Final answer:
Chitin is the polysaccharide found in fungi cell walls and in the exoskeleton of insects and other arthropods, while cellulose is the polysaccharide in plant cell walls.
Step-by-step explanation:
The polysaccharide found in the cell walls of fungi is chitin, which is also present in the exoskeleton of insects and other arthropods. Chitin is a tough, complex carbohydrate that is an integral structural component of fungal cell walls, offering necessary support and protection. In arthropods, such as crustaceans and insects, it provides a hard external shell known as the exoskeleton that shields their internal body parts.
In contrast, cellulose is another polysaccharide that comprises the cell walls of plants and provides structural support to the plant cells, but it is not found in the exoskeleton of insects or fungi. Chitin and cellulose serve similar purposes in providing rigidity and structure to various biological entities but are present in different groups of organisms.