Answer:
The answer is "Solute molecules move across a cell membrane from areas of higher concentration to areas of lower concentration."
Explanation:
Simple diffusion specifically involves the movement of (small, uncharged) solutes across a cell membrane. Since diffusion is part of the passive transport umbrella, it also requires no energy since the solutes move down the concentration gradient - from areas of high concentration to areas of low concentration.
Hope that helps! :)
