The elements found in carbohydrates are oxygen, hydrogen and carbon. Carbohydrates comprise one of the four essential biomolecules of living organisms, and provide the main source of biological fuels that drive cellular respiration.
Carbohydrates are generally classified into three main groups: monosaccharides, dissacharides and polysaccharides. Monosaccharides are the simplest form of carbohydrates, consisting of only one sugar molecule called a monomer. The elements carbon, hydrogen and oxygen form a 1:2:1 ratio, respectively, in a single monomer. Glucose, which is the primary molecule of cellular respiration, is an example of a monosaccharide. Dissaccharides are produced from the combination of two monosaccharides; examples include maltose and lactose. Polysaccharides are complex molecules built from a long string of sugar monomers. Some examples include starch, cellulose and pectin.