshopper → Eagle
D. Grasshopper → Grass → Eagle → Snake
Answer: ___________
4. In a food web, organisms that feed on both plants and animals are classified as
A. producers.
B. herbivores.
C. carnivores.
D. omnivores.
Answer: ___________
5. Which process in the carbon cycle returns carbon dioxide to the atmosphere?
A. Photosynthesis only
B. Respiration only
C. Respiration and combustion
D. Decomposition only
Answer: ___________
6. A pyramid of numbers may be inverted when
A. the producer is very large, such as a single tree supporting many insects.
B. energy is lost at each trophic level.
C. the ecosystem has more carnivores than herbivores.
D. decomposers outnumber producers.
Answer: ___________
7. Which of the following is a likely consequence of deforestation on the water cycle?
A. Increased transpiration
B. Decreased surface runoff
C. Reduced water vapour in the atmosphere
D. Increased groundwater recharge
Answer: ___________
8. Biological magnification refers to the
A. increase in population size of top predators.
B. accumulation of non-biodegradable toxins in organisms at higher trophic levels.
C. increase in biodiversity at each trophic level.
D. magnification of prey organisms by predators.
Answer: ___________
9. Which of the following best describes a food web?
A. A single linear pathway of energy transfer
B. A network of interconnected food chains
C. A diagram showing only producers and primary consumers
D. A pyramid showing biomass at each trophic level
Answer: ___________
10. Nitrogen-fixing bacteria in the root nodules of leguminous plants convert
A. atmospheric nitrogen into ammonia.
B. ammonia into nitrites.
C. nitrites into nitrates.
D. nitrates into atmospheric nitrogen.
Answer: ___________
Section B: Structured Response Questions (20 marks)
Questions 11–16: Answer each question in the spaces provided.
11. Table 1 shows the number of organisms counted in a grassland quadrat sample.
Table 1
| Organism | Number counted |
|---|---|
| Grass plants | 120 |
| Grasshoppers | 35 |
| Field mice | 8 |
| Snakes | 2 |
| Hawks | 1 |
(a) Name the organism in Table 1 that is the producer. [1]
(b) Construct a food chain using ALL the organisms in Table 1. [2]
(c) Explain why the number of hawks is the smallest in the sample. [2]
12. Fig. 12 shows a simplified carbon cycle.
(Imagine a diagram showing: atmosphere CO₂ → photosynthesis in plants → consumption by animals → respiration by animals → CO₂ to atmosphere; also fossil fuels → combustion → CO₂ to atmosphere; dead organisms → decomposition → CO₂ to atmosphere)
(a) Name process X that removes carbon dioxide from the atmosphere. [1]
(b) Name two processes that return carbon dioxide to the atmosphere. [2]
(c) Explain how the burning of fossil fuels disrupts the carbon cycle. [2]
13. Fig. 13 shows the population sizes of species P and Q over 10 years in a forest ecosystem.
(Imagine a graph: x-axis = Year (1–10), y-axis = Population size. Species P (prey) rises and falls. Species Q (predator) rises and falls with a slight time lag behind P.)
(a) Identify species P and Q as either predator or prey. Give a reason for each identification. [2]
Species P: _________________ Reason: _____________________________________________
Species Q: _________________ Reason: _____________________________________________
(b) Describe the relationship between species P and Q. [1]
(c) Suggest what would happen to the population of species Q if species P were removed from the ecosystem. Explain your answer. [2]
14. Explain the term ecological pyramid of energy and state why energy transfer between trophic levels is inefficient. [3]
15. Describe two ways in which human activities have contributed to the increase in atmospheric carbon dioxide concentration. For each way, explain its effect on the environment. [4]
Way 1: _____________________________________________
Effect: _____________________________________________
Way 2: _____________________________________________
Effect: _____________________________________________
16. Fig. 16 shows a food web in a mangrove ecosystem.
(Imagine a food web with: Mangrove leaves → Crabs → Herons; Mangrove leaves → Insects → Mudskippers → Herons; Algae → Shrimps → Mudskippers → Herons; Detritus → Crabs; Detritus → Shrimps)
(a) Name the food chain in Fig. 16 that contains four trophic levels. [1]
(b) State the trophic level of the heron. [1]
(c) If a pesticide that is non-biodegradable is introduced into the mangrove ecosystem, explain which organism would be most affected and why. [2]
Section C: Data-Based / Source-Based Question (10 marks)
Questions 17–20: Study the information provided and answer the questions that follow.
Read the following passage and answer Questions 17–20.
A group of students investigated the effect of light intensity on the distribution of two species of algae, Species A and Species B, in a freshwater lake. They collected water samples at five different depths and counted the number of algal cells per cm³ at each depth. Light intensity decreases with increasing depth.
Table 2
| Depth (m) | Light intensity (arbitrary units) | Number of Species A cells per cm³ | Number of Species B cells per cm³ |
|---|---|---|---|
| 0 | 100 | 200 | 50 |
| 2 | 60 | 350 | 80 |
| 4 | 30 | 150 | 200 |
| 6 | 10 | 40 | 300 |
| 8 | 2 | 5 | 100 |
17. (a) Describe the trend in the number of Species A cells as depth increases from 0 m to 8 m. [2]
(b) Suggest an explanation for the distribution pattern of Species A. [2]
18. (a) Describe the relationship between the number of Species B cells and light intensity. [2]
(b) Suggest one advantage that Species B has over Species A at low light intensities. [1]
19. Using the data in Table 2, explain how the two species demonstrate competition and how resource partitioning allows them to coexist in the same lake. [3]
20. Predict what would happen to the population of Species B if Species A were completely removed from the lake. Explain your answer with reference to the concept of competition. [2]
End of Quiz
Answers
Secondary 4 Pure Biology Quiz - Ecology
Answer Key
Section A: Multiple Choice Questions
1. B — Dissolved oxygen [1]
Note: Abiotic factors are non-living physical/chemical components. Algae, water fleas, and aquatic plants are biotic.
