In photosynthesis, which compound serves as the electron acceptor?

In photosynthesis, the compound that serves as the electron acceptor is NADPH. During the light-dependent reactions of photosynthesis, light energy is absorbed by chlorophyll, leading to the excitation of electrons. These high-energy electrons are then transferred through a series of proteins known as the electron transport chain.

As the electrons move through this chain, they lose energy, which is utilized to pump protons into the thylakoid lumen, creating a gradient used by ATP synthase to produce ATP. At the end of the electron transport chain, the electrons are transferred to NADP+, the oxidized form of NADPH. This process of accepting electrons reduces NADP+ to NADPH, which then carries the electrons to the Calvin cycle, where they play a crucial role in synthesizing glucose and other carbohydrates.

This makes NADPH an essential molecule in photosynthesis as it not only accepts electrons but also provides the reducing power needed for the synthesis of organic compounds from carbon dioxide during the dark reactions, or Calvin cycle. The other compounds listed—ATP, oxygen, and carbon dioxide—play different roles in photosynthesis but do not serve as electron acceptors in the way NADPH does.