ATP and NADPH produced by the light reactions are used in which process?

• A. Glycolysis in the cytosol.
• B. The Calvin cycle to produce glucose.
• C. The citric acid cycle.
• D. The oxidation of NADPH to NADP+

Answer: (B)

ATP and NADPH from the light reactions power the Calvin cycle, where CO2 is fixed and reduced to carbohydrate. In the chloroplast stroma, ATP provides the energy to drive the steps that convert CO2 into sugar, while NADPH donates the electrons needed to reduce carbon intermediates toward glyceraldehyde-3-phosphate, which is eventually used to synthesize glucose. This use of energy and reducing power is specific to the Calvin cycle among the options. Glycolysis occurs in the cytosol and relies on ATP and NADH, not NADPH, and the citric acid cycle in mitochondria uses NADH and FADH2 rather than NADPH. Oxidation of NADPH to NADP+ would remove the reducing power needed to build carbohydrate. So the Calvin cycle is the process that uses light-reaction products to produce glucose.