Explain why the development of antibiotic-resistant bacteria is a serious threat to human health, and describe how the misuse of antibiotics by patients contributes to this problem.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In recent decades, strains of bacteria such as MRSA have become resistant to many commonly used antibiotics. Scientists and doctors are concerned that antibiotic resistance is increasing at a faster rate than new antibiotics are being developed.
Model answer (5 marks)
Antibiotics kill or inhibit the growth of bacteria, but they do not affect viruses or human cells.
Some bacteria acquire a random mutation that renders the antibiotic ineffective.
The resistant bacteria survive and reproduce, passing the mutation on – this is natural selection or survival of the fittest.
When resistance spreads widely, infections become very difficult or impossible to treat, leading to more severe illness or death.
Patients who do not finish a prescribed course or who use antibiotics unnecessarily leave some bacteria alive; this gives resistant strains a selective advantage and increases the likelihood that resistance will spread.
Some bacteria acquire a random mutation that renders the antibiotic ineffective.
The resistant bacteria survive and reproduce, passing the mutation on – this is natural selection or survival of the fittest.
When resistance spreads widely, infections become very difficult or impossible to treat, leading to more severe illness or death.
Patients who do not finish a prescribed course or who use antibiotics unnecessarily leave some bacteria alive; this gives resistant strains a selective advantage and increases the likelihood that resistance will spread.
Examiner tips
- Use the exact terms ‘antibiotics kill or inhibit bacteria’, ‘random mutation’, ‘natural selection’, ‘selective advantage’
- Show the causal chain from mutation to treatment failure
- Mention both incomplete courses and unnecessary use
Common mistakes
- Confusing antibiotics with antiviral drugs
- Forgetting that resistance spreads through reproduction, not just mutation
- Over‑generalising that all bacteria are resistant
Mark scheme (5 marks)
- Antibiotics kill or prevent the growth of bacteria (but have no effect on viruses/host cells)
- Some bacteria have a random mutation that makes them resistant to an antibiotic
- Resistant bacteria survive and reproduce, passing on the resistance (natural selection / survival of the fittest)
- If resistance spreads widely, infections become very difficult or impossible to treat, leading to more serious illness or death
- Patients not completing their course of antibiotics (or taking antibiotics unnecessarily) means non-resistant bacteria are not all killed, giving resistant strains a greater selective advantage / increasing the chance of resistant strains surviving and spreading
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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