A student tested extracts from three plants for antibacterial chemicals.
Paper discs soaked in each extract were placed on agar plates covered with bacteria. A paper disc soaked in sterile water was also placed on each plate.
After 2 days, the student measured the diameter of the clear zone around each disc. The investigation was repeated three times.
The Table shows the results.
Table
| Disc soaked in | Diameter of clear zone in mm (test 1) | Diameter of clear zone in mm (test 2) | Diameter of clear zone in mm (test 3) | Mean diameter of clear zone in mm |
|---|---|---|---|---|
| garlic extract | 18 | 20 | 19 | |
| mint extract | 9 | 11 | 10 | 10 |
| ginger extract | 7 | 6 | 8 | 7 |
| sterile water | 0 | 0 | 0 | 0 |
Calculate the mean diameter of the clear zone for the garlic extract.
Explain why a disc soaked in sterile water was used.
Explain which plant extract is most effective at killing the bacteria.
Explain why plants produce antibacterial chemicals.
Give one reason why the garlic extract cannot yet be used as a medicine for humans.
45 exam-style questions on Edexcel GCSE Biology 5.2 Plant and body defences, covering 5.2.1 Physical plant defences, 5.2.2 Chemical plant defences, 5.2.3 Detecting plant diseases, and 5.2.4 Human physical and chemical defences. Each one has a worked solution and a mark scheme showing where the marks go.