Cell Wall is the outermost, thick, rigid, protective and semi transparent covering surrounding the plant cell except the gametes and zoospores. Besides plant cell it is found in the cell of fungi, bacteria and some protists. It was discovered by Robert Hooke
TYPES OF CELL WALL
1. Fungal Cell Wall = made up of chitin
2. Bacterial Cell Wall = made up of peptidoglycan or mucopeptide or muerin
3. Plant Cell Wall = made up of cellulose, hemicellulose and protein
STRUCTURE OF PLANT CELL WALL
Cell Wall has following different layers:
1. MIDDLE LAMELLA
- It is outermost thin cementing layer between two adjacent cells.
- Formed during cytokinesis.
- Composed of Calcium and Magnesium pectate.
2. PRIMARY CELL WALL
- More or less elastic layer formed after formation of middle lamella.
- Composed of cellulose hemicellulose and loose network of microfibril of cellulose.
- Primary cell wall and middle lamella is found in all types of plant cells.
3. SECONDARY CELL WALL
- Much thicker, rigid and inelastic layer formed inner to primary cell wall.
- Formed only when cell attains maximum size.
- Is common in achlerenchyma, collenchyma, tracheid and vessels.
- Composed of cellulose, hemicellulose, lignin and pectin.
- It's sub-layers are S1, S2 and S3.
- May contain wax, cutin, suberin and silica.
Primary and secondary cells are not formed continuously. They form gaps known as plasmodesmata. It is a cytoplasmic bridge between two cell.
FUNCTIONS OF CELL WALL
- It provides definite shape to the cell due to it's rigidity.
- It protects the inner contents of cell from mechanical injury.
- It prevents osmotic brusting of cells.
- Cell wall of root hair absorb water.
- It has some enzymatic activity.
- It prevents undue expansion of cell.