Glucose units are linked in a linear way with α(1→4) bonds. Branching takes place with α(1→6) bonds occurring every 24 to 30 glucose units.
Its counterpart in animals is glycogen which has the same composition and structure, but with more extensive branching that occurs every 8 to 12 glucose units.
Plants store starch within specialized organelles called amyloplasts. When energy is needed for cell work, the plant hydrolyzes the starch releasing the glucose subunits. Humans and other animals that eat plant foods also have enzymes to hydrolyze starch.
Starch is made of about 70% amylopectin. Amylopectin is highly branched, being formed of 2,000 to 200,000 glucose units. Its inner chains are formed of 20-24 glucose subunits.