CHAPTER 5 Homeostasis & Transport 7.3 Cell Transport I. Passive Transport A. Intro 1. In addition to chemical signals, cells transport H2O, food, and ions across membrane a. Ion charged particle B. Diffusion 1. The mixing of 2 substances by the random motion of molecules 2. Molecules will always diffuse from and area of high [ ] to an area of low [ ]

C. Facilitated Transport 1. Not all substances can pass freely across plasma membrane like water 2. Protein channels a. Channels 1. Passageways across plasma membrane 2. Allows only certain molecules to cross membrane depending on shape of molecule 3. Facilitated diffusion a. “free of charge” 1. Costs the cell no energy to perform b. If molecule can fit through the protein channel it may enter or leave the cell c. Movement occurs due to diffusion, hence the name 1. high [ ] to low[ ] d. Called facilitated because channels assist, or facilitate the diffusion of molecule

D. Osmosis: Diffusion of H2O 1. The diffusion of H2O across a selectively permeable membrane 2. Again from an area of high [ ] to an area of low [ ] 3. Requires no energy by the cell a. Water moves freely across membrane

4. Controlling osmosis a. [ ] gradient 1. The difference in the [ ] of particles that occurs across a selectively permeable membrane 2. Remember that water moves from high [ ] to low [ ] 3. Moving with or down the [ ] gradient a. Particles moving from high [ ] to low [ ] 4. Moving against or up the [ ] gradient a. Particles moving from low [ ] to high [ ] 5. Isotonic solution a. [ ] of particles is equal on both sides of the membrane b. Cells in an isotonic solution do not experience osmosis 6. Hypotonic solution a. [ ] of particles outside the cell is lower than inside the cell 1. More water outside the cell than inside b. Water moves inside the cell causing the cell to swell 1. If solution is to hypotonic cell will burst

7. Hypertonic solution a. [ ] of particles outside the cell is higher than inside the cell 1. More water inside the cell than outside b. Water leaves the cell causing it to shrink 8. Osmotic pressure a. The pressure that results from the force of water pushing against the plasma membrane b. Also called turgor pressure

II. Active Transport A. Intro 1. Pumps a. Passageways across plasma membrane that requires a certain amount of energy b. Used to pump a molecules against or up the [ ] gradient 1. Molecules move from a low [ ] to a high [ ] B. Sodium/potassium pump 1. Pumps potassium into the cell from low [ ] outside to high [ ] inside 2. Pumps sodium outside the cell from low [ ] inside to high [ ] outside C. Moving large particles 1. Some particles are to large to fit through any protein channels 2. Endocytosis a. The process of bringing molecules into a cell using extensions of the cell membrane

D. Exocytosis 1. Molecules w/in a sac inside the cell are discharged from the cell in an opposite manner to endocytosis