Sugars and their polymers such as starches and cellulose belong to the class of organic chemicals known as carbohydrates. Carbohydrates contain carbon, hydrogen and oxygen in a ratio of approximately 1:2:1 (CH20). The simplest carbohydrates are monosaccharides (single or simple sugars). Disaccharides are double sugars, consisting of two simple sugars joined by condensation synthesis. Polysaccharides are polymers of many sugars. Starch, glycogen and cellulose are long chain polysaccharides that differ in the kind of linkage between glucose molecules.