A scientist investigated two causes of reduced growth in crop seedlings.
In group P, a fungus caused disease in the leaves. In group Q, insect larvae fed on the roots.
All the seedlings were the same species and age and were grown under the same conditions for 28 days.
| Group | Mean volume of water absorbed per seedling in 28 days in cm³ | Mean increase in dry mass per seedling in g |
|---|---|---|
| P | 120 | 2.6 |
| Q | 70 | 1.4 |
The scientist tested samples from both groups using a kit containing monoclonal antibodies that bind only to the fungus.
Decide which group should give a positive result. Explain why a negative result for the other group would not show that its seedlings were healthy.
Calculate the difference between the mean increases in dry mass for groups P and Q.
Use the other data in the table and your knowledge to explain why this difference occurred.
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.