A gardener notices that the leaves of a houseplant have turned yellow. The gardener adds a fertiliser containing magnesium ions to the soil. Four weeks later the leaves are green again.
Explain why the leaves of the houseplant were yellow before the fertiliser was added.
The gardener says that a pathogen caused the yellow leaves. Explain why the gardener is wrong.
58 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.