If you think back to your middle school science classes, you might remember learning about chlorophyll. Chlorophyll is what makes plants green, but its purpose is not merely aesthetic.
Chlorophyll is the substance in plants that is responsible for absorbing sunlight. It draws in and stores sunlight, and this stored sunlight energy combines carbon dioxide from the air and water from the soil and atmosphere to foster growth and development. The entire process is known as photosynthesis.