Which carbohydrate is used for energy storage in animals?

Glycogen is the carbohydrate that serves as the primary energy storage form in animals. It is a polysaccharide, composed of numerous glucose units linked together. The structure of glycogen allows it to be quickly mobilized when the body requires energy, particularly during intense physical activity or when blood glucose levels drop. Glycogen is stored mainly in the liver and muscle tissues.

In contrast, starch is primarily used by plants for energy storage, while fructose is a simple sugar found in fruits and serves as an energy source rather than a storage form. Cellulose, another polysaccharide, is a structural component found in plant cell walls and is not used for energy storage in animals. Therefore, glycogen is the correct answer, as it directly fulfills the role of energy storage in the animal kingdom.