When the food made of carbohydrates is broken in the organism, it creates glucose, which is a type of sugar that the body uses as a form of energy. The amount that is not used gets stored in various tissues of the body, but the places where the glycogen is stored in larger amounts are the liver and skeletal muscle.
Glucose is used primarily as a source of energy and as such it has to go inside the cell. Excess glucose that is not immediately needed as a source of energy is combined into long strands of clucose units called glycogen and it is stored in the liver and skeletal muscle tissue. Glycogen is later broken dowin into its constituent glucose units and used as a source of energy when needed.
The advantage of small cell size is that substances like organic molecules and ions can diffuse easily into the cells whereas wastes can diffuse easily out of the cells.