What is the difference between simple diffusion and osmosis?
Simple diffusion is the movement of molecules from an area of higher concentration to lower concentration. The “simple” in simple diffusion refers to the fact that there is no assistance needed for the diffusion to happen. The opposite case, where assistance is used, is called facilitated diffusion.
Osmosis is the movement of water from an area of less concentration of dissolved particles to an area of high concentration, thus equalizing the concentrations on each side. Both osmosis and simple diffusion happen without assistance. I find it helpful to look at a diagram to help the concept make a little more sense.
Basically, the water moved to make the concentrations of the dissolved particles equal on both sides of the membrane. The water level is not necessarily even, but the concentration of particles is more balanced.