Deaminate excess amino acids
When amino acids are in excess, deamination removes their amino group; nitrogenous waste can return to the soil cycle after excretion and decomposition.
Section B15.3 · Carbon cycle
Cross-referenced to the 2028–2029 0653 section using original teaching from the related single-science courses. A 0653-specific objective-by-objective and Core/Supplement review is in progress. Written practice is self-checked and does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Use the food-web pathway and distinguish matter cycling from energy flow.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What happens in deamination?
What you will learn
- Describe deamination of excess amino acids
- Connect nitrogenous waste with later decomposition
Remove excess amino groups
Amino acids absorbed from digestion can be used to make proteins. Excess amino acids are deaminated, mainly in the liver: the amino group is removed from the molecule. In mammals, the nitrogen-containing waste is converted to urea and excreted in urine.
Deamination is not the same as digestion. Digestion makes amino acids from proteins; deamination removes an amino group from excess amino acids. The nitrogen may later enter soil compounds when waste is decomposed.
Return waste nitrogen through the cycle
Urea in urine and nitrogen in dead animal material can be decomposed by microorganisms. Decomposition releases ammonium ions, reconnecting organic waste nitrogen with soil nitrogen compounds.
Keep the arrows separate: animal protein → amino acids by digestion; excess amino acids → nitrogenous waste by deamination; waste → ammonium by decomposition.
Sources for this lesson
Pause and explain
Which nitrogenous waste is made from excess amino-acid nitrogen in mammals?
Worked example
A person has excess amino acids after protein digestion. Name the process and the nitrogenous waste route.
Show the worked solution
- Excess amino acids undergo deamination.
- Nitrogen is converted into urea and excreted.
- Decomposition can later return nitrogen to ammonium ions.
Answer Deamination removes the amino group from excess amino acids. In mammals the nitrogen is excreted as urea; decomposers can later return waste nitrogen to ammonium ions.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
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.
Differentiate digestion of protein from deamination of excess amino acids.
Give me a hint
Compare the starting molecule and the process outcome.
Compare my reasoning
- Digestion breaks proteins into amino acids.
- Deamination removes an amino group from excess amino acids.
Digestion breaks proteins into amino acids; deamination removes the amino group from excess amino acids, producing nitrogenous waste such as urea in mammals.
Look for these in your work
- Starting material distinguished
- Processes and outcomes separated
Trace nitrogen from excess amino acid in a mammal into ammonium ions in soil.
Give me a hint
Include deamination, excretion and decomposition.
Compare my reasoning
- Deamination forms nitrogenous waste such as urea.
- Waste is excreted.
- Decomposers release ammonium ions.
Excess amino acid nitrogen → urea by deamination → urine/waste → ammonium ions in soil by decomposition.
Look for these in your work
- All stages ordered
- Ammonium endpoint
A learner claims that all absorbed amino acids are deaminated. Correct the claim.
Give me a hint
State the main use and limit the waste route to excess.
Compare my reasoning
- Amino acids can be used to build proteins.
- Excess amino acids are deaminated.
Absorbed amino acids can be used to make proteins; excess amino acids are deaminated, so not all absorbed amino acids follow the waste route.
Look for these in your work
- Protein synthesis retained
- Excess qualifier included
Common mistakes
- Calling deamination the breakdown of protein into amino acids
- Saying urea is made by nitrification
- Claiming all amino acids are deaminated
What can you explain now?
What happens in deamination?
Compare with the explanation
The amino group is removed from excess amino acids
This distinguishes it from protein digestion.
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Make it stick
Define deamination and show how nitrogen from urea can later return to soil ammonium ions.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.