The second stage of the Calvin cycle needs an input of energy to reduce the 3PG molecules that resulted from the first stage. Where does this energy input come from?
ATP and NADPH that were supplied through the light reactions
The second stage of the Calvin cycle, also known as the reduction stage, requires the input of energy to reduce the 3-phosphoglycerate (3PG) into glyceraldehyde-3-phosphate (G3P). This energy comes from the light-dependent reactions of photosynthesis, specifically from the molecule ATP, which is produced during the light reactions via photophosphorylation.
The reduced molecule NADPH, produced by the light-dependent reactions, also provides electrons for the reduction of 3PG into G3P. Together, ATP and NADPH power the second stage of the Calvin cycle and allow for the synthesis of G3P, which is a key intermediate in the production of glucose and other carbohydrates. Once the G3P is produced, some of it is used to regenerate the molecule RuBP, enabling the cycle to continue.
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