Q. Photosynthesis is the most significant producer of molecular oxygen (O2) on our planet. From which molecule do oxygen atoms liberated by photosynthesis come and from which other molecule could one suspect they have come and what are the destinations of those oxygen atoms?
The oxygen atoms liberated as molecular oxygen by the photosynthesis procedure come from water.
One certainly could suspect that those oxygen atoms would have come from carbon dioxide. Oxygen atoms from carbon dioxide however are incorporated into water molecules and into glucose molecules liberated in the chemical stage of photosynthesis.