A scientist investigates changes in a bacterial culture during repeated treatment with an antibiotic. The culture has not previously been treated with this antibiotic. It is treated and then allowed to reproduce before each subsequent treatment.
The table shows the numbers of viable cells counted in a small sample of the culture taken immediately before each treatment.
| Treatment cycle | Cells with the resistance allele | Susceptible cells |
|---|---|---|
| 1 | 20 | 980 |
| 2 | 40 | 160 |
| 3 | 80 | 40 |
Calculate the percentage of cells with the resistance allele before treatment cycle 3.
Compare the changes in the numbers of the two types of cell between cycles 1 and 2 and between cycles 2 and 3.
A student concludes that the antibiotic caused some susceptible cells to mutate and become resistant. Evaluate this conclusion using the data and your knowledge of antibiotic resistance.
85 exam-style questions on Edexcel GCSE Biology 4.1 Evolution and natural selection, covering 4.1.1 Work of Darwin and Wallace and 4.1.2 Resistant organisms and evolution. Each one has a worked solution and a mark scheme showing where the marks go.