Chitin is primarily made up of which monomer?

Chitin is primarily composed of N-acetyl-ß-D-glucosamine, which is a derivative of glucose. It is a polymer that features repeating units of this specific amino sugar, linked together by beta-1,4-glycosidic bonds. The presence of the N-acetyl group distinguishes chitin from cellulose, which consists solely of glucose units. This structural characteristic contributes to the unique physical properties of chitin, making it a vital component in the exoskeletons of arthropods and the cell walls of fungi.

The other choices represent polysaccharides or sugars that do not specifically relate to the composition of chitin. For instance, alpha-D-glucose is the precursor unit for starch and glycogen but does not form chitin. Cellulose consists of linear chains of glucose units, and glycogen is a branched polysaccharide made of glucose as well, but neither are related in structure or function to chitin. Thus, the correct answer reflects the specific monomeric building block that constitutes chitin.