Now we are going to discuss the outermost non living protective covering of plant, bacteria and fungi cell wall, we already discussed major differences between cell wall and cell membrane but now we will focus on the structure and function of cell wall.
Table of Contents
Basic Introduction About Cell Wall:
In all plants cells, most of the bacterial cell and in fungi cell the plasma membrane is covered by a thick non living layer which most of the time allows to pass most of the solvent and most of the time they determine the shape of cell and separate the living cellular part from surroundings other cells and from external environment.
Cell wall in different organisms show great variation in their chemical composition, for example cell wall in plant are made of mainly cellulose but other chemicals like suberin, lignin, pectin also present in some plant cells but in case of fungi the cell wall is mainly made of chitin, here one interesting facts is the chitin present in the cell wall of fungi is also available in animal kingdom where the exoskeleton in arthropods is made of chitin.
But in case of prokaryotic cell the bacterial cell wall are made of peptidoglycan and depending upon the chemical composition of bacteria cell wall they are two types gram positive and gram negative and their cell wall have two layer outer layer made of lipopolysaccharide and lipoprotein while the inner layer is made of peptidoglycan.
Structure of Cell Wall:
The chemical composition of the cell wall makes the cell wall categories into three layers: primary cell wall, middle lamella and secondary cell wall and we will discuss all the three layers and their chemical composition below one by one.
Primary Cell Wall:
The name primary suggest about its nature, it is the immediate layer in the cell wall which is mainly made of cellulose and due to presence of cellulose fibres this layer is highly elastic which is useful for a growing cell who increase their size with time and it is comparatively thinner layer of cell wall.
Middle Lamella:
Middle lamella is present between different plant cells which helps to attach all the plant cells inside a tissue together and separate from one cell to another and also give mechanism strength to the plant tissues and this layer is made of pectin, protein and lignin.
Secondary Cell Wall:
When a cell grows sufficient and need not to grow further then between the primary cell wall and the middle lamella an extra layer is secreted which is known as secondary cell wall and it is rigid due to its chemical composition.
Due to its rigidity the secondary cell wall does not stretch and prevent the growth of the plant cell but on the other hand the primary cell wall is elastic and stretch because if the cell grows then its cell wall also has to stretch accordingly to allow the increase in cell size.
Major Functions of Cell Wall:
- Cell wall is a non living rigid structure which helps the plants to maintain its specific shape especially some plant cell like cells in vascular tissue, it is very important to have a shape and cell wall give the shape but the elastic nature of cell wall do not restrict the cell growth.
- The cell wall makes the cell safe against mechanical stresses and absorbs the mechanism shock which does not allow damage to the inner living part of the plant cell.
- Cell walls have a special role to expand the cell because the cellulose fibres present in cell walls have a special power of water intake.
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