Final answer:
The exoskeleton in arthropods serves as protective armor against predators, prevents water loss, provides structural support, and serves as attachment sites for muscles. It is composed of chitin, requires molting for growth, and its density restricts the size of the organism.
Step-by-step explanation:
An arthropod's exoskeleton performs several crucial functions. The exoskeleton is a multi-layered structure comprised of the cuticle, which provides protection against predation and environmental stresses, prevents water loss, and acts as a supportive frame. Made of chitin, often combined with calcium carbonate, it also serves as a counterforce for the contraction of muscles. Arthropods have specialized structures called apodemes that function as attachment sites for muscles, similar to tendons. To accommodate growth, arthropods must undergo molting, a process where they shed the old exoskeleton and replace it with a new, larger one. This is because the exoskeleton does not expand as the organism grows. Despite its strength, the exoskeleton limits the size of arthropods due to the increasing density required to support larger bodies.