Carbohydrates (a basic class of substance in biochemistry) are a primary means in organisms of storing or consuming energy. In autotrophs, such as plants, food is converted in to starch for compressed storage. In heterotrophs such as animals they have a use as metabolic fuel.
Typically carbohydrates are split in to the sweet sugars: monosaccharides, disaccharides and the unsweet starchy polysaccharides. Monosaccharides are simple, crystalline sugars. Disaccharides are made by joining two monosaccharides together (hence di-saccharides). Polysaccharides are very large molecules such as starch or glycogen which are formed by many monosaccharides joining together (poly-saccharides).
Carbohydrates consist almost exclusively of just three elements: carbon, hydrogen, and oxygen. The ratio vary, but not much. Usually amount of carbon is the same or slightly greater than amount of oxygen, and amount of hydrogen is twice or slightly greater than amount of oxygen. Traditional general structure of carbohydrates is CxH2yOy, but many important carbohydrates, like deoxyribose C5O4H10 have more hydrogen.
The structural components of plants are primarily composed of carbohydrates.
Some important carbohydrates are: