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A Level H2 Biology Ecology Quiz
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A-Level Biology H2 Quiz - Ecology
Name: _________________________ Class: _________________________ Date: _________________________ Score: ______ / 50
Duration: 45 minutes Total Marks: 50
Instructions:
- This quiz contains 20 questions on the topic of Ecology.
- Answer ALL questions in the spaces provided.
- The number of marks for each question or part question is shown in brackets.
- Where appropriate, use diagrams and examples to support your answers.
- You are advised to spend no more than 45 minutes on this quiz.
Section A: Short Answer (Questions 1–5)
Answer all questions in this section. Each question carries 2 marks.
1. Define the term community in ecological terms.
2. Distinguish between a food chain and a food web.
3. State what is meant by the term gross primary productivity (GPP).
4. Name the process by which certain bacteria convert ammonium ions (NH₄⁺) into nitrite ions (NO₂⁻) and then into nitrate ions (NO₃⁻).
5. Explain why the number of trophic levels in an ecosystem is usually limited to four or five.
Section B: Structured Questions (Questions 6–15)
Answer all questions in this section.
6. Figure 1 shows the flow of energy through a grassland ecosystem. The values represent energy in kJ m⁻² yr⁻¹.
| Trophic Level | Energy Input | Energy Lost in Respiration | Energy Lost in Faeces/Urine | Energy to Next Level |
|---|---|---|---|---|
| Producers | 3,000,000 | 1,200,000 | – | 300,000 |
| Primary Consumers | 300,000 | 150,000 | 120,000 | 30,000 |
| Secondary Consumers | 30,000 | 18,000 | 9,000 | 3,000 |
(a) Calculate the percentage of energy transferred from producers to primary consumers. Show your working. [2]
(b) Explain why only a small percentage of energy is transferred from one trophic level to the next. [3]
(c) Suggest what happens to the energy that is lost in faeces and urine from the primary consumers. [2]
7. The nitrogen cycle involves several key processes carried out by different groups of microorganisms.
(a) Name the process by which nitrogen gas (N₂) is converted into ammonia (NH₃). [1]
(b) Explain the role of Nitrosomonas and Nitrobacter in the nitrogen cycle. [3]
(c) Describe how denitrification can lead to a loss of soil fertility. [2]
8. A student investigated the distribution of two plant species, Plantago major (greater plantain) and Plantago lanceolata (ribwort plantain), along a transect from a heavily trampled footpath into an undisturbed meadow. The results are shown in Table 1.
| Distance from path (m) | % cover P. major | % cover P. lanceolata |
|---|---|---|
| 0 | 85 | 2 |
| 2 | 60 | 15 |
| 4 | 35 | 30 |
| 6 | 15 | 55 |
| 8 | 5 | 75 |
| 10 | 2 | 80 |
(a) Describe the trend shown by P. major along the transect. [1]
(b) Suggest an explanation for the distribution of P. major in relation to trampling. [2]
(c) Explain why it is important to take several replicate samples at each distance when collecting this type of data. [2]
9. Figure 2 shows a simplified diagram of the carbon cycle.
(a) Identify the processes labelled A and B in the carbon cycle. [2]
Process A: Carbon dioxide in atmosphere → Organic compounds in plants Process B: Organic compounds in dead organisms → Carbon dioxide in atmosphere
A: _________________________ B: _________________________
(b) Explain how the combustion of fossil fuels disrupts the balance of the carbon cycle. [3]
(c) Peat bogs are important carbon sinks. Suggest why the destruction of peat bogs for agriculture contributes to global warming. [2]
10. A population of rabbits on an island was studied over a 10-year period. The population size was estimated each year. The results are shown in Table 2.
| Year | Population Size |
|---|---|
| 1 | 50 |
| 2 | 120 |
| 3 | 280 |
| 4 | 450 |
| 5 | 460 |
| 6 | 440 |
| 7 | 200 |
| 8 | 180 |
| 9 | 350 |
| 10 | 420 |
(a) Describe the pattern of population growth shown in the table. [2]
(b) Suggest two density-dependent factors that could have caused the decline in population between Year 6 and Year 8. [2]
(c) Explain why the population did not continue to increase exponentially after Year 4. [3]
11. A farmer applies nitrate fertiliser to a field. After heavy rain, the fertiliser runs off into a nearby lake. Several weeks later, the lake experiences an algal bloom followed by the death of many fish.
