Monosaccharides are carbohydrates made up of a single sugar unit. Examples of monosaccharides are fructose, glucose, ribose or glactose. Monosaccharides are used to make more complex sugars such as disaccharides or polysaccharides. Monosaccharides are made up of the elements carbon, hydrogen and oxygen. Monosaccharides are classified by how many carbon atoms they have. For example, glucose has 6 carbon atoms (C6H12O6) and therefore is a hexose monosaccharide.