Use Calvin-cycle intermediates to build organic molecules
State how GP and TP from the Calvin cycle contribute to amino acids, carbohydrates and lipids.
A Level; Cambridge International Biology 9700, 2028–2030. Written practice is self-checked; practical investigations need supervised work and human subject-teacher review remains pending.
Before you begin
- Chloroplasts contain photosynthetic pigments, and enzymes catalyse metabolic reactions.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which intermediate can be used to produce some amino acids?
What you will learn
- Relate GP to synthesis of some amino acids
- Relate TP to carbohydrates, lipids and amino acids
Build the explanation
Calvin-cycle intermediates are not only recycled within the cycle. Some GP can be used to produce certain amino acids. TP can leave the cycle and provide carbon skeletons for carbohydrates, lipids and amino acids. ATP and reduced NADP have supported the formation of these carbon-rich intermediates during the cycle. This connects photosynthetic carbon fixation with synthesis of several classes of organic molecule.
Apply it carefully
Use the syllabus-limited pairings: GP to some amino acids; TP to carbohydrates, lipids and amino acids. Do not say every molecule of GP or TP leaves the cycle; much of the TP is used to regenerate RuBP.
Pause and explain
Name three classes of molecule that can be produced from TP.
Worked example
Which Calvin-cycle intermediate can be used to produce carbohydrates and lipids?
Show the worked solution
- Distinguish GP from TP.
- TP can be used to produce carbohydrates and lipids.
Answer Triose phosphate (TP).
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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.
State how GP and TP can be used to make other organic molecules.
Give me a hint
Keep the two intermediate-to-product pairings distinct.
Compare my reasoning
- GP can produce some amino acids.
- TP can produce carbohydrates, lipids and amino acids.
GP can be used to produce some amino acids. TP can be used to produce carbohydrates, lipids and amino acids; much TP also remains in the Calvin cycle to regenerate RuBP.
Look for these in your work
- GP product correct
- TP products correct
- Cycle retention noted
A learner claims all TP is converted into carbohydrate. Explain why that is inaccurate.
Give me a hint
Include both TP's exit products and its role in cycle regeneration.
Compare my reasoning
- Some TP can form carbohydrates, lipids or amino acids.
- Most TP is used in reactions that regenerate RuBP.
Some TP leaves the cycle to contribute to carbohydrates, lipids and amino acids, but much TP is used to regenerate RuBP. It is inaccurate to say all TP becomes carbohydrate.
Look for these in your work
- Multiple TP products stated
- RuBP regeneration included
- Absolute claim corrected
A labelled intermediate is GP rather than TP. Which product class is explicitly linked to it in the syllabus, and what does the label not prove?
Give me a hint
Use the narrower listed GP role.
Compare my reasoning
- GP can be used to produce some amino acids.
- The label does not show that all GP leaves the cycle or identify a particular amino acid without more information.
GP can be used to produce some amino acids. That does not mean every GP molecule leaves the cycle or that a specific amino acid is identified without further evidence.
Look for these in your work
- GP role stated
- Some qualified
- No unsupported identity
Common mistakes
- Swapping GP and TP roles
- Saying all TP leaves the cycle
- Ignoring RuBP regeneration
What can you explain now?
Which intermediate can be used to produce some amino acids?
Compare with the explanation
GP
The syllabus also lists TP as a source for amino acids.
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Make it stick
Which organic products can be made from GP and from TP?
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