A class investigated water pollution in two drainage ditches beside neighbouring fields. The same area was sampled for the same length of time in each ditch, and the ditches had similar physical conditions.
| Organism | Willow ditch | Hawthorn ditch |
|---|---|---|
| Stonefly nymphs | 15 | 2 |
| Freshwater shrimps | 17 | 4 |
| Bloodworms | 3 | 20 |
| Sludgeworms | 2 | 16 |
Which statement about the two ditches is best supported by these results?
Hawthorn ditch provides stronger evidence of clean, oxygen-rich water because fewer stonefly nymphs and freshwater shrimps would use less oxygen.
The results provide no evidence about which ditch is cleaner because they do not identify the pollutant present.
Willow ditch provides stronger evidence of clean, oxygen-rich water because stonefly nymphs and freshwater shrimps are much more abundant there.
Hawthorn ditch provides stronger evidence of clean, oxygen-rich water because the total number of invertebrates collected there is greater.
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.