What is the function of photosystem I in noncyclic photosynthesis?

What is the function of photosystem I in noncyclic photosynthesis?

• A. Photosystem I reduces NADP+.
• B. Photosystem I splits water.
• C. Photosystem I captures carbon dioxide.
• D. Photosystem I pumps protons to generate ATP directly.

Answer: (A)

Photosystem I's job in noncyclic photosynthesis is to use light energy to re-energize electrons and transfer them to NADP+, forming NADPH. This NADPH provides the reducing power needed to convert carbon dioxide into sugars in the Calvin cycle. It doesn’t split water (that’s done by Photosystem II), it doesn’t fix CO2 directly (that happens in the Calvin cycle with ATP and NADPH), and it doesn’t pump protons to make ATP directly (ATP comes from the proton gradient built up mainly by the earlier steps and then used by ATP synthase). So reducing NADP+ to NADPH is the key function of Photosystem I here.

Photosystem I's job in noncyclic photosynthesis is to use light energy to re-energize electrons and transfer them to NADP+, forming NADPH. This NADPH provides the reducing power needed to convert carbon dioxide into sugars in the Calvin cycle. It doesn’t split water (that’s done by Photosystem II), it doesn’t fix CO2 directly (that happens in the Calvin cycle with ATP and NADPH), and it doesn’t pump protons to make ATP directly (ATP comes from the proton gradient built up mainly by the earlier steps and then used by ATP synthase). So reducing NADP+ to NADPH is the key function of Photosystem I here.