Why is facilitated diffusion necessary?

It allows polar and charged molecules, such as carbohydrates, amino acids, nucleosides, and ions, to cross the plasma membrane. Two classes of proteins that mediate facilitated diffusion are generally distinguished: carrier proteins and channel proteins. The plasma membrane needs these molecules in order for the cells and the body to function

to cross the plasma membrane.

Explanation:

Two classes of proteins that mediate facilitated diffusion are generally distinguished: carrier proteins and channel proteins.