Practice question

Arthropod exoskeleton consists primarily of chitin, linear polymer of N-acetylglucosamine with beta-1,4 glycosidic linkages, embedded in protein matrix of arthropodin and cross-linked via sclerotization with quinones to harden cuticle, further mineralized with calcium carbonate in crustaceans for crushing resistance. Two layered organization: outer epicuticle with waxes preventing desiccation and inner procuticle with exocuticle and endocuticle showing helicoidal Bouligand fiber arrangement conferring strength. Cellulose builds plant cell walls, keratin vertebrate hair, collagen vertebrate tendon. Chitinous exoskeleton mandates ecdysis under ecdysteroid regulation, hallmark of Ecdysozoa.