Unlike the cell membrane, the cell wall is not common to all types of cells. A protective layer that surrounds the cell membrane, one of its main functions is to prevent over-expansion of a cell.
All living cells are surrounded by thin membranes called cell membranes. However, some cells, notably plant, bacteria and fungi, have an additional protective layer called the cell wall.
Cell membranes are composed of proteins and phospholipids. They also contain cholesterol in varying amounts. Cell walls are composed differently. Plant cell walls are made of cellulose, while those of bacteria contain murein. Chitin is the major component of fungi cell walls.