The leaves of a tomato plant show a mosaic pattern of discolouration. A testing kit for tobacco mosaic virus gives a negative result. Which is the best conclusion?
Another cause is responsible, so a further test is needed to identify it
The mosaic pattern must have been caused by a magnesium deficiency
The plant is healthy, because the result of the testing kit was negative
The kit is faulty, because mosaic patterns are always caused by a virus
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.