Answer :
During the Calvin cycle, plants fixate CO₂, and use ATP and NADPH to produce sugar molecules G3P, while regenerating RUBP to keep the cycle going. Option A. regeneration of ATP.
What is the Calvin cycle?
The Calvin cycle is the series of chemical reactions that occur during the light-independent phase of photosynthesis.
During the Calvin cycle, sugars or carbohydrates are synthesized.
Carbón dioxide -CO₂- enters the leaves through stomas, and diffuses to the chloroplast stroma. These molecules are used to produce 3-C sugars.
The whole process is impulsed by ATP and NADPH coming from light-dependent reactions.
1) During the carbon fixation phase, the CO₂ molecule combinates with a ribulose-1,5-bisphosphate (5-C molecule) to form 6-C molecules, which will divide into two 3-phosphoglycerate molecules, 3-PGA (3-C molecules).
CO₂ + ribulose-1,5-bisphosphate ⟶ 6-C molecule ⟶ 2 3-PGA
2) During the reduction phase, ATP and NADPH are used to produce the sugar molecule glyceraldehyde-3-phosphate (G3P) from 3-PGA molecules.
NADPH donates its electrons to turn 3-PGA into glyceraldehyde 3-phosphate, G3P.
3-PGA + ATP + NADPH ⟶ G3P + ADP + NADP⁺
3) During the regeneration phase,
- some glyceraldehyde 3-phosphate molecules leave the cycle and go to the cytosol to form glucose.
- Other G3P get recycled to regenerate the RuBP acceptor. This last reaction needs ATP and a series of other reactions.
When three CO₂ enter the cycle, 6 G3P are produced. One of them leaves the cycle, and the remaining five are recycled and generate three RuBP.
According to this framework, the only option that is not part of the Calvin cycle is regeneration of ATP. Option A.
You can learn more about the Calvin cycle at
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