Final answer:
The correct statement about cell functions is C. keratin is produced by keratinocytes, which are skin cells responsible for producing the protein keratin. Melanin is produced by melanocytes, not Merkel cells, and myelin is produced by oligodendrocytes and Schwann cells.
Step-by-step explanation:
The correct statement is C. keratin is produced by keratinocytes. Keratinocytes are the most prevalent cell type in the epidermis, the outermost layer of the skin, and are responsible for the production of keratin, a key structural protein that contributes to the protection and waterproofing of the skin. Melanocytes, not Merkel cells, are the cells that produce the pigment melanin, which gives hair and skin its color and helps protect cells from ultraviolet (UV) radiation damage.
Oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system are responsible for the production of myelin, a lipid-rich substance that forms the myelin sheath around nerve fibers to insulate them and enhance the transmission speed of neural impulses. Dendrites, which are not produced by 'dendrocytes' (a term not typically used in neuroscience or biology), are the branched extensions of a neuron that receive signals from other neurons.