Scientists investigated barley powdery mildew on 24 farms. They compared the percentage of each farm sown with resistant barley varieties with the percentage of leaves showing infection.
There was a negative correlation between these two variables. However, among farms that had similar percentages of resistant barley, infection was more common in mild, damp locations than in other locations.
Which statement gives the best evaluation of this evidence?
The evidence supports an association between resistant varieties and reduced infection, but also indicates that growing conditions affect infection.
The evidence suggests that mild, damp conditions improve the protection provided by resistant barley varieties.
The association with resistant varieties explains the infection pattern, so the evidence about location adds little to the conclusion.
The differences between locations weaken the evidence that resistant varieties are associated with reduced infection.
181 exam-style questions on OCR GCSE Biology 6.3 Monitoring and maintaining health, covering 6.3.1 Health and disease, 6.3.2 Interactions between diseases, 6.3.3 Spread of communicable diseases, 6.3.4 Common infections and diseases, 6.3.5 Physical plant defence responses, 6.3.6 Chemical plant defence responses, 6.3.7 Detecting and identifying plant diseases, 6.3.8 White blood cells and platelets, 6.3.9 Non-specific defence systems, 6.3.10 The immune system, 6.3.11 Monoclonal antibodies, 6.3.12 Vaccines and medicines, 6.3.13 Aseptic techniques, 6.3.14 Discovery and development of new medicines, 6.3.15 Causes of non-communicable diseases, 6.3.16 Treatments for cardiovascular disease, 6.3.17 Lifestyle factors and non-communicable diseases, 6.3.18 Cancer, 6.3.19 Stem cells in medicine, 6.3.20 Gene technology in medicine, and 6.3.21 The human genome and medicine. Each one has a worked solution and a mark scheme showing where the marks go.