Ladybirds are released in greenhouse P to control aphids. No ladybirds are released in greenhouse Q. The greenhouses otherwise have the same conditions.
Table
| Greenhouse | Aphids at start | Aphids after one week |
|---|---|---|
| P | 200 | 60 |
| Q | 200 | 140 |
Why would it be incorrect to conclude that ladybirds caused all of the decrease in P?
The final aphid numbers were different, so the initial populations cannot be compared.
Aphid numbers also fell without ladybirds, so ladybirds could not have eaten any aphids.
Aphid numbers also fell without ladybirds, so another factor may have contributed.
The final aphid numbers were different, so biological control must have increased aphids.
44 exam-style questions on Edexcel GCSE Biology 4.3 Selective breeding and genetic modification, covering 4.3.1 Selective breeding and its impact, 4.3.2 Tissue culture, 4.3.3 Genetic engineering overview, 4.3.4 Main stages of genetic engineering, 4.3.5 Advantages and disadvantages of GM organisms, 4.3.6 Agricultural solutions for a growing population, and 4.3.7 Evaluating genetic engineering and breeding. Each one has a worked solution and a mark scheme showing where the marks go.