2. B — population [1]
Note: A community includes all species; an ecosystem includes abiotic factors; a habitat is the physical environment.
3. A — Grass → Grasshopper → Snake → Eagle [1]
Note: Food chains must begin with a producer and flow in the direction of energy transfer.
4. D — omnivores [1]
5. C — Respiration and combustion [1]
Note: Decomposition also releases CO₂, but the best answer from the options is C as it captures two major processes. Photosynthesis removes CO₂.
6. A — the producer is very large, such as a single tree supporting many insects [1]
7. C — Reduced water vapour in the atmosphere [1]
Note: Deforestation reduces transpiration, which decreases water vapour returned to the atmosphere.
8. B — accumulation of non-biodegradable toxins in organisms at higher trophic levels [1]
9. B — A network of interconnected food chains [1]
10. A — atmospheric nitrogen into ammonia [1]
Section B: Structured Response Questions
11. (a) Grass plants [1]
(b) Grass → Grasshopper → Field mouse → Snake → Hawk [2]
Marking: 1 mark for correct order, 1 mark for including all five organisms. Direction arrows must be correct.
(c) Energy is lost at each trophic level (as heat through respiration, uneaten parts, faeces) [1]. Therefore, less energy is available at higher trophic levels, supporting fewer organisms / smaller populations [1].
Common mistake: Students may say "hawks eat fewer things" without explaining energy loss.
12. (a) Photosynthesis [1]
(b) Any two of: Respiration, Combustion (of fossil fuels), Decomposition [2 — 1 mark each]
(c) Burning fossil fuels releases carbon that was stored underground over millions of years [1]. This adds extra CO₂ to the atmosphere faster than natural processes can remove it, increasing the atmospheric CO₂ concentration / enhancing the greenhouse effect / contributing to global warming [1].
13. (a) Species P: Prey [1] — Reason: Its population rises first, followed by the rise in Species Q (the predator). When P decreases, Q subsequently decreases.
Species Q: Predator [1] — Reason: Its population changes lag behind those of Species P; it depends on P as a food source.
(b) Predator–prey relationship [1]
(c) The population of species Q would decrease sharply / become extinct [1]. Species Q depends on species P as a food source; without P, Q would starve and its population would decline [1].
14. An ecological pyramid of energy is a diagram that shows the amount of energy available at each trophic level in an ecosystem [1]. Energy transfer between trophic levels is inefficient because: energy is lost as heat during respiration / metabolic processes [1]; not all parts of the organism are consumed or digested, and energy is lost in faeces and uneaten material [1].
Note: Typically only about 10% of energy is transferred from one trophic level to the next.
15. Way 1: Burning of fossil fuels [1]
Effect: Releases large amounts of CO₂ into the atmosphere, enhancing the greenhouse effect and contributing to global warming / climate change [1].
Way 2: Deforestation / clearing of forests for agriculture or development [1]
Effect: Reduces the number of trees available to absorb CO₂ through photosynthesis; also releases stored carbon when trees are burned or decompose, increasing atmospheric CO₂ [1].
Acceptable alternatives for Way 2: Industrial processes, vehicle emissions, slash-and-burn agriculture. Must link to environmental effect for full marks.
16. (a) Mangrove leaves → Insects → Mudskippers → Herons [1]
(Also acceptable: Algae → Shrimps → Mudskippers → Herons)
(b) Tertiary consumer / Third trophic level as consumer (fourth trophic level overall) [1]
Note: The heron feeds on mudskippers (secondary consumers), making it a tertiary consumer.
(c) The heron would be most affected [1]. Due to biological magnification, the non-biodegradable pesticide accumulates at each trophic level. The heron, being at the highest trophic level, would accumulate the highest concentration of the toxin, which could cause illness, reproductive failure, or death [1].
Section C: Data-Based / Source-Based Question
17. (a) The number of Species A cells increases from 200 at 0 m to a peak of 350 at 2 m [1], then decreases steadily to 5 at 8 m [1].
(b) Species A thrives at moderate light intensities (around 60 arbitrary units at 2 m depth) [1]. At the surface (0 m), very high light intensity may be damaging / cause photoinhibition. At greater depths, light intensity is too low for efficient photosynthesis, so the population declines [1].
18. (a) As light intensity decreases (with increasing depth), the number of Species B cells increases [1], reaching a maximum at 6 m depth (300 cells per cm³ at 10 light units), then decreases slightly at 8 m [1].
(b) Species B is better adapted to low light conditions / has a lower light compensation point / possesses more chlorophyll or accessory pigments to capture light more efficiently at low intensities [1].
19. The two species compete for the same resource — light [1]. Species A dominates at shallower depths (higher light) while Species B dominates at greater depths (lower light) [1]. This is resource partitioning — the two species utilise different parts of the habitat (different depths/light intensities), reducing direct competition and allowing them to coexist in the same lake [1].
20. The population of Species B would increase [1]. With Species A removed, competition for light and other resources (e.g., nutrients) would be reduced, allowing Species B to expand into shallower depths and grow to a larger population size [1].
End of Answer Key