Polysaccharides, which include starch and cellulose, are sugar polymers, or molecules composed of numerous individual sugar units, as many as several thousand. Usually only one or a very few kinds of sugars are found in a given polysaccharide. Polysaccharides are classified according to the overall characteristics of the large molecules: a general size range, an average composition, and a common set of properties. Like the sugars of which they’re composed, polysaccharides contain many exposed oxygen and hydrogen atoms, so they can form hydrogen bonds and absorb water. However, they may or may not dissolve in water, depending on the attractive forces among the polymers themselves.