What does light do to make plants grow?

The light really doesn’t “do” anything. It’s the plant that does all the work! Plants make much of their own food using water and carbon dioxide, and they use the energy from the sunlight to combine the two. Many of their leaf cells have chloroplasts, which absorb energy from sunlight and use this energy to link together carbon, hydrogen, and oxygen molecules (in the water and the carbon dioxide) into carbohydrates and sugars. These chemical reactions are “sparked” by the energy they take in form light.