1. AP Bio Chap 7 Osmosis and Diffusion

2. So, how does a membrane regulates what goes in and out? Depends on: 1)Lipid solubility - Hydrophobic molecules, such as hydrocarbons, O 2, CO 2 pass freely - Ions, polar molecules need transport molecules (proteins) with hydrophilic channels or actually bind to the carrier protein to pass through - Aquaporins facilitate water passage 2) Size of the molecule 3) Concentration of the molecule

3. Cell membranes are semipermeable.

4. Types of transport: PASSIVE TRANSPORT – no energy required 1) Diffusion - movement of a substance from greater to lesser concentration (down its concentration gradient) will continue until dynamic equilibrium; no more NET movement most common method of movement for nonpolar molecules across the membrane most efficient when large surface area, well- defined concentration gradient, short distance.

5. Diffusion

6. Molecules of dye Fig. 7-11a Membrane (cross section) WATER Net diffusion (a) Diffusion of one solute Equilibrium

7. (b) Diffusion of two solutes Fig. 7-11b Net diffusion Equilibrium The diffusion of one solute is unaffected by the diffusion of another solute.

8. 2) Osmosis is the diffusion of water across a selectively permeable membrane Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration Direction of water flow is determined by the number (not kinds) of solute particles (molecules and ions) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

9. Lower concentration of solute (sugar) Fig. 7-12 H2OH2O Higher concentration of sugar Selectively permeable membrane Same concentration of sugar Osmosis

10. Fig. 7-UN3 Environment: 0.01 M sucrose 0.01 M glucose 0.01 M fructose “Cell” 0.03 M sucrose 0.02 M glucose What will happen here if the sucrose cannot diffuse? Glucose, fructose, and water can.

11. Fig. 7-UN4

12. Water Balance of Cells Without Walls Tonicity is the ability of a solution to cause a cell to gain or lose water Isotonic solution: Solute concentration is the same as that inside the cell; no NET water movement across the plasma membrane Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water

14. REMEMBER! WATER ALWAYS FLOWS INTO A HYPERTONIC SITUATION!

15. What happens to animal cells in the following situations? Hypertonic environment – lose water, shrivel Hypotonic environment – water moves in, cell swell and possibly bust Adaptations to contend with this: - contractile vacuoles in protists - membranes less permeable to water - isotonic internal conditions to their environment

16. Fig. 7-13 Hypotonic solution (a ) Animal cell (b ) Plant cell H2OH2O Lysed H2OH2O Turgid (normal) H2OH2O H2OH2O H2OH2O H2OH2O Normal Isotonic solution Flaccid H2OH2O H2OH2O Shriveled Plasmolyzed Hypertonic solution

17. Fig. 7-14 Filling vacuole 50 µm (a) A contractile vacuole fills with fluid that enters from a system of canals radiating throughout the cytoplasm. Contracting vacuole (b) When full, the vacuole and canals contract, expelling fluid from the cell.

18. Water Balance of Cells with Walls Cell walls help maintain water balance A plant cell in a hypotonic solution swells until the wall opposes uptake; the cell is now turgid (firm) If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt In a hypertonic environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called plasmolysis

19. ??? The ideal environment for animal cells is ________________________. The ideal environment for plant cells is ________________________.

20. Hypertonic or hypotonic environments create osmotic problems for organisms Osmoregulation, the control of water balance, is a necessary adaptation for life in such environments Transport Videos