7-3 MOVEMENT OF MATERIALS THROUGH THE CELL MEMBRANE

1. 7-3 MOVEMENT OF MATERIALS THROUGH THE CELL MEMBRANE

2. Background Info… • Every living cell contains a liquid interior (cytoplasm) and is surrounded by a liquid. • One of the most important functions of the cell membrane is to regulate the movement of molecules from one side of the membrane to the other.

3. Background Info… • The core of nearly all cell membranes is a LIPID BILAYER which is a tough flexible structure

4. Carbohydrates act like chemical identification cards for other cells Protein channel pumps-- help move materials across Please label the diagram that in your notes.

5. PASSIVE TRANSPORT • No energy needed because movement occurs down the concentration gradient (from high concentration to low concentration) There are 3 types of passive transport: 1. Diffusion 2. Osmosis 3. Facilitated Diffusion

6. 1. Diffusion • Movement of moleculesfrom an area of greater concentration to an area of lesser concentration *movement continues until equilibrium is reached meaning concentrations of the substances will be the same on each side of the membrane.

7. 2. Osmosis • Diffusion (movement) of water across a selectively permeable membrane • Some substances can pass through the membrane & others cannot • Ex: carrot in salt water; water can pass through the carrot cell membrane but salt cannot Equilibrium is reached when concentrations of water and sugar (for example) are the same on both sides of the membrane = ISOTONIC solution (“same strength”)

8. Selectively Permeable Membrane Osmosis Sugar molecule INSIDE THE CELL OUTSIDE THE CELL Water molecule Please label the diagram in your notes

9. Osmotic Pressure • Pressure created by osmosis (pg. 187) • Cells are filled with sugars, salts, proteins, and other molecules which cause a pressure to build up on the hypertonic side of the membrane. • If a cell is placed in fresh water, which way will the water move? Why? • INTO THE CELL!! Which will cause the cell to swell and burst • Why doesn’t this happen in your body? • Blood is isotonic with cells • Plant cells are surrounded by tough cell walls prevents cells from expanding!

10. Lower concentration of solute (sugar) Higher concentration of sugar Same concentration of sugar H2O Selectively permeable mem- brane: sugar mole- cules cannot pass through pores, but water molecules can Osmosis

11. Water Balance of Cells Without Walls • 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

12. Hypotonic Environment The water concentration is greater outside the cell; the solute concentration is greater inside. Result: Water flows into the cell.

13. 50 µm Filling vacuole Paramecium 50 µm Contracting vacuole

14. 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

15. Isotonic solution Hypertonic solution Hypotonic solution Animal cell H2O H2O H2O H2O Shriveled Normal Lysed Plant cell H2O H2O H2O H2O Plasmolyzed Turgid (normal) Flaccid

16. 3. Facilitated Diffusion • involves the use of protein channels located in the cell membrane • protein channels help materials cross the membrane *Example: glucose transported across this way (remember movement is from high to low concentrations)

17. ACTIVE TRANSPORT • requires energy because material is moved across the membrane goingagainst the concentration gradient (from low concentration to high concentration) It’s like a pump!!!

18. WHY DO WE NEED THIS PROCESS?:

19. We need active transport in order to… 1. Transport (or pump) macromolecules across the cell membrane Ex: Na+/ K+ pump; Ca+2 ions (responsible for nerve impulses)……..

20. Cell Interior Cell Exterior

21. We need active transport for… 2. Endocytosis- taking materials into a cell (forms a vacuole within the cytoplasm) ex: phagocytosis: a kind of endocytosis in which large particles are engulfed

23. We need active transport for… • Exocytosis- bulk passage out of the cell (removal of waste material from cell)