Final answer:
The major component of fungal cell walls and arthropod exoskeletons is chitin, a nitrogen-containing polysaccharide that provides strength and protection, distinguishing these organisms from plants and animals.
Step-by-step explanation:
The major component of both fungal cell walls and arthropod exoskeletons is chitin. Chitin is a nitrogen-containing polysaccharide, which provides structural strength due to its complex molecular composition of repeating units of N-acetyl-ß-d-glucosamine. This substance makes up the rigid layers of fungal cell walls and also forms the exoskeleton of arthropods, such as insects and crustaceans. Furthermore, it differentiates the fungal cell wall from plant cell walls, which primarily contain cellulose, and its absence in human cells makes it a target for antifungal medications such as polyoxins and nikkomycin Z.
In fungal cells, chitin adds to the cellular integrity by providing resistance to desiccation and protection from some predators. The fungal plasma membrane, much like other eukaryotes, is stabilized by ergosterol, replacing cholesterol found in animal cell membranes. These unique features of the fungal cell wall and membrane are critical for the survival and function of fungus in various environments.