Although not as concentrated a fuel as fats, sugars are the most important source of energy for many cells. Starches are polysaccharides. Polysaccharides Starches Starches are polymers of glucose. The total number of glucose residues in a molecule of amylopectin is several thousand. Starches are insoluble in water and thus can serve as storage depots of glucose.
Plants convert excess glucose into starch for storage.
Rice, wheat, and corn are also major sources of starch in the human diet. The hydrolysis of starch is done by amylases. Animals store excess glucose by polymerizing it to form glycogen . The structure of glycogen is similar to that of amylopectin, although the branches in glycogen tend to be shorter and more frequent. Glycogen is digested back into glucose when energy is needed.