A communicable disease of seedlings is caused by a pathogen that spreads by direct contact between plants.
A scientist used ten greenhouse compartments. Each compartment contained 30 uninfected seedlings of the same species and age. One infected seedling was then placed in each compartment.
The seedlings were tested for the pathogen every 2 days for 20 days. In five compartments, every newly infected seedling was removed as soon as it was identified. In the other five compartments, infected seedlings were not removed.
All other conditions were kept the same. The table shows the number of new infections recorded in each compartment during the 20 days.
| Treatment | Compartment 1 | Compartment 2 | Compartment 3 | Compartment 4 | Compartment 5 |
|---|---|---|---|---|---|
| Infected seedlings removed | 5 | 6 | 4 | 5 | 15 |
| Infected seedlings not removed | 20 | 21 | 19 | 20 | 22 |
The result of 15 new infections was anomalous.
Calculate the percentage reduction in the mean number of new infections when infected seedlings were removed. Do not include the anomalous result in your calculation.
Evaluate the conclusion that removing infected seedlings is an effective way to limit the spread of the disease.
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.