(a) Name the process by which excess nutrients enter the lake. [1]
(b) Explain the sequence of events that leads to the death of fish following the algal bloom. [4]
12. Figure 3 shows the survivorship curves for three different species.
(a) Identify which curve (Type I, Type II, or Type III) is typical of a species that produces many offspring but provides little parental care. [1]
(b) Explain why a Type I survivorship curve is characteristic of large mammals, such as elephants. [2]
(c) Suggest how a Type III survivorship curve affects the life history strategy of a species. [2]
13. A group of students used the mark-release-recapture method to estimate the population size of woodlice in a woodland habitat.
- First sample: 80 woodlice captured, marked, and released.
- Second sample (one week later): 60 woodlice captured, of which 12 were marked.
(a) Use the Lincoln Index to calculate the estimated population size. Show your working. [2]
(b) State two assumptions that must be made when using the mark-release-recapture method. [2]
(c) Suggest one reason why the calculated estimate might be inaccurate. [1]
14. Explain how the greenhouse effect maintains temperatures suitable for life on Earth. [3]
15. Conservation biologists often focus on preserving keystone species within an ecosystem.
(a) Define the term keystone species. [1]
(b) Using a named example, explain how the removal of a keystone species can lead to a loss of biodiversity. [3]
Section C: Data-Based and Extended Response (Questions 16–20)
Answer all questions in this section.
16. Figure 4 shows the predator-prey relationship between the Canada lynx and the snowshoe hare, based on fur-trapping records from the Hudson Bay Company over a 90-year period.
(a) Describe the relationship between the population cycles of the lynx and the hare. [2]
(b) Explain why the peak in the lynx population usually occurs slightly after the peak in the hare population. [3]
(c) Suggest why the hare population does not continue to increase indefinitely, even when lynx numbers are low. [2]
17. A study was conducted to investigate the effect of temperature on the rate of decomposition of leaf litter in a forest ecosystem. Bags containing a known mass of leaf litter were placed in two locations: a lowland forest (mean annual temperature 25°C) and a montane forest (mean annual temperature 15°C). The percentage of original mass remaining was measured after 12 months.
| Location | Mean Annual Temperature (°C) | % Mass Remaining After 12 Months |
|---|---|---|
| Lowland Forest | 25 | 22 |
| Montane Forest | 15 | 48 |
(a) Calculate the percentage of leaf litter decomposed in the lowland forest after 12 months. [1]
(b) Explain the difference in decomposition rates between the two forests. [3]
(c) Predict how the results might differ if the experiment were repeated in a waterlogged soil. Justify your answer. [2]
18. Discuss the advantages and disadvantages of using biological control agents, rather than chemical pesticides, to manage agricultural pests. [5]
19. Figure 5 shows the estimated global carbon dioxide emissions from fossil fuel combustion and land-use change from 1960 to 2020, alongside the atmospheric CO₂ concentration measured at Mauna Loa Observatory.
(a) Describe the trend in atmospheric CO₂ concentration shown in the figure. [1]
(b) Explain the relationship between fossil fuel emissions and the increase in atmospheric CO₂ concentration. [2]
(c) Suggest two strategies, other than reducing fossil fuel use, that could help to reduce the concentration of CO₂ in the atmosphere. Explain how each strategy works. [4]
20. With reference to specific examples, explain how the principles of energy flow and nutrient cycling can be applied to design sustainable agricultural systems. [6]
END OF QUIZ
Check your answers carefully before submitting.
Answers
A-Level Biology H2 Quiz - Ecology: Answer Key and Marking Scheme
Total Marks: 50
Section A: Short Answer (Questions 1–5)
1. Define the term community in ecological terms. [2]
Answer: A community is all the populations of different species (1) living and interacting in a particular habitat/area at the same time (1).
