Amylopectin is a highly branched polymer of glucose found in plants. It is one of the two components of starch, the other being amylose. It is soluble in water.
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 by weight. Amylopectin is highly branched, being formed of 2,000 to 200,000 glucose units. Its inner chains are formed of 20-24 glucose subunits.