Long, chain-like molecules formed of glucose units.

Starch and cellulose are two very similar polysaccharides. There are only two small chemical differences between the compounds: 1.) The glucose units of the polysaccharide chain are connected in a slightly different way. Starch molecules therefore form wide helices, whereas cellulose forms linearly extended chains. 2.) In contrast to linear cellulose molecules, the main part of starch consists of branched amylopectin, and contains only a small percentage of linear amylose (20-30%). Because of these differences, starch and cellulose have different properties and are used for different aims by living organisms. Starch is a typical plant storage compound for chemical energy, cellulose serves as one major constituent of plant cell walls.