A plant health laboratory investigated the spread of tobacco mosaic virus (TMV). A source enclosure contained infected tomato plants. Each of four test enclosures contained 20 healthy tomato plants at the start of the investigation.
The investigation lasted four weeks. All conditions other than those shown in the table were kept the same.
| Test enclosure | Worker visits from the source enclosure | Hygiene before entering the test enclosure | Could insects move from the source enclosure? | Number of test plants infected after four weeks |
|---|---|---|---|---|
| P | 10 | Hands not washed and gloves not changed | No | 16 |
| Q | 10 | Hands washed and gloves changed | No | 0 |
| R | 0 | Not applicable | Yes | 7 |
| S | 0 | Not applicable | No | 0 |
Suggest two conclusions about how TMV reached the test plants. Support each conclusion with data from the investigation.
The laboratory expects worker visits and insect movement to continue at the same rates. It can introduce only one control measure throughout the laboratory.
Suggest whether cleaning hands and changing gloves or excluding insects should be prioritised to prevent the greatest number of infections. Explain your answer.
An infected plant is later found in one of the test enclosures.
Suggest what should be done with this plant and explain how this would reduce the spread of TMV.
The laboratory introduces hand-washing and glove-changing throughout. A worker says that this will also cure the infected plants in the source enclosure.
Explain why the worker is wrong.
252 exam-style questions on AQA GCSE Biology 3.1 Communicable diseases, covering 3.1.1 Communicable (infectious) diseases, 3.1.2 Viral diseases, 3.1.3 Bacterial diseases, 3.1.4 Fungal diseases, 3.1.5 Protist diseases, 3.1.6 Human defence systems, 3.1.7 Vaccination, 3.1.8 Antibiotics and painkillers, and 3.1.9 Discovery and development of drugs. Each one has a worked solution and a mark scheme showing where the marks go.