A scientist investigated a coastal plant that makes a poison in its leaves.
A treatment was used to stop some plants making the poison. The treatment did not affect any other process in the plants.
All the plants had a mean height of 5.0 cm at the start. The plants were grown for four weeks under the same conditions.
| Plants | Mean final height without grazing mammals in cm | Mean final height with grazing mammals in cm |
|---|---|---|
| Made poison | 14.0 | 12.0 |
| Did not make poison | 17.0 | 8.0 |
Calculate the percentage by which grazing mammals reduced the increase in height of the plants that made poison.
Evaluate whether making the poison was advantageous to the plants in this investigation.
A bacterial pathogen entered the leaves of plants that made the poison.
Suggest why these plants could still develop a disease.
The scientist tested leaf extracts from three other coastal plant species. The same volume of each extract was added to separate samples of the same bacterium.
| Treatment | Mean area covered by bacteria after 24 hours in mm² |
|---|---|
| No plant extract | 80 |
| Extract P | 65 |
| Extract Q | 12 |
| Extract R | 48 |
Suggest which plant extract should be investigated further as a possible source of an antibacterial medicine. Use the results to justify your answer.
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.