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Secondary 4 Combined Science Biology Ecology Quiz
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Questions
Secondary 4 Combined Science Biology Quiz - Ecology
Name: _________________________ Class: _________________________ Date: _________________________ Score: ______ / 40
Duration: 45 minutes Total Marks: 40
Instructions:
- Answer ALL questions in the spaces provided.
- Write your answers clearly and legibly.
- The number of marks for each question or part question is shown in brackets [ ].
- Where appropriate, use scientific terminology in your answers.
Section A: Short Answer Questions (10 marks)
Answer all questions in this section.
1. State the original source of energy for most ecosystems on Earth. [1 mark]
2. Define the term population in the context of ecology. [1 mark]
3. Name the process by which nitrogen gas (N₂) in the atmosphere is converted into nitrates that plants can absorb. [1 mark]
4. State one role of decomposers in an ecosystem. [1 mark]
5. Identify the trophic level occupied by herbivores in a food chain. [1 mark]
6. Explain why a food web provides a more stable representation of feeding relationships in an ecosystem than a single food chain. [2 marks]
7. State what is meant by the term biodiversity. [1 mark]
8. Name two greenhouse gases that contribute to global warming. [2 marks]
Section B: Structured Questions (10 marks)
Answer all questions in this section.
9. The diagram below shows a simple food chain in a grassland ecosystem.
Grass → Grasshopper → Frog → Snake → Hawk
(a) Name the producer in this food chain. [1 mark]
(b) Explain why the number of organisms generally decreases at each successive trophic level in this food chain. [3 marks]
(c) A disease kills most of the frogs in this ecosystem. Predict and explain the effect this would have on the grasshopper population. [2 marks]
10. The carbon cycle describes how carbon moves between the atmosphere, living organisms, and the Earth.
(a) Name the process by which plants remove carbon dioxide from the atmosphere. [1 mark]
(b) Describe two ways in which carbon dioxide is returned to the atmosphere from living organisms. [4 marks]
(c) Explain how the burning of fossil fuels affects the carbon cycle and contributes to climate change. [3 marks]
11. A student investigated the population of dandelion plants in two different fields using a quadrat.
| Field | Number of dandelions counted in 10 quadrats (0.5 m × 0.5 m) |
|---|---|
| A | 2, 0, 1, 3, 0, 2, 1, 0, 2, 1 |
| B | 8, 7, 9, 6, 8, 10, 7, 9, 8, 6 |
(a) Calculate the mean number of dandelions per quadrat in Field A. Show your working. [2 marks]
(b) The area of each quadrat is 0.25 m². Calculate the estimated population density of dandelions per m² in Field B. Show your working. [2 marks]
12. State one reason why the introduction of a non-native species can disrupt an ecosystem. [1 mark]
13. Explain the difference between a habitat and a niche. [2 marks]
Section C: Data-Based and Extended Response Questions (10 marks)
Answer all questions in this section.
14. The graph below shows changes in the population sizes of a predator (lynx) and its prey (snowshoe hare) over a 20-year period in a Canadian forest ecosystem.
[Imagine a graph with two oscillating curves: hare population peaks approximately every 8-10 years, lynx population peaks shortly after hare peaks but at lower numbers. Both populations fluctuate between high and low points.]
(a) Describe the relationship between the population sizes of the lynx and the snowshoe hare shown in the graph. [2 marks]
(b) Explain why the lynx population peaks shortly after the hare population peaks. [3 marks]
(c) Suggest one reason, other than predation, that could cause the hare population to decrease. [1 mark]
15. Deforestation is the large-scale removal of trees from forests, often to clear land for agriculture or urban development.
(a) Describe two negative effects of deforestation on the carbon cycle. [4 marks]
(b) Explain how deforestation can lead to a reduction in biodiversity. [2 marks]
Section D: Application and Analysis (10 marks)
Answer all questions in this section.
