PASSIVE TRANSPORT In Passive processes, substances cross the membrane from an area of high concentration to an area of low concentration (move with the concentration gradient, or difference), without any expenditure of energy (ATP) by the cell. Passive process or Passive transport includes (i) Simple Diffusion, (ii) Facilitated Diffusion and (iii) Osmosis. (i) SIMPLE DIFFUSION Simple diffusion is the net (overall) movement of molecules or ions from an area of high concentration to an area of low concentration. For Example - After a dye pellet is put into a beaker of water, the molecules of dye in the pellet diffuse into the water from an area of high dye concentration to areas of low dye concentration. The movement continues until the molecules or ions are evenly distributed. The point of even distribution is called Equilibrium. Cells rely on simple diffusion to transport certain small molecules, such as Water, Oxygen and Carbon-di-oxide across their cell membranes. (ii) FACILITATE...