CELL WALL

CELL WALL

DISCOVERY
The cell wall was discovered by Robert Hooke in 1665.

OCCURRENCE
It is found in all plant cells, fungi, algae and bacteria, but absent in animals cell and protozoa. it is the outer most boundaries of the plant cells.

CHEMICAL COMPOSITION
Cell wall is composed of micro fibrils, these fibrils are cemented together by lignin pectin and other substances. Chemical composition of cell wall varies depending on the type of cell.

CELL WALL IN BACTERIA:
Bacterial cell wall is chemically composed of peptidoglycan.

CELL WALL IN PLANTS:
Cell wall of plants cell is composed of cellulose, hemicellulose, pectin and lignin.

STRUCTURE OF CELL WALL
The cell waLls have three fundamental parts.

MIDDLE LAMELLA
Middle lamella joins together the two adjacent cells. it is usually thin and about 1 um in thickness. Middle lamella is formed during cytokinesis by the cell plate during cytokinesis,

CHEMICAL COMPOSITION:
In woody tissue it is mainly composed of magnesium and calcium pectate. Middle lamella is commonly lignified.

PRIMARY WALL
Primary wall is the first wall formed during development. it is usually 1-3 um in thickness.

CHEMICAL COMPOSITION:
It is composed of cellulose, pectin mostly polysaccharides and hemicellulose.

SECONDARY WALL
It is laid down inside the primary wall. It is usually thick about 5-10 um. It is more or less rigid, both the wood and bark are the secondary cell walls. Secondary cell wall give rigidity to the plant.

CHEMICAL COMPOSITION:
Secondary cell wall is composed of hemicellulose (xylan) and lignin minerals (Ca,Mg)

PLASMODESMATA:
Plasmodesmata are small pores in the cell wall. Cells interact though plasmodemata with the protoplasts of adjacent cells across the wall.

IMPORTANCE OF CELL WALL/FUNCTIONS OF CELL WALL
*) Cell wall gives strength and rigidity to the cell.
*) Cell wall prevents the cell from osmotic lysis.
*) Cell wall limits the entry of larger molecules inside the cell.
*) Cell wall is porous and allow free passage of water and dissolved minerals.