Antibiotic-Resistant Bacteria
Revise Antibiotic-Resistant Bacteria for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. MRSA shows evolution happening in real time — resistance is slowed by not overusing antibiotics and by completing the full course.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Antibiotic-resistant bacteria are a serious and growing problem, and they are the clearest modern example of natural selection in action.
Bacteria mutate rapidly, producing new strains. By chance, some mutations make a bacterium resistant to an antibiotic. When the antibiotic is used, the non-resistant bacteria are killed but the resistant ones survive, reproduce, and their population increases.
MRSA is the well-known example. Resistance is reduced by doctors not prescribing antibiotics inappropriately or for viral infections, by patients completing the full course so all bacteria are killed and none survive to mutate, and by restricting the use of antibiotics in agriculture.
Revision notes
How resistance develops
Bacteria mutate rapidly, producing new strains. By chance, a mutation may make a bacterium resistant to an antibiotic.
When the antibiotic is used, non-resistant bacteria are killed but the resistant individual survives. It reproduces, and because bacteria reproduce very quickly the resistant population rises rapidly.
Why it spreads
The resistant strain then spreads because people are not immune to it and there is no effective treatment.
MRSA is the best-known example. Developing new antibiotics is costly and slow, so it cannot keep pace with the emergence of new resistant strains.
Reducing resistance
Doctors should not prescribe antibiotics inappropriately, such as for viral infections or non-serious conditions.
Patients should complete the full course so all bacteria are killed and none survive to mutate. The agricultural use of antibiotics should be restricted.
Key points
- Bacteria mutate to produce new strains.
- Some mutations produce antibiotic resistance.
- The antibiotic kills non-resistant bacteria only.
- Resistant bacteria survive and reproduce.
- MRSA is a well-known resistant strain.
- Completing the full course reduces resistance.
Worked examples
Example 1
Explain how a strain of antibiotic-resistant bacteria develops. [4 marks]
Model answer
Bacteria mutate rapidly, and by chance a mutation may make one resistant to an antibiotic (1 mark). When the antibiotic is used, the non-resistant bacteria are killed but the resistant one survives (1 mark). The resistant bacterium reproduces (1 mark), and because bacteria reproduce very rapidly the resistant population increases quickly (1 mark).
Example 2
Explain why patients should complete a full course of antibiotics. [2 marks]
Model answer
Completing the course ensures all the bacteria are killed (1 mark), so none survive that could mutate and produce a resistant strain (1 mark).
Example 3
Explain why antibiotic-resistant strains such as MRSA spread rapidly in the population. [2 marks]
Model answer
People are not immune to the new strain (1 mark), and there is no effective treatment available, so it can pass between individuals unchecked (1 mark).
Common mistakes
Saying bacteria become resistant because they need to.
Mutation is random. The antibiotic then selects the already-resistant individuals.
Saying antibiotics cause the mutation.
The mutation occurs by chance; the antibiotic selects for it.
Forgetting to mention that non-resistant bacteria are killed.
That selection step is central to the explanation.
Giving only one way to reduce resistance.
Prescribing practice, completing courses, and agricultural restriction are all valid.
Exam tips
- Structure the answer as mutation, selection, reproduction, spread.
- Say the mutation is random and occurs by chance.
- Name MRSA if asked for an example.
- Give several measures when asked how resistance is reduced.
Key terms
- Antibiotic resistance
- The ability of bacteria to survive treatment with an antibiotic.
- Mutation
- A random change to the DNA.
- Strain
- A variety of a bacterial species.
- MRSA
- A well-known antibiotic-resistant bacterium.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.