The cell wall is a rigid and dense membrane located above the cytoplasmic membrane. This element is characteristic of bacterial cells, fungi and plants. In addition to protecting the cell, the hard shell performs a number of other equally important functions.
Cell Wall: General
The cell wall of each organism has a number of features. For example, in bacteria, it consists mainly of murein. By the way, bacterial strains are divided into two types - gram-positive and gram-negative - precisely because of the structural features of the hard shell. This determines their sensitivity to antibiotics.
If we talk about the cell walls of fungi, then their main components are chitin and glucans. But the shells of algae can consist of different polysaccharides - mainly glucose and its compounds. By the way, the composition of the cell membrane of algae is a very important taxon. It is worth recalling the group of Diatoms, representatives of which synthesize their own wall of silica.
The cell wall of plants and its functions
The principles of the structure of the rigid cell membrane are most conveniently studied using the example of a plant cell. And although mechanical protection is one of the most important functions of the cell wall, it is of much greater importance:
- provides mechanical and chemical resistance of the cell;
- prevents cell rupture in a hypotonic environment;
- the cell wall is also an ion exchanger, since through it the absorption and release of ions is carried out;
- takes part in the transport of organic compounds.
Cell wall structure
In the plant wall, it is customary to distinguish three main components: frame, matrix and inlaid substances.
The cell wall framework of the plant consists of cellulose. Due to the formation of hydrogen bonds, cellulose molecules form strong microfibrils, which are immersed in the main substance, or matrix.
The cell membrane matrix is approximately 60% of its total mass. It fills the space between microfibrils, and also creates strong bonds between macromolecules, provides elasticity and strength of this cell structure. The main components of the matrix are hemicellulose and pectin.
- Hemicellulose is a polysaccharide similar in structure to cellulose, but with shorter and branched chains of monomers.
- Pectin is also a polysaccharide, but it also contains methyl alcohol residues . Due to the formation of chemical bonds with calcium and magnesium ions, pectin takes part in the formation of the middle plates - places where two adjacent cells are interconnected. By the way, a large amount of pectin is contained in the fruits of plants.
Inlaid substances in most cases are represented by lignin, which is approximately 30% of the dry mass of the cell wall.
- Lignin can be deposited both in the form of a continuous layer, and in the form of individual elements - spirals, nets or rings. This substance acts like cement - it holds cellulose fibers together. Due to lignification, the cell wall becomes more resistant and less permeable. By the way, it is lignin that is responsible for lignification of plants.
Quite often, substances such as cutin, suberin and wax are deposited on the outer surface of the cell membrane.
Suberin is deposited on the inner side of the cell membrane, providing a sampling process. Such a cell becomes absolutely impermeable to moisture, so its contents quickly die off, and the free space is filled with air.
The main function of wax substances and cuticles is to protect cells from infection, as well as reduce the evaporation of water.
We can say that the cell wall is a very important element of the plant cell, which ensures its normal development.