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Secondary 3 Biology Ecology Quiz
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Questions
Secondary 3 Biology Quiz - Ecology
Name: _________________________ Class: _________________________ Date: _________________________ Score: ________ / 40
Duration: 45 minutes Total Marks: 40
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 is indicated in brackets.
- Read each question carefully before answering.
Section A: Short Answer (Questions 1-5) Answer all questions in this section.
1. Define the term 'ecosystem'. [2]
2. State the role of decomposers in an ecosystem. [1]
3. Explain why the flow of energy through an ecosystem is described as non-cyclical. [2]
4. Distinguish between a food chain and a food web. [2]
5. Name the process by which carbon is removed from the atmosphere by plants. [1]
Section B: Structured Response (Questions 6-15) Answer all questions in this section.
6. Fig. 6.1 shows a simple food chain in a grassland ecosystem.
Grass → Grasshopper → Frog → Snake → Hawk
(a) Identify the producer in this food chain. [1]
(b) State the trophic level occupied by the frog. [1]
(c) Explain why there are usually fewer hawks than grasshoppers in this ecosystem. [2]
7. A student investigated the carbon cycle and drew a diagram showing the movement of carbon between the atmosphere, living organisms, and fossil fuels.
(a) State one way in which carbon is returned to the atmosphere from living organisms. [1]
(b) Explain how the burning of fossil fuels affects the concentration of carbon dioxide in the atmosphere. [2]
8. Fig. 8.1 shows a pyramid of numbers for a forest ecosystem.
1
--------
100
--------
10,000
--------
100,000
(a) State what the numbers in each level of the pyramid represent. [1]
(b) Suggest why the pyramid of numbers for this forest ecosystem has this shape. [2]
9. Describe how deforestation can contribute to global warming. [3]
10. Explain the term 'bioaccumulation' using a named example of a pollutant. [3]
11. A farmer uses an insecticide spray on crops to kill insect pests. The insecticide is non-biodegradable.
(a) Explain what is meant by the term 'non-biodegradable'. [1]
(b) Describe how this insecticide could affect organisms at higher trophic levels in a nearby pond ecosystem. [3]
12. Fig. 12.1 shows the energy flow through a food chain.
Sunlight → Producer (10,000 kJ) → Primary Consumer (1,000 kJ) → Secondary Consumer (100 kJ)
(a) Calculate the percentage of energy transferred from the producer to the primary consumer. Show your working. [2]
(b) Explain why most of the energy from the producer is not passed on to the primary consumer. [2]
13. Discuss the importance of forests and oceans as carbon sinks in regulating the Earth's climate. [3]
14. Explain how sewage pollution in a river can lead to a decrease in the dissolved oxygen concentration of the water. [3]
15. Suggest and explain two ways in which an individual can reduce their carbon footprint. [4]
Section C: Data-Based Question (Questions 16-20) Answer all questions in this section.
16. Fig. 16.1 shows a graph of the carbon dioxide concentration in the atmosphere measured at a monitoring station between 1960 and 2020.
CO2 Concentration (ppm)
420 |
| *
400 | *
| *
380 | *
| *
360 | *
| *
340 | *
|___________________________________
1960 1970 1980 1990 2000 2010 2020
Year
(a) Describe the trend shown in the graph. [2]
(b) State one human activity that has contributed to this trend. [1]
(c) Explain the link between the trend shown in the graph and the enhanced greenhouse effect. [2]
17. A biologist studied the population of rabbits and foxes in a woodland area over a period of 10 years. The results are shown in Table 17.1.
