Which molecule serves as a primary component of fungal cell walls?

Chitin is the primary component of fungal cell walls, providing structural integrity and rigidity. It is a polysaccharide similar to cellulose but contains nitrogen, which differentiates it from the cellulose found in plant cell walls. Chitin's unique molecular structure allows fungi to maintain their shape and protect themselves from environmental stresses and pathogens.

In contrast, cellulose primarily makes up the cell walls of plants and is not found in fungi. Keratin, a fibrous protein, is a key structural component in animal tissues like skin, hair, and nails but is not related to fungal cell structure. Lignin is a complex organic polymer found in the cell walls of plants, contributing to their rigidity and resistance to decay, but again, it is not a component of fungal cell walls. Thus, chitin is specific to fungi, making it the correct answer in the context of the composition of fungal cell walls.