The cell membrane protects the cell from unwanted things coming inside. It is a barrier. Composed of a phospholipid bilayer with embedded proteins, the plasma membrane is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of cells.
The cell membrane keeps the cell together and protects it at the same time. It also helps give it shape, gives it structure to fit with other cells, and keeps foreign substances out/let certain substances in.
