Final answer:
The stratum corneum, the outermost layer of the epidermis, is formed by the combination of keratinocytes and keratin.
Step-by-step explanation:
The stratum corneum, the outermost layer of the epidermis, is formed by the combination of keratinocytes and keratin. Keratinocytes are epithelial cells that produce keratin, a tough, fibrous protein. As new keratinocytes form at the bottom of the epidermis, they become filled with keratin and move upward toward the surface of the skin, where they create a protective, waterproof layer called the stratum corneum.