AQA · GCSE · Biology

    Course version: 8461 · Version from Sept 2018

    Ammonia is toxic and so it is immediately converted to urea for safe…

    Full specification wording

    Maintaining water and nitrogen balance in the body (biology only): Ammonia is toxic and so it is immediately converted to urea for safe excretion.

    Ammonia formed by deamination is highly toxic, so it cannot be allowed to accumulate in the body.

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

    • Point 9 of 17
    • 2 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Ammonia formed by deamination is highly toxic, so it cannot be allowed to accumulate in the body. The liver immediately converts ammonia into urea, a less toxic nitrogenous compound that can be transported safely in the blood. Urea is then carried to the kidneys, filtered from the blood and excreted in urine. For example, a person eating a high-protein diet produces more ammonia and therefore more urea, which is why urine contains urea. This two-step sequence, ammonia then urea, protects cells while still removing surplus nitrogen. The word immediately matters because rapid conversion prevents toxic ammonia from building up.

    What earns the marks

    • Ammonia is toxic to cells and must not accumulate.
    • The liver converts ammonia to urea.
    • Urea is less toxic than ammonia and can be transported safely in the blood.
    • Urea is excreted by the kidneys in urine.
    • The conversion happens immediately after deamination.
    • A high-protein diet increases urea production because more amino acids are deaminated.

    Common mistakes and how to put them right

    • Stating that ammonia itself is excreted in urine.

      Put it right by stating ammonia is converted to urea first.

    • Saying urea is more toxic than ammonia.

      Put it right by stating urea is less toxic.

    • Naming the kidneys as the site of conversion.

      Put it right by naming the liver.

    Exam tips

    • Use the sequence deamination → ammonia → urea → urine.
    • Compare toxicity explicitly: ammonia toxic, urea less toxic.
    • Mention the liver as the conversion site and the kidneys as the excretion route.

    Try the lesson

    The start of the Maintaining water and nitrogen balance in the body (biology only): Ammonia is toxic and so it is immediately converted to urea for safe excretion. lesson, made from checked teaching notes for this specification point.

    Have a go first

    Ammonia is toxic, so it is immediately converted into which substance for safe excretion?

    Listen

    Ammonia formed by deamination is highly toxic, so it cannot be allowed to accumulate in the body. The liver immediately converts ammonia into urea, a less toxic nitrogenous compound that can be transported safely in the blood. Urea is then carried to the kidneys, filtered from the blood and excreted in urine. For example, a person eating a high-protein diet produces more ammonia and therefore more urea, which is why urine contains urea. This two-step sequence, ammonia then urea, protects cells while still removing surplus nitrogen. The word immediately matters because rapid conversion prevents toxic ammonia from building up. A strong answer earns marks for these points. Ammonia is toxic to cells and must not accumulate. The liver converts ammonia to urea. Urea is less toxic than ammonia and can be transported safely in the blood. Urea is excreted by the kidneys in urine. A common slip: Stating that ammonia itself is excreted in urine. Instead, stating ammonia is converted to urea first. Exam tip: Use the sequence deamination → ammonia → urea → urine.

    See it

    A top-to-bottom flowchart with six boxes joined by arrows. The first box says ammonia is toxic. An arrow leads to the second box, which says the liver immediately converts ammonia to urea. An arrow leads to the third box, which says urea is less toxic than ammonia. An arrow leads to the fourth box, which says urea is transported safely in the blood. An arrow leads to the fifth box, which says the kidneys filter urea from the blood. A final arrow leads to the sixth box, which says urea is excreted in urine.
    It shows the sequence from toxic ammonia being converted immediately to less toxic urea in the liver, then carried in the blood to the kidneys and excreted in urine.

    Put it in order

    Put these steps in the order they happen.

    1. 1. Urea is less toxic than ammonia
    2. 2. Liver immediately converts ammonia to urea
    3. 3. Ammonia is toxic
    4. 4. Urea excreted in urine
    5. 5. Kidneys filter urea from the blood
    6. 6. Urea transported safely in the blood

    Key words

    Say what each word means before you turn the card.

    Liver function

    Try answering aloud or in your head before turning the card.

    Kidney function

    Try answering aloud or in your head before turning the card.

    See every definition
    Liver function
    The liver converts ammonia formed by deamination into urea, a less toxic nitrogenous compound.
    Kidney function
    The kidneys filter urea from the blood and excrete it in urine.

    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 six boxes joined by arrows. The first box says ammonia is toxic. An arrow leads to the second box, which says the liver immediately converts ammonia to urea. An arrow leads to the third box, which says urea is less toxic than ammonia. An arrow leads to the fourth box, which says urea is transported safely in the blood. An arrow leads to the fifth box, which says the kidneys filter urea from the blood. A final arrow leads to the sixth box, which says urea is excreted in urine.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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