A virus infects cucumber plants. A grower investigates how the virus spreads in four separate greenhouse areas. Each area contains 40 plants, including four infected plants at the start. Workers prune every plant once each week.
| Greenhouse area | Leaves of neighbouring plants | Secateurs used for pruning | Number of infected plants after 21 days |
|---|---|---|---|
| A | allowed to touch | not sterilised between plants | 31 |
| B | kept apart | not sterilised between plants | 19 |
| C | allowed to touch | sterilised between plants | 16 |
| D | kept apart | sterilised between plants | 7 |
Calculate the percentage decrease in the number of new infections in area D compared with area A.
Give your answer to the nearest whole number.
Evaluate the evidence that keeping leaves apart and sterilising secateurs both reduce the spread of the virus.
Recommend how the grower should manage the plants in the rest of the greenhouse.
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.