2. Distinguish between a food chain and a food web. [2]
Answer: A food chain is a single linear sequence showing the transfer of energy from one organism to another (1), whereas a food web is a network of interconnected food chains showing multiple feeding relationships within a community (1).
3. State what is meant by the term gross primary productivity (GPP). [2]
Answer: Gross primary productivity is the total amount of light energy converted into chemical energy (organic matter) by photosynthesis (1) by producers in a given area over a given time period (1).
4. Name the process by which certain bacteria convert ammonium ions (NH₄⁺) into nitrite ions (NO₂⁻) and then into nitrate ions (NO₃⁻). [2]
Answer: Nitrification (2). (Accept: nitrification carried out by nitrifying bacteria; 1 mark for naming the process, 1 mark for linking to nitrifying bacteria if not explicitly stated.)
5. Explain why the number of trophic levels in an ecosystem is usually limited to four or five. [2]
Answer: Only about 10% of energy is transferred from one trophic level to the next (1). By the fourth or fifth trophic level, there is insufficient energy remaining to support a viable population of organisms at a higher trophic level (1).
Section B: Structured Questions (Questions 6–15)
6. Energy flow in a grassland ecosystem.
(a) Calculate the percentage of energy transferred from producers to primary consumers. [2]
Answer: Percentage transfer = (Energy to primary consumers / Energy input to producers) × 100 = (300,000 / 3,000,000) × 100 (1) = 10% (1)
(b) Explain why only a small percentage of energy is transferred from one trophic level to the next. [3]
Answer:
- Some energy is lost as heat during respiration (1).
- Not all of the organism is consumed by the next trophic level (e.g., bones, roots) (1).
- Some energy is lost in faeces/urine/excretory products, which are not assimilated (1).
(c) Suggest what happens to the energy that is lost in faeces and urine from the primary consumers. [2]
Answer: The energy in faeces and urine is available to decomposers/detritivores (1), which break down the organic matter and release energy through respiration, or the energy becomes trapped in detritus and may eventually form fossil fuels (1).
7. The nitrogen cycle.
(a) Name the process by which nitrogen gas (N₂) is converted into ammonia (NH₃). [1]
Answer: Nitrogen fixation (1).
(b) Explain the role of Nitrosomonas and Nitrobacter in the nitrogen cycle. [3]
Answer: Nitrosomonas oxidises ammonium ions (NH₄⁺) to nitrite ions (NO₂⁻) (1). Nitrobacter oxidises nitrite ions (NO₂⁻) to nitrate ions (NO₃⁻) (1). Together, these nitrifying bacteria convert ammonia (which can be toxic at high concentrations) into nitrates, which are the form most easily absorbed by plant roots (1).
(c) Describe how denitrification can lead to a loss of soil fertility. [2]
Answer: Denitrifying bacteria convert nitrate ions (NO₃⁻) in the soil into nitrogen gas (N₂), which is released into the atmosphere (1). This reduces the availability of nitrates for plant uptake, leading to reduced plant growth and lower soil fertility (1).
8. Distribution of plantain species along a trampling transect.
(a) Describe the trend shown by P. major along the transect. [1]
Answer: The percentage cover of P. major decreases as distance from the path increases (1).
(b) Suggest an explanation for the distribution of P. major in relation to trampling. [2]
Answer: P. major is tolerant of trampling (1). It may have adaptations such as a low-growing rosette form and tough leaves, allowing it to survive in areas of high foot traffic where other species cannot compete (1).
(c) Explain why it is important to take several replicate samples at each distance when collecting this type of data. [2]
Answer: Replicates allow the calculation of a mean/average, which reduces the effect of random variation/anomalies (1). This increases the reliability of the data and allows a more accurate representation of the true percentage cover at each distance (1).
9. The carbon cycle.
(a) Identify the processes labelled A and B. [2]
Answer: A: Photosynthesis (1) B: Decomposition / respiration by decomposers (1)
(b) Explain how the combustion of fossil fuels disrupts the balance of the carbon cycle. [3]
Answer: Fossil fuels contain carbon that was locked away from the active carbon cycle for millions of years (1). Combustion releases this carbon as carbon dioxide into the atmosphere at a rate much faster than it can be removed by photosynthesis and dissolution in oceans (1). This leads to a net increase in atmospheric CO₂ concentration, enhancing the greenhouse effect (1).
