Cell wall

Anon-living roald structure called the cell walL forms an guter.covering for the plasma membrane.of Bacteria.

Some protists and.Fungi. Algae and Plants.

 Algoe have cell wall made of cellulose, galactans, mannans and mineral like calcium carbonate.

 In other plants cell wall consists of cellulose, hemicellulose, pectins and proteins.

Cell Wall:

i) Primary wall  :  Thin elite Composed of cellulose, hemicellulose and pectin Gradually diminishes as cell matures. Capable of growth

ii) Secondary Wall  :  Rigid, thick

(S1, S2, S3)  

Composed of cellulose, hertil- cellulose, Pectin. Absent in meristem cells. Imer side of primary wall (toward cell membrane)

iii) Tertiary wall  :   Present only in tracheids of Gymnosperms.Componed of hemi cellulose and xylan.

Middle lamella  :  Common layer between two cells.

Fig : Cell Wall

Middle lamella consists of Ca and Mg pectates (Plant cement). Amount of Ca is more.

Cellulose main constituent of cell wall but addition to cellulose-Hemicellilose,  Cutin, Pectin. Lignin, Suberin an also presents in cell wall.

 Cell will worked as frame or protective layer of cell (Exoskeleton of cell)

 Cellulose microfibrils and microfibrils are arranged in layers to form skeleton of cell wall. In between these Layers other substances like pectin, hemicellulose may be present. These form matrix of cell wall.

Cell wall materials (Hemicellulose, Pectin, lignin) are synthesized in plant golgibodies or dictyosomes. Formation of cellulose occurs by cell membrane.

PLASMODESMATA :- Name proposed by Strasburger (1901). These are cytoplasmic connections between two adjacent plant cells. Plasmodesmata in characteristic of multi-cellular plants. E.R. tubules (Desmotubules) help to maintain continuity of cytoplasm. The cell wall and middle lamella may be traversed by plasmodesmata which connect the cytoplasm of neighbouring cells.

FUNCTIONS OF CELL WALL :

• Cell wall gives shape to the cell.
• It protects the cell from mechanical damage and infection.
• It also helps in cell-to-cell interaction.
• It provides barrier to undesirable macromolecules.