Explain why the development of antibiotic-resistant bacteria is a serious problem for treating bacterial infections, and describe how antibiotic resistance develops in a bacterial population.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Antibiotic resistance is an increasing global health concern. Some strains of bacteria, such as MRSA, can no longer be killed by many commonly used antibiotics.
Model answer (5 marks)
Antibiotics kill or inhibit the growth of bacteria, but antibiotic‑resistant bacteria are not killed by the drug.
Random mutations in the DNA of some bacteria give them a resistance trait.
When the antibiotic is present, the resistant bacteria survive while the non‑resistant ones are killed.
The surviving resistant bacteria reproduce and pass the resistance gene (allele) to their offspring – natural selection.
Over time the proportion of resistant bacteria in the population rises, so infections become harder to treat and existing antibiotics become ineffective.
Random mutations in the DNA of some bacteria give them a resistance trait.
When the antibiotic is present, the resistant bacteria survive while the non‑resistant ones are killed.
The surviving resistant bacteria reproduce and pass the resistance gene (allele) to their offspring – natural selection.
Over time the proportion of resistant bacteria in the population rises, so infections become harder to treat and existing antibiotics become ineffective.
Examiner tips
- Use the exact terms ‘antibiotic‑resistant’, ‘mutation’, ‘natural selection’, and ‘proportion of resistant bacteria’.
- Show the causal chain: mutation → survival → reproduction → increase in proportion.
Common mistakes
- Confusing ‘kill’ with ‘inhibit’ – both are acceptable but ‘kill or inhibit’ is preferred.
- Losing the word ‘natural selection’ – examiners look for this phrase.
Mark scheme (5 marks)
- Antibiotics kill or prevent the growth of bacteria / antibiotics cannot kill antibiotic-resistant bacteria
- Random mutation(s) occur in the DNA of some bacteria
- Resistant bacteria survive and reproduce when antibiotic is present / non-resistant bacteria are killed by the antibiotic
- Resistant bacteria reproduce and pass on the resistance gene / resistant allele to offspring (natural selection)
- Over time the proportion of resistant bacteria in the population increases, making infections harder to treat / existing antibiotics become ineffective
Key terms in this question
antibiotic · antibiotic resistance · bacteria
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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