A culture contains 8.0 × 106 bacteria, of which 0.025% are resistant to an antibiotic. Treatment kills 99.9% of the sensitive bacteria and none of the resistant bacteria. Each surviving bacterium then divides three times. No further cells die or mutate.
Approximately what percentage of the final population is resistant?
0.20%, because three divisions multiply the initial resistant percentage by eight.
2.0%, because treatment leaves approximately one resistant cell per fifty survivors.
80%, because the sensitive cells remaining after treatment become resistant during division.
20%, because equal subsequent division preserves the resistant proportion among survivors.
40 exam-style questions on AQA GCSE Biology 6.3 The development of understanding of genetics and evolution, covering 6.3.1 Theory of evolution, 6.3.2 Speciation, 6.3.3 The understanding of genetics, 6.3.4 Evidence for evolution, 6.3.5 Fossils, 6.3.6 Extinction, and 6.3.7 Resistant bacteria. Each one has a worked solution and a mark scheme showing where the marks go.