Explain why a patient with a bacterial chest infection may be at greater risk of developing antibiotic-resistant bacteria if they stop taking their prescribed course of antibiotics early.

OCR GCSE Biology A: Gateway Science (J247) — B6.3 Monitoring and maintaining health · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A GP prescribes a patient a full 10-day course of antibiotics for a bacterial chest infection. The patient begins to feel better after five days and decides to stop taking the medication.

Model answer (4 marks)

Some bacteria in the infection may survive if the full course is not completed
The surviving bacteria may be those that have natural resistance to the antibiotic
These resistant bacteria reproduce and pass on their resistance to offspring
This leads to a population of bacteria that can no longer be killed by that antibiotic

Examiner tips

  • Use the exact wording from the mark scheme (e.g., "natural resistance")
  • Show the logical sequence: survival → resistance → reproduction → population change
  • Keep each point concise and separate

Common mistakes

  • Confusing resistance with tolerance or over‑treatment
  • Failing to mention that the surviving bacteria are the resistant ones
  • Using vague terms like "more dangerous" instead of the specific mechanism

Mark scheme (4 marks)

  1. Some bacteria in the infection may survive if the full course is not completed
  2. The surviving bacteria may be those that have (natural) resistance to the antibiotic
  3. These resistant bacteria reproduce and pass on their resistance to offspring
  4. This leads to a population of bacteria that can no longer be killed by that antibiotic

Key terms in this question

antibiotic · bacteria

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