Cell wall



Cell wall is outermost, rigid, protective and semi-transparent covering of plant cells and cell of fungi, bacteria and some protists. It was discovered by Robert Hooke in 1665.

  • Fungal cell wall – of chitin
  • Bacterial cell wall – of peptidoglycan or mucopeptide or murein
  • Plant cell wall – of cellulose, hemicelluloses and protein.

Structure of cell wall:

cell

Cell wall has the following different layers:

  1. Middle Lamella
    • It is outermost thin cementing layer between adjacent cells
    • Formed during cytokinesis
    • Composed of magnesium pectate and calcium.
  2. Primary Wall
    • More or less elastic layer formed after the formation of middle lamella.
    • Composed of protein, hemicelluloses and loose network of microfibril of cellulose.
    • Primary wall and middle lamella are found in all types of plant cells.
  3. Secondary wall
    • Much thicker, rigid and inelastic layer formed inner to primary wall.
    • Is formed only when cells attain maximum size
    • Is common in aclerenchyma, collenchymas, tracheid and vessels.
    • Composed of cellulose, hemicellular, pectin and lignin.
    • S1, S2, and S3 are its sublayers.
    • May contain wax, cutin and suberin and silica.

 

Plasmodesmata:

Primary and secondary walls are not formed continuously. They form gaps, known as plasmodesmata. It is a cytoplasmic bridge between two cells.

Desmosomes:

It is the protoplasmic bridge between two cells of animal cells.

 

Functions of Cell Wall:

  1. It provides definite shape to cell due to its rigidity.
  2. It protects the protoplasm against mechanical injury.
  3. It prevents the cell from osmotic burstiong.
  4. Cell wall of root hairs absorbs water.
  5. It has some enzymatic activity.
  6. Cutin and suberin of cell wall of stem and leaves help to reduce the rate of transpiration.
  7. The permeable nature of cell wall allows the exchange of any substance through it.

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