what's the difference between simple diffusion and facilitated diffusion?

Answer 1

Things (e.g. ions, molecules) must get across the plasma membrane for different reasons. Sometimes, the lipid bilayer of the membrane is virtually impermiable and will not "allow" these things to pass. Therefore, they must be "facilitated" by proteins that span the membrane and provide an alternative route or bypass.

On the other hand, in simple diffusion, a substance passes through a membrane without the aid of anything, like a protein.

Facilitated diffusion It is similar to simple diffusion in the sense that it does not require expenditure of energy and transport is down an electrochemical gradient.

Answer 2

The short answer is that both are diffusion, both involve molecules moving down the concentration gradient, both are passive processes.

The difference is that facilitated diffusion involves a carrier protein. This protein helps molecules move across the membrane. These molecules can not move directly across the cell membrane due to their size, chemical properties or charges. And so they need the assistance of the carrier protein. This process does not require any energy input from the cell because molecules are moving down their concentration gradient.

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