A factory reduces its sulfur dioxide emissions. Students survey a pollution-sensitive lichen near the factory and at a distant comparison site before and after the reduction.
At each survey, trees are selected randomly from the same sampling area.
| Site and survey | Trees examined | Trees with the lichen |
|---|---|---|
| Near factory, before | 40 | 8 |
| Near factory, after | 100 | 30 |
| Distant site, before | 50 | 20 |
| Distant site, after | 100 | 50 |
Which conclusion is best supported?
The factory reduction is supported as the cause because the number of occupied trees near the factory rises almost fourfold.
The factory reduction is supported as the cause because the proportion of occupied trees increases only near the factory.
The factory reduction is not isolated as the cause because the occupied proportion increases by 10 percentage points at both sites.
The factory reduction is not isolated as the cause because the occupied proportion near the factory falls when sample size is considered.
40 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.