Final answer:
The protein found in large amounts in the superficial layer of the epidermis is keratin, which fills the cells as they move up through the skin layers and provides a protective barrier once they die and reach the surface.
Step-by-step explanation:
The protein found in large amounts in the superficial layer of epidermal cells is keratin. Keratin is an intracellular fibrous protein that provides hardness and water-resistant properties to the skin, hair, and nails. The epidermis is mainly made up of cells called keratinocytes, which produce keratin.
As these cells move upwards through the layers of the epidermis, they become filled with keratin and eventually die, forming a protective, waterproof barrier on the skin's surface known as the stratum corneum. This layer is continuously shed and replaced by newer cells from the layers below.
Answering the options directly, the correct option is C. Keratin. Insulin is a hormone regulating blood glucose levels, hemoglobin is a protein in red blood cells for carrying oxygen, and collagen is a structural protein found in connective tissues.