Polysaccharides are vast chains of sugar units joined together. The chains should be branched or linear depending on the polysaccharide. In animals, excess glucose is stored as a vast branched polysaccharide called as glycogen, while in most plants the storage form of glucose is the polysaccharide called as starch. The Bacteria and yeasts store glucose as still another part of polysaccharide called as dextran. In every case these are nutritional reserves; when requires, they are broken down and the monosaccharide products are metabolized to yield energy. In compare, cellulose is a structural polysaccharide used to build plant cell walls.