The figure shows a testing kit used to find out whether a plant is infected by one particular pathogen. A sample of liquid from the plant is added to the kit. The figure also shows the results given by three of these kits, A, B and C.
Figure: A testing kit for a plant pathogen, and the results given by three of these kits

Explain why this kit detects only one type of pathogen.
Give the conclusion that should be made from the result shown by kit A and from the result shown by kit B.
Kit C shows no coloured lines. Suggest why the grower should not conclude from kit C that the plant is free from the pathogen.
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.