Chitin is a long-chain polymer of N-acetylglucosamine, which is a derivative of glucose, and it serves as a structural component in the cell walls of fungi and the exoskeletons of arthropods like insects and crustaceans. This polysaccharide is a crucial biopolymer that contributes to the rigidity and strength of these organisms, linking it closely to the study of complex carbohydrates and their biological significance.