Which structure in the cheek cell did you observe that separates and protects the cell from the environment?

The answer is epithelium. In particular, stratified squamous epithelium. Epithelium is protective tissue that is found on the outer surfaces of organs and  blood vessels and inner surfaces of cavities in many internal organs. Epithelium contains no blood vessels, and nutrients reach the epithelial cells through diffusion from the underlying tissue.

It is evolution, because we all have some of the same traits like eye color or shape or ears.