Untreated sewage was released into a river from a pipe.
Scientists sampled the invertebrates at three sites in the river. Site A was 100 m upstream of the pipe. Site B was 100 m downstream of the pipe. Site C was 2 km downstream of the pipe.
The Table shows the results.
Table
| Invertebrate | Number at site A | Number at site B | Number at site C |
|---|---|---|---|
| stonefly nymphs | 25 | 0 | 6 |
| freshwater shrimps | 40 | 2 | 18 |
| sludgeworms | 3 | 60 | 22 |
| bloodworms | 2 | 45 | 15 |
Describe the differences between the invertebrates found at site A and at site B.
Explain why large numbers of sludgeworms and bloodworms are found at site B.
Explain what the results for site C show about the water at site C.
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.