Which one of the following is important for cartilage but NOT a globin protein ?

Collagen is the correct answer as it is the primary structural protein found in connective tissues, including cartilage, tendons, and ligaments. Cartilage specifically contains a high density of Type II collagen fibers which provide tensile strength and structural support.

• Globin proteins (like Haemoglobin and Myoglobin) are a family of globular proteins involved in binding and transporting oxygen; they are not structural components of cartilage.
• Keratin is a fibrous structural protein, but it is primarily found in hair, nails, and the outer layer of skin (epidermis), rather than cartilage.

Since collagen is a fibrous protein and not a globular "globin" protein, it satisfies both conditions of the question.