What biological structure is primarily associated with arthropods for protection and structural support?

Arthropods, which include insects, arachnids, and crustaceans, are characterized by having an exoskeleton, a hard outer structure that provides both protection and structural support. The exoskeleton is composed mainly of chitin, which is a robust and flexible material. This feature is essential for arthropods as it offers defense against predators and helps prevent desiccation by reducing water loss, an important adaptation, especially for terrestrial species.

The exoskeleton also plays a crucial role in locomotion. Unlike internal skeletons, an exoskeleton allows for attachment points for muscles that facilitate movement when they contract. This contributes to the diverse range of movements and behaviors observed in arthropod species.

In contrast, the cell membrane, while critical for cellular integrity and function, does not provide the structural support or protection needed for larger organisms like arthropods. The terms "skeleton" and "cartilage" are more closely associated with vertebrates. Vertebrates possess an internal skeleton made of bone or cartilage, which serves a different purpose than the exoskeleton found in arthropods, highlighting the distinct evolutionary adaptations of these two groups.