Organic material entered a canal between sampling sites A and B. The same sampling effort was used at each site.
| Site | Bloodworms counted | Sludgeworms counted | Freshwater shrimps counted | Stonefly nymphs counted | Dissolved oxygen concentration (mg/L) |
|---|---|---|---|---|---|
| A, upstream | 1 | 0 | 14 | 8 | 8.4 |
| B, downstream | 19 | 12 | 2 | 0 | 3.1 |
Explain why the distributions of the four organisms differ between sites A and B.
101 exam-style questions on Edexcel GCSE Biology 9.3 Material cycles and decomposition, covering 9.3.1 Cycling of materials through ecosystems, 9.3.2 The carbon cycle, 9.3.3 The water cycle, 9.3.4 The nitrogen cycle, 9.3.5 Indicator species and pollution, 9.3.6 Decomposition in preservation and composting, and 9.3.7 Rate changes in decay of biological material. Each one has a worked solution and a mark scheme showing where the marks go.