The part of the hair that contains the cortex and the bonds responsible for elasticity is the

• A. Cortex
• B. Medulla
• C. Cuticle
• D. Follicle

Answer: (A)

Hair elasticity comes from the bonds inside the cortex, the thick middle layer of the hair shaft. The cortex houses the keratin fibers that give hair its strength and stretch, and the bonds between those keratin molecules—especially disulfide bonds—are what provide resilience. Hydrogen bonds and other weaker bonds also contribute to how hair can bend and recover; they can be temporarily broken by water or heat and then reform as hair dries or cools. The outer cuticle is the protective covering, the medulla is the central core (when present), and the follicle is the root structure in the skin. So the part that contains the cortex and the elastic bonds is the cortex.