Students sampled invertebrates at four sites in a river. A pipe releases waste into the river between site 1 and site 2.
Table
| Site | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| Distance from pipe in m | 100 upstream | 50 downstream | 500 downstream | 1500 downstream |
| Dissolved oxygen in mg/dm3\text{mg}/\text{dm}^3mg/dm3 | 9.5 | 2.0 | 4.5 | 8.0 |
| Number of mayfly nymphs | 25 | 0 | 3 | 18 |
| Number of rat-tailed maggots | 0 | 32 | 15 | 2 |
Which statement explains the distribution of the two organisms?
Rat-tailed maggots use up the oxygen at site 2, so mayfly nymphs are unable to survive there.
Mayfly nymphs need a high oxygen concentration, but rat-tailed maggots can tolerate low oxygen.
Mayfly nymphs need a low oxygen concentration, but rat-tailed maggots need a high oxygen level.
Rat-tailed maggots eat the mayfly nymphs at site 2, so the oxygen concentration falls there.
109 exam-style questions on OCR GCSE Biology 6.1 Monitoring and maintaining the environment, covering 6.1.1 Field investigation of distribution and abundance, 6.1.2 Human interactions and biodiversity, 6.1.3 Maintaining biodiversity, and 6.1.4 Environmental change and distribution of organisms. Each one has a worked solution and a mark scheme showing where the marks go.