1.  Plasma membrane is a phospholipid bilayer  Protein “icebergs” float in a “sea” of phospholipids The Cell Membrane

2. Phospholipids  Phosphate group forms a hydrophilic head  Fatty acid tails are hydrophobic

3. Membrane proteins perform a variety of cell functions : Cell Signaling

4. The Plasma Membrane is Selectively Permeable What does this mean? Permeable to: small molecules, nonpolar molecules Less Permeable to: charged ions, large molecules, or hydrophilic molecules

5. What molecules can go directly through? Carbohydrates?  No, large & hydrophilic Proteins?  No, large; many hydrophilic Lipids?  Yes; hydrophobic Nucleic acids?  No, hydrophilic Water?  No; hydrophilic

6. TRANSPORT WHY? To maintain Homeostasis

7. TRANSPORT HOW? A. By Passive Processes B. By Active Processes

8. Passive Processes: Diffusion The movement of molecules from a region of their high concentration to a region of their low concentration.

9. A drop of food coloring diffuses through gelatin in a petri dish

10. Figure 8.10 The diffusion of solutes across membranes

11. Additional Terminology Equilibrium Concentration Gradient Difference in concentration between 2 regions All molecules diffuse down their concentration gradient

12. OSMOSIS Special case of Diffusion 1. Movement of Water 2. from an area of high concentration to an area of low concentration 3. across a selectively permeable membrane. Osmosis Animation Osmosis Animation

13. Gatorade vs. Powerade Osmosis Lab

16. Solutes and Their Effects Hypotonic A solution is hypotonic to a second solution if it has less solute dissolved in it than the second solution Hypertonic A solution is hypertonic to a second solution if it has more solute dissolved in it than the second solution Isotonic A solution that has equal amounts of solute as the second solution

18. Solutes and Their Effects Water moves from a ________ solution to a _________ one

19. Water flow equal in both directions (Equilibrium) Net water flow into the cell which can burst (Hemolysis) Net water flow out of cell which shrinks (Crenation) Water Balance in Animal Cells

20. The contractile vacuole of Paramecium: an evolutionary adaptation for osmoregulation

22. Plasmolysis Shrinking of cytoplasm due to water loss Plasmolyzed cells become FLACCID. What is the opposite? Swollen cells are TURGID.

23. A watered tomato plant regains its turgor

24. Water Balance in Plant Cells Red Onion Cells Turgid Flaccid

25. Concept Generalizations Diffusion: equilibrium, molecules, high concentration, low concentration, passive process, concentration gradient Osmosis: water, passive, high concentration, low concentration, selectively permeable membrane, hypotonic, hypertonic, isotonic, plasmolyzed, flaccid, shrivel

26. Passive transport – diffusion across a selectively permeable membrane No energy is required. The random movement of molecules move them across the membrane

27. Facilitated diffusion – specific transport proteins provide a pathway for certain molecules to pass Is this active or passive transport?

28. Active transport : ATP (an energy rich molecule) is used to move materials across the membrane against their concentration gradient. EXAMPLES: 1.Metabolic Pumps: A specific transport protein pumps solute across a membrane Example Na+(Sodium) K+(Potassium) pump operates in all cells to maintain charge on the membrane

29. Figure 8.16 Review: passive and active transport compared

30. Endocytosis – Vesicles form to engulf materials and bring them inside the cell Exocytosis – spills contents outside the cell BOTH transport large molecules packaged in vesicles (small membrane sacs) Phagocytosis Pinocytosis