plasma membrane is called selectively permeable membrane because it selects the substances first and then allow it to pass through it

Why is the Plasma Membrane called a Selectively Permeable Membrane?
The plasma membrane, also known as the cell membrane, is referred to as a selectively permeable membrane because of its unique structure and function that allows it to regulate the passage of substances in and out of the cell.

Structure of the Plasma Membrane:
- The plasma membrane is composed of a phospholipid bilayer with embedded proteins.
- The phospholipid bilayer has a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails.

Selective Permeability:
- The plasma membrane is selectively permeable due to its structure, which allows only certain substances to pass through.
- Small, non-polar molecules such as oxygen and carbon dioxide can freely pass through the lipid bilayer via simple diffusion.
- Larger or polar molecules require specific transport proteins to facilitate their passage through the membrane.

Functions of the Plasma Membrane:
- Regulates the entry and exit of ions, nutrients, and waste products to maintain cellular homeostasis.
- Helps in communication between cells through receptor proteins on the membrane.
- Provides structural support and shape to the cell.

Importance of Selective Permeability:
- Prevents harmful substances from entering the cell while allowing essential nutrients to pass through.
- Helps in maintaining the internal environment of the cell by controlling the movement of ions and molecules.
In conclusion, the plasma membrane is called a selectively permeable membrane because of its ability to selectively allow certain substances to pass through while restricting the passage of others. This crucial function is essential for the proper functioning and survival of cells.