What is glycogen? How is it different from starch?

The carbohydrates are stored in animal body as glycogen. It is also called animal starch and its structure is similar toamylopectin which means that it is a branched chain polymer of a-D-glucose units in which the chain is formed by ${\mathrm{C}}_1-{\mathrm{C}}_4$ glycosidic linkage whereas branching occurs by the formation of ${\mathrm{C}}_1-$ ${\mathrm{C}}_6$ glycosidic linkage. One main difference between glycogen and amylopectin is the length of the chain. In amylopectin, the chain consists of $20-25a-D$ - glucose molecules whereas in glycogen, there are $10-14$ molecules of $a$ - $D$ - glucose present. Glycogen is more branched than amylopectin. It is present mainly in liver, muscles and also in brain. Glycogen gets converted into glucose when the body needs it with the help of certain enzymes present in the body. Glycogen has also been found to be present in yeast and fungi.
Starch is a major source of carbohydrates which are very much essential to the human body since they supply energy to the body. It occurs as granules mainly in seeds, fruits, tubers and also in the roots of the plants. The chief commercial sources of starch are wheat, maize, rice, potatoes etc.