Which of the following structures is not a skeletal material?

1. Analyze the question You are asked to find the one option that is NOT a skeletal material, meaning it does not form part of the supporting framework of an animal's body.

2. Explain the concept Skeletal materials give support, shape and protection to the body. They include:

• Chitin: a tough polysaccharide that forms the exoskeleton of arthropods such as insects, crabs and spiders.
• Cartilage: a flexible supporting tissue. It makes up the skeleton of sharks and rays, and is found in the human ear, nose and joints.
• Bone: a hard, mineralised tissue that forms the endoskeleton of most vertebrates.

Muscle is different. It is a contractile tissue that produces movement. Muscles attach to the skeleton (usually by tendons) and pull on it to move the body, but they do not form the skeleton.

3. Step-by-step solution

• Chitin forms the exoskeleton of arthropods, so it is skeletal.
• Cartilage supports and shapes parts of the body, so it is skeletal.
• Bone forms the vertebrate endoskeleton, so it is skeletal.
• Muscle brings about movement and does not provide structural framework, so it is not skeletal.

4. Answer The correct option is D. Muscle.

5. Exam tip Remember: skeleton = support, muscle = movement. Whenever a question asks for the "odd one out" among skeletal materials, look for the tissue that moves the body instead of supporting it. Chitin, cartilage and bone are the usual skeletal materials JAMB likes to test.