Final answer:
The oxygen released during photosynthesis comes from the process of water molecules being split during the photosynthetic reaction, facilitated by chlorophyll in plants and certain microbes.
Step-by-step explanation:
The oxygen released by plants during photosynthesis comes from the splitting of water molecules (H2O). In this process, light energy absorbed by chlorophyll triggers a series of redox reactions, leading to the conversion of water into oxygen. The chemical equation representing photosynthesis, which summarizes this process, is:
6CO2 + 6H2O → C6H12O6 + 6O2
This equation shows that six molecules of carbon dioxide (CO2) and six molecules of water (H2O) produce one molecule of glucose (C6H12O6) and six molecules of oxygen (O2), which are released as a byproduct.
Animals and humans rely on this oxygen for breathing, and without the photosynthetic organisms like plants and certain microbes, there would not be enough oxygen in the atmosphere. The byproduct of photosynthesis is thus vital for the sustenance of aerobic life on Earth.