1. Cell Membranes and Transport Go to Section:

2. The Cell Membrane The cell membrane is: selectively permeable  Permeable = Pass through (Latin)  Cell membrane regulates what can and can’t enter the cell.  Cell membrane helps cell maintain homeostasis

3. 1. phospholipid bi-layer (2 membranes)  Phosphate head is polar (water loving)  Fatty acid tails non-polar (water fearing)  Proteins embedded in membrane Structure of cell membrane

4. Outside of cell Inside of cell (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains Structure of the Cell Membrane Cell membrane has pores (holes) in it a.Selectively permeable: Allows some molecules in and keeps other molecules out b.Structure is related to its function!

5. The Cell Membrane Which molecules pass freely? Small molecules like water, carbon dioxide, or oxygen can easily pass through the pores of the membrane. Which molecules are regulated? Large molecules like glucose Charged molecules like salts.

6. Molecule Movement Recall cells are small because they need to obtain sufficient nutrients and dispose of their wastes. This is done by the cell membrane by three means:  Diffusion– Passive; NO ENERGY  Osmosis- Passive; NO ENERGY  Active Transport; REQUIRES ENERGY

7. Definitions. Solution = A homogenous, liquid mixture of two or more substances. Solvent = The dissolving agent of a solution. Water is the most versatile solvent known. Solute = Substance that is dissolved in a solution.

8. Diffusion The process by which molecules tend to move from an area of higher concentration to an area of lower concentration. Concentration= amount of substance in a given volume.

9. Why Diffusion? Molecules are always moving Collisions occur between molecules, which causes the molecules to move away from one another. If there is space these molecules want to spread out evenly.

10. What direction will the molecules move?

11. Diffusion and the Cell Movement of molecules by diffusion is how the cell fulfills its needs. Nutrients: Low concentration in the cells, high concentration outside of the cells. What direction will the nutrients diffuse?  From outside the cell to inside the cell.  High to Low Concentration!!

12. Diffusion and the Cell Wastes (including CO 2 ): High concentration in the cell, low outside of the cell. What direction will the wastes move?  From inside the cell to outside the cell.  High to Low concentration

13. Types of Passive Transport Facilitated diffusion: movement of specific molecules (glucose) across cell membranes through protein channels  Protein channels are specific – only allow certain molecules across  Passive – does not use energy to move glucose  Movement occurs from high to lower concentration Facilitated diffusion Diffusion

14. Low Concentration High Concentration Glucose molecules Cell Membrane Protein channel Facilitated Diffusion Go to Section: Molecules move through a protein channel from high to lower concentration What is the only way glucose can enter the cell? What would happen if the protein channel is removed?

15. A special case of diffusion: Osmosis Water moves through the pores of the cell membrane like other molecules. The movement of water from a high concentration to a low concentration (thru a semi-permeable membrane) is called: Osmosis  Osmosis = movement of water (the solvent)  Diffusion = movement of dissolved materials (the solutes)

16. Osmosis is the movement of water (red dots) through a semipermeable membrane to a higher concentration of solutes (blue dots).

17. Activity — Predicting Movement of Water This “U” tube has a selectively permeable membrane separating side A and B. Side A has a 40% solution of sugar and side B has a 60% solution of sugar. Which side has more water? Which way will the water move? Selectively Permeable Membrane

18. **Summary** Both osmosis and diffusion involve the movement of molecules from an area of high concentrations to a area of low concentrations. Osmosis = movement of water (the solvent) Diffusion = movement of dissolved materials (the solutes)

19. Water Balance The cell membrane doesn’t actually control the movement of water. The environment around the cell determines the direction of water movement.

20. Water Regulation Without other mechanisms the cell would burst or shrivel. Plant vacuoles store water even when the environment is dry.  The cell wall is rigid to prevent bursting or shriveling.  Animals can increase or decrease their amount of water intake and outtake (Urine concentration/amount of water that is drank)

21. Hypertonic Solution – More solute in solution than inside cell Plasmolysis Cells shrink and die

22. Isotonic Solution – same concentration of solute inside and outside cell Animal cell Plant cell No net gain or loss of water

23. Hypotonic Solution –less solute outside cell than inside Cytolysis – cell swells and bursts Builds up turgor pressure – cell becomes stiff, keeping plant upright

24. What would happen to a cell placed in pure water? 90% water 10% solute 100% water Cell’s are about 90% water. Human Red Blood Cell Before: After

25. What would happen to a cell placed in a 20% salt solution? 90% water 10% solute Cell’s are about 90% water. 80% water Human Red Blood Cell Before: After