Carbohydrates are made up of carbon, hydrogen, and oxygen. The simplest carbohydrates are monosaccharides, which have the general formula (CH2O)n. Monosaccharides include glucose, fructose, and galactose. More complex carbohydrates are polysaccharides, which are made up of long chains of monosaccharides. Polysaccharides include starch, cellulose, and glycogen.