Explain how the use of antibiotics can lead to the development of antibiotic-resistant bacteria in a population.

Eduqas GCSE Biology — 3.1 Health and disease · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Some bacteria in the population possess a mutation or genetic variation that confers resistance to the antibiotic. When the antibiotic is used, it kills the susceptible bacteria, leaving the resistant ones alive. The surviving resistant bacteria then reproduce and pass the resistance genes to their offspring. Over time, natural selection favours the resistant bacteria, so the proportion of resistant bacteria in the population increases.

Examiner tips

Use the exact terms ‘mutation’, ‘genetic variation’, ‘susceptible’, ‘resistant’, ‘natural selection’
Show the sequence: mutation → antibiotic kills susceptibles → resistant survive → reproduce → increase in proportion
Keep answer concise – 4 points only

Common mistakes

Confusing ‘mutation’ with ‘mutation in the antibiotic’
Omitting the step that resistant bacteria reproduce and pass on resistance
Using vague terms like ‘different bacteria’ instead of ‘susceptible’ and ‘resistant’

Mark scheme (4 marks)

Some bacteria in the population have a mutation / genetic variation that makes them resistant to the antibiotic
When antibiotic is used, non-resistant bacteria are killed
The resistant bacteria survive and reproduce / pass on the resistance to offspring
Over time the proportion of resistant bacteria in the population increases / natural selection favours the resistant bacteria

Key terms in this question

antibiotic · antibiotic-resistant bacteria