Question 1 · MCQ · Analyse · 1 mark
Energy reaching a second consumer
Food chains and energy flow
Grass stores 10,000 J of energy. In the chain grass → grasshopper → frog, apply the approximate 10% energy-transfer model. How much reaches the frog?
(A) 1 J
(B) 10 J
(C) 100 J
(D) 1,000 J
Show answer and solution
Answer: (C) 100 J
Worked solution: Two transfers occur: grasshopper receives about 1,000 J, and frog about 100 J. The 10% rule is an approximate model, not an exact constant for every ecosystem.
Question 2 · MCQ · Analyse · 1 mark
A persistent pesticide in a chain
Biomagnification
A persistent, non-biodegradable pesticide enters the chain phytoplankton → small fish → large fish → fish-eating bird. Where is its concentration expected to be greatest?
(A) Fish-eating bird
(B) Phytoplankton always
(C) Water molecules only
(D) All trophic levels must have identical concentrations
Show answer and solution
Answer: (A) Fish-eating bird
Worked solution: The chemical can accumulate in organisms and become more concentrated at higher trophic levels through biomagnification, so the top consumer is most affected in this chain.
Question 3 · MCQ · Analyse · 1 mark
Sorting a compost bin
Biodegradable and non-biodegradable waste
Which item is most suitable for an ordinary compost bin?
(A) Glass fragments
(B) Vegetable peels
(C) Aluminium foil
(D) Plastic wrapper
Show answer and solution
Answer: (B) Vegetable peels
Worked solution: Vegetable peels can be decomposed biologically under suitable composting conditions. Glass, metal foil and conventional plastic do not decompose in the same way in an ordinary compost bin.
Question 4 · MCQ · Analyse · 1 mark
A protective atmospheric layer
Ozone layer
What is the main protective role of stratospheric ozone?
(A) It supplies all drinking water.
(B) It converts all waste to compost.
(C) It blocks every form of sunlight.
(D) It absorbs much harmful ultraviolet radiation.
Show answer and solution
Answer: (D) It absorbs much harmful ultraviolet radiation.
Worked solution: Stratospheric ozone absorbs a substantial part of the Sun’s harmful ultraviolet radiation. It does not block all sunlight.
Question 5 · A-R · Analyse · 1 mark
Why food chains are usually short
Food chains and energy flow
Assertion (A): Food chains generally cannot sustain an unlimited number of trophic levels.
Reason (R): Only a fraction of energy at one trophic level becomes available to the next.
(a) Both A and R are true, and R correctly explains A.
(b) Both A and R are true, but R does not correctly explain A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show answer and solution
Answer: (A) Both A and R are true, and R correctly explains A.
Worked solution: Energy is used in life processes and dissipated as heat at each transfer. Progressively less remains to support consumers at higher levels.
Question 6 · A-R · Analyse · 1 mark
Does biodegradable mean harmless
Biodegradable and non-biodegradable waste
Assertion (A): A biodegradable waste can never cause an environmental problem.
Reason (R): Large amounts of biodegradable organic waste in water can increase microbial activity and reduce dissolved oxygen.
(a) Both A and R are true, and R correctly explains A.
(b) Both A and R are true, but R does not correctly explain A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show answer and solution
Answer: (D) A is false, but R is true.
Worked solution: Biodegradable waste can still be harmful when quantities overwhelm a system. Its decomposition can use oxygen needed by aquatic organisms.
Question 7 · VSA · Apply · 2 marks
A world without decomposers
Ecosystems and decomposers
Predict one effect on dead organic matter and one effect on nutrient recycling if decomposers disappeared from an ecosystem.
Show answer and solution
Answer: Dead organic matter would accumulate and nutrient recycling would be disrupted.
Worked solution: Bacteria and fungi break down dead organisms and wastes, returning mineral nutrients to the environment. Without this process, nutrients remain locked in organic material.
Question 8 · VSA · Apply · 2 marks
Identifying a trophic level
Food chains and energy flow
In grass → rabbit → fox, identify the producer and the trophic level of the fox.
Show answer and solution
Answer: Grass is the producer; the fox is at the third trophic level.
Worked solution: The producer occupies level one, the herbivorous rabbit level two, and the fox that eats the rabbit level three.
Question 9 · SA · Analyse · 3 marks
Planning a school waste system
Waste management
A school produces fruit peels, paper, plastic wrappers and used batteries. Suggest a separate handling route for each broad category and explain why mixing everything is inefficient.
Show answer and solution
Answer: Compost suitable fruit peels; collect clean paper and accepted plastics for recycling; send batteries to an authorised collection channel.
Worked solution: Segregation keeps biodegradable material suitable for composting and recyclable material cleaner. Batteries require separate handling because of their chemicals and metals. Mixing wet waste, recyclables and batteries contaminates materials and makes safe recovery more difficult.
Question 10 · SA · Analyse · 3 marks
Distinguishing two environmental issues
Ozone layer
A student says ozone depletion and global warming are exactly the same process. Explain the main mechanism and a major consequence of each.
Show answer and solution
Answer: Ozone depletion reduces UV protection; global warming is a rise in average temperature associated with an enhanced greenhouse effect.
Worked solution: Ozone depletion involves loss of stratospheric ozone, including through reactions involving chlorine released from CFCs, allowing more harmful UV to reach the surface. Global warming involves increased trapping of outgoing infrared energy by greenhouse gases. Some substances affect both, but the mechanisms are different.
Question 11 · LA · Analyse · 5 marks
An energy-flow calculation with limits
Food chains and energy flow
In a simplified chain plants → insect → frog → snake, plants store 20,000 J. Using the approximate 10% transfer model, (i) find energy available to insects, (ii) frogs, (iii) snakes, (iv) explain why the chain does not return energy to plants, and (v) distinguish energy flow from nutrient recycling.
Show answer and solution
Answer: Insects: 2,000 J; frogs: 200 J; snakes: 20 J. Energy flows mainly one way and is dissipated as heat; nutrients can cycle.
Worked solution: Each transfer retains about one tenth in this model: 20,000 → 2,000 → 200 → 20 J. Organisms use energy for metabolism, and much is dissipated as heat. Decomposers recycle matter and mineral nutrients, but do not recycle all lost energy back to producers. Producers need a continuing external energy source, usually sunlight.
Question 12 · Case Study · Analyse · 4 marks
Reading pesticide measurements
Biomagnification
A persistent pesticide is measured in a pond food chain. Concentrations are: water 0.0002 mg/L; phytoplankton 0.02 mg/kg; small fish 0.20 mg/kg; large fish 2.0 mg/kg; fish-eating bird 10 mg/kg. Compare organism concentrations using the same mg/kg unit.
Answer the following:
(i) Which listed organism has the highest concentration? [1 mark]
(ii) Name the process shown by increasing concentration along the food chain. [1 mark]
(iii) Calculate the ratio of the bird concentration to the small-fish concentration and explain why the water value should not be directly treated as mg/kg. [2 marks]
Show answer and solution
Answer: (i) The fish-eating bird. (ii) Biomagnification. (iii) 50:1; the water measurement uses mg/L, whereas organism measurements use mg/kg.
Worked solution: For the two organisms, 10/0.20 = 50. The persistent chemical can accumulate and become concentrated as predators consume contaminated prey. Directly comparing mg/L with mg/kg requires an appropriate conversion and assumptions about the sampled medium.
