The cell boundary is called the cell membrane. In plant cells, it is called the cell wall, and it is made of cellulose. The cell membrane separates a cell from its surroundings.
The cell membrane provides structure and form to the cell. It encloses the vital cell organelles and the dense jelly-like substance called the protoplasm. It protects the cell from the harsh environment outside the cell. The cell membrane is porous, allowing the exchange of gases, nutrients and excretory products. It is made up of proteins and phospholipids. These proteins and lipids are layered to give the membrane a bi-layered structure.