They are different by the way they are made up. They are each composed of different isomers. Cellulose is exclusively a plant product. Glycogen is nicknamed "animal starch" and is found in the liver...
No!
Polypeptides are polymers of amino acids, joined by peptide bonds. They are the constituents of proteins.
Starch, glycogen and cellulose are polysaccharides, which are polymers of simple sugars...