Relate amino-acid deamination to urea
Explain why the liver converts excess amino-acid nitrogen into urea.
A Level; Cambridge International Biology 9700, 2028–2030. Written answers are self-checked; this is not a practical skills certification.
Before you begin
- A control system detects a change, communicates information and changes an effector response.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Where is urea formed?
What you will learn
- State that urea is produced in the liver
- Relate urea production to deamination of excess amino acids
Build the explanation
Urea is produced in the liver from deamination of excess amino acids. Deamination removes the amino group; nitrogen-containing waste is converted into urea, which is carried in blood to the kidneys for excretion in urine. The remaining carbon-containing material can enter other metabolic pathways.
Apply the limits
Urea is formed in the liver after amino-acid deamination; the kidney filters urea from blood for excretion. Do not say the kidney produces urea or that deamination removes the carbon skeleton.
Pause and explain
Why does the body convert excess amino-acid nitrogen to urea rather than retaining it as amino acids?
Worked example
Which organ produces urea from excess amino acids?
Show the worked solution
- Deamination occurs in the liver.
- Urea then travels in blood to the kidneys.
Answer The liver.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Trace urea from excess amino acid to excretion.
Give me a hint
Name the relevant structure or signal, then state its effect.
Compare my reasoning
- Excess amino acids are deaminated in the liver.
- Urea enters blood, reaches kidneys and is excreted in urine.
The liver deaminates excess amino acids and produces urea. Urea travels in blood to the kidneys, where it is removed into urine.
Look for these in your work
- Correct mechanism
- Direction of response explained
A diagram shows urea being formed inside a nephron. Correct the organ label.
Give me a hint
Separate the observed change from the body's response.
Compare my reasoning
- Urea is produced during liver deamination.
- The kidney removes urea from blood into urine.
The production label belongs at the liver. The nephron is involved in processing filtrate and excreting urea, not producing it from amino acids.
Look for these in your work
- Evidence interpreted
- Control step identified
Why does the body convert excess amino-acid nitrogen to urea rather than retaining it as amino acids?
Give me a hint
Apply the mechanism to the new context without claiming more than the evidence shows.
Compare my reasoning
- Excess amino acids cannot be stored as such.
- Deamination produces nitrogen-containing waste that is converted to urea for excretion.
Excess amino acids are deaminated in the liver because they cannot be stored as amino acids. Their nitrogen is converted to urea and carried to the kidneys for excretion.
Look for these in your work
- New context applied
- Limits preserved
Common mistakes
- Saying urea is made in the kidney
- Treating the whole amino acid as nitrogen waste
What can you explain now?
Where is urea formed?
Compare with the explanation
In the liver
The liver deaminates excess amino acids and forms urea.
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Make it stick
What happens to the amino group of an excess amino acid?
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