Final answer:
Glycogen is stored primarily in the liver and skeletal muscle cells of animals. It serves as an important form of energy storage and is rapidly converted to glucose when needed, helping to maintain metabolic balance.
Step-by-step explanation:
Glycogen is the primary storage form of glucose in humans and other vertebrates. This polysaccharide is analogous to starch in plants and is significantly concentrated in the liver and skeletal muscle cells. In the liver, it constitutes about 4% to 8% by weight, serving as a critical buffer to maintain blood glucose levels, while in muscles, it ranges from 0.5% to 1.0%, mainly used as an energy source during muscle contractions.
The process of converting glycogen back into glucose when the body needs energy is termed glycogenolysis. As an energy reserve, glycogen is readily mobilized to provide glucose during periods of fasting or increased physical activity, ensuring the maintenance of metabolic balance. Therefore, liver and muscle tissues are the main sites where animals, including humans, store excess energy as glycogen.