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A Level H2 Biology Ecology Quiz
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Questions
A-Level Biology H2 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 is given in brackets [ ] at the end of each question or part question.
- Use precise biological terminology.
Section A: Ecosystem Dynamics and Energy Flow (Questions 1–5)
1. Define the term ecosystem. [2]
2. Distinguish between gross primary productivity (GPP) and net primary productivity (NPP). [2]
3. Explain why energy transfer between trophic levels is inefficient, citing two specific reasons for energy loss. [2]
4. A farmer observes that a field of crops has a higher biomass than the herbivores feeding on it. Explain this observation using the concept of the pyramid of biomass. [2]
5. In a freshwater ecosystem, algae are the producers. Zooplankton feed on algae, and small fish feed on zooplankton.
(a) Identify the trophic level of the small fish. [1]
(b) Suggest why the population of small fish is usually smaller than the population of zooplankton. [1]
Section B: Nutrient Cycling (Questions 6–10)
6. Describe the role of saprobionts in the carbon cycle. [2]
7. Explain how nitrogen-fixing bacteria in the root nodules of leguminous plants benefit the plant. [2]
8. State the process by which ammonium ions () are converted into nitrites () and then nitrates (). Name the type of bacteria involved. [2]
Process: __________________________
Bacteria: __________________________
9. Explain why waterlogging of soil can lead to a decrease in soil fertility due to the action of denitrifying bacteria. [2]
10. Describe how the combustion of fossil fuels affects the carbon cycle and contributes to global warming. [2]
Section C: Populations and Conservation (Questions 11–15)
11. Define carrying capacity in the context of population growth. [1]
12. Sketch the general shape of a sigmoid (S-shaped) population growth curve. Label the lag phase, exponential phase, and stationary phase. [2]
(Draw in the box below)
<br><br><br><br><br><br>
13. Distinguish between density-dependent and density-independent factors affecting population size, giving one example of each. [2]
Density-dependent: __________________________
Density-independent: __________________________
14. Explain how interspecific competition differs from intraspecific competition. [2]
15. A population of deer increases rapidly after the removal of their main predator, wolves. Eventually, the deer population stabilizes. Explain this stabilization in terms of limiting factors. [2]
Section D: Human Impact and Biodiversity (Questions 16–20)
16. Define biodiversity at the genetic level. [1]
17. Explain how eutrophication leads to the death of fish in a lake. Include the role of aerobic bacteria in your answer. [3]
18. Describe one method used to conserve biodiversity, such as the establishment of protected areas or seed banks. [2]
19. Explain why indicator species are useful in monitoring environmental pollution. Give one example of an indicator species and what its presence/absence indicates. [2]
20. Discuss the ethical and ecological arguments for preserving biodiversity. [2]
End of Quiz
Answers
A-Level Biology H2 Quiz - Ecology (Answer Key)
1. Define the term ecosystem. [2]
- A community of living organisms (biotic factors) [1]
- Interacting with their physical environment (abiotic factors) as a system. [1]
2. Distinguish between gross primary productivity (GPP) and net primary productivity (NPP). [2]
- GPP is the total chemical energy stored in plant biomass/organic molecules via photosynthesis. [1]
- NPP is GPP minus the energy lost/respired by the plants (R). (). [1]
3. Explain why energy transfer between trophic levels is inefficient, citing two specific reasons for energy loss. [2]
- Energy is lost as heat during respiration/metabolic processes. [1]
- Energy is lost in excretory materials (urine/faeces) or uneaten parts (bones/roots). [1]
(Accept: Energy used for movement/active transport)
4. A farmer observes that a field of crops has a higher biomass than the herbivores feeding on it. Explain this observation using the concept of the pyramid of biomass. [2]
- Energy transfer is inefficient (only ~10% passed on). [1]
- Therefore, there is insufficient energy to support a biomass of herbivores equal to or greater than the producers. [1]
