Cell wall is a tough, rigid layer that surrounds some types of cells. Cell wall is a characteristic feature to cells of plants, bacteria, fungi, algae and some archaea. It is located outside the cell membrane. The major function of the cell wall is to provide rigidity, tensile strength, structural support, protection against mechanical stress and infection. It also aids in diffusion of gases in and out of the cell.
Cell wall composition varies from species to species and also depends on the developing stage of the organism. Protozoans and animals do not have a cell wall.
Robert Hooke in 1678 discovered cell wall while observing a thin section of cork. Around the same time an Italian doctor Marcello Malphigi claimed cell cavities are surrounded by a firm cell wall.
Cell Wall Definition
The cell wall is a rigid layer that surrounds some types of cells. It is located outside the cell membrane whose main function is to provide rigidity, strength, protection against mechanical stress and infection.It also provides the cell with limited plasticity that prevents the cell from rupturing due to the tugor pressure.As the cell wall are cutinized they prevent water loss and also aid in cell-cell communication.
Cell wall is a characteristic feature to cells of plants, bacteria, fungi,many algae and some archaea. Protozoans and animals do not have a cell wall.
Cell Wall Function
- Gives the cell a definite shape and structure.
- Provides structural support.
- 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.
- Prevents water loss.
- 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
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
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 – 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
Bacterial cell wall is made up of peptidoglycans also known as murein. The cell wall of bacteria is essential for the survival of bacteria.
Cell wall of bacteria is broadly classified into two types: gram positive and gram negative. The names are given to the reaction of the cells to gram staining. This experiment is employed for the classification of bacterial species.
The gram positive bacteria have a thick cell wall and is made up of many layers of peptidoglycan and teichoic acids.
The gram negative bacteria have thinner cell walls, and is made up of few layers of peptidoglycans and is surrounded by a lipid membrane containing lipopolysacccharides and lipoproteins.
Fungi Cell Wall
Fungi cell wall consists of chitin and other polysaccharides. They do not have cellulose in their cell walls. Species of fungi that possess a cell wall have a plasma membrane and three layers of cell wall material surrounding it. These layers are made up of chitin, glucans and a layer a of mannoproteins (mannose containing glycoproteins).
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