A brewery installed a system to remove organic material from its wastewater before the wastewater entered a stream.
Scientists repeatedly sampled invertebrates at the same location in the stream. They used the same sampling method each time.
The table shows the mean number of each invertebrate per sample.
| Invertebrate | Before wastewater entered the stream | While untreated wastewater entered the stream | Six months after treatment began |
|---|---|---|---|
| Stonefly nymphs | 24 | 0 | 23 |
| Bloodworms | 2 | 41 | 1 |
Explain what the data suggest about the success of the treatment system.
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.