Here's how it works:

* Light-dependent reactions: Sunlight is absorbed by chlorophyll in the chloroplasts of plant cells. This energy excites electrons in the chlorophyll molecules.

* Water splitting: The energized electrons from chlorophyll are used to split water molecules. This process, called photolysis, releases oxygen (O₂) as a byproduct and generates hydrogen ions (H+) and electrons (e-).

* Electron transport chain: The electrons released from water are passed along a series of electron carriers in the thylakoid membrane of chloroplasts. This process releases energy that is used to generate ATP (adenosine triphosphate), the cell's energy currency.

* NADPH formation: The electrons are ultimately used to reduce NADP+ to NADPH, another important energy carrier used in the light-independent reactions of photosynthesis.

So, in summary, water provides the electrons that drive the entire process of photosynthesis.