Two glucose units form maltose, a glucose and a fructose produce sucrose (table sugar), a glucose and galactose form lactose (milk sugar). Continued combining to form a long chain produces a polysaccharide. Polysaccharides include starch and glycogen which are used as stored fuel in plants and animals respectively. The difference between starch and glycogen is the amount of branching with glycogen being the most highly branched. Cellulose also consists of glucose units but the linkage differs from that in starch and glycogen and cannot be digested by most animals. For humans cellulose is indigestible fiber, an important component of our diet, but not used for food. Only microorganisms have the necessary enzymes. Termites and other animals that eat wood, grass and the like have the microorganisms in their guts which perform the digestive process known as hydrolysis.