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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.
- Write your answers in the spaces provided.
- The number of marks is given in brackets [ ] at the end of each question or part question.
- You may use a calculator.
Section A: Multiple Choice Questions (Questions 1–5)
Choose the correct answer and write the letter in the box provided.
1. Which of the following best describes the flow of energy in a food chain?
A. Energy flows from consumers to producers and is recycled.
B. Energy flows from producers to consumers and is eventually lost as heat.
C. Energy flows from decomposers to producers and is conserved.
D. Energy flows in a cycle between producers and consumers.
Answer: [ ] [1]
2. In the carbon cycle, which process removes carbon dioxide from the atmosphere?
A. Respiration
B. Combustion
C. Photosynthesis
D. Decomposition
Answer: [ ] [1]
3. A farmer notices that the population of aphids on his crops has increased rapidly. He introduces ladybirds, which feed on aphids. What is the likely immediate effect on the aphid population?
A. It will increase due to competition.
B. It will decrease due to predation.
C. It will remain constant due to homeostasis.
D. It will decrease due to disease.
Answer: [ ] [1]
4. Which of the following is a biotic factor in an ecosystem?
A. Soil pH
B. Temperature
C. Availability of water
D. Presence of bacteria
Answer: [ ] [1]
5. Why is the transfer of energy between trophic levels inefficient?
A. Energy is created during respiration.
B. Energy is lost as heat and in waste materials.
C. Producers do not capture all sunlight.
D. Consumers eat only a small part of the producer.
Answer: [ ] [1]
Section B: Structured Questions (Questions 6–15)
6. The diagram below represents a simple food web in a forest ecosystem.
(Imagine a diagram where: Grass is eaten by Rabbit and Grasshopper. Rabbit is eaten by Fox. Grasshopper is eaten by Frog. Frog is eaten by Snake. Snake is eaten by Hawk. Fox is eaten by Hawk.)
(a) Identify the primary consumers in this food web.
_________________________________________________________________________ [1]
(b) State the trophic level of the Hawk when it feeds on the Fox.
_________________________________________________________________________ [1]
(c) Explain why food chains rarely have more than four or five trophic levels.
_________________________________________________________________________ [2]
7. Nitrogen is essential for the synthesis of proteins and DNA.
(a) Name the process by which nitrogen gas from the atmosphere is converted into nitrates in the soil by bacteria.
_________________________________________________________________________ [1]
(b) Explain how nitrates in the soil are taken up by plants and used to form proteins.
_________________________________________________________________________ [2]
8. The graph below shows the change in population size of two species, X and Y, over a period of time. Species X is a prey animal, and Species Y is its predator.
(Imagine a graph with two oscillating lines. Line X peaks first, followed by Line Y. The peaks of Y are lower than X.)
(a) Describe the relationship between the population sizes of species X and Y.
_________________________________________________________________________ [1]
(b) Explain why the population of species Y decreases after the population of species X decreases.
_________________________________________________________________________ [2]
9. Deforestation is a major human activity affecting ecosystems.
(a) State one immediate effect of deforestation on the carbon cycle.
_________________________________________________________________________ [1]
(b) Explain how deforestation can lead to soil erosion.
_________________________________________________________________________ [2]
10. A student investigated the effect of light intensity on the rate of photosynthesis of an aquatic plant. The student counted the number of bubbles produced per minute at different distances from a lamp.
(a) Identify the independent variable in this investigation.
_________________________________________________________________________ [1]
(b) Suggest one variable that must be kept constant to ensure a fair test.
_________________________________________________________________________ [1]
(c) The student observed that at very high light intensities, the rate of photosynthesis stopped increasing. Explain why this happens.
_________________________________________________________________________ [2]
11. Eutrophication is a process that can occur in lakes and rivers.
(a) Name the primary cause of eutrophication in agricultural areas.
_________________________________________________________________________ [1]
(b) Describe the sequence of events that leads to the death of fish in a eutrophic lake.
_________________________________________________________________________ [3]
12. Decomposers play a vital role in ecosystems.
(a) Name one group of organisms that acts as decomposers.
_________________________________________________________________________ [1]
(b) Explain the importance of decomposers in the recycling of nutrients.
_________________________________________________________________________ [2]
13. The table below shows the energy content at different trophic levels in a grassland ecosystem.
| Trophic Level | Organism | Energy (kJ/m²/year) |
|---|---|---|
| 1 | Grass | 20,000 |
| 2 | Grasshopper | 2,000 |
| 3 | Frog | 200 |
| 4 | Snake | 20 |
(a) Calculate the percentage efficiency of energy transfer from the Grasshopper to the Frog.
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Answer: __________________ % [2]
(b) Suggest two reasons why energy transfer between trophic levels is not 100% efficient.
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- ______________________________________________________________________ [2]
14. Conservation efforts often focus on maintaining biodiversity.
(a) Define the term biodiversity.
_________________________________________________________________________ [1]
(b) Suggest one economic reason for conserving biodiversity.
_________________________________________________________________________ [1]
15. In a closed ecosystem, such as a sealed bottle garden, plants and small insects can survive for a long time.
(a) Explain how the carbon cycle operates within this sealed system.
_________________________________________________________________________ [2]
(b) Why would the system eventually fail if it were kept in complete darkness?
_________________________________________________________________________ [1]
Section C: Free Response Questions (Questions 16–20)
16. Describe the role of photosynthesis and respiration in the carbon cycle.
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_________________________________________________________________________ [4]
17. Explain how the use of pesticides can have negative effects on non-target organisms in an ecosystem.
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_________________________________________________________________________ [3]
18. "Energy flows, but nutrients cycle." Explain this statement with reference to an ecosystem.
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_________________________________________________________________________ [4]
19. A local pond is being polluted by sewage discharge.
(a) Explain the effect of sewage on the dissolved oxygen levels in the pond.
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_________________________________________________________________________ [3]
(b) Suggest one method to reduce the impact of sewage on the pond ecosystem.
_________________________________________________________________________ [1]
20. Evaluate the effectiveness of using biological control agents (such as introducing natural predators) compared to chemical pesticides for managing pest populations.
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_________________________________________________________________________ [4]
End of Quiz
Answers
Secondary 4 Combined Science Biology Quiz - Ecology (Answer Key)
Total Marks: 40
Section A: Multiple Choice Questions
1. B
Energy flows from producers to consumers and is eventually lost as heat. It is not recycled. [1]
2. C
Photosynthesis removes CO2 from the atmosphere to produce glucose. [1]
3. B
Ladybirds are predators of aphids. An increase in predators leads to a decrease in prey. [1]
4. D
Bacteria are living organisms (biotic). pH, temperature, and water are abiotic. [1]
5. B
Energy is lost as heat during respiration and in excretory products/uneaten parts. [1]
Section B: Structured Questions
6.
(a) Rabbit and Grasshopper. [1]
(b) Tertiary consumer (or Quaternary trophic level). [1]
(c) Energy is lost at each trophic level (as heat/waste). [1] There is insufficient energy remaining to support a viable population at higher levels. [1]
7.
(a) Nitrogen fixation. [1]
(b) Plants absorb nitrates from the soil through their roots (via active transport). [1] Nitrates are used to synthesize amino acids, which are then joined to form proteins. [1]
8.
(a) The populations oscillate/cycle. The peak of the predator (Y) follows the peak of the prey (X). [1]
(b) With fewer prey (X) available, there is less food for the predators (Y). [1] This leads to starvation/decreased reproduction in Y, causing their population to drop. [1]
9.
(a) Fewer trees are available to absorb carbon dioxide via photosynthesis. [1] (Or: Burning trees releases stored carbon as CO2).
(b) Tree roots hold the soil together. [1] Without roots, rain/wind washes/blows the topsoil away more easily. [1]
10.
(a) Light intensity (or distance from the lamp). [1]
(b) Temperature / CO2 concentration / Type of plant. [1]
(c) Another factor becomes limiting (e.g., CO2 concentration or temperature). [1] The enzymes involved in photosynthesis are working at their maximum rate. [1]
11.
(a) Excess fertilizers (nitrates/phosphates) leaching into water bodies. [1]
(b) Algae grow rapidly (algal bloom) blocking light. [1] Submerged plants die due to lack of light/photosynthesis. [1] Decomposers break down dead matter, using up oxygen via respiration. [1] Fish die due to lack of dissolved oxygen. [1] (Max 3 marks)
12.
(a) Bacteria or Fungi. [1]
(b) They break down dead organic matter/waste. [1] Releasing minerals/nutrients (like nitrates) back into the soil for plants to use. [1]
13.
(a) Efficiency = (Energy in Frog / Energy in Grasshopper) × 100
= (200 / 2000) × 100 = 10%. [2]
(b) 1. Energy lost as heat during respiration. [1]
2. Energy lost in waste (feces/urine) or uneaten parts. [1]
14.
(a) The variety of different species of organisms in an ecosystem. [1]
(b) Source of new medicines / drugs. [1] (Or: Tourism / Genetic resources for crops).
15.
(a) Plants take in CO2 for photosynthesis and release O2. [1] Insects/animals take in O2 for respiration and release CO2. [1] This creates a balanced cycle within the sealed system.
(b) Plants cannot perform photosynthesis without light. [1] They will die, stopping the production of oxygen and food for the insects. [1] (Note: Question asks for 1 mark, so "No photosynthesis occurs" is sufficient).
Section C: Free Response Questions
16.
Marking Points:
- Photosynthesis removes CO2 from the atmosphere/water. [1]
- Converts it into organic compounds (glucose/carbohydrates) in producers. [1]
- Respiration (by producers, consumers, and decomposers) releases CO2 back into the atmosphere. [1]
- This maintains the balance of carbon in the ecosystem. [1]
(Max 4 marks)
17.
Marking Points:
- Pesticides are not specific; they may kill beneficial insects (e.g., bees/pollinators). [1]
- Bioaccumulation: Pesticides build up in the tissues of organisms. [1]
- Biomagnification: Concentration increases up the food chain, harming top predators (e.g., birds of prey). [1]
(Max 3 marks)
18.
Marking Points:
- Energy Flow: Energy enters as sunlight, is converted by producers, passed to consumers, and is eventually lost as heat. It does not cycle back to the sun. [2]
- Nutrient Cycling: Nutrients (C, N, P) are taken up by plants, passed to animals, and returned to the soil/atmosphere by decomposers/excretion. They are reused by producers. [2]
(Max 4 marks)
19.
(a) Sewage contains organic matter. [1] Decomposers (bacteria) multiply to break down the sewage. [1] These bacteria use up dissolved oxygen during aerobic respiration, lowering oxygen levels for fish. [1]
(b) Treat sewage before discharge (e.g., sewage treatment plant). [1] (Or: Reduce fertilizer use / Create buffer zones).
20.
Marking Points:
- Biological Control Advantages: Specific to the pest (less harm to non-targets); No chemical pollution; Long-term solution if established. [2]
- Biological Control Disadvantages: Slow acting; Introduced agent might become a pest itself; May not completely eradicate the pest. [1]
- Comparison: Chemical pesticides act fast but cause pollution/resistance. Biological control is more environmentally friendly but requires careful planning. [1]
(Max 4 marks. Award marks for balanced evaluation.)