A Level Biology Practice Exam

What is an exoskeleton?

1. An internal skeleton found in mammals

2. An external skeleton of some organisms

3. Part of the vertebral column

4. The skeletal structure of birds

The correct answer is: An external skeleton of some organisms

An exoskeleton is defined as an external skeleton that provides structural support and protection for certain organisms, particularly invertebrates such as arthropods (e.g., insects, crustaceans, and arachnids). Unlike an internal skeleton, which is found within the body (as in mammals), an exoskeleton serves as a hard outer layer that can safeguard the organism against physical damage, predators, and environmental factors. This external structure is often composed of materials such as chitin or calcium carbonate and can be subject to molting as the organism grows, allowing for an increase in size while maintaining protection. The other choices refer to different types of skeletal structures: an internal skeleton, the vertebral column, and the skeletal structure of birds, none of which accurately describe an exoskeleton.