AQA · GCSE · Biology

    Course version: 8461 · Version from Sept 2018

    Some strains might be resistant to antibiotics, and so are not killed.

    Full specification wording

    Resistant bacteria: Some strains might be resistant to antibiotics, and so are not killed.

    Antibiotics are medicines that kill bacteria or stop their growth.

    Checked against the AQA 8461 specification (opens in a new tab) on .

    • Point 3 of 10

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Antibiotics are medicines that kill bacteria or stop their growth. Within a bacterial population, random mutations can give some cells resistance, meaning the antibiotic no longer harms them. When a patient takes an antibiotic, susceptible bacteria die, but resistant cells survive and reproduce. Their offspring inherit the resistance, so the resistant strain becomes more common. For example, a mutation may change the bacterial protein that the antibiotic targets, so the drug cannot bind. This is natural selection in action. Resistance is a serious problem because infections caused by resistant strains are harder to treat, and resistant bacteria can spread between people. Completing prescribed courses and avoiding unnecessary antibiotic use help limit the spread of resistant strains.

    What earns the marks

    • States that some bacterial strains carry mutations giving resistance to an antibiotic.
    • Explains that the antibiotic kills susceptible bacteria but not resistant ones.
    • Describes how surviving resistant bacteria reproduce and pass resistance to their offspring.
    • Links the process to natural selection, where the antibiotic acts as the selection pressure.
    • Explains a consequence, such as infections becoming harder to treat or resistant strains spreading.

    Common mistakes and how to put them right

    • Saying the antibiotic makes bacteria resistant.

      Put it right: Resistance arises from random mutation and the antibiotic selects resistant cells.

    • Believing resistance develops in an individual bacterium during treatment.

      Put it right: The population changes over generations.

    • Thinking antibiotics work against viruses.

      Put it right: Antibiotics act on bacteria, not viruses.

    Exam tips

    • Use the sequence: variation, antibiotic selection pressure, survival, reproduction, increased frequency of resistance.
    • State clearly that resistant bacteria are not killed by the antibiotic.
    • Mention a practical consequence, such as difficulty treating infections, to show wider understanding.

    Try the lesson

    The start of the Resistant bacteria: Some strains might be resistant to antibiotics, and so are not killed. lesson, made from checked teaching notes for this specification point.

    Have a go first

    What does it mean if a strain of bacteria is resistant to an antibiotic?

    Listen

    Antibiotics are medicines that kill bacteria or stop their growth. Within a bacterial population, random mutations can give some cells resistance, meaning the antibiotic no longer harms them. When a patient takes an antibiotic, susceptible bacteria die, but resistant cells survive and reproduce. Their offspring inherit the resistance, so the resistant strain becomes more common. For example, a mutation may change the bacterial protein that the antibiotic targets, so the drug cannot bind. This is natural selection in action. Resistance is a serious problem because infections caused by resistant strains are harder to treat, and resistant bacteria can spread between people. Completing prescribed courses and avoiding unnecessary antibiotic use help limit the spread of resistant strains. A strong answer earns marks for these points. States that some bacterial strains carry mutations giving resistance to an antibiotic. Explains that the antibiotic kills susceptible bacteria but not resistant ones. Describes how surviving resistant bacteria reproduce and pass resistance to their offspring. Links the process to natural selection, where the antibiotic acts as the selection pressure. A common slip: Saying the antibiotic makes bacteria resistant. Instead, resistance arises from random mutation and the antibiotic selects resistant cells. Exam tip: Use the sequence: variation, antibiotic selection pressure, survival, reproduction, increased frequency of resistance.

    See it

    A top-to-bottom flowchart with nine boxes connected by arrows. The first box reads 'Bacterial population' and points to 'Random mutation gives some cells resistance'. This points to 'Patient takes antibiotic', which branches into two boxes: 'Antibiotic kills susceptible bacteria' and 'Resistant bacteria are not killed'. The second of these points to 'Resistant bacteria survive and reproduce', then to 'Offspring inherit the resistance', then to 'Resistant strain becomes more common', and finally to 'Infections harder to treat'.
    This flowchart shows how random mutation, antibiotic selection and reproduction lead to resistant bacterial strains becoming more common and infections becoming harder to treat.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-to-bottom flowchart with nine boxes connected by arrows. The first box reads 'Bacterial population' and points to 'Random mutation gives some cells resistance'. This points to 'Patient takes antibiotic', which branches into two boxes: 'Antibiotic kills susceptible bacteria' and 'Resistant bacteria are not killed'. The second of these points to 'Resistant bacteria survive and reproduce', then to 'Offspring inherit the resistance', then to 'Resistant strain becomes more common', and finally to 'Infections harder to treat'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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