Final answer:
Collagen is the protein that provides firmness and strength to the skin.
Step-by-step explanation:
The protein that provides firmness and strength to the skin is collagen.
Collagen is a fibrous protein that forms a major component of the extracellular matrix in the dermis layer of the skin. It provides structural support and tensile strength to the skin, making it firm and resilient.
For example, collagen fibers in the dermis give the skin its ability to stretch and recoil, allowing movements such as facial expressions without damaging the skin.