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.