1. Thursday November 20 Objectives You will be able to: – Explain the concept of diffusion and how it relates to cells – Describe the different ways that molecules can be passively transported across the cell membrane Agenda – Reading Quiz – Start Notes on Passive Transport (Chapter 5-1) Homework Due today – Read section 5-1 – Outline of section

2. Passive Transport Section 5-1

3. Passive Transport Doesn’t require energy Concentration is the amount of solute dissolved in a fixed amount of solvent Concentration gradient is the difference in the concentration across space

4. Diffusion Diffusion - the movement of molecules from high concentrations to low concentrations – Molecules are in constant motion (kinetic energy) – This movement drives diffusion

5. Equilibrium Concentration is the same throughout – Solutions move to equilibrium Even at equilibrium, molecules are still moving – Movement in many directions balances concentration

6. Diffusion Across Membranes Some molecules can move from high concentration to low across the cell membrane – Depends on size, shape, and nature Molecules that dissolve in lipids can move across the membrane – Molecules that don’t must move through protein pores

7. Osmosis Water moving across a membrane Hypotonic is when the solute concentration outside is lower (water moves in- cell expands) Hypertonic is when the solute concentration outside is higher (water moves out- cell shrinks) Isotonic is when concentrations are equal

8. HypOtonic Inside Outside

9. HypERtponic Inside Outside

10. Osmosis in Cells Hypotonic environment – Contractile vacuole- collects water and pumps out – Plants use cell wall- holds up against turgor pressure (the pressure water exerts) – Some pump solutes out of cytosol – Cytolysis (bursting) (red blood cells) Hypertonic environment – Plant cell membrane shrinks against cell wall (plasmolysis), plant wilts – Red blood cells shrink and shrivel

11. Plants Hypotonic environment Hypertonic environment

12. Red Blood Cells

13. Facilitated Diffusion Carrier proteins help some molecules that cant diffuse rapidly through the membrane Not soluble in lipids, or too large – Still diffusion because moving from high to low Molecule binds to protein, shields it from the hydrophobic cell membrane, and releases to other side of the cell – Carrier molecule is specific to molecule Example: glucose

15. Ion Channels Provide passage for ions that can’t diffuse on their own (not soluble) Specific to each ion (Na + K + Ca 2+ Cl - ) Some are always open but some have gates that respond to: – Stretching of cell membrane – Electrical signals – Chemicals in cytosol or environment

16. Active Transport Section 5-2

17. Sodium Potassium Pump Same as passive transport but from low to high NA + binds to a carrier protein from inside Phosphate from ATP changes shape of the protein New shape allows K + to bind to protein (outside) and phosphate leaves Loss of phosphate changes shape again and K + is released into the cell Inside becomes negative while outside becomes positive- – conducts electrical impulses

19. Endocytosis Cells ingest external fluid, macromolecules, and large cells Materials enclosed by cell and pinched off into a vesicle – Can fuse with organelles and digested Pinocytosis involves fluid Phagocytosis involves large particles – Phagocytes ingest bacteria and viruses destroyed by lysozymes

21. Exocytosis The reverse of endocytosis Vesicles fuse with cell membrane and contents are released into the environment Used to export large molecules such as proteins