A cell wall refers to the rigid and semi-permeable protective layer in some types of cells. This outer covering is located next to the plasma membrane of the cells of plants, algae, bacteria and fungi. The cells of animals do not have a cell wall.
The cell wall of plants is composed mostly of fibers of the carbohydrate polymer cellulose. Cell walls have several functions such as providing framework, protection and support for the cell, regulating diffusion and growth, withstanding turgor pressure, serving as storage and facilitating communication.
The main function of the cell wall is to provide a framework and prevent overexpansion. The polysaccharides, cellulose fibers and proteins in cell walls maintain the shape of the cell. Moreover, the cell wall also gives mechanical strength and support, and regulates the direction of the growth of the cell. This outer covering protects the organism from pathogens as well. Lastly, the cell wall is responsible for preventing water loss and storing carbohydrates that are essential for growth.
The cell walls of plants are multilayered and may consist of up to three layers namely, the middle lamella, primary cell wall and secondary cell wall. All plant cells have the first two layers, but not all have a secondary cell wall.