16. Explain how the use of fertilisers in agriculture can lead to eutrophication in nearby water bodies. [3 marks]
17. A farmer decides to stop using pesticides on a crop field. Explain how this could affect the population of birds in the area. [2 marks]
18. Describe one way in which carbon is stored long-term in the ocean. [1 mark]
19. Explain why energy transfer between trophic levels is inefficient. [2 marks]
20. Suggest and explain one conservation method that can help protect endangered species. [2 marks]
END OF QUIZ
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Answers
Secondary 4 Combined Science Biology Quiz - Ecology: Answer Key
Total Marks: 40
Section A: Short Answer Questions (10 marks)
1. State the original source of energy for most ecosystems on Earth. [1 mark]
- Answer: The Sun / Sunlight / Solar energy
- Marking note: Accept any of these. Do not accept "light" alone without context.
2. Define the term population in the context of ecology. [1 mark]
- Answer: A group of organisms of the same species living in the same area/habitat at the same time.
- Marking note: Must include "same species" and "same area" for the mark. Accept "all the members of one species in a particular habitat."
3. Name the process by which nitrogen gas (N₂) in the atmosphere is converted into nitrates that plants can absorb. [1 mark]
- Answer: Nitrogen fixation
- Marking note: Accept "nitrogen-fixing bacteria action" or "lightning nitrogen fixation." Do not accept "nitrification" alone (that is the conversion of ammonium to nitrates).
4. State one role of decomposers in an ecosystem. [1 mark]
- Answer: Break down dead organic matter / Release nutrients back into the soil / Recycle nutrients / Return mineral salts to the soil for plant uptake.
- Marking note: Accept any one valid role. Must imply breakdown or recycling.
5. Identify the trophic level occupied by herbivores in a food chain. [1 mark]
- Answer: Primary consumer / Second trophic level
- Marking note: Accept either term.
6. Explain why a food web provides a more stable representation of feeding relationships in an ecosystem than a single food chain. [2 marks]
- Answer: A food web shows multiple interconnected food chains / shows that most organisms eat more than one type of food. If one food source becomes unavailable, organisms can switch to alternative food sources, so the ecosystem is less likely to be disrupted / more stable.
- Marking note: 1 mark for describing what a food web shows (interconnectedness/multiple feeding relationships), 1 mark for explaining stability (alternative food sources/buffering against disruption).
7. State what is meant by the term biodiversity. [1 mark]
- Answer: The variety of living organisms / the variety of species in an ecosystem / the variety of life on Earth.
- Marking note: Accept any definition that includes "variety" and "living organisms/species."
8. Name two greenhouse gases that contribute to global warming. [2 marks]
- Answer: Any two from: Carbon dioxide (CO₂), Methane (CH₄), Nitrous oxide (N₂O), Water vapour (H₂O), CFCs.
- Marking note: 1 mark for each correct gas. Accept chemical formulas or full names.
Section B: Structured Questions (10 marks)
9. Food chain: Grass → Grasshopper → Frog → Snake → Hawk
(a) Name the producer in this food chain. [1 mark]
- Answer: Grass
- Marking note: Must name the organism, not just "producer."
(b) Explain why the number of organisms generally decreases at each successive trophic level in this food chain. [3 marks]
- Answer: Energy is lost at each trophic level (1 mark). Energy is lost through respiration, movement, heat, and as undigested waste/egestion (1 mark). Only about 10% of energy is transferred from one trophic level to the next, so less energy is available to support organisms at higher trophic levels, resulting in fewer organisms (1 mark).
- Marking note: Must include energy loss concept, examples of how energy is lost, and link to fewer organisms supported.
(c) A disease kills most of the frogs in this ecosystem. Predict and explain the effect this would have on the grasshopper population. [2 marks]
- Answer: The grasshopper population would increase (1 mark) because there are fewer frogs to prey on/eat the grasshoppers, reducing predation pressure (1 mark).
- Marking note: Must state the direction of change and give a reason linked to reduced predation.
