Question 4
FA student investigated the effect of three antiseptics, A, B and C, on the growth of bacteria.
The student soaked paper discs in each antiseptic and placed them on agar covered with bacteria. Disc D was soaked in sterile water.
The Figure shows the Petri dish after two days.
Figure
The student measured the diameter of the clear zone around each disc.
The Table shows the results.
Table
| Disc | Diameter of clear zone in mm |
|---|---|
| A | 10 |
| B | 14 |
| C | 8 |
| D | 0 |
a.[1]
State the independent variable in this investigation.
b.[2]
Explain why disc D was soaked in sterile water.
c.[2]
Calculate the area of the clear zone around disc B.
Use the equation area=πr2\text{area} = \pi r^2area=πr2.
d.[2]
The student concluded that antiseptic B is the most effective at killing bacteria.
Explain why the student should repeat the investigation with more Petri dishes.
5.3 Immune system and medicines Questions
45 exam-style questions on Edexcel GCSE Biology 5.3 Immune system and medicines, covering 5.3.1 The specific immune system, 5.3.2 Response to immunisation, 5.3.3 Advantages and disadvantages of immunisation, 5.3.4 Antibiotics and bacterial infections, 5.3.5 Aseptic techniques in culturing, 5.3.6 Cross-sectional areas of cultures, 5.3.7 Stages of developing new medicines, and 5.3.8 Production of monoclonal antibodies. Each one has a worked solution and a mark scheme showing where the marks go.