What is the overall flow of electrons in the light reactions?

What is the overall flow of electrons in the light reactions?

• A. The flow is from water to NADPH.
• B. The flow is from NADPH to water.
• C. The flow is from oxygen to water.
• D. The flow is from NADPH to ATP.

Answer: (A)

In the light reactions, electrons start from water, which is split by the oxygen-evolving complex in photosystem II. This releases electrons, protons, and oxygen as a byproduct. The electrons travel through an electron transport chain from photosystem II to plastoquinone, then to the cytochrome b6f complex, to plastocyanin, and finally to photosystem I. From there they are transferred to ferredoxin and then to NADP+ reductase, which reduces NADP+ to NADPH. As electrons move along the chain, their energy pumps protons across the thylakoid membrane to build a gradient that powers ATP synthase, producing ATP. The produced NADPH and ATP provide the reducing power and energy for the Calvin cycle.

In the light reactions, electrons start from water, which is split by the oxygen-evolving complex in photosystem II. This releases electrons, protons, and oxygen as a byproduct. The electrons travel through an electron transport chain from photosystem II to plastoquinone, then to the cytochrome b6f complex, to plastocyanin, and finally to photosystem I. From there they are transferred to ferredoxin and then to NADP+ reductase, which reduces NADP+ to NADPH. As electrons move along the chain, their energy pumps protons across the thylakoid membrane to build a gradient that powers ATP synthase, producing ATP. The produced NADPH and ATP provide the reducing power and energy for the Calvin cycle.