OCR · A-Level · Biology
Course version: H420 · Version from Sept 2025
Photosynthesis: (f) the uses of triose phosphate (TP)
Triose phosphate (TP) is the three-carbon product of the light-independent stage, and it has several fates.
Checked against the OCR H420 specification (opens in a new tab) on .
- Point 7 of 9
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Triose phosphate (TP) is the three-carbon product of the light-independent stage, and it has several fates. Most TP is used to regenerate ribulose bisphosphate (RuBP) so the Calvin cycle can continue. Some TP is converted to glycerol and fatty acids, which combine to form lipids. Some TP is built into amino acids, and therefore proteins, when nitrogen is available. Some TP is converted to hexose sugars such as glucose, which can be used in respiration or polymerised into starch for storage or cellulose for cell walls. Sucrose is also formed for transport in the phloem. A useful method is to sort each use into 'regenerate RuBP', 'make carbohydrate', 'make lipid' and 'make amino acid'.
What earns the marks
- Most triose phosphate is used to regenerate ribulose bisphosphate (RuBP) so the Calvin cycle continues.
- Triose phosphate is converted to hexose sugars such as glucose, which can be used in respiration or stored as starch.
- Glucose from triose phosphate can be polymerised into cellulose for cell walls, and sucrose can be formed for transport.
- Triose phosphate is used to synthesise glycerol and fatty acids, which form lipids.
- Triose phosphate is used to make amino acids, and so proteins, when nitrogen is available.
Common mistakes and how to put them right
Claiming all triose phosphate is converted to glucose.
Put it right by noting most TP regenerates RuBP and the rest is shared among several products.
Saying TP is made into proteins without nitrogen.
Put it right by stating amino acid synthesis requires a nitrogen source.
Confusing TP with GP.
Put it right by remembering GP is reduced to TP, and TP is the branching-point product.
Exam tips
- Group the uses of TP into regeneration, carbohydrate, lipid and amino acid categories to recall them quickly.
- State the nitrogen requirement when describing amino acid and protein synthesis from TP.
- Link each product to its role, such as starch for storage or cellulose for cell walls.
Try the lesson
The start of the Photosynthesis: (f) the uses of triose phosphate (TP) lesson, made from checked teaching notes for this specification point.
Have a go first
Triose phosphate can be converted into which of the following groups of useful organic compounds in a plant?
Listen
Triose phosphate (TP) is the three-carbon product of the light-independent stage, and it has several fates. Most TP is used to regenerate ribulose bisphosphate (RuBP) so the Calvin cycle can continue. Some TP is converted to glycerol and fatty acids, which combine to form lipids. Some TP is built into amino acids, and therefore proteins, when nitrogen is available. Some TP is converted to hexose sugars such as glucose, which can be used in respiration or polymerised into starch for storage or cellulose for cell walls. Sucrose is also formed for transport in the phloem. A useful method is to sort each use into 'regenerate RuBP', 'make carbohydrate', 'make lipid' and 'make amino acid'. A strong answer earns marks for these points. Most triose phosphate is used to regenerate ribulose bisphosphate (RuBP) so the Calvin cycle continues. Triose phosphate is converted to hexose sugars such as glucose, which can be used in respiration or stored as starch. Glucose from triose phosphate can be polymerised into cellulose for cell walls, and sucrose can be formed for transport. Triose phosphate is used to synthesise glycerol and fatty acids, which form lipids. A common slip: Claiming all triose phosphate is converted to glucose. Instead, noting most TP regenerates RuBP and the rest is shared among several products. Exam tip: Group the uses of TP into regeneration, carbohydrate, lipid and amino acid categories to recall them quickly.
See it
Key words
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Regeneration of RuBP
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Carbohydrate synthesis and storage
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Lipid synthesis
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Amino acid and protein synthesis
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See every definition
- Regeneration of RuBP
- Most triose phosphate is used to regenerate ribulose bisphosphate so the Calvin cycle can continue.
- Carbohydrate synthesis and storage
- Triose phosphate is converted to hexose sugars such as glucose, which can be used in respiration or stored as starch, polymerised into cellulose for cell walls, or formed into sucrose for transport.
- Lipid synthesis
- Triose phosphate is converted to glycerol and fatty acids, which combine to form lipids.
- Amino acid and protein synthesis
- Triose phosphate is built into amino acids, and therefore proteins, when nitrogen is available.
Label the diagram
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