A sports ground beside a river is treated with fertiliser. After heavy rain, some surplus fertiliser is washed into the river. Algae-covered area is measured at an upstream site and a downstream site before and two weeks after the runoff.
The results are shown in the table.
| Site | Algae-covered area before the runoff (m²) | Algae-covered area two weeks after the runoff (m²) |
|---|---|---|
| Upstream of the sports ground | 24 | 25 |
| Downstream of the sports ground | 20 | 61 |
Explain how the results support the explanation that the surplus fertiliser increased algal growth downstream of the sports ground.
127 exam-style questions on OCR GCSE Biology 6.2 Feeding the human race, covering 6.2.1 Biological factors affecting food security, 6.2.2 Agricultural solutions to growing demand, 6.2.3 Selective breeding, 6.2.4 Genetic engineering, 6.2.5 Steps in genetic engineering, 6.2.6 Benefits and risks of gene technology in agriculture, and 6.2.7 Biotechnological solutions to growing demand. Each one has a worked solution and a mark scheme showing where the marks go.