CELL WALL

Akanksha MishraBotany (hons.)

1year

CELL WALL: It is the outer most layer of the cell

outside the plasma membrane whose width is 0.2 micrometer.

It is a very rigid structure ,hence provides protection to the cell and also determine the shape of the cell.

It also prevent cells from swelling and bursting as a result of osmotic pressure.

CHEMICAL COMPOSITION : Cellulose Hemi cellulose Pectin Extensin Lignin

CELLULOSE:Cellulose is a structural polysaccharide where beta-glucose are linked to form ,1 glycan chain and the linkage is known as beta-1,4 glycosidic bond.40-70 glycan chain are interlinked by hydrogen bond to form one cellulose molecule.

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100 CELLULOSE MOLECULES TOGETHER FORM 1 MICELLE BUNDLE20 MICELLE ARE INTERLINKED WITH EACH OTHER TO FORM 1 CELLULOSE MICROFIBRIL.250 MICROFIBRIL MAKES 1 CELLULOSE MACROFIBRIL.

.... Hemicellulose is a polysaccharide made

up of 50 sugar molecules .It cross link the cellulose bundles.

Pectin is a polymer of D-galactouronic and D-glucouronic acid.It makes matrix of cell wall.

Extensin is the glycoprotein made up of protein chain which is 300 amino acid long,having repetitive sequence of 4 amino acids:serine-hydroxyprolein -hydroxyprolein-hydroxyprolein.

Lignin is polymer of phenolic compounds and deposit at maturity.

CELL WALL IS OF 2 TYPES:1.PRIMARY CELL WALL2.SECONDARY CELL WALL

DIFFERENCE: PRIMARY: First formation

below lamella. Thin and single

layered. Cellulose in plywood

like arrangement. Made of many

components. Elastic and pr. In

young cells.

Secondary: Form at maturity

below pr.wall. Thick having S1 S2

S3. Arrangement diff. In

diff layer. Mostly made of

cellulose and lignin. Inelastic and pr in

mature dead cells.

PITS: THESE ARE THE CAVITY OR DEPRESSION IN THE CELL WALL.

Simple pit: It is the cavity formed by not deposition of sec. wall over prim. wall. Pits of adjacent cells are opposite to each other.

2 primary wall +middle lamella=pit membrane

BORDER PIT:Not deposition of secondary wall over primary wall.The secondary wall projects over enclosing a pit chamber which opens to the periphery through pit aperture .Pit membrane possess a torus region in the pit region which is formed by excess deposition of primary cell wall.It is circular in shape.

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PLASMODESMATA: It is a cylindrical structure

having a diameter of 0.2 nm. Present in pit region where

pit membrane possess pores.Through these pores ,cytoplasmic strand of one cell is connected to others.This cytoplasmic strand is known as PLASMODESMATA.

Its function is transporting solute and water from one cell to another.

FUNCTION OF CELL WALL: Protects cell from mechanical injury. Maintains shape of cell. Cell wall possessing plasmodesmata

helps in the transport of solute[ions,water]from one cell to another.

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