Which carbohydrate is typically defined by having both structural and energy storage functions?

The carbohydrate recognized for having both structural and energy storage functions is glycogen. Glycogen serves as a significant energy reserve in animals, functioning similarly to starch in plants by storing glucose for energy. This polysaccharide is primarily found in the liver and muscle tissues, where it can be quickly mobilized to meet energy demands during physical activity or fasting.

In terms of structure, glycogen has a branched structure that allows for rapid release of glucose molecules when they are needed. This capability is essential for maintaining blood sugar levels and providing energy in a form that can be easily accessed.

While starch does serve a similar role in energy storage for plants, it lacks the structural versatility that glycogen possesses in animal systems. Other carbohydrates like cellulose and chitin are more focused on structural roles; cellulose is a key component of plant cell walls, providing rigidity, while chitin is an essential structural component in the exoskeletons of arthropods and the cell walls of fungi. Neither cellulose nor chitin has a primary function in energy storage, distinguishing glycogen as the correct choice.