“A plasma membrane or cell membrane is the outermost covering of cell.”
Plasma Membrane
Structure and functions of Plasma Membrane
Plasma membrane is composed of organic molecules like lipids and proteins. It acts as a semipermeable membrane that allows the exchange of materials between cell and its surrounding. A semipermeable membrane allows the passage of specific material, whereas, it restrict other materials to pass through it. Exchange of material takes place, from higher concentration of material towards the lower concentration of material by diffusion. A process in which solvent from higher concentration is transported to lower concentration areas through a semipermeable membrane is called as osmosis.
Hypotonic solutions, isotonic solution and hypertonic solutions are some conditions for osmosis.
- Hypotonic solution: When cell is placed in water, concentration of water is high outside the cell and low inside the cell. Plasma membrane of cell acts as semipermeable membrane. It allows the movement of water particles in both the direction. Here, process of osmosis occurs, as large amount of water particles moves from high concentration to low concentration of water. That is, large amount of water from outside of cell enters inside the cell . This results in the swelling of cell.
- Isotonic solution: When cell is placed in water such that concentration of solution inside and outside the cell is equal, then same amount of water particles enters and leaves the cell through semi permeable membrane. Hence, there is no net movement across semipermeable membrane. Therefore, shape of cell remains unchanged.
- Hypertonic solution: When cell is placed in water, such that concentration of water in low outside the cell and high inside the cell . Water moves in both direction through the plasma membrane which is a semi permeable membrane. But more number of water particles leaves the cell as compared to water particles entering the cell. This results in shrinking of cell.
This article is helpful for Class 9 Science
Keywords: Plasma membrane, semipermeable membrane, osmosis, hypotonic solution, isotonic solution, hypertonic solution.
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