Cell wall
Cell wall is a fairly rigid, protective and supportive layer surrounding the cell external to plasma membrane of plants, bacteria, archaea, fungi and algae.
It is absent in animals and most protists. It was first observed by Robert Hooke in 1665. It is not an entirely rigid structure as the cell wall expands due to the growth of the cell.
It varies in thickness from o.1mm to I0mm.in most of the cells, cell wall is present from the very beginning to the last, but in slime molds (myxomycetes) cell wall is present for a very short time.
The cell wall is made of different materials depending on cell type. Only plant cell walls have cellulose which is an unbranched polysaccharide of D-Glucose linked together by p - 1-4 glycoside bonds.
Bacterial cell walls are composed of peptidoglycan. The cell walls in Archea are composed of various substances including glycoprotein s-layers, pseudo peptidoglycan or polysaccharides. Fungi have cell walls made up of chitin and algae have glycoprotein and polysaccharides. However, certain algae have silicic acid and often other accessory molecules found anchored to the cell wall.
In general, the plant cell wall consists of middle lamella, primary wall and secondary wall and is derived from the living protoplast.
8.1.1 Middle Lamella It is the cementing layer of a thin amorphous substance between two adjacent cells. This layer is the first formed layer and is laid down during cytokine sis. The primary wall is deposited inner to middle lamella.
The surface cells on their outer or exposed sides lack middle lamella. It is constituted by Calcium and Magnesium pectate. The actual structure is not clearly defined and several models are there to explain the structure of the middle lamella.
They are, covalently linked crossed model, tether model, diffuse layer model and stratified layer models. The pectic substances of this layer are enzymatic ally converted to partially soluble
Primary wall:
This layer is laid down
It is absent in animals and most protists. It was first observed by Robert Hooke in 1665. It is not an entirely rigid structure as the cell wall expands due to the growth of the cell.
It varies in thickness from o.1mm to I0mm.in most of the cells, cell wall is present from the very beginning to the last, but in slime molds (myxomycetes) cell wall is present for a very short time.
The cell wall is made of different materials depending on cell type. Only plant cell walls have cellulose which is an unbranched polysaccharide of D-Glucose linked together by p - 1-4 glycoside bonds.
Bacterial cell walls are composed of peptidoglycan. The cell walls in Archea are composed of various substances including glycoprotein s-layers, pseudo peptidoglycan or polysaccharides. Fungi have cell walls made up of chitin and algae have glycoprotein and polysaccharides. However, certain algae have silicic acid and often other accessory molecules found anchored to the cell wall.
In general, the plant cell wall consists of middle lamella, primary wall and secondary wall and is derived from the living protoplast.
8.1.1 Middle Lamella It is the cementing layer of a thin amorphous substance between two adjacent cells. This layer is the first formed layer and is laid down during cytokine sis. The primary wall is deposited inner to middle lamella.
The surface cells on their outer or exposed sides lack middle lamella. It is constituted by Calcium and Magnesium pectate. The actual structure is not clearly defined and several models are there to explain the structure of the middle lamella.
They are, covalently linked crossed model, tether model, diffuse layer model and stratified layer models. The pectic substances of this layer are enzymatic ally converted to partially soluble
Primary wall:
This layer is laid down