A researcher tested extracts from two plant species, P and Q. Equal volumes of each extract were added to equal volumes of the same bacterial culture. Water was added to a third sample. All three samples were kept under the same conditions.
| Substance added | Number of living bacterial cells per cm³ at the start | Number of living bacterial cells per cm³ after 6 hours |
|---|---|---|
| Water | 200 000 | 1 600 000 |
| Extract from plant P | 200 000 | 50 000 |
| Extract from plant Q | 200 000 | 400 000 |
Use the results to explain which plant is likely to be best protected against invading bacteria. Predict what would happen to the number of bacteria in this plant if it stopped making the substances in its extract.
133 exam-style questions on AQA GCSE Biology 3.3 Plant disease, covering 3.3.1 Detection and identification of plant diseases and 3.3.2 Plant defence responses. Each one has a worked solution and a mark scheme showing where the marks go.