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 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.
