In photosynthesis, the energy stored as ATP and NADPH as a result of light-dependent reactions is later used in which process?

• A. The Calvin cycle.
• B. Fermentation.
• C. Glycolysis in the cytoplasm.
• D. Oxidative phosphorylation.

Answer: (A)

The energy carriers ATP and NADPH produced during the light-dependent reactions power carbon fixation and sugar synthesis in the Calvin cycle. In the Calvin cycle, ATP provides the chemical energy to drive the phosphorylation steps, while NADPH supplies reducing power to convert the fixed carbon into glyceraldehyde-3-phosphate and other sugars. This process happens in the chloroplast stroma and ultimately builds carbohydrate molecules from carbon dioxide using the energy captured from light.

Other processes listed are part of cellular respiration or fermentation and rely on different carriers (like NADH or FADH2) and different steps. They don’t use the ATP and NADPH generated by the light reactions to fix carbon, so they aren’t driven by the energy stored during photosynthesis in the way the Calvin cycle is.