* Oxidation is the loss of electrons.

* Reduction is the gain of electrons.

In photosynthesis, water molecules are split, and the electrons from the oxygen atoms are transferred to carbon dioxide to create glucose.

Here's the simplified equation for photosynthesis:

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂

* H₂O (water) is the source of electrons.

* CO₂ (carbon dioxide) gains the electrons.

* O₂ (oxygen) is produced as a byproduct.

Since water loses electrons (it's oxidized), it is considered the electron donor in photosynthesis.