2. Osmosis Movement of Water across the Cell Membrane

3. Let’s review diffusion! Diffusion requires NO ENERGYDiffusion requires NO ENERGY Molecules move from HIGH to LOWMolecules move from HIGH to LOW Downhill!!!! Let’s see!Downhill!!!! Let’s see!Let’s see!Let’s see! Osmