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A Level H1 Biology Ecology Quiz

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Questions

A-Level Biology H1 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 clear scientific terminology.

Section A: Ecological Concepts and Definitions (Questions 1-5)

1. Which of the following best describes the role of decomposers in an ecosystem?
A. They convert light energy into chemical energy.
B. They break down dead organic matter and release inorganic nutrients.
C. They consume primary producers to transfer energy to higher trophic levels.
D. They fix atmospheric nitrogen into ammonia.
[1]

2. Define the term niche.
[2]

3. Distinguish between primary succession and secondary succession.
[2]

4. Fig. 1 shows the carbon cycle.

Image pending generation for this question.

Identify the process represented by arrow X, which moves carbon from the atmosphere into plants.
[1]

5. Explain why pyramids of biomass are generally more accurate than pyramids of numbers for representing energy flow in an ecosystem.
[2]

Section B: Energy Flow and Population Dynamics (Questions 6-10)

6. In a food chain, why is the transfer of energy between trophic levels inefficient?
A. Energy is lost as heat during respiration and through excretion.
B. Primary consumers digest 100% of the plant material they consume.
C. Decomposers recycle all energy back to the producers.
D. Secondary consumers have a lower metabolic rate than primary consumers.
[1]

7. Fig. 2 shows the population growth curve of a species of deer introduced to an island with limited resources.

(Imagine a sigmoid curve with phases A, B, C, and D)

At which phase is the environmental resistance highest?
A. Phase A (Lag phase)
B. Phase B (Exponential phase)
C. Phase C (Deceleration phase)
D. Phase D (Stationary phase)
[1]

8. Fig. 3 shows the energy flow through a freshwater ecosystem.

Image pending generation for this question.

The energy values are:

Algae: $10,000 \text{ kJ m}^{-2} \text{ year}^{-1}$
Zooplankton: $1,000 \text{ kJ m}^{-2} \text{ year}^{-1}$
Small Fish: $100 \text{ kJ m}^{-2} \text{ year}^{-1}$

Calculate the percentage efficiency of energy transfer from Algae to Zooplankton. Show your working.
[2]

Answer space

9. Explain two reasons why the energy transfer efficiency calculated in Question 8 is not 100%.
[2]

10. Large fish are often harvested by humans. Explain how overfishing of Large Fish might affect the population of Zooplankton.
[3]

Section C: Environmental Factors and Decomposition (Questions 11-15)

11. A student investigated the effect of temperature on the rate of decomposition of leaf litter. Leaf discs were placed in soil samples at different temperatures, and the percentage mass loss was recorded after 4 weeks.

Table 1: Effect of Temperature on Decomposition

Temperature (°C)	Mean % Mass Loss of Leaf Discs
5	12
10	25
15	40
20	58
25	70
30	72
35	65

Describe the trend shown in Table 1.
[2]

12. Explain the results at 25°C and 35°C with reference to enzyme activity in decomposers.
[3]

13. Suggest one other abiotic factor, besides temperature, that could affect the rate of decomposition and explain its effect.
[2]

14. Define biological magnification.
[1]

15. Explain why biological magnification is a concern for top predators like Large Fish.
[3]

Section D: Pest Management and Conservation (Questions 16-20)

16. Explain the concept of integrated pest management (IPM).
[2]

17. Give two examples of techniques used in IPM.
[2]

18. State one advantage of using biological control agents compared to chemical pesticides.
[1]

19. State one disadvantage of using biological control agents compared to chemical pesticides.
[1]

20. Discuss why chemical pesticides might still be used despite the environmental risks associated with them.
[2]

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Answers

A-Level Biology H1 Quiz - Ecology (Answer Key)

1. B
Reasoning: Decomposers (saprotrophs) secrete enzymes to break down dead organic matter externally and absorb the nutrients, releasing inorganic ions back into the soil.

The role or position of a species in its ecosystem [1].
Includes its habitat, feeding habits, and interactions with other organisms (biotic and abiotic factors) [1].

Primary succession occurs on bare land/rock where no soil exists previously (e.g., after volcanic eruption) [1].
Secondary succession occurs on land where soil remains but vegetation has been removed (e.g., after fire or deforestation) [1].

4. Photosynthesis [1]

Pyramids of numbers do not account for the size/mass of organisms (e.g., one tree supports many insects) [1].
Pyramids of biomass represent the actual amount of organic matter at each trophic level, giving a better indication of energy available [1].

6. A
Reasoning: Energy is lost primarily as heat from respiration, in undigested material (faeces), and in excretory products (urine). Only a small fraction is assimilated into biomass.

7. D
Reasoning: Environmental resistance (limiting factors like food, space, disease) is highest at the carrying capacity (Stationary phase), where the population size stabilizes.

Efficiency = (Energy in Zooplankton / Energy in Algae) × 100
Efficiency = $(1,000 / 10,000) \times 100$ [1]
Efficiency = $10\%$ [1]

Energy is lost as heat during respiration by the algae and zooplankton [1].
Not all parts of the algae are eaten or digested (e.g., cell walls), so energy is lost in faeces [1].

10.

Overfishing reduces the population of Large Fish [1].
This reduces predation pressure on Small Fish, causing the Small Fish population to increase [1].
Increased Small Fish population leads to higher predation on Zooplankton, causing the Zooplankton population to decrease [1].

11.

As temperature increases from 5°C to 25°C, the percentage mass loss increases [1].
Above 25°C (at 30°C and 35°C), the rate of mass loss decreases/plateaus [1].

12.

Decomposers secrete enzymes to break down leaf litter; enzyme activity increases with temperature due to increased kinetic energy/collision frequency up to an optimum (25°C) [1].
At 35°C, the temperature exceeds the optimum, causing enzymes to denature [1].
Denaturation changes the shape of the active site, reducing the rate of decomposition [1].

13.

Moisture/Water: Decomposers require water for enzymatic reactions and transport of nutrients. Dry conditions slow down decomposition [1+1].
OR
pH: Extreme pH levels can denature decomposer enzymes or inhibit microbial growth, slowing decomposition [1+1].
OR
Oxygen: Aerobic decomposers require oxygen for respiration. Waterlogged (anaerobic) soils slow down decomposition [1+1].

14. Biological magnification is the increase in concentration of non-biodegradable toxins (e.g., pesticides, heavy metals) in the tissues of organisms at higher trophic levels [1].

15.

Toxins are not excreted or broken down, so they accumulate in the body fat/tissues [1].
As energy transfers up the food chain, the toxin concentration increases because predators consume many prey items, each containing small amounts of the toxin [1].
Top predators like Large Fish accumulate the highest concentrations, which can lead to toxicity, reproductive failure, or death [1].

16.

A sustainable approach to managing pests by combining biological, cultural, physical, and chemical tools [1].
Aim is to minimize economic, health, and environmental risks [1].

17. (Any two accepted)

Use of natural predators/parasites (biological control) [1].
Crop rotation or planting resistant varieties (cultural control) [1].
Use of pheromone traps or sterile male technique [1].

18. (Any one accepted)

Specific to the pest, so non-target species are not harmed [1].
Pests do not develop resistance as easily [1].
No chemical residues on crops [1].

19. (Any one accepted)

Slower action than chemicals [1].
The control agent may become a pest itself [1].
Difficult to establish/requires specific conditions [1].

20.

Rapid action; kills pests quickly to prevent immediate crop loss [1].
Easy to apply and widely available/cost-effective in the short term [1].