DENDROLOGY

Detailed explanation-1: -After a photon hits the photosystem II (PSII) reaction center, energy from sunlight is used to extract electrons from water. The electrons travel through the chloroplast electron transport chain to photosystem I (PSI), which reduces NADP+ to NADPH (Figure 3).

Detailed explanation-2: -ATP synthase in thylakoids generates ATP using the proton gradient. Excited electrons from Photosystem I are used to reduce NADP.

Detailed explanation-3: -Photosystem I, however, does not act as a proton pump; instead, it uses these high-energy electrons to reduce NADP+ to NADPH. The reaction center chlorophyll of photosystem I transfers its excited electrons through a series of carriers to ferrodoxin, a small protein on the stromal side of the thylakoid membrane.

Detailed explanation-4: -Thus, whole-chain photosynthetic electron transport uses the energy of sunlight to oxidize low energy water, and reduce high-energy NADPH.