AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
They survive and reproduce, so the population of the resistant strain rises.
Full specification wording
Resistant bacteria: They survive and reproduce, so the population of the resistant strain rises.
This statement explains natural selection in bacteria during antibiotic treatment.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 4 of 10
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This statement explains natural selection in bacteria during antibiotic treatment. When an antibiotic is used, most bacteria of a strain are killed, but a few may carry a random mutation that makes them resistant. Those resistant bacteria survive because the antibiotic does not kill them. They then reproduce rapidly by binary fission, passing the resistance allele to their offspring. As a result, the proportion and number of resistant bacteria in the population increase. For example, a patient with a bacterial infection may start with a mostly non-resistant population; after antibiotic treatment, the resistant survivors multiply, so the resistant strain becomes more common. This is evolution by natural selection acting on variation within a bacterial population.
What earns the marks
- Resistant bacteria are not killed by the antibiotic, so they survive the treatment.
- Surviving resistant bacteria reproduce, often rapidly by binary fission.
- The resistance allele is inherited by offspring, so resistant bacteria become more common.
- The population of the resistant strain rises because selection favours resistant individuals.
- A named example such as MRSA can be used to illustrate the process.
Common mistakes and how to put them right
Thinking that the antibiotic causes the mutation.
Put it right: The mutation arises randomly before exposure, and the antibiotic selects survivors.
Saying that bacteria 'learn' to become resistant.
Put it right: Resistance is inherited through genes, not learned.
Confusing the rise of a resistant strain with the rise of all bacteria.
Put it right: The total bacterial population may fall, but the resistant proportion rises.
Exam tips
- Use the terms 'survive', 'reproduce' and 'population rises' in a logical sequence.
- Refer to random mutation and natural selection rather than saying bacteria 'adapt' in a vague way.
- Link the process to a real example such as MRSA to show understanding.
Try the lesson
The start of the Resistant bacteria: They survive and reproduce, so the population of the resistant strain rises. lesson, made from checked teaching notes for this specification point.
Have a go first
A patient is given an antibiotic for a bacterial infection. A few bacteria in the infection are resistant to this antibiotic. What happens to these resistant bacteria?
Listen
This statement explains natural selection in bacteria during antibiotic treatment. When an antibiotic is used, most bacteria of a strain are killed, but a few may carry a random mutation that makes them resistant. Those resistant bacteria survive because the antibiotic does not kill them. They then reproduce rapidly by binary fission, passing the resistance allele to their offspring. As a result, the proportion and number of resistant bacteria in the population increase. For example, a patient with a bacterial infection may start with a mostly non-resistant population; after antibiotic treatment, the resistant survivors multiply, so the resistant strain becomes more common. This is evolution by natural selection acting on variation within a bacterial population. A strong answer earns marks for these points. Resistant bacteria are not killed by the antibiotic, so they survive the treatment. Surviving resistant bacteria reproduce, often rapidly by binary fission. The resistance allele is inherited by offspring, so resistant bacteria become more common. The population of the resistant strain rises because selection favours resistant individuals. Exam tip: Use the terms 'survive', 'reproduce' and 'population rises' in a logical sequence.
Key words
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Natural selection
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Antibiotic resistance
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Bacterial reproduction
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Evolution of populations
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See every definition
- Natural selection
- Evolution by natural selection acts on variation within a bacterial population, as when resistant survivors multiply after antibiotic treatment.
- Antibiotic resistance
- A few bacteria may carry a random mutation that makes them resistant, so the antibiotic does not kill them.
- Bacterial reproduction
- Surviving resistant bacteria reproduce, often rapidly by binary fission, passing the resistance allele to their offspring.
- Evolution of populations
- The population of the resistant strain rises because selection favours resistant individuals, so resistant bacteria become more common.
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