The outer surface of the stems of a woody crop can be scraped away during harvesting. A scientist investigated whether a protective coating could reduce fungal infection in damaged stems.
The coating contained no chemicals that killed fungi. The scientist applied the same quantity of a fungal pathogen to every stem. The results after two weeks are shown in the table.
| Treatment | Number of stems tested | Number of stems infected |
|---|---|---|
| Outer layers intact | 50 | 2 |
| Outer layers scraped away, no coating | 50 | 31 |
| Outer layers scraped away, coating applied | 50 | 8 |
The scientist claimed that the coating restored the same protection as the undamaged outer layers.
Evaluate the scientist's claim. In your answer, calculate the percentage reduction in infection caused by the coating, relative to damaged stems with no coating.
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.