Describe the role of the liver and the kidneys in the removal of urea from the body.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
1. In the liver, excess amino acids are deaminated, removing the amino group.
2. The amino group is converted into urea, which is the main nitrogenous waste product.
3. Urea is released into the bloodstream and carried to the kidneys.
4. The kidneys filter urea from the blood into the urine, which is then excreted.
2. The amino group is converted into urea, which is the main nitrogenous waste product.
3. Urea is released into the bloodstream and carried to the kidneys.
4. The kidneys filter urea from the blood into the urine, which is then excreted.
Examiner tips
- Use the exact terms ‘deaminated’, ‘urea’, ‘filtered’, ‘excreted’
- Show the flow: liver → blood → kidneys → urine
- Keep each point short and to the point
Common mistakes
- Confusing urea with ammonia or other nitrogenous wastes
- Not mentioning the transport via blood
- Using vague words like ‘removed’ without specifying filtration
Mark scheme (4 marks)
- Excess amino acids are broken down / deaminated in the liver
- Urea is produced / formed in the liver (from deamination)
- Urea is transported (in the blood) from the liver to the kidneys
- Urea is filtered / removed from the blood by the kidneys and excreted in urine
Key terms in this question
Related
- All Pearson Edexcel International GCSE Biology (4BI1) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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