A shrub has a waxy cuticle, stiff hairs and a poisonous chemical in its leaves.
A scientist removed the waxy cuticle or the hairs from some leaves without damaging the underlying leaf tissue. The scientist carried out investigations using a pathogenic bacterium and leaf-eating animals. Each animal used for the leaf-area measurements had no previous experience of the shrub.
| Leaf treatment | Mean number of bacteria found inside each leaf after 2 days | Mean leaf area eaten by one animal in 6 hours in cm² |
|---|---|---|
| Nothing removed | 12 | 1.8 |
| Waxy cuticle removed | 86 | 2.0 |
| Hairs removed | 14 | 7.6 |
| Waxy cuticle and hairs removed | 91 | 7.9 |
Use the results to suggest how the waxy cuticle defends the shrub against the pathogenic bacterium.
The scientist carried out a second animal investigation using a different group of 50 leaf-eating animals with no previous experience of the shrub. The hairs were removed from the shrub leaves used in this investigation.
The animals were given a choice between a shrub leaf and a leaf from a non-poisonous food plant. After the first test, all 50 animals were fed some shrub leaf and became unwell. The same animals were tested again one week later.
| Time of test | Number choosing the shrub leaf | Number choosing the non-poisonous leaf |
|---|---|---|
| Before eating the shrub | 24 | 26 |
| One week after eating the shrub | 4 | 46 |
Use the leaf-area results and the leaf-choice results to explain how the hairs affected leaf damage and why the animals' choice changed after they became unwell.
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.