Which of the following best explains why antibiotic-resistant bacteria increase in a population after antibiotic treatment?

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Question

Which of the following best explains why antibiotic-resistant bacteria increase in a population after antibiotic treatment?

Accepted Answer

Bacteria that are already resistant survive and reproduce more — Natural selection acts on pre-existing variation: resistant bacteria already present in the population survive antibiotic treatment, reproduce, and pass on resistance genes — this is natural selection. Option A is a very common misconception; mutation is random and not directed by the antibiotic. Option C is incorrect because not all bacteria become resistant; susceptible ones are killed. Option D describes horizontal gene transfer which is not part of the AQA GCSE specification explanation for this process.

Answer

All bacteria become resistant after repeated exposure to antibiotics

Answer

Antibiotics cause bacteria to share resistance genes with each other

Answer

Bacteria that are already resistant survive and reproduce more

Answer

Bacteria mutate in response to the antibiotic to become resistant

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