Case study·Hard exam skill (4/5)·No calculator
Difficulty guide
The label describes the problem, not your ability.
1/5 - Foundational
Warm-up setup; checks one basic idea.
2/5 - Routine exam skill
Normal syllabus skill; usually one main rule or interpretation.
3/5 - Standard multi-step
Exam-style problem with multiple steps or a common trap.
4/5 - Hard exam skill
High-end exam problem; combines methods carefully.
5/5 - Challenge
Stretch problem beyond normal exam pressure.
Question
A village pond food web contains algae, mosquito larvae, small fish, frogs, snakes and birds. Pesticide spraying near the pond reduces mosquito larvae but also kills many small fish.
Total: 6 marks
(a) Name the producer in this food web. (1 mark)
(b) Predict one possible effect on fish-eating birds if small fish die in large numbers. (1 mark)
(c) Why can pesticide use disturb more than one population? (2 marks)
(d) Suggest one safer control idea that reduces mosquito breeding without poisoning the pond food web. (2 marks)
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