The table shows the results of equal sampling effort at two river sites with similar physical conditions.
Table
| Organism | Number at site P | Number at site Q |
|---|---|---|
| Stonefly nymphs | 18 | 0 |
| Freshwater shrimps | 24 | 1 |
| Bloodworms | 2 | 35 |
| Sludgeworms | 0 | 42 |
Which conclusion is best supported by the combined evidence?
P is more likely to be organically polluted, because sensitive species are common.
Q is more likely to be unpolluted, because tolerant species are common.
P and Q have similar pollution, because both sites contain invertebrates.
Q is more likely to be organically polluted, because tolerant species dominate.
44 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.