noun, plural: cell walls
A membrane of the cell that forms external to the cell membrane whose main role is to give cells rigidity, strength and protection against mechanical stress. It is found in cells of plants, bacteria, archaea, fungi, and algae. Animals and most protists do not have cell walls.
In plant cells, the cell wall is a tough, rigid structure that may consist of: (1) the primary cell wall which is generally a thin, flexible and extensible layer composed of cellulose, pectin and hemicellulose, and (2) a secondary cell wall which is a thick layer rich in lignin that strengthens and waterproofs the wall and is formed inside the primary cell wall that has stopped increasing in surface area when the cell is fully grown. In between the primary walls is a middle lamella which is a pectin-rich intercellular material that glues the adjacent cells together. The cell wall is very essential in plants as it helps resist osmotic pressure.
In bacteria, the cell wall is composed of peptidoglycan, and is essential to the survival of many bacteria. Bacteria have been classified into Gram-positive and Gram-negative based on the structure of the cell wall. Gram-positive bacteria possess thick cell wall consisting of many layers of peptidoglycan and teichoic acids. Gram-negative bacteria have relatively thin cell wall consisting of few layers of peptidoglycan
In fungi, the cell wall is composed of chitin and other polysaccharides while in algae, it is made up of glycoproteins and polysaccharides, and in certain algal species it may be composed of silicic acid.
Compare: cell membrane.