What does the term exoskeleton refer to?

The term exoskeleton refers to an external skeleton that provides protection and support for many invertebrates, such as insects, crustaceans, and arachnids. This rigid structure is made of chitin and serves several important functions, including shielding the organism from predators, preventing water loss, and aiding in locomotion by providing attachment points for muscles. The exoskeleton is a critical adaptation for these animals, allowing them to thrive in a variety of environments.

The other options do not accurately describe an exoskeleton. The mention of an internal bone structure pertains to vertebrates, which have an endoskeleton, not an external one. The idea of a covering that helps fish maintain buoyancy relates more to swim bladders rather than a skeleton. Finally, an outer layer of plant tissues describes plant structures such as the cuticle or epidermis, which are not related to the concept of an exoskeleton in animals.