The building blocks of carbohydrates are simple sugars, also known as monosaccharides. Monosaccharides are the basic units that make up larger carbohydrate molecules. The most common monosaccharides include glucose, fructose, and galactose. These monosaccharides can combine to form disaccharides such as sucrose and lactose, and polysaccharides such as starch and cellulose. The combination and arrangement of monosaccharides determine the type and function of the larger carbohydrate molecule.