10. Carbon cycle questions.
(a) Name the process by which plants remove carbon dioxide from the atmosphere. [1 mark]
- Answer: Photosynthesis
- Marking note: Must be the exact term.
(b) Describe two ways in which carbon dioxide is returned to the atmosphere from living organisms. [4 marks]
- Answer:
- Respiration: Living organisms (plants, animals, decomposers) carry out respiration, which releases carbon dioxide as a waste product into the atmosphere (2 marks).
- Decomposition: When organisms die, decomposers (bacteria, fungi) break down dead organic matter through respiration, releasing carbon dioxide (2 marks).
- Marking note: 2 marks for each correctly described way (1 mark for naming the process, 1 mark for brief description). Accept "combustion of biomass" if linked to living organisms (e.g., burning wood).
(c) Explain how the burning of fossil fuels affects the carbon cycle and contributes to climate change. [3 marks]
- Answer: Burning fossil fuels releases carbon dioxide that was stored underground for millions of years into the atmosphere (1 mark). This increases the atmospheric concentration of carbon dioxide, a greenhouse gas (1 mark). Increased greenhouse gases trap more heat/infrared radiation in the Earth's atmosphere, leading to global warming and climate change (1 mark).
- Marking note: Must include release of stored carbon, increased atmospheric CO₂, and greenhouse effect/climate change link.
11. Quadrat investigation.
(a) Calculate the mean number of dandelions per quadrat in Field A. Show your working. [2 marks]
- Answer: Total = 2 + 0 + 1 + 3 + 0 + 2 + 1 + 0 + 2 + 1 = 12 (1 mark). Mean = 12 ÷ 10 = 1.2 dandelions per quadrat (1 mark).
- Marking note: 1 mark for correct total, 1 mark for correct mean. Accept 1.2 or 1.20.
(b) The area of each quadrat is 0.25 m². Calculate the estimated population density of dandelions per m² in Field B. Show your working. [2 marks]
- Answer: Total dandelions in Field B = 8 + 7 + 9 + 6 + 8 + 10 + 7 + 9 + 8 + 6 = 78. Mean per quadrat = 78 ÷ 10 = 7.8 (1 mark). Population density = 7.8 ÷ 0.25 = 31.2 dandelions per m² (1 mark).
- Marking note: 1 mark for correct mean per quadrat, 1 mark for correct density calculation. Accept 31.2 or 31.
12. State one reason why the introduction of a non-native species can disrupt an ecosystem. [1 mark]
- Answer: It may have no natural predators, so its population grows rapidly / It may outcompete native species for resources (food, space) / It may introduce diseases to which native species have no immunity / It may prey on native species that have no defence against it.
- Marking note: Accept any one valid reason.
13. Explain the difference between a habitat and a niche. [2 marks]
- Answer: A habitat is the place/environment where an organism lives (1 mark). A niche is the role/function of an organism in an ecosystem, including its interactions with other organisms and its use of resources (1 mark).
- Marking note: Must clearly distinguish between "where it lives" (habitat) and "what it does/its role" (niche).
Section C: Data-Based and Extended Response Questions (10 marks)
14. Predator-prey graph (lynx and snowshoe hare).
(a) Describe the relationship between the population sizes of the lynx and the snowshoe hare shown in the graph. [2 marks]
- Answer: The populations show a cyclical/oscillating pattern (1 mark). When the hare population increases, the lynx population also increases after a short time lag; when the hare population decreases, the lynx population also decreases (1 mark).
- Marking note: Must describe the cyclical nature and the time lag relationship.
(b) Explain why the lynx population peaks shortly after the hare population peaks. [3 marks]
- Answer: When the hare population is high, there is more food/prey available for the lynx (1 mark). This allows more lynx to survive and reproduce, so the lynx population increases (1 mark). The lynx population continues to increase until it peaks shortly after the hare peak because it takes time for the lynx to reproduce and for the population to grow in response to increased food availability (1 mark).
