The substance that typically provides rigidity to fungal cell walls, and is also found in the external skeletons of insects and other arthropods, is called .

Chitin

Explanation:

Chitin is a natural biopolymer that is made of the N-acetylglucosamine, modified glucose.

Chitin is an important polymer mainly for the fungi and the arthropod insects as it is present in the cell wall of the fungi and the exoskeleton of the insects.

The chitin provides a protective function to this organism that the digestive enzymes cannot degrade this chitin but only the symbiotic bacteria can digest eat therefore they are sometimes avoided to be eaten.

Thus, chitin is the correct answer.

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