Photosynthesis.

http://en.wikipedia.org/wiki/Photosynthesis

                         Photosynthesis can be represented using a chemical equation.

The overall balanced equation is...

6CO₂ + 6H₂O ------> C₆H₁₂O₆ + 6O_{2
^{Sunlight energy}}

Where: CO₂ = carbon dioxide H₂O = water
Light energy is required
C₆H₁₂O₆ = glucose
O₂ = oxygen