In the light reactions of photosynthesis, what is the primary function of NADP$+$?

• A. It splits water molecules to release $O_2$ and protons for the proton gradient.
• B. It acts as the terminal electron acceptor, becoming NADPH to carry high-energy electrons to the Calvin cycle.
• C. It directly generates ATP by transferring a phosphate group to ADP in the thylakoid lumen.
• D. It donates electrons to photosystem II to replace those lost from chlorophyll.

Answer: (B)

Verified step by step guidance

1. Understand the context: The light reactions of photosynthesis occur in the thylakoid membranes of chloroplasts and involve the conversion of light energy into chemical energy.
2. Identify the role of NADP\+ in these reactions: NADP\+ is a coenzyme that participates in redox reactions by accepting electrons.
3. Recognize that during the light reactions, electrons are excited by light energy and passed through an electron transport chain, eventually reaching NADP\+.
4. Know that NADP\+ accepts these high-energy electrons (along with a proton) to form NADPH, which is a carrier molecule that transports these electrons to the Calvin cycle for use in carbon fixation.
5. Conclude that the primary function of NADP\+ is to act as the terminal electron acceptor, becoming NADPH to carry high-energy electrons to the Calvin cycle.