5. In a freshwater ecosystem...
(a) Identify the trophic level of the small fish. [1]
- Secondary consumer (or Tertiary trophic level). [1]
(b) Suggest why the population of small fish is usually smaller than the population of zooplankton. [1] - Less energy is available at the higher trophic level to support individual organisms. [1]
6. Describe the role of saprobionts in the carbon cycle. [2]
- They secrete extracellular enzymes to digest dead organic matter externally. [1]
- They absorb the nutrients and release carbon dioxide back into the atmosphere via respiration. [1]
7. Explain how nitrogen-fixing bacteria in the root nodules of leguminous plants benefit the plant. [2]
- They convert atmospheric nitrogen () into ammonia/ammonium ions. [1]
- The plant uses these ions to synthesize amino acids/proteins/DNA. [1]
8. State the process by which ammonium ions () are converted into nitrites () and then nitrates (). Name the type of bacteria involved. [2]
- Process: Nitrification. [1]
- Bacteria: Nitrifying bacteria (e.g., Nitrosomonas and Nitrobacter). [1]
9. Explain why waterlogging of soil can lead to a decrease in soil fertility due to the action of denitrifying bacteria. [2]
- Waterlogging creates anaerobic conditions. [1]
- Denitrifying bacteria convert nitrates back into atmospheric nitrogen gas, removing usable nitrogen from the soil. [1]
10. Describe how the combustion of fossil fuels affects the carbon cycle and contributes to global warming. [2]
- Combustion releases carbon that was stored underground for millions of years as into the atmosphere. [1]
- Increased atmospheric enhances the greenhouse effect, trapping heat and raising global temperatures. [1]
11. Define carrying capacity in the context of population growth. [1]
- The maximum population size that an environment can sustain indefinitely. [1]
12. Sketch the general shape of a sigmoid (S-shaped) population growth curve. [2]
- Correct S-shape drawn. [1]
- Labels: Lag phase (initial slow growth), Exponential/Log phase (rapid growth), Stationary phase (plateau at carrying capacity). [1]
13. Distinguish between density-dependent and density-independent factors... [2]
- Density-dependent: Effect intensifies as population density increases (e.g., competition, disease, predation). [1]
- Density-independent: Effect is not related to population density (e.g., natural disasters, temperature, floods). [1]
14. Explain how interspecific competition differs from intraspecific competition. [2]
- Interspecific: Competition between individuals of different species. [1]
- Intraspecific: Competition between individuals of the same species. [1]
15. A population of deer increases... Explain this stabilization in terms of limiting factors. [2]
- As population increases, resources (food/space) become limited. [1]
- This increases competition and mortality/reduces birth rate until the population stabilizes at carrying capacity. [1]
16. Define biodiversity at the genetic level. [1]
- The variety of different alleles/genes within a species or population. [1]
17. Explain how eutrophication leads to the death of fish in a lake. [3]
- Algal bloom blocks sunlight, causing underwater plants to die. [1]
- Saprobionts/aerobic bacteria decompose the dead matter, consuming large amounts of dissolved oxygen. [1]
- Fish die due to lack of oxygen (hypoxia/anoxia). [1]
18. Describe one method used to conserve biodiversity... [2]
- Example: Seed Banks. Seeds are collected, dried, and stored at low temperatures. [1]
- This preserves genetic diversity and allows for future restoration of plant species. [1]
(Alternative: Protected Areas – restricts human activity/hunting, allowing habitats to recover.)
19. Explain why indicator species are useful... [2]
- Their presence, absence, or abundance reflects specific environmental conditions/pollution levels. [1]
- Example: Mayfly larvae indicate clean, oxygenated water; their absence indicates pollution. [1]
20. Discuss the ethical and ecological arguments for preserving biodiversity. [2]
- Ethical: Species have a right to exist; humans have a moral stewardship responsibility. [1]
- Ecological: High biodiversity ensures ecosystem stability/resilience and provides ecosystem services (e.g., pollination, nutrient cycling). [1]