A plant extract contains chemicals P and Q. Tests use equal concentrations under the same conditions.
Table
| Treatment | Bacterial growth as a percentage of the untreated control |
|---|---|
| P alone | 95 |
| Q alone | 30 |
| P and Q together | 28 |
The difference between 28 and 30 is within the variation between repeats. Which conclusion is best supported?
P accounts for most of the inhibition; an extra effect of Q is not established
Q accounts for most of the inhibition; an extra effect of P is not established
both chemicals are essential; neither chemical inhibits growth when used alone
neither chemical inhibits growth; only their combination has an effect
45 exam-style questions on Edexcel GCSE Biology 5.2 Plant and body defences, covering 5.2.1 Physical plant defences, 5.2.2 Chemical plant defences, 5.2.3 Detecting plant diseases, and 5.2.4 Human physical and chemical defences. Each one has a worked solution and a mark scheme showing where the marks go.