Cellulose and glycogen are both types of carbohydrates, but they serve distinct functions in different organisms. Cellulose is a structural polysaccharide primarily found in plants, while glycogen functions as an energy storage polysaccharide in animals.

Cellulose is a complex carbohydrate, or polysaccharide, that serves as a fundamental structural component in plants. It is predominantly located in the cell walls of green plants, providing them with rigidity and strength. The structure of cellulose is linear, consisting of glucose monomers linked together by β-1,4-glycosidic bonds. This specific type of bond renders cellulose indigestible for most animals, with the exception of certain species, such as cows and termites, which harbor symbiotic bacteria in their digestive systems that can break down these bonds.

In contrast, glycogen is the primary form of carbohydrate storage in animals and fungi. It is mainly stored in the liver and muscle tissues, where it can be rapidly mobilized to meet the body’s energy demands. Glycogen has a branched structure, with glucose units linked by α-1,4-glycosidic bonds, along with branching points formed by α-1,6-glycosidic bonds. This configuration enables the quick release of glucose when energy is required.

Regarding their chemical structure, both cellulose and glycogen are polymers composed of glucose units; however, the types of linkages between these units differ significantly. In cellulose, the glucose units are alternately flipped relative to each other, resulting in a straight, rigid structure. Conversely, in glycogen, all glucose units are aligned in the same direction, yielding a more flexible and branched configuration.

In summary, while cellulose and glycogen are both carbohydrates made up of glucose units, they differ markedly in their structure, function, and localization. Cellulose acts as a structural element in plants, whereas glycogen serves as an energy reserve in animals and fungi.