The Fundamental Unit of Life

Tutormate > CBSE Syllabus-Class 9th Biology > The Fundamental Unit of Life

05 Cell Wall

  • In plant cells, there is a rigid cell wall which lies outside the plasma membrane known as cell wall.
  • It is the outermost covering mainly composed of cellulose, long fibers of carbohydrates including hemicellulose, lignin, and pectin.
  • It is not present in animal cells.
  • Cell wall is non-living and freely permeable.
  • For the protection of its plasma membrane and cytoplasm, cell wall is secreted by the cell itself.
cellWall

Functions of a Cell Wall:

  • It permits the plant cell to become turgid. During osmosis, when water enters the vacuole, the plant cell expands. In order to resist this expansion, the cell wall has to be strong enough. This enables the cell to become turgid
  • Cell wall provides mechanical strength to support the cell. The cellulose microfibrils are very strong. This strength may be further increased by the addition of lignin in tissues such as xylem. In cells such as collenchyma, extra cellulose is added to the cell wall to increase mechanical support.
  • It is freely permeable to water and substance in solution.
  • It has narrow pores, called pits. Fine strands of cytoplasm, called plasmodesmata, are able to pass through these pits. And such intercellular connections allow exchange of materials between the living cell contents.
  • The cell walls of adjacent cells are glued together by the middle lamella. Middle lamella is jelly- like substance which is made up of calcium and magnesium pectate.
  • It protects the cell against physical damage and invading pathogens.
  • It regulates and controls the direction of cell growth.
  • It functions as a storage unit by storing carbohydrates for use in plant growth, especially in seeds.

Plasmolysis:

  • When a living plant cell loses water through osmosis, there is a shrinkage or contraction of the protoplasm away from the cell wall. This phenomenon is called plasmolysis.

Differences between cell wall and plasma membrane:

Cell Wall Plasma membrane
It is present in plant cells, some fungi, bacteria, algae. It is present in both plant and animal cells.
It lies outside of the plant cells. It lies outside of the animal cells and inner to cell wall in case of plant cells.
It is nonliving and quite thick and rigid. It is living and quite thin.
It is rigid. It is flexible.
It is generally permeable. It is selectively permeable.
Cell wall is formed by cellulose, hemicellulose and pectin. Plasma membrane is formed by lipids and proteins and small number of small carbohydrates (i.e. oligosaccharides).
The major function of cell wall is to provide protection and strength to the cell. The major function of plasma membrane is to hold cellular contents and control passage of materials in and out of the cell.

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