Which of the following is not a skeletal tissue?

Step 1: Analyze the question We need to find the option that is NOT a skeletal tissue, meaning it does not form part of the supporting framework of an organism.

Step 2: Explain the concept Skeletal tissues give support, shape, and protection to the body.

• Bone: hard, mineralized connective tissue that forms the skeleton of vertebrates.
• Cartilage: flexible connective tissue that forms the skeleton of cartilaginous fish (e.g., sharks). It also forms parts of the human skeleton such as the ear, nose, and joint surfaces.
• Chitin: a tough polysaccharide that forms the exoskeleton of arthropods (insects, crustaceans). It is a skeletal material, and some textbooks count it as a skeletal tissue.
• Plasma: the liquid part of blood. It transports nutrients, hormones, and wastes. It has no supporting role.

Step 3: Solve

• Bone gives support, so it is skeletal.
• Cartilage gives support, so it is skeletal.
• Chitin forms the exoskeleton of arthropods, so it is skeletal.
• Plasma is a fluid blood component used for transport, so it is not skeletal.

Step 4: Answer The correct option is A. Plasma.

Tip: Link each tissue with its job. Bone and cartilage are for support in vertebrates, and chitin is for support in arthropods. Plasma belongs with blood and transport, so remember "plasma flows, it doesn't support." In "which is NOT" questions, look for the option that belongs to a different system.