Here's how it works:
* During the light-dependent reactions of photosynthesis, light energy is used to split water molecules.
* This process, called photolysis, releases electrons, hydrogen ions (H+), and oxygen gas (O₂).
* The oxygen gas is released as a byproduct of photosynthesis and is what we breathe.
So, while carbon dioxide is the source of carbon in glucose, it's water that provides the oxygen.