(c) Peat bogs are important carbon sinks. Suggest why the destruction of peat bogs for agriculture contributes to global warming. [2]
Answer: Peat bogs store large amounts of organic carbon in waterlogged, anaerobic conditions where decomposition is very slow (1). When peat bogs are drained and destroyed, the peat is exposed to oxygen, and aerobic decomposition by microorganisms releases the stored carbon as CO₂ into the atmosphere, contributing to global warming (1).
10. Rabbit population study.
(a) Describe the pattern of population growth shown in the table. [2]
Answer: The population initially shows exponential growth from Year 1 to Year 4 (1), then fluctuates around a carrying capacity of approximately 440–460 individuals, with a decline between Year 6 and Year 8 followed by recovery (1).
(b) Suggest two density-dependent factors that could have caused the decline in population between Year 6 and Year 8. [2]
Answer:
- Competition for food/resources as population density increased (1).
- Spread of disease/parasitism, which is more rapid at high population densities (1). (Accept: predation, accumulation of toxic wastes.)
(c) Explain why the population did not continue to increase exponentially after Year 4. [3]
Answer: As the population increased, density-dependent factors began to limit further growth (1). Resources such as food and space became limiting, increasing competition (1). The population reached the carrying capacity of the environment, where birth rate equals death rate and net growth is zero (1).
11. Eutrophication of a lake.
(a) Name the process by which excess nutrients enter the lake. [1]
Answer: Eutrophication (1). (Accept: leaching/runoff.)
(b) Explain the sequence of events that leads to the death of fish following the algal bloom. [4]
Answer:
- Excess nitrates/phosphates from fertiliser runoff cause rapid growth of algae (algal bloom) (1).
- The dense algal layer blocks light from reaching submerged aquatic plants, which die (1).
- Decomposers/aerobic bacteria break down the dead algae and plants, using up dissolved oxygen in the water through respiration (1).
- The resulting low oxygen concentration (hypoxia) causes fish and other aerobic organisms to suffocate and die (1).
12. Survivorship curves.
(a) Identify which curve (Type I, Type II, or Type III) is typical of a species that produces many offspring but provides little parental care. [1]
Answer: Type III (1).
(b) Explain why a Type I survivorship curve is characteristic of large mammals, such as elephants. [2]
Answer: Large mammals produce few offspring and invest significant parental care, resulting in low infant/juvenile mortality (1). Most individuals survive to old age, with mortality concentrated in the older age classes (1).
(c) Suggest how a Type III survivorship curve affects the life history strategy of a species. [2]
Answer: Species with a Type III curve produce a very large number of offspring to compensate for the extremely high mortality rate in early life stages (1). They typically invest little or no energy in parental care and rely on sheer numbers to ensure that at least some offspring survive to reproductive age (1).
13. Mark-release-recapture of woodlice.
(a) Use the Lincoln Index to calculate the estimated population size. [2]
Answer: Lincoln Index: N = (M × C) / R N = (80 × 60) / 12 (1) N = 4800 / 12 = 400 woodlice (1)
(b) State two assumptions that must be made when using the mark-release-recapture method. [2]
Answer: Any two from:
- The marked individuals have mixed randomly with the unmarked population (1).
- Marking does not affect the survival or behaviour of the individuals (e.g., does not make them more visible to predators) (1).
- No immigration or emigration occurs between the two sampling events (1).
- No births or deaths occur between the two sampling events, or the population is closed (1).
- The marks are not lost between the two samples (1).
(c) Suggest one reason why the calculated estimate might be inaccurate. [1]
Answer: Any one from:
- Marked individuals may have been more easily detected by predators, reducing the proportion of marked individuals in the second sample (leading to overestimation) (1).
- The population may not be closed; immigration or emigration could have occurred (1).
- The marks may have been lost, making marked individuals appear unmarked (leading to overestimation) (1).
