# Explain why the kidneys are described as organs of excretion.

> Pearson Edexcel International GCSE Biology (4BI1) — 2.13 Excretion: humans · Explain · 4 marks

> Excretion is the removal from the body of toxic materials and the waste products of metabolism. Urea is produced in the liver when excess amino acids are broken down. It is then transported in the blood to the kidneys.

## Mark scheme (4 marks)

1. Excretion is the removal of waste products of metabolism (from the body) / toxic materials
2. The kidneys remove / filter urea from the blood
3. Urea is a waste product / toxic product formed when excess amino acids are broken down (in the liver)
4. The kidneys also excrete excess water / ions / salts in urine

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-kidneys-are-described-cd29a1f2) · Published by Druglandscape Ltd.