Two initially equivalent bacterial cultures contain the same proportion of bacteria resistant to an antibiotic. Both cultures are exposed to the antibiotic. The antibiotic is then removed from culture A but remains in culture B. The cultures are assessed after the same elapsed time.
Which statement explains why resistant bacteria may form a larger proportion of culture B?
In culture B, the antibiotic directs susceptible bacteria to produce a resistance mutation because they need to survive.
In culture B, susceptible bacteria inherit resistance from unrelated bacteria that survive the antibiotic treatment.
In culture B, susceptible bacteria are killed or their reproduction is inhibited for longer, while resistant bacteria are more likely to survive and reproduce.
In culture B, resistant bacteria become larger during treatment, so they account for a greater proportion of the bacteria.
122 exam-style questions on OCR GCSE Biology 5.2 Natural selection and evolution, covering 5.2.1 Genetic variation within a population, 5.2.2 Developments in classification systems, 5.2.3 How evolution occurs through natural selection, 5.2.4 Evolution as change over time, 5.2.5 Evidence for evolution, and 5.2.6 Darwin and Wallace. Each one has a worked solution and a mark scheme showing where the marks go.