Which of the following statements about photosynthesis is false?

• A. The Calvin cycle directly produces ATP by photophosphorylation in photosystem II.
• B. In oxygenic photosynthesis, $O_2$ is produced from the splitting of $H_{2}O$ during the light reactions.
• C. The light reactions occur in the thylakoid membranes and generate a proton gradient used to synthesize ATP.
• D. The Calvin cycle uses ATP and NADPH to reduce $C_{\mathrm{O}}2$ and produce carbohydrate.

Answer: (A)

Verified step by step guidance

1. Review the process of photosynthesis, which consists of two main stages: the light reactions and the Calvin cycle (also called the dark reactions).
2. Understand that the light reactions occur in the thylakoid membranes where light energy is used to split water (H\_2O), producing oxygen (O\_2), and to generate ATP and NADPH through photophosphorylation.
3. Recognize that photophosphorylation, the process of producing ATP using light energy, happens during the light reactions and is associated with photosystem II and photosystem I, but ATP is not produced directly by the Calvin cycle.
4. Recall that the Calvin cycle takes place in the stroma of the chloroplast and uses the ATP and NADPH generated by the light reactions to fix carbon dioxide (CO\_2) into carbohydrates.
5. Identify the false statement by noting that the Calvin cycle does not directly produce ATP by photophosphorylation; instead, it consumes ATP produced during the light reactions.