- Marking note: Must include increased food availability, increased survival/reproduction, and time lag explanation.
(c) Suggest one reason, other than predation, that could cause the hare population to decrease. [1 mark]
- Answer: Disease/epidemic / Food shortage (due to overgrazing or environmental change) / Harsh winter/severe weather / Competition for resources / Human hunting.
- Marking note: Accept any valid reason other than predation.
15. Deforestation questions.
(a) Describe two negative effects of deforestation on the carbon cycle. [4 marks]
- Answer:
- Reduced photosynthesis: Fewer trees means less carbon dioxide is removed from the atmosphere by photosynthesis, leading to higher atmospheric CO₂ levels (2 marks).
- Release of stored carbon: When trees are burned or decompose after deforestation, the carbon stored in their biomass is released into the atmosphere as carbon dioxide (2 marks).
- Marking note: 2 marks for each correctly described effect (1 mark for identifying the effect, 1 mark for explaining the link to the carbon cycle). Accept other valid effects, e.g., soil erosion exposing stored carbon.
(b) Explain how deforestation can lead to a reduction in biodiversity. [2 marks]
- Answer: Deforestation destroys habitats (1 mark). This leads to the loss of plant and animal species that depend on the forest for food and shelter, reducing the variety of life/biodiversity (1 mark).
- Marking note: Must link habitat destruction to loss of species.
Section D: Application and Analysis (10 marks)
16. Explain how the use of fertilisers in agriculture can lead to eutrophication in nearby water bodies. [3 marks]
- Answer: Fertilisers contain nitrates and phosphates that are washed/leached into water bodies by rain (1 mark). These nutrients cause rapid growth of algae (algal bloom) on the water surface (1 mark). The algae block sunlight, causing underwater plants to die; decomposers then break down the dead plants and algae, using up oxygen in the water, which leads to the death of aquatic animals like fish (1 mark).
- Marking note: Must include nutrient runoff, algal bloom, and oxygen depletion for full marks.
17. A farmer decides to stop using pesticides on a crop field. Explain how this could affect the population of birds in the area. [2 marks]
- Answer: The bird population may increase (1 mark) because there would be more insects available as food (pesticides are no longer killing them), or because the birds are no longer directly poisoned by the pesticides (1 mark).
- Marking note: Accept either increased food supply or reduced direct poisoning as valid explanations.
18. Describe one way in which carbon is stored long-term in the ocean. [1 mark]
- Answer: Carbon is stored in the shells and skeletons of marine organisms (calcium carbonate) which eventually form limestone/sedimentary rock on the ocean floor / Carbon is dissolved in deep ocean water as carbonates and bicarbonates / Carbon is stored in fossil fuels (oil, gas) formed from dead marine organisms buried under the seabed.
- Marking note: Accept any one valid long-term ocean carbon sink.
19. Explain why energy transfer between trophic levels is inefficient. [2 marks]
- Answer: Energy is lost at each trophic level because organisms use energy for respiration, movement, growth, and maintaining body temperature (1 mark). Some energy is also lost as heat or in undigested waste materials (egestion) and excretory products (excretion) (1 mark).
- Marking note: 1 mark for identifying energy use by organisms, 1 mark for identifying energy lost as heat/waste.
20. Suggest and explain one conservation method that can help protect endangered species. [2 marks]
- Answer:
- Establishing protected areas/nature reserves: This protects the natural habitat of endangered species from destruction or human interference, allowing populations to recover (2 marks).
- Captive breeding programmes: Endangered species are bred in captivity and then reintroduced into the wild to increase population numbers (2 marks).
- Legislation/laws against hunting and trade: Making it illegal to hunt or trade endangered species and their products reduces direct threats to their survival (2 marks).
- Marking note: 1 mark for naming a valid method, 1 mark for explaining how it helps protect the species. Accept other valid methods.
END OF ANSWER KEY