Which statement describes the reduction step of the Calvin cycle?

• A. 3-PGA is oxidized to G3P
• B. 3-PGA reduced to G3P
• C. 3-PGA phosphorylated to G3P
• D. 3-PGA hydrolyzed to G3P

Answer: (B)

In the Calvin cycle, the reduction step is where 3-phosphoglycerate (3-PGA) gains electrons to become glyceraldehyde-3-phosphate (G3P). This redox change is powered by NADPH, with ATP providing the energy earlier in the sequence to activate the 3-PGA substrate (through phosphorylation to a higher-energy intermediate) before the reduction occurs. So the essential idea is that 3-PGA is reduced to G3P, not oxidized, not directly phosphorylated to G3P, and not hydrolyzed. This is why describing the step as 3-PGA being reduced to G3P is the correct statement.