AQA · GCSE · Physics

    Course version: 8463 · Version from Sept 2016

    X-rays and gamma rays are ionising radiation that can cause the mutation…

    Full specification wording

    Properties of electromagnetic waves 2: X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer.

    X-rays and gamma rays have the highest frequencies in the spectrum, so each one carries enough energy to knock an electron off an atom it passes; that is what ionising means.

    Checked against the AQA 8463 specification (opens in a new tab) on .

    • Point 11 of 11

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    X-rays and gamma rays have the highest frequencies in the spectrum, so each one carries enough energy to knock an electron off an atom it passes; that is what ionising means. Inside a cell, the ions and reactive fragments produced can break or alter a strand of DNA. If a gene is changed rather than repaired, the mutation is passed on when the cell divides and can lead to a tumour, which is cancer. Because both radiations penetrate deeply, the damage is not limited to the skin. That is why radiographers stand behind lead screens and why medical doses are kept as low as possible, and it is also why the same penetrating, ionising property is used deliberately in radiotherapy to kill cancer cells.

    What earns the marks

    • Stating that X-rays and gamma rays are ionising.
    • Explaining that ionisation can damage or alter the DNA or genes in a cell.
    • Linking a mutation to uncontrolled cell division and cancer.
    • Stating that both penetrate the body, so internal organs are affected.

    Common mistakes and how to put them right

    • Saying an X-ray scan is not dangerous because it is quick, with no mention of dose.

    • Describing ionisation as heating the cell.

    • Saying gamma rays cure cancer without noting that they can also cause it.

    • Claiming X-rays come from the nucleus in the way gamma rays do.

    Exam tips

    • Spell out the chain: ionisation, damage to DNA, mutation, cancer; each step can carry a mark.
    • Mention the precaution as well as the hazard when the question is set in a hospital.
    • Keep X-rays and gamma rays together for hazard questions, but remember they are produced differently.

    Try the lesson

    The start of the Properties of electromagnetic waves 2: X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer. lesson, made from checked teaching notes for this specification point.

    Have a go first

    What type of radiation are X-rays and gamma rays?

    Listen

    X-rays and gamma rays have the highest frequencies in the spectrum, so each one carries enough energy to knock an electron off an atom it passes; that is what ionising means. Inside a cell, the ions and reactive fragments produced can break or alter a strand of DNA. If a gene is changed rather than repaired, the mutation is passed on when the cell divides and can lead to a tumour, which is cancer. Because both radiations penetrate deeply, the damage is not limited to the skin. That is why radiographers stand behind lead screens and why medical doses are kept as low as possible, and it is also why the same penetrating, ionising property is used deliberately in radiotherapy to kill cancer cells. A strong answer earns marks for these points. stating that X-rays and gamma rays are ionising. explaining that ionisation can damage or alter the DNA or genes in a cell. linking a mutation to uncontrolled cell division and cancer. stating that both penetrate the body, so internal organs are affected. Exam tip: Spell out the chain: ionisation, damage to DNA, mutation, cancer; each step can carry a mark.

    See it

    A top-down flowchart. The first box reads 'X-rays and gamma rays are ionising'. An arrow leads down to a box reading 'Ionisation damages or alters DNA or genes in a cell', which leads to 'Gene changed rather than repaired: mutation', then to 'Mutation passed on when the cell divides', and finally to 'Uncontrolled cell division leads to a tumour, which is cancer'. A separate arrow from the first box leads to a box reading 'Both penetrate the body, so internal organs are affected'.
    It shows the chain from ionising X-rays and gamma rays through DNA damage and mutation to cancer, plus the point that both penetrate the body.

    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-down flowchart. The first box reads 'X-rays and gamma rays are ionising'. An arrow leads down to a box reading 'Ionisation damages or alters DNA or genes in a cell', which leads to 'Gene changed rather than repaired: mutation', then to 'Mutation passed on when the cell divides', and finally to 'Uncontrolled cell division leads to a tumour, which is cancer'. A separate arrow from the first box leads to a box reading 'Both penetrate the body, so internal organs are affected'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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