Here's why:

* Oxidation is the loss of electrons.

* During photosynthesis, water molecules are split apart in the light-dependent reactions.

* The electrons from water are transferred to the electron transport chain, where they are used to generate ATP (energy) and NADPH (a reducing agent).

* The splitting of water also releases oxygen (O₂) as a byproduct.

So, in summary:

* Water (H₂O) is oxidized (loses electrons).

* Carbon dioxide (CO₂) is reduced (gains electrons).

This process allows plants to convert light energy into chemical energy stored in glucose, which is the primary energy source for most living organisms.