A coastal ecosystem contains this food chain.
green alga → sea urchin → sea otter
A disease affected the sea otter population. Researchers collected data before the disease and two years later.
| Measurement | Before the disease | Two years later |
|---|---|---|
| Mean number of sea otters counted per survey | 18 | 6 |
| Mean number of sea urchins per 10 m2 | 42 | 95 |
| Mean biomass of green alga per 10 m2 in kg | 16.0 | 6.5 |
Explain why removing the green alga would eventually affect every organism in this food chain.
Suggest and explain how the disease caused the change in the biomass of the green alga. Use data from the table.
83 exam-style questions on AQA GCSE Biology 7.2 Organisation of an ecosystem, covering 7.2.1 Levels of organisation, 7.2.2 How materials are cycled, 7.2.3 Decomposition, and 7.2.4 Impact of environmental change (HT only). Each one has a worked solution and a mark scheme showing where the marks go.