Here's why:

* Photosynthesis is the process where plants use sunlight, water, and carbon dioxide to create their own food (glucose) and release oxygen as a waste product.

* The chemical equation for photosynthesis is:

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

* This shows that carbon dioxide and water are used, glucose and oxygen are produced, and light energy is needed for the reaction.

So, while the main product of photosynthesis is glucose, the byproduct that is released into the atmosphere is oxygen. This oxygen is essential for the survival of most living organisms on Earth, including humans.