A diagnostic test detects only pathogen X. A diseased plant gives a negative result, and the positive control gives the expected positive result.
Which conclusion is justified?
X was not detected, so all possible pathogens have been excluded
X must be present, because the positive control gave a positive result
X was not detected, but a different pathogen could be present
X must be absent from the control, because the plant result was negative
45 exam-style questions on Edexcel GCSE Biology 5.2 Plant and body defences, covering 5.2.1 Physical plant defences, 5.2.2 Chemical plant defences, 5.2.3 Detecting plant diseases, and 5.2.4 Human physical and chemical defences. Each one has a worked solution and a mark scheme showing where the marks go.