Which of the following is directly associated with Photosystem I during the light reactions of photosynthesis?

• A. Pumping of protons into the thylakoid lumen
• B. Reduction of NADP\(^+\) to NADPH
• C. Photolysis of water to release oxygen
• D. Generation of ATP via ATP synthase

Answer: (B)

Verified step by step guidance

1. Understand the role of Photosystem I in the light reactions of photosynthesis. Photosystem I is primarily involved in the reduction of NADP\(^+\) to NADPH, which is a key step in the light-dependent reactions.
2. Recall that Photosystem I absorbs light energy to excite electrons, which are then transferred through a series of proteins in the electron transport chain.
3. Recognize that the reduction of NADP\(^+\) to NADPH occurs when the high-energy electrons from Photosystem I are passed to NADP\(^+\) via the enzyme ferredoxin-NADP\(^+\) reductase.
4. Differentiate the functions of Photosystem I from other processes in the light reactions, such as the photolysis of water (associated with Photosystem II) and the generation of ATP via ATP synthase (driven by the proton gradient created by the electron transport chain).
5. Conclude that the correct association with Photosystem I is the reduction of NADP\(^+\) to NADPH, as this is its primary function during the light reactions of photosynthesis.