What is the similarity between simple diffusion and facilitated diffusion?
a. both move molecules from lower concentration to higher concentration.
b. both move molecules from higher concentration to lower concentration.
c. both need energy.
d. both need transport protein.

The answer is the option b, Both move molecules from higher concentration to lower concentration.The process of diffusion is the movement of molecules due to the difference on concentrations, which only can occurs in one direction: from high concentration to lower concentration. Facilitate diffusion is a specific diffusion that happens in the cells and requires the pass through membrane cell via transmembrane specific proteins, but that does not change the fact that it has to be from higher concentrations to lower concentrations regions.