14. Explain how the greenhouse effect maintains temperatures suitable for life on Earth. [3]
Answer: Short-wave solar radiation passes through the atmosphere and is absorbed by the Earth's surface, warming it (1). The Earth re-radiates this energy as long-wave infrared radiation (1). Greenhouse gases (e.g., CO₂, methane, water vapour) in the atmosphere absorb some of this outgoing infrared radiation and re-radiate it back towards the Earth's surface, trapping heat (1). Without this natural greenhouse effect, the Earth's average temperature would be approximately −18°C instead of the current +15°C, which is too cold to support most life (1). (Max 3 marks.)
15. Keystone species.
(a) Define the term keystone species. [1]
Answer: A keystone species is a species that has a disproportionately large effect on its ecosystem relative to its abundance (1).
(b) Using a named example, explain how the removal of a keystone species can lead to a loss of biodiversity. [3]
Answer: Example: Sea otter (1). Sea otters prey on sea urchins, which feed on kelp. When sea otters are removed (e.g., by hunting), sea urchin populations increase unchecked (1). The urchins overgraze the kelp forests, destroying the habitat for many other species that depend on kelp, leading to a dramatic loss of biodiversity (1). (Accept other valid examples, e.g., wolves in Yellowstone, starfish Pisaster ochraceus.)
Section C: Data-Based and Extended Response (Questions 16–20)
16. Lynx and hare predator-prey cycles.
(a) Describe the relationship between the population cycles of the lynx and the hare. [2]
Answer: The populations of lynx and hare show regular, cyclic fluctuations (1). The peaks and troughs in the lynx population follow those of the hare population with a slight time lag (1).
(b) Explain why the peak in the lynx population usually occurs slightly after the peak in the hare population. [3]
Answer: When the hare population is high, there is abundant food for the lynx, so the lynx population increases through higher birth rates and lower death rates (1). However, population growth takes time, so the lynx population continues to increase even after the hare population has started to decline (1). The lynx population peaks when the hare population has already fallen, leading to a time lag (1).
(c) Suggest why the hare population does not continue to increase indefinitely, even when lynx numbers are low. [2]
Answer: The hare population is also limited by the availability of its own food supply (vegetation) (1). When hare numbers are high, overgrazing can reduce food availability, leading to starvation and a decline in the hare population regardless of predation pressure (1).
17. Decomposition of leaf litter at different temperatures.
(a) Calculate the percentage of leaf litter decomposed in the lowland forest after 12 months. [1]
Answer: Percentage decomposed = 100% − 22% = 78% (1).
(b) Explain the difference in decomposition rates between the two forests. [3]
Answer: Decomposition is carried out by decomposers (bacteria and fungi), whose metabolic activity is enzyme-driven and temperature-dependent (1). The higher temperature in the lowland forest (25°C) provides more kinetic energy, increasing the rate of enzyme-catalysed reactions in decomposers (1). This leads to faster breakdown of organic matter compared to the cooler montane forest (15°C), where enzyme activity is slower (1).
(c) Predict how the results might differ if the experiment were repeated in a waterlogged soil. Justify your answer. [2]
Answer: The percentage of mass remaining would be higher / decomposition would be slower (1). Waterlogged soils are anaerobic, and aerobic decomposers cannot function efficiently. Anaerobic decomposition is much slower than aerobic decomposition, so organic matter accumulates (1).
18. Discuss the advantages and disadvantages of using biological control agents, rather than chemical pesticides, to manage agricultural pests. [5]
Answer: Award marks for a balanced discussion with clear advantages and disadvantages.
Advantages (max 3 marks):
- Biological control agents are often species-specific, reducing harm to non-target organisms, including beneficial insects and pollinators (1).
- Pests are less likely to develop resistance to biological control agents compared to chemical pesticides (1).
- Once established, biological control agents can provide long-term, self-sustaining pest control without the need for repeated applications (1).
- Biological control does not leave toxic chemical residues on crops or in the environment (1).
Disadvantages (max 3 marks):
- Biological control agents may not completely eradicate the pest; some pest damage may still occur (1).
- There is a time lag between introducing the control agent and achieving effective pest suppression (1).
- The control agent may become invasive itself, attacking non-target native species or disrupting local ecosystems (1).
