Structure of Cell wall

Structure of Cell wall -The cell wall contain the following part

1- Primary Cell wall

2- Secondary cell wall

3- Tertiary Cell wall

4- Middle lamella

Structure of Cell wall

1- Primary cell wall

• It is first formed outermost layer of cell
• It is Secreted by cytoplasm on the side of middle lamella
• It is a thin tender and elastic layer
• In this the microfibrils are not properly arranged but at the maturity they arrange slowly in length.
• In young meristematic and parenchymatous cells Primary wall is the main limiting membrane. 
• It is relatively thin and permeable membrane.
• It is elastic and can extend as cells grow but when more cellulose is deposited on this layer it become more rigid
• In Certain epidermal cell cutin and cutin waxes are also deposited on it that make it impermeable to water.

2- Secondary cell wall

• It is made by the deposition of other substances such as lignin on plasma membrane.
• The cellulose fiber are arranged parallel in this wall and embded in hemicellulose and lignin.
• It is comparatively thicker than primary cell wall.
• It is generally present in mature permanent or non growing cells
• It is composed of cellulose, Pectins non cellulose polysaccharides, Lignin and a Phenolic polymer which give hardness and mechanical rigidity to the wood.
• In mature cells it appears to be 9 -10µm thick layer.
• It is divided into three layers 

A- Outer layer – S1

B- Middle layer – S2

C- Inner Layer – S3

• The outer S1 layer are attached with primary cell wall.
• The middle S2 layer comparatively thick
• The inner layer S3 is very thin and delicate.
• The secondary cell wall gives extra protection and strength to cell.

3- Tertiary cell wall

• It is a xylane rich layer which is deposited inner to the secondory wall
• Generally they are present in tracheids of gymnosperms particularly in coniferous woods.
• It is very thin and occurs in the form of small swelling or warty out growth on the innermost side of the cell wall.

4- Middle lamella

• It is present in between cells walls of two adjacent cells.
• It unite to primary cell wall of other adjacent cell.
• Chemically it is composed of pectin (Carbohydrate, Glucuronic acid, galacturonic acid + Ca++ and Mg++ (Pactates))
• The pactates are viscous and gelatinous.
• The young cells are compactly bounded with middle lamella but in mature cell the middle lamella is dissolved and consequently cells are loosened.
• It is non crystalized layer which is dissolved in pectinase enzyme.
• It is a porous layer through these pores the cytoplasm of other cells via cytoplasmic threads.
• These cytoplasmic threads are called plasmodesmata. They Differ in shapes and size.