BIOL 206 Lecture Notes - Lecture 17: Facilitated Diffusion, Osmosis, Phospholipid
Document Summary
In simple diffusion, small noncharged molecules or lipid soluble molecules pass between the phospholipids to enter or leave the cell, moving from areas of high concentration to areas of low concentration (they move down their concentration gradient). Oxygen and carbon dioxide and most lipids enter and leave cells by simple diffusion. Another way to describe the two solutions in the example of above is to use the terms hypertonic and hypotonic. A hypertonic solution has more solutes and less water than a hypotonic solution. So, in the example above, the solution inside the cell is hypertonic to the solution outside the cell. During osmosis, water moves from the hypotonic solution (more water, less solutes) to the hypertonic solution (less water, more solutes). In facilitated diffusion, substances move into or out of cells down their concentration gradient through protein channels in the cell membrane. Simple diffusion and facilitated diffusion are similar in that both involve movement down the concentration gradient.
