1. Membranes regulate the traffic of molecules Ch. 6.3

2. Water, nutrients, dissolved gases, ions, and wastes must move across a cell’s plasma membrane Plasma membranes act as gatekeepers; allowing certain things in, but not others

3. Diffusion DIFFUSION  net movement of particles from a high concentration to a low concentration PERMEABLE  allows molecules in and out

4. EQUILIBRIUM  = # of molecules on both sides

5. Passive Transport SELECTIVELY PERMEABLE MEMBRANE  allows some substances to cross the membrane more easily; blocks the passage of other substances all together. PASSIVE TRANSPORT  molecules will move across the plasma membrane; NO ENERGY IS NEEDED!!!

6. FACILITATED DIFFUSION  special proteins HELP molecules move in and out of the plasma membrane

7. Osmosis Passive transport of WATER  OSMOSIS – HYPOTONIC SOLN  LOWER solute conc. – HYPERTONIC SOLN  HIGHER solute conc. – ISOTONIC SOLN  EQUAL solute conc.

8. Examples HYPOTONIC HYPERTONIC ISOTONIC

9. Water Balance in Animal Cells HYPOTONIC  cell GAINS water, swells, and will pop like an overfilled balloon HYPERTONIC  cell LOSES water, shrivels, and will die.

10. Water Balance in Plant Cells HYPOTONIC  firm and healthy cell (water moves in to the cell) ISOTONIC  limp (no flow of water in to the cell) HYPERTONIC  loses water, shrivels, dies

12. Active Transport ACTIVE TRANSPORT  uses energy to move molecules or ions across the plasma membrane – Uses TRANSPORT PROTEINS

14. Transport of Large Molecules Larger molecules need to be packaged in to VESICLES  small membrane sacs that specialize in moving products in, out, and within a cell Pushing a vesicle OUT of the cell  EXOCYTOSIS Engulfing a vesicle IN to the cell  ENDOCYTOSIS

16. Concept Check What is diffusion? What role does a cellular membrane play in passive transport? Distinguish between hypertonic, hypotonic, and isotonic solutions, and give an example of how each affects an animal cell. What role does active transport play in cell function? How do vesicles transport large molecules out of a cell?