Cell Wall |Function, Cell Wall Structure, Bacterial Cell Wall | Biology@TutorVista.com
Protection against infection and mechanical stress.
Separates interior of the cell from the outer environment.
It enables transport of substances and information from the cell insides to the exterior and vice versa.
Also helps in osmotic-regulation.
The physiological and biochemical activity of the cell wall helps in cell-cell communication.
It prevents the cell from rupturing due to tugor pressure.
Aids in diffusion of gases in and out of the cell. 
Also provides mechanical protection from insects and pathogens.
Cell Wall Structure
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The composition of the cell wall differs from one species to the other. In bacteria the cell wall is made up of peptidoglycans. The Archean cell wall is made of glycoproteins and polysaccharides. In fungi cell walls are made of glucosamine and chitin. In algae it is composed of glycoproteins and polysaccharides. The plant cell wall is mainly composed of cellulose, hemicellulose, glycoproteins, pectins and lignin.
Plant Cell Wall
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Presence of Cell wall is the major difference between plant cell and animal cell.
Plant cell wall performs essential functions like providing shape, tensile strength and protection and also helps the cell develop tugor pressure to maintain the pressure of the cell contents.
Plant cell walls are primarily made up of cellulose. cellulose is the most abundant macro-molecule on Earth.
Plant cell wall consists of three layers: the primary cell wall, secondary cell wall and the middle lamella.
The middle lamella - It is first layer formed during cell division. This layer  is rich in pectin. It is the outermost layer,  joins together adjacent plant cells and holds them together.
The primary cell wall â It is formed after the middle lamella. It is composed of pectin compounds, hemicellulose and glycoproteins. The layer consists of a framework of cellulose micro-fibrils, in a gel-like matrix. It is thin, flexible and extensible layer.
The secondary cell wall - It is a thick layer formed inside the primary cell wall. It is extremely rigid and provides strength. It is composed of cellulose,hemicellulose and lignin.
Composition of plant cell wall
In the growing cell wall the carbohydrates are cellulose, hemicellulose and pectin as well as lignin, proteins and enzymes. 
The outer part of the primary cell wall of the plant epidermis usually forms a permeability barrier and is known as the plant cuticle.
The secondary cell wall contains cellulose, xylan and lignin.
Plant cell walls also contain enzymes such as hydrolases, esterases, peroxidase and transglycolases. also contain structural proteins and silica crystals. 
Bacterial Cell Wall