What is the difference between osmosis and diffusion?

Osmosis is strictly the movement of water. Its definition is the net movement of water across a partially permeable membrane from a high water potential to a low water potential. Therefore this is only the answer to questions about the movement of water and no other particles. An example of this is the movement of water into red blood cells (erythrocytes) when there is low blood glucose levels in the blood. Water moves into the cell across the membrane as the water potential is higher in the blood plasma than in the cell.Diffusion is the movement of particles from a high concentration to a low concentration. This can be any partial. For example, oxygen atoms diffuse across the alveolar wall and the capillary endothelium into the capillary during the gas exchange for respiration to occur. This is because there is a higher concentration of oxygen in the alveolus than in the capillary.