A botanist finds circular brown spots on the leaves of a rare shrub. Three pathogens, P, Q and R, are known to infect this species. The botanist sends a sample from the shrub to a laboratory.
| Pathogen | Sign the pathogen can cause | Match with DNA in the sample (%) |
|---|---|---|
| P | Circular brown spots | 12.4 |
| Q | Circular brown spots | 99.7 |
| R | Distorted leaves | 15.1 |
Using the results, explain which pathogen caused the disease and why the leaf signs alone are not enough to identify it.
Suggest one reason why identifying the pathogen quickly is useful.
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.