Why is the plasma membrane called a selectively permeable membrane?


-Aqsa, Subject Matter Expert at Edumarz

Solution: Plasma membrane also called the cell membrane is a living membrane situated inside the cell wall. It is similar to the cell membranes of all other organisms. It consists mainly of phospholipids and proteins. A plasma membrane is a phospholipid bilayer in which phospholipid molecules are arranged in two parallel rows. The phospholipid molecule contains a polar head and non-polar tail. The polar head is composed of a phosphate group and glycerol.

The plasma membrane is selectively permeable. It is because it allows some molecules and ions to enter readily while allowing others more slowly and does not allow certain molecules at all. The cell membrane allows the passage of:

  • gases like carbon dioxide oxygen, and nitrogen

  • solvents like water, alcohol, ether, chloroform, etc.

But organic substances like mono- and disaccharides, fatty acids, glycerols, amino acids, and some electrolytes pass slowly through the plasma membrane. Substances like polysaccharides, phospholipids, and proteins do not pass through the cell membrane, which is impermeable to them. The selective permeability of the plasma membrane is a dynamic character. The permeability of the cell membrane is affected by the external and internal environment of the cell membrane.

Leave a Reply