# The liver is an organ involved in excretion. One of its roles is to break down excess amino acids through a process called deamination. The nitrogen-containing waste product produced is eventually excreted by the kidneys in urine. Explain how the liver and kidneys work together to remove the waste products of excess amino acids from the body.

> OCR A-Level Biology B — Advancing Biology (H422) — 5.6 Excretion · Explain · 5 marks

> The human body cannot store excess amino acids. Instead, the liver converts them into a less harmful substance before they are removed from the body in urine.

## Mark scheme (5 marks)

1. Excess amino acids are broken down in the liver by deamination
2. Deamination produces ammonia (from the nitrogen-containing part of the amino acid)
3. Ammonia is toxic / harmful, so it is converted into urea in the liver
4. Urea passes from the liver into the blood and is transported to the kidneys
5. The kidneys filter urea from the blood and it is excreted in urine

## Key terms

- [excretion](https://www.gradenine.co.uk/glossary/excretion)
- [deamination](https://www.gradenine.co.uk/glossary/deamination)

## Related

- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/the-liver-is-an-organ-involved-c120642a) · Published by Druglandscape Ltd.