Question

Why is a cell membrane called a selectively permeable membrane?

• A. It is permeable only during certain stage of the cell division.
• B. It allows only selective molecules to pass through it.
• C. It allows only water to pass.
• D. It is made up of lipids.

Answer 1

The correct option is (B):

Explanation of the correct option:

1. ​The cell membrane is called selectively permeable as it only allows specific molecules to pass.
   
2. Only specific molecules like water and gaseous molecules can pass through the cell membrane directly.
   
3. It stops the flow of other molecules towards the two sides.
   

Explanation of the incorrect options:

Option (A):

1. The permeability of the cell membrane remains the same at the time of cell division or dormancy in the cell.
2. ​There are no special changes during division as it still only allows the same selective molecules.
   

Option (C):

1. Along with water molecules, respiratory gasses can pass through the cell membrane.
   

Option (D):

1. ​The selective permeability facilitated by the present of lipids forming the cell membrane.
   
2. But along with the lipid there are proteins present in the cell membrane.
   

Final Answer: Cell membrane is called a selectively permeable membrane because it allows only selective molecules to pass through it..