During the Calvin cycle, which step involves the reduction of 3-phosphoglycerate to glyceraldehyde-3-phosphate?

During the Calvin cycle, which step involves the reduction of 3-phosphoglycerate to glyceraldehyde-3-phosphate?

• A. Reduction phase.
• B. Carboxylation phase.
• C. RuBP regeneration phase.
• D. Photorespiration phase.

Answer: (A)

The step being tested is the reduction phase. After carbon dioxide is fixed by RuBP to form 3-phosphoglycerate, these molecules are converted into glyceraldehyde-3-phosphate through a reduction that uses NADPH as the electron donor and ATP to supply the energy for phosphorylation. This reduction transforms the molecules into a form (G3P) that can be used to synthesize sugars or to rebuild RuBP in the cycle. The carboxylation phase is where CO2 is attached to RuBP, not reduced, and the RuBP regeneration phase rebuilds RuBP from G3P using ATP. Photorespiration is a separate process that can waste fixed carbon and isn’t the reduction step producing G3P.

The step being tested is the reduction phase. After carbon dioxide is fixed by RuBP to form 3-phosphoglycerate, these molecules are converted into glyceraldehyde-3-phosphate through a reduction that uses NADPH as the electron donor and ATP to supply the energy for phosphorylation. This reduction transforms the molecules into a form (G3P) that can be used to synthesize sugars or to rebuild RuBP in the cycle. The carboxylation phase is where CO2 is attached to RuBP, not reduced, and the RuBP regeneration phase rebuilds RuBP from G3P using ATP. Photorespiration is a separate process that can waste fixed carbon and isn’t the reduction step producing G3P.