Final answer:
Exoskeletons of arthropods, like insects and crustaceans, are primarily made of chitin, a strong and flexible material that requires molting for the organism to grow.
Step-by-step explanation:
Exoskeletons in organisms such as arthropods are made primarily of chitin, which is a nitrogen-containing polysaccharide made up of repeating units of N-acetyl-ß-d-glucosamine, a modified sugar. This material is not only tough and resistant but also flexible enough to allow for movement. Arthropods, including insects and crustaceans, rely on their exoskeletons for protection, body support, and facilitation of muscle attachment, much like tendons do in more advanced animals. However, the rigid nature of the exoskeleton requires these organisms to molt in order to grow, as the exoskeleton does not expand with the creature's growth.