A polysaccharide is a type of carbohydrate made up of long chains of monosaccharide units linked together by glycosidic bonds. These complex carbohydrates serve various functions, including energy storage (e.g., starch in plants and glycogen in animals) and structural roles (e.g., cellulose in plant cell walls and chitin in fungal cell walls). Polysaccharides play crucial roles in living organisms and contribute to overall metabolic processes.