BRAINCAKEThe Light-Independent Stage
The light-independent reactions are the second stage of photosynthesis. They take place in the stroma and use the ATP and reduced NADP made in the light-dependent reactions to convert carbon dioxide into carbohydrate. They are also known as the Calvin cycle, after Melvin Calvin, who worked out the pathway.
They do not use light directly, but they do depend on light, because they need a constant supply of ATP and reduced NADP. In the dark these run out within seconds, and the light-independent reactions soon stop.
In outline, three things happen:
• Fixation: carbon dioxide combines with a 5-carbon acceptor, RuBP, catalysed by the enzyme RUBISCO. This forms GP.
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Key terms in this lesson
- nadp
- A coenzyme that acts as a hydrogen acceptor in the light-dependent reactions of photosynthesis, becoming reduced NADP when it accepts hydrogen.
- rubisco
- The enzyme that catalyses the fixation of carbon dioxide by combining it with RuBP in the Calvin cycle, and can also catalyse a competing reaction with oxygen (photorespiration).
More in Photosynthesis
- Photosystems
- The Light-Dependent Reactions
- Cyclic Photophosphorylation
- Non-Cyclic Photophosphorylation
- The Calvin Cycle
- The Products of Photosynthesis
- C4 Plants
- Rubisco
All 20 lessons in Photosynthesis · All Edexcel A-level Biology topics