What changes melanin granules under the influence of ultraviolet radiation?

Melanocytes are the cells responsible for the production of melanin, the pigment that gives skin its color and protects against ultraviolet (UV) radiation. When the skin is exposed to UV radiation, melanocytes respond by increasing the production of melanin granules in a process known as melanogenesis. This increase in melanin acts as a natural sunscreen, absorbing and dissipating UV rays to protect deeper layers of the skin from damage and reducing the risk of skin cancer.

In this context, keratinocytes, dermal fibroblasts, and Langerhans cells do not directly produce melanin. Keratinocytes are the predominant cell type in the epidermis and are responsible for forming the skin barrier and producing keratin, while dermal fibroblasts are found in the dermis and are essential for producing collagen and elastin, which contribute to skin structure and elasticity. Langerhans cells are part of the immune system and play a role in skin immunity but are not involved in melanin production.

Thus, melanocytes are the key players that change melanin granules in response to UV exposure, making them the correct answer.