Final answer:
The cell membrane, which is a phospholipid bilayer with embedded cholesterol and proteins, surrounds animal cells and allows selective permeability.
Step-by-step explanation:
The cell membrane surrounds animal cells but there is no additional structure that envelops it like a cell wall in plant cells. The membrane enclosing a typical animal cell is a phospholipid bilayer with embedded cholesterol and protein molecules. Short oligosaccharide chains are attached to the outer surface, which contribute to the cell's ability to interact with its environment. The composition and structure of the cell membrane make it selectively permeable, which allows it to regulate the movement of substances into and out of the cell.