A laboratory needs to choose one antiseptic to use against two species of bacterium, J and K.
A researcher prepared four agar plates containing a lawn of species J and four agar plates containing a lawn of species K. One paper disc soaked in antiseptic R and one paper disc soaked in antiseptic S were placed on each plate.
The disc size, volume of antiseptic, incubation temperature and incubation time were kept the same.
The table shows the diameter of the inhibition zone around each disc.
| Species of bacterium | Antiseptic | Plate 1 diameter in mm | Plate 2 diameter in mm | Plate 3 diameter in mm | Plate 4 diameter in mm |
|---|---|---|---|---|---|
| J | R | 24 | 23 | 25 | 24 |
| J | S | 19 | 20 | 19 | 20 |
| K | R | 11 | 12 | 10 | 11 |
| K | S | 18 | 17 | 19 | 18 |
Calculate the difference between the inhibition-zone areas produced by antiseptic S, using the mean diameter for each species.
Area of a circle = 3.14 × radius²
Give your answer in mm².
The laboratory needs one antiseptic to use against both species.
A technician recommends antiseptic R because it produced the single largest inhibition zone.
Evaluate this recommendation.
282 exam-style questions on AQA GCSE Biology 1.1 Cell structure, covering 1.1.1 Eukaryotes and prokaryotes, 1.1.2 Animal and plant cells, 1.1.3 Cell specialisation, 1.1.4 Cell differentiation, 1.1.5 Microscopy, and 1.1.6 Culturing microorganisms. Each one has a worked solution and a mark scheme showing where the marks go.