A scientist investigated a woody climbing plant. Its stems were covered by layers of dead cells.
The scientist placed 240 spores from a disease-causing fungus onto each of several stem sections. On some stem sections, loose outer layers were allowed to fall away. On the other stem sections, a mesh sleeve retained most of the loose outer layers against the stem. A small number of pieces passed through an opening at the bottom of the sleeve and fell below the stem. The mesh allowed air and water through and did not remove any spores.
After 6 days, the scientist counted the mean number of fungal spores in each location.
| Treatment of the dead outer layers | Mean number of spores still on the stem | Mean number of spores on dead outer layers collected below the stem |
|---|---|---|
| Allowed to fall away | 48 | 187 |
| Most retained against the stem | 216 | 12 |
Calculate the percentage of the initial fungal spores that were collected below the stem when the dead outer layers were allowed to fall away.
Use the results to explain how the falling away of dead outer layers can defend the plant against disease.
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.