Osmosis is the diffusion of molecules through a semipermeable membrane, from higher concentration to a lower concentration, until the concentration on both sides is equal. Osmosis is very important in living organisms, Osmosis influences the distribution of nutrients and the release of waste products. If the membrane didn't form a selective barrier between the cell and its environment, toxic materials would enter the cell.
Diffusion is the movement of molecules from a high concentration to a low concentration. This is important to organisms because this is the process where molecules enter the body cells and waste products are removed.