- Biological control agents may be less effective if environmental conditions are unfavourable (e.g., temperature, humidity) (1).
Overall (max 5 marks): Award up to 5 marks for a well-structured answer that includes at least two advantages and two disadvantages, with clear explanations. A concluding evaluative statement is not required but may strengthen the answer.
19. Global CO₂ emissions and atmospheric concentration.
(a) Describe the trend in atmospheric CO₂ concentration shown in the figure. [1]
Answer: Atmospheric CO₂ concentration has increased steadily/continuously from 1960 to 2020 (1).
(b) Explain the relationship between fossil fuel emissions and the increase in atmospheric CO₂ concentration. [2]
Answer: The combustion of fossil fuels releases CO₂ that was previously stored in geological reservoirs into the atmosphere (1). The rate of CO₂ release from fossil fuel burning exceeds the rate at which carbon sinks (oceans, forests) can absorb it, leading to a net accumulation of CO₂ in the atmosphere (1).
(c) Suggest two strategies, other than reducing fossil fuel use, that could help to reduce the concentration of CO₂ in the atmosphere. Explain how each strategy works. [4]
Answer: Any two from:
- Afforestation/reforestation: Planting trees increases the rate of photosynthesis, removing CO₂ from the atmosphere and storing carbon in biomass (wood, leaves, roots) (2).
- Protecting and restoring peatlands/wetlands: Peatlands store large amounts of carbon in waterlogged, anaerobic conditions. Protecting them prevents the release of stored CO₂, and restoring degraded peatlands can increase carbon sequestration (2).
- Carbon capture and storage (CCS): CO₂ is captured directly from industrial emissions or the atmosphere and injected into deep geological formations (e.g., depleted oil and gas reservoirs) for long-term storage, preventing its release into the atmosphere (2).
- Enhancing soil carbon sequestration: Agricultural practices such as no-till farming, cover cropping, and adding organic matter to soil can increase the amount of carbon stored in soil organic matter (2).
(2 marks per strategy: 1 for naming/describing the strategy, 1 for explaining the mechanism of CO₂ reduction.)
20. With reference to specific examples, explain how the principles of energy flow and nutrient cycling can be applied to design sustainable agricultural systems. [6]
Answer: Award marks for clear application of ecological principles to agricultural design, with specific examples.
Energy Flow Principles (max 3 marks):
- In natural ecosystems, energy flows from producers to consumers, with losses at each trophic level. Sustainable agriculture can shorten food chains to improve energy efficiency (1). For example, consuming plants directly (primary consumers) rather than feeding plants to livestock (secondary consumers) reduces energy loss and produces more food per unit area (1).
- Integrated farming systems can use waste energy: crop residues not suitable for human consumption can be fed to livestock, converting otherwise wasted energy into useful products (meat, milk) (1).
- Agroforestry systems combine trees with crops or livestock. Trees capture solar energy and provide multiple products (fruit, timber, fuel), increasing overall energy capture and productivity per unit area (1).
Nutrient Cycling Principles (max 3 marks):
- Natural ecosystems recycle nutrients through decomposition. Sustainable agriculture can mimic this by composting crop residues and animal manure, returning nutrients to the soil and reducing the need for synthetic fertilisers (1). For example, organic farms use compost and green manures to maintain soil fertility (1).
- Crop rotation, including nitrogen-fixing legumes (e.g., clover, beans), replenishes soil nitrogen naturally through biological nitrogen fixation by Rhizobium bacteria, reducing reliance on energy-intensive Haber-process fertilisers (1).
- Intercropping and polyculture systems, where different crops are grown together, can improve nutrient use efficiency. For example, the "Three Sisters" system (maize, beans, squash) used by Native Americans: beans fix nitrogen for the maize, maize provides support for beans, and squash covers the ground, reducing erosion and nutrient loss (1).
Overall (max 6 marks): Award up to 6 marks for a well-structured answer that integrates both energy flow and nutrient cycling principles, with at least one specific, named example for each. Answers should demonstrate understanding of how ecological knowledge can inform practical agricultural design.
END OF ANSWER KEY