Question

2.
Why is the plasma membrane
called a selectively permeable
membrane?
​

Answer 1

The plasma membrane is called a selectively permeable membrane as it permits the movement of only certain molecules in and out of the cells. Not all molecules are free to diffuse. If plasma membrane ruptures or breaks down then molecules of some substances will freely move in and out of the cells. As the plasma membrane acts as a mechanical barrier, the exchange of material from its surroundings through osmosis or diffusion in a cell won’t take place. Consequently, the cell would die due to the disappearance of the protoplasmic material. It allows hydrophobic molecules and small polar molecules diffuse through the lipid layer, but does not allow ions and large polar molecules cannot diffuse through the membrane.

Answer 2

The plasma membrane is called a selectively permeable membrane as it permits the movement of only certain molecules in and out of the cells. ... If plasma membrane ruptures or breaks down then molecules of some substances will freely move in and out of the cells.