Why cell membrane is called selectively permeable membrane?

Explanation:

The plasma membrane is called a selectively permeable membrane b/c it permits the movement of only certain molecules in and out of the cells. 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.

Remember selectively means; in a way that  involves the selection of only particular people or things.

a scenario where a cell may be needed to perform a form of endocytosis is when transporting large molecules. a scenario where a cell may be needed to perform a form of exocytosis is when releasing the large molecule from the cell.