What layer of skin contains keratinocytes?

The epidermis is the outermost layer of the skin and is primarily composed of keratinocytes. These cells are responsible for producing keratin, a fibrous protein that helps protect the skin from damage, pathogens, and dehydration. As keratinocytes move from the deeper layers of the epidermis to the surface, they undergo a process called keratinization, where they become filled with keratin and eventually form a protective barrier.

The dermis, while being a thicker layer under the epidermis, contains structures such as blood vessels, nerves, and connective tissues but does not primarily consist of keratinocytes. The hypodermis, also known as the subcutaneous layer, lies beneath the dermis and serves to insulate the body and connect the skin to underlying tissues but does not contain keratinocytes either. The basement layer, or basement membrane, serves as a boundary between the epidermis and dermis and is involved in supporting the epidermal layers but does not contain keratinocytes itself.

Thus, the epidermis is the correct answer, as it is the layer where keratinocytes are present and play a crucial role in the skin's protective function.