- Books Name
- Science Made Easy Science Book
- Science Made Easy
- CBSE Class 9
Plasma membrane or Cell membrane
• This is the outermost covering of the cell that separates the contents of the cell from its external
• The plasma membrane allows or permits the entry and exit of some materials in and out of the
• It also prevents movement of some other materials. The cell membrane is called selectively
• It is made up of lipid and protein.
→ Properties of Plasma membrane
• It is flexible (made up of organic molecules called lipids and proteins).
• Its flexibility enables cell to engulf in food and other from the external environment. This process
called endocytosis. Amoeba acquire food through this process.
→ Functions of Plasma membrane
• It permits the entry and exit of some materials in and out of the cell.
• It prevents movement of some other materials not required for the cell as it acts like selectively
• Cell wall is another rigid outer covering in addition to the plasma membrane found in plant cell.
The cell wall lies outside the plasma membrane.
• The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance which
provides structural strength to plants.
→ Function of Cell Wall
• Cell walls permit the cells of plants, fungi and bacteria to withstand very dilute (hypotonic) external
media without bursting.
• In such media the cells tend to take up water by osmosis. The cell swells, building up pressure
against the cell wall. The wall exerts an equal pressure against the swollen cell.
• Because of cell wall, cells can withstand much greater changes in the surrounding medium than
• When a living plant cell loses water through osmosis there is shrinkage or contraction of the
contents of the cell away from the cell wall. This phenomenon is known as plasmolysis.