Table 17.1
| Year | Rabbit Population | Fox Population |
|---|---|---|
| 1 | 200 | 50 |
| 2 | 350 | 55 |
| 3 | 500 | 80 |
| 4 | 300 | 100 |
| 5 | 150 | 70 |
| 6 | 100 | 40 |
| 7 | 250 | 45 |
| 8 | 450 | 60 |
| 9 | 550 | 90 |
| 10 | 350 | 100 |
(a) Describe the relationship between the rabbit population and the fox population shown in the table. [2]
(b) Suggest a reason for the change in the rabbit population between Year 3 and Year 5. [2]
18. Fig. 18.1 shows a diagram of the carbon cycle.
Atmosphere (CO2)
^ |
| v
[Process A] [Process B]
| ^
v |
Green Plants → Animals
| ^
v |
[Process C] [Process D]
| ^
v |
Fossil Fuels Decomposers
(a) Name Process A and Process B. [2]
Process A: _________________________ Process B: _________________________
(b) Name Process C and Process D. [2]
Process C: _________________________ Process D: _________________________
(c) Explain why the burning of fossil fuels (Process C) is considered to upset the balance of the carbon cycle. [2]
19. A group of students investigated the effect of plastic pollution on marine ecosystems. They read an article stating that microplastics have been found in the tissues of fish at all levels of the food chain.
(a) Explain how microplastics can enter the marine food chain. [2]
(b) Discuss the potential consequences of microplastic accumulation for top predators, such as sharks or tuna, and for humans who consume seafood. [3]
20. Fig. 20.1 shows the energy flow in a marine ecosystem. The figures represent energy in kJ per m² per year.
Sunlight
2,000,000
|
v
Phytoplankton (Producers)
10,000
|
v
Zooplankton (Primary Consumers)
1,000
|
v
Small Fish (Secondary Consumers)
100
|
v
Large Fish (Tertiary Consumers)
10
(a) Calculate the percentage of energy transferred from the phytoplankton to the zooplankton. Show your working. [2]
(b) Explain why large predatory fish are more vulnerable to extinction due to environmental changes compared to organisms lower in the food chain. [2]
END OF QUIZ
Answers
Secondary 3 Biology Quiz - Ecology: Answer Key
Total Marks: 40
Section A: Short Answer (Questions 1-5)
1. Define the term 'ecosystem'. [2]
- An ecosystem is a community of living organisms (biotic factors) interacting with one another [1]
- and with their non-living (abiotic) environment, such as air, water, and soil [1].
2. State the role of decomposers in an ecosystem. [1]
- Decomposers (e.g., bacteria and fungi) break down dead organic matter and waste materials, returning nutrients to the soil for reuse by producers.
3. Explain why the flow of energy through an ecosystem is described as non-cyclical. [2]
- Energy enters the ecosystem as light energy from the sun and is converted to chemical energy by producers [1].
- Energy is lost from the ecosystem at each trophic level as heat through respiration and metabolic activities; it cannot be recycled or reused by the ecosystem [1].
4. Distinguish between a food chain and a food web. [2]
- A food chain is a single, linear sequence showing the transfer of energy from one organism to another [1].
- A food web is a network of interconnected food chains, showing the multiple feeding relationships within an ecosystem [1].
5. Name the process by which carbon is removed from the atmosphere by plants. [1]
- Photosynthesis.
Section B: Structured Response (Questions 6-15)
6. Grass → Grasshopper → Frog → Snake → Hawk
(a) Identify the producer in this food chain. [1]
- Grass.
(b) State the trophic level occupied by the frog. [1]
- Secondary consumer (or third trophic level).
(c) Explain why there are usually fewer hawks than grasshoppers in this ecosystem. [2]
- Energy is lost at each trophic level (e.g., through respiration, heat, uneaten parts, excretion) [1].
- Only about 10% of the energy is transferred to the next level. Therefore, less energy is available to support organisms at higher trophic levels, resulting in a smaller population of hawks compared to grasshoppers [1].
7. Carbon cycle diagram.
(a) State one way in which carbon is returned to the atmosphere from living organisms. [1]
- Respiration (by plants, animals, or decomposers).
(b) Explain how the burning of fossil fuels affects the concentration of carbon dioxide in the atmosphere. [2]
- Burning fossil fuels (combustion) releases carbon that was stored underground for millions of years as carbon dioxide [1].
- This adds extra CO₂ to the atmosphere, increasing its concentration beyond the natural balanced levels of the carbon cycle [1].
8. Pyramid of numbers.
(a) State what the numbers in each level of the pyramid represent. [1]
- The number of organisms at each trophic level.
