Final answer:
Keratin is a hard protein found in skin, hair, and nails, its presence in cells helps create a tough barrier for protection. Nails provide protection and improve tactile sensation, while hair aids in temperature regulation and water shedding. Keratins are not found in the tongue or bones.
Step-by-step explanation:
What is Keratin?
Keratin is a tough, fibrous protein found in the skin, hair, and nails. It is the key structural material making up the outer layer of human skin. Keratinized cells contain keratin and are found not only in the skin but also in places such as the mouth and nose, creating a tough and impermeable barrier.
Functions of Nails and Hair
Nails serve as protective plates over the fingertips and toes, while also enhancing the sense of touch. Hair serves several functions including acting as a filter, keeping the body warm, and aiding in shedding water.
Hair is a defining characteristic of mammals, consisting of dead, keratin-filled cells that overlap each other. Keratins are found in hair and feathers but are not naturally found in the tongue or bones.
Animals other than mammals, such as birds with their feathers, also have keratins but not as hair. The amphibian skin contains a form of keratin, though it is not as tough as the one found in mammalian hair and nails.