A term applied to a group of substances which include the sugars, starches, and cellulose, along with many other related substances. This group of compounds is vital in the lives of plants and animals, both as structural elements and in the maintenance of functional activity. Plants are unique in that they have the power to synthesize carbohydrates from carbon dioxide and water in the presence of the green pigment chlorophyll through the energy derived from sunlight, by the process of photosynthesis. This process is responsible not only for the existence of plants but for the maintenance of animal life as well, since animals obtain their entire food supply directly or indirectly from the carbohydrates of plants.