A laboratory tested a sterile wound dressing using gel to represent the tissues beneath damaged skin. The same amount of liquid containing disease-causing bacteria was used in each test.
| Covering above the gel | Mean number of bacteria reaching the gel |
|---|---|
| No covering | 2400 |
| Sterile wound dressing | 120 |
Calculate the percentage decrease in the mean number of bacteria reaching the gel when the dressing was used.
A person has a cut. A scab forms but is pulled off before the cut has healed.
Using the results and your knowledge of body defences, explain why a new sterile dressing should be put over the cut.
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.