Here's why:

* Photosynthesis is the process plants use to convert light energy into chemical energy (in the form of sugars).

* This process requires water and carbon dioxide as inputs, and releases oxygen as a byproduct.

The chemical equation for photosynthesis summarizes this:

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

* CO₂: Carbon dioxide

* H₂O: Water

* light energy: Energy from sunlight

* C₆H₁₂O₆: Glucose (a sugar)

* O₂: Oxygen