Where do lost electrons from photosystem II get replaced?

The lost electrons from photosystem II are replaced by electrons derived from water molecules during the process of photolysis. When light energy is absorbed by photosystem II, it energizes electrons in the pigments of the photosystem, allowing them to be transferred to the electron transport chain. This process results in the loss of electrons from photosystem II, necessitating a replacement source to ensure the continuity of the light-dependent reactions of photosynthesis.

Water serves as the crucial source for replacing these lost electrons. The splitting of water molecules, which occurs in a process termed photolysis, generates oxygen gas as a byproduct and releases electrons that are utilized to replenish those lost from photosystem II. This mechanism not only provides the necessary electrons but also contributes to the overall production of ATP and NADPH, which are essential for the light-independent reactions (Calvin cycle) thereafter.

In contrast, NADP+ is involved in accepting electrons at a later stage, after they have moved through the electron transport chain, and ATP is generated during the light-dependent reactions but does not replace lost electrons. Electrons from photosystem I are associated with a different part of the photosynthetic pathway and do not contribute to replacing those lost in photosystem II. Thus, the role