During the light reactions, photosystem I functions to_________, and photosystem II functions to __________.

• A. Reduce CO₂; oxidize NADPH
• B. Synthesize ATP; Produce O₂.
• C. Produce O₂; oxidize NADPH.
• D. Reduce NADP⁺; oxidize H₂O.

Answer: (D)

Verified step by step guidance

1. Understand the role of photosystems in the light reactions of photosynthesis. Photosystem I and Photosystem II are integral components of the thylakoid membranes in chloroplasts.
2. Photosystem II is the first complex in the light-dependent reactions. It absorbs light energy, which excites electrons and initiates the process of water splitting (photolysis). This results in the oxidation of water (H2O), releasing oxygen (O2) and providing electrons.
3. Photosystem I follows Photosystem II in the electron transport chain. It absorbs light energy to further excite electrons, which are then used to reduce NADP+ to NADPH. This is crucial for the Calvin cycle, where NADPH acts as a reducing agent.
4. Recognize that the primary function of Photosystem II is to oxidize water, releasing oxygen and providing electrons for the electron transport chain.
5. Identify that the primary function of Photosystem I is to reduce NADP+ to NADPH, which is essential for the subsequent stages of photosynthesis, particularly the Calvin cycle.