Which energy-rich molecules are produced by the light reactions and used by the Calvin Cycle?

• A. ATP and NADPH
• B. NADPH and FADH2
• C. Oxygen and ATP
• D. Glucose and NADPH

Answer: (A)

Energy-rich molecules produced by the light reactions and used by the Calvin Cycle are ATP and NADPH. In the light reactions, light energy drives the production of ATP through photophosphorylation and NADPH by transferring electrons to NADP+. These carriers then power the Calvin Cycle in the stroma, with ATP supplying the energy to drive the carbon-fixation and sugar-synthesis steps and NADPH providing the reducing power to convert carbon dioxide into carbohydrate. For each CO2 fixed, the cycle consumes ATP and NADPH to build sugars. The other options don’t fit because FADH2 is not part of the photosynthetic electron transport, oxygen is released as a byproduct rather than used by the Calvin Cycle, and glucose is produced only after multiple turns of the cycle, not directly by the light reactions.