Which molecule is known as a polysaccharide that can be used as an energy source in animals?

Glycogen is a polysaccharide that serves as a key energy source for animals. It is composed of numerous glucose units linked together and functions as the primary storage form of glucose in animal cells, especially in the liver and muscle tissue. When energy is needed, glycogen can be rapidly broken down into glucose monomers through a process called glycogenolysis, providing a readily available source of energy for metabolic activities.

In contrast, starch, while also a polysaccharide and an energy source, is primarily utilized by plants, and animals do not store starch for their energy needs. Cellulose, another polysaccharide, is a structural component of plant cell walls and is not digestible by humans and most animals, which means it cannot be used as an energy source. Sucrose is a disaccharide composed of glucose and fructose, and while it can be used for energy, it does not qualify as a polysaccharide since it consists of only two sugar units.