A power station releases warm water into a river.
A student measured the temperature of the water and counted the number of mayfly larvae in samples taken at different places along the river.
The Table shows the results.
Table
| Position in river | Water temperature in ∘C^\circ\text{C}∘C | Number of mayfly larvae in sample |
|---|---|---|
| 50 m upstream of outlet | 12 | 48 |
| at outlet | 22 | 6 |
| 100 m downstream of outlet | 19 | 14 |
| 200 m downstream of outlet | 16 | 30 |
| 400 m downstream of outlet | 13 | 45 |
Describe the relationship between water temperature and the number of mayfly larvae.
Calculate the percentage decrease in the number of mayfly larvae between 50 m upstream of the outlet and the outlet.
Warm water contains less dissolved oxygen than cold water.
Explain why fewer mayfly larvae are found at the outlet.
Fish in the river eat mayfly larvae.
Explain how the number of fish near the outlet is likely to be different from the number upstream.
The student concluded that temperature was the only abiotic factor affecting the number of mayfly larvae.
Give one other abiotic factor the student should have measured.
39 exam-style questions on Edexcel GCSE Biology 9.1 Ecosystems and interdependence, covering 9.1.1 Levels of organisation in ecosystems, 9.1.2 Abiotic and biotic factors, 9.1.3 Importance of interdependence, 9.1.4 Parasitism and mutualism, and 9.1.5 Determining number of organisms in an area. Each one has a worked solution and a mark scheme showing where the marks go.