Final answer:
Hair is an appendage of the skin that contains 90% hard keratin. Nails are another appendage of the skin that contain sheets of dead keratinocytes. Both hair and nails protect the body and enhance the sense of touch.
Step-by-step explanation:
Hair is an appendage of the skin that contains 90% hard keratin. Keratin is a tough, fibrous protein found in the skin, hair, and nails. Nails are another appendage of the skin that contain sheets of dead keratinocytes. Both hair and nails protect the body and enhance the sense of touch. Keratin is a fibrous structural protein that makes up the main component of hair, nails, feathers, horns, hooves, and the outer layer of human skin. It is a tough and insoluble protein that provides strength and rigidity to these biological structures. Keratin is particularly abundant in tissues that undergo mechanical stress or friction, such as the epidermis (the outer layer of skin) and appendages like hair and nails.