1. Cell Membrane What’s its function?

2. How does the membrane control what enters or leaves the cell? PASSIVE TRANSPORT (without energy input) -Diffusion -Facilitated Diffusion -Osmosis ACTIVE TRANSPORT (requires energy input) We’ll learn more about this later

3. Movement of molecules from area of high concentration to area of low concentration Diffusion R E M E M B E R : passive = NO energy input Continues to equilibrium (even distribution)

4. High Concentration Low Concentration Concentration Gradient Why does it become constant here instead of going lower? Molecules have reached equilibrium! PASSIVE TRANSPORT

5. dialysis tubing: 15 mL starch & glucose beaker: water & iodine During diffusion lab… After 30 minutes

6. inside dialysis tubing starch & glucose outside dialysis tubing water & iodine High Concentration of IodineHigh Concentration of Starch

7. inside dialysis tubing starch, glucose & iodine outside dialysis tubing water, iodine, & glucose High Concentration of StarchLower Concentration of Iodine

9. Facilitated Diffusion Diffusion with the help of protein channels and transport proteins Still moves from high concentration of solute (dissolved stuff) to low concentration until it reaches equilibrium Still does not use energy

10. Diffusion & Facilitated Diffusion: What’s the difference? DIFFUSIONFACILITATED DIFFUSION transports small molecules (O 2, water) transports larger molecules (glucose) transports nonpolar molecules (can dissolve in lipids) transports charged ions (salts)

11. Diffusion of water across a selectively permeable membrane Osmosis high water concentration, low solute concentration high solute concentration, low water concentration

12. Tonicity Isotonic solution: both solutions are equal in concentration Hypertonic solution: higher concentration of solute Hypotonic solution: lower concentration of solute

13. Tonicity example: red blood cell The red blood cell has an internal salt concentration that matches the 9 grams of salt in 1 liter of solution Salt Sucks! So water always moves into saltier solution

14. Always moves from high to low concentration Never requires energy In the cell it occurs as: –diffusion of solute through lipid bilayer –facilitated diffusion (solute helped through membrane by proteins) –osmosis (diffusion of water molecules) Slide 3.7 Summary of PASSIVE TRANSPORT