Why is the Plasma Membrane called a Selectively Permeable Membrane

Answer: The plasma membrane is a thin layer of protein and fat surrounding the cell. It is called a selectively permeable membrane because it enables only certain chemicals and molecules to enter or exit the cell. 

Proteins, lipids and carbohydrates are the primary components of the plasma membrane.

Lipids

1. Phospholipids: Phospholipids are glycerol molecules with one or two fatty acids and one extra polar group replaced. 

2. Cholesterol: Cholesterol molecules are selectively dispersed between membrane phospholipids. 

3. Glycolipids: Glycolipids are lipids with a connected carbohydrate sugar chain found on cell membrane surfaces. 

Proteins

Interactions with other proteins connect peripheral membrane proteins to the membrane from the outside. Integral membrane proteins are introduced into the membrane, with the majority passing through. 

Structural proteins aid in the support and structure of cells. Transport proteins, such as globular proteins, assist the passage of molecules across cell membranes. A carbohydrate chain is connected to glycoproteins.

Functions 

• Physical Barrier: The plasma membrane separates the cytoplasm from the rest of the cell, protecting all of the cell’s components from the outside environment and allowing for independent activities inside and outside the cell

• Selective Permeability: Water, oxygen, and carbon dioxide can easily pass across the plasma membrane due to selective permeability, whereas Ions (such as sodium and potassium) and polar molecules

• Endocytosis and Exocytosis: A cell can take in enormous amounts of molecules or even complete bacteria from the extracellular fluid via endocytosis. The cell releases these molecules by exocytosis. In each of these processes, the cell membrane plays a significant role

• Cell Signalling: The membrane accomplishes communication and signalling by using a variety of proteins and carbohydrates in the membrane and receptors.