Homeostasis general model.
Both diffusion and osmosis are forms of passive transport, meaning that they will pass from one level of concentration to another. Ions or molecules will pass through the cell membrane from the area of highest concentration to an area of low concentration. Osmosis only occurs with water and across a semipermeable membrane. Diffusion sometimes requires energy and sometimes does not, but follows the same principle of particles moving from one higher concentration to another lower concentration. Whenever energy is required, it is called facilitated diffusion and it requires ATP in order to work.