Amylose is a glucose polymer with long chain-like molecules, while amylopectin consists of larger highly branched molecules (1 to 6). Glycogen consists of even more branches than amylopectin. Amylose and amylopectin are classified as starch, and are found in plants, while glycogen serves as the main energy reserve for animals.
Starch serves as one of the key sources of carbohydrates in the human diet. Roughly 50 percent of the human carbohydrate intake comes from it. Starch occurs most often in grains, seeds and tubers. Starch can be divided into two groups, amylose and amylopectin, and each offers slightly different properties. When dissolved in hot water, amylose forms a colloidal suspension, while amylopectin is insoluble. Amylopectin comprises nearly 80 percent of starch.
Glycogen can be found in almost every mammalian cell but occurs in higher concentration within the liver and muscle. Although glycogen is structurally similar to amylopectin, as both are polysaccharides, it has more branches and these branches are shorter.
The iodine test is sometimes used to determine the presence of starch or glycogen. Glycogen gives of a reddish brown color when treated with iodine, while starch turns blue-black. The blue color is caused by the presence of amylose. Starch consisting of only amylopectin will stay either yellow or turn orange.