An ecologist monitors three water channels in a wetland reserve. At each site, the ecologist samples the same area for the same time on four occasions. The table shows the mean number of each organism per sample, the dissolved oxygen concentration and the pH.
| Site | Mean number of stonefly nymphs | Mean number of freshwater shrimps | Mean number of bloodworms | Mean number of sludgeworms | Dissolved oxygen concentration / mg/dm³ | pH |
|---|---|---|---|---|---|---|
| A | 16 | 21 | 1 | 0 | 9.2 | 7.1 |
| B | 2 | 4 | 19 | 15 | 3.4 | 7.0 |
| C | 0 | 0 | 1 | 0 | 8.9 | 4.5 |
Compare the evidence about water pollution at Sites A and B.
A student concludes that Site C has the most polluted water because no stonefly nymphs or freshwater shrimps were found. Evaluate this conclusion.
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.