Which statement best describes the relationship between light reactions and the Calvin cycle?

Which statement best describes the relationship between light reactions and the Calvin cycle?

• A. The light reactions generate ATP and NADPH, which the Calvin cycle uses to fix carbon.
• B. The Calvin cycle uses energy produced by respiration.
• C. Both reactions occur in the dark only.
• D. The light reactions fix carbon dioxide.

Answer: (A)

Energy flow in photosynthesis hinges on two connected stages. The light-dependent reactions capture light energy and convert it into chemical energy in the form of ATP and NADPH, while releasing oxygen from water. The Calvin cycle then uses that ATP as energy and NADPH as reducing power to fix carbon dioxide into organic molecules, ultimately forming sugars. In other words, the light reactions supply the energy carriers that drive carbon fixation in the Calvin cycle. The Calvin cycle doesn’t rely on respiration for its energy, it doesn’t occur only in the dark, and it is the Calvin cycle that fixes carbon, not the light reactions.

Energy flow in photosynthesis hinges on two connected stages. The light-dependent reactions capture light energy and convert it into chemical energy in the form of ATP and NADPH, while releasing oxygen from water. The Calvin cycle then uses that ATP as energy and NADPH as reducing power to fix carbon dioxide into organic molecules, ultimately forming sugars. In other words, the light reactions supply the energy carriers that drive carbon fixation in the Calvin cycle. The Calvin cycle doesn’t rely on respiration for its energy, it doesn’t occur only in the dark, and it is the Calvin cycle that fixes carbon, not the light reactions.