(b) Suggest why the pyramid of numbers for this forest ecosystem has this shape. [2]
- The producer level (e.g., a single large tree) has a small number of large organisms [1].
- This single tree can support a large number of smaller primary consumers (e.g., insects), which in turn support fewer secondary consumers, resulting in an inverted or partially inverted pyramid shape [1].
9. Describe how deforestation can contribute to global warming. [3]
- Deforestation involves the large-scale removal of trees. Trees act as carbon sinks, absorbing carbon dioxide from the atmosphere for photosynthesis [1].
- When trees are cut down and burned or left to decay, the carbon stored in their biomass is released back into the atmosphere as carbon dioxide [1].
- The reduction in the number of trees means less CO₂ is absorbed, leading to a net increase in atmospheric CO₂, which enhances the greenhouse effect and contributes to global warming [1].
10. Explain the term 'bioaccumulation' using a named example of a pollutant. [3]
- Bioaccumulation is the process by which a non-biodegradable or toxic substance builds up in the tissues of an organism over its lifetime [1].
- This occurs because the organism absorbs the substance faster than it can excrete or metabolise it [1].
- Example: DDT (an insecticide) accumulates in the fatty tissues of organisms. Mercury in fish is also an acceptable example [1].
11. Non-biodegradable insecticide.
(a) Explain what is meant by the term 'non-biodegradable'. [1]
- A substance that cannot be broken down by decomposers (bacteria or fungi) in the environment.
(b) Describe how this insecticide could affect organisms at higher trophic levels in a nearby pond ecosystem. [3]
- The insecticide can be washed from the field into the pond [1].
- It is absorbed by primary producers (e.g., algae) and then passed along the food chain to primary consumers (e.g., zooplankton) [1].
- Because it is non-biodegradable, the concentration of the insecticide increases at each successive trophic level (biomagnification). Top predators (e.g., fish-eating birds) accumulate the highest concentrations, which can cause death, reproductive failure, or other health issues [1].
12. Energy flow calculation.
(a) Calculate the percentage of energy transferred from the producer to the primary consumer. Show your working. [2]
- Energy transfer = (Energy in primary consumer / Energy in producer) × 100% [1]
- = (1,000 kJ / 10,000 kJ) × 100% = 10% [1]
(b) Explain why most of the energy from the producer is not passed on to the primary consumer. [2]
- Energy is lost through the producer's respiration (as heat) [1].
- Energy is also lost in uneaten parts of the producer (e.g., roots, stems), in undigested material egested as faeces by the consumer, and as heat from the consumer's metabolic activities [1].
13. Discuss the importance of forests and oceans as carbon sinks in regulating the Earth's climate. [3]
- Forests absorb CO₂ from the atmosphere during photosynthesis and store carbon in their biomass (wood, leaves, roots), acting as a major terrestrial carbon sink [1].
- Oceans dissolve CO₂ from the atmosphere. Marine organisms like phytoplankton also absorb CO₂ for photosynthesis, and shell-forming organisms lock carbon into calcium carbonate sediments on the ocean floor [1].
- By removing CO₂, a major greenhouse gas, from the atmosphere, these sinks help to reduce the enhanced greenhouse effect and moderate global temperatures, playing a critical role in climate regulation [1].
14. Explain how sewage pollution in a river can lead to a decrease in the dissolved oxygen concentration of the water. [3]
- Sewage contains organic matter and nutrients (e.g., nitrates, phosphates), which act as a food source for decomposer bacteria [1].
- The population of aerobic bacteria increases rapidly (algal bloom may also occur, followed by decay) [1].
- These bacteria use up the dissolved oxygen in the water for their respiration, leading to a significant decrease in oxygen levels (biochemical oxygen demand/BOD increases) [1].
15. Suggest and explain two ways in which an individual can reduce their carbon footprint. [4]
- Way 1: Reduce energy consumption at home (e.g., switching off lights, using energy-efficient appliances) [1]. This reduces the demand for electricity, much of which is generated by burning fossil fuels, thereby lowering CO₂ emissions [1].
- Way 2: Use public transport, cycle, or walk instead of using private cars [1]. This reduces the combustion of petrol/diesel, directly lowering the amount of CO₂ emitted per person [1].
- (Accept other valid suggestions, e.g., reducing meat consumption, buying local products, reducing air travel, practising the 3Rs - reduce, reuse, recycle).
Section C: Data-Based Question (Questions 16-20)
16. CO₂ concentration graph.
(a) Describe the trend shown in the graph. [2]
- The concentration of CO₂ in the atmosphere has increased steadily from 1960 to 2020 [1].
- The rate of increase appears to be accelerating over time (the curve gets steeper) [1].
(b) State one human activity that has contributed to this trend. [1]
- Burning of fossil fuels (for industry, transport, or electricity generation). (Accept deforestation).
(c) Explain the link between the trend shown in the graph and the enhanced greenhouse effect. [2]
- The increasing concentration of CO₂ (a greenhouse gas) in the atmosphere traps more infrared radiation (heat) that is reflected from the Earth's surface [1].
- This enhanced trapping of heat leads to a rise in the Earth's average global temperature, a phenomenon known as the enhanced greenhouse effect or global warming [1].
17. Rabbit and fox population data.
(a) Describe the relationship between the rabbit population and the fox population shown in the table. [2]
- The fox population generally follows the same pattern as the rabbit population, but with a time lag [1].
- When the rabbit population increases, the fox population increases shortly after; when the rabbit population decreases, the fox population also decreases shortly after (predator-prey relationship) [1].
(b) Suggest a reason for the change in the rabbit population between Year 3 and Year 5. [2]
- The rabbit population increased from Year 1 to Year 3, providing more food for the foxes [1].
- This allowed the fox population to grow. The larger fox population then preyed heavily on the rabbits, causing the rabbit population to crash between Year 3 and Year 5 [1].
18. Carbon cycle diagram.
(a) Name Process A and Process B. [2]
- Process A: Photosynthesis
- Process B: Respiration
(b) Name Process C and Process D. [2]
- Process C: Combustion (Burning)
- Process D: Decomposition (Decay)
(c) Explain why the burning of fossil fuels (Process C) is considered to upset the balance of the carbon cycle. [2]
- Combustion releases carbon that has been locked away in fossil fuels for millions of years back into the atmosphere as CO₂ [1].
- This happens at a much faster rate than the natural processes (photosynthesis, dissolving in oceans) can remove it, leading to a net increase in atmospheric CO₂ and disrupting the natural balance [1].
19. Microplastics in marine ecosystems.
(a) Explain how microplastics can enter the marine food chain. [2]
- Microplastics are tiny plastic fragments that are mistaken for food and ingested by primary consumers, such as zooplankton or filter feeders [1].
- These organisms are then eaten by secondary consumers, introducing the microplastics into the food chain at a low trophic level [1].
(b) Discuss the potential consequences of microplastic accumulation for top predators, such as sharks or tuna, and for humans who consume seafood. [3]
- Microplastics can bioaccumulate and biomagnify up the food chain, meaning top predators ingest high concentrations from all the prey they eat [1].
- This can cause physical damage (e.g., blocking digestive tracts), release toxic chemicals, and lead to malnutrition or death in these predators [1].
- Humans who consume seafood, especially top predators, are at risk of ingesting these accumulated microplastics and associated toxins, with potential but not yet fully understood health risks [1].
20. Marine energy flow.
(a) Calculate the percentage of energy transferred from the phytoplankton to the zooplankton. Show your working. [2]
- Energy transfer = (Energy in zooplankton / Energy in phytoplankton) × 100% [1]
- = (1,000 kJ / 10,000 kJ) × 100% = 10% [1]
(b) Explain why large predatory fish are more vulnerable to extinction due to environmental changes compared to organisms lower in the food chain. [2]
- Large predatory fish are at the top of the food chain and rely on a large biomass of organisms at lower trophic levels for energy [1].
- Due to inefficient energy transfer (~10% per level), their populations are naturally small. Any environmental change that reduces the population of their prey will have a severe impact, and their small population size makes them less resilient and more susceptible to extinction [1].
END OF ANSWER KEY