Distinguish protein building from excess amino acid breakdown
Choose assimilation or deamination from the stated material fate.
Section 13.1 · Excretion in humans
Exam scope and assessment notes
Extended only (Supplement) · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall cell metabolism, blood transport, amino acids and the distinction between excretion and egestion.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Can amino acids have a useful incorporation fate?
What you will learn
- One material has different possible fates
- Use the destination to distinguish the pathways
Distinguish protein building from excess amino acid breakdown
| Feature | Meaning |
|---|---|
| Assimilation | Amino acids → proteins |
| Excess pathway | Deamination removes nitrogen-containing part |
| Waste formation | Liver processes nitrogen → urea |
| Quantitative limit | No allocation percentages supplied |
One material has different possible fates
Available amino acids can be incorporated into proteins during assimilation. The liver is one site of that role in the required account. Excess amino acids can instead undergo deamination, in which the nitrogen-containing part is removed and processed into urea. These are distinct pathways rather than opposite names for the same product.
A branched teaching model therefore starts with amino acids and separates incorporation into proteins from the excess-material nitrogen route. The branches do not mean that every individual molecule simultaneously becomes an entire protein and an entire urea molecule. They describe alternative material fates across the available amino-acid supply.
Use the destination to distinguish the pathways
The context tells you which term to use. A record of amino acids being used to synthesise the body’s own proteins supports assimilation. A statement about removal of nitrogen-containing parts from excess amino acids and urea formation supports deamination and the excretion account. Merely naming the liver without specifying the material change is incomplete.
Do not infer quantities from the widths or colours of the branches. The diagram has no measured allocation percentages, balanced stoichiometry or personal dietary prescription. Blood can carry formed urea to kidneys for excretion, while the proteins formed by assimilation are useful body substances; neither liver branch should be confused with urine storage in the bladder.
Pause and explain
Which contrast is correct?
Worked example
Choose the pathway when absorbed amino acids are incorporated into liver proteins.
Show the worked solution
- The product is a body substance.
- This is incorporation rather than nitrogenous waste formation.
Answer Assimilation: amino acids are converted into proteins.
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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.
Compare the liver’s two amino-acid roles in this section.
Give me a hint
Use starting context and products.
Compare my reasoning
- Assimilation converts amino acids into proteins.
- Excess amino acids lose nitrogen-containing parts leading to urea.
Liver assimilation builds proteins from amino acids; deamination of excess amino acids removes their nitrogen-containing part, with liver processing forming urea.
Look for these in your work
- State useful incorporation
- State excess nitrogen processing
A record says nitrogen-containing parts are removed from excess amino acids. Name the process and subsequent liver waste product.
Give me a hint
Use the defining chemical change.
Compare my reasoning
- The process is deamination.
- The liver forms urea from the nitrogen pathway.
Deamination, followed by liver processing of the nitrogen into urea.
Look for these in your work
- Name deamination
- Name urea
A branched drawing has no numbers. Can it show that exactly sixty percent of amino acids become proteins?
Give me a hint
A qualitative branch is not a measured fraction.
Compare my reasoning
- The drawing identifies different fates.
- No allocation data are supplied.
No. It shows possible routes but supplies no quantitative allocation, so sixty percent is unsupported.
Look for these in your work
- Separate qualitative and quantitative
- Name the missing data
Common mistakes
- Calling every amino acid waste.
- Reading branch thickness as an allocation percentage.
What can you explain now?
Which contrast is correct?
Compare with the explanation
Assimilation builds proteins; excess-material deamination leads to urea
The destinations distinguish the routes.
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Make it stick
Compare assimilation and deamination without losing their material destinations.
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.