Carbohydrates
Carbohydrates, a class of chemical compounds that are composed of carbon, hydrogen, and oxygen. Carbohydrates are essential for the growth of plants, and provide energy for animals.
Plants make carbohydrates from carbon dioxide and water in the process called photosynthesis. Animals obtain carbohydrates mostly by eating foods derived from plants.
Carbohydrates are classified according to the relative complexity and size of their molecules. Simple carbohydrates consist of such sugars as glucose and fructose; complex carbohydrates include starch and some forms of dietary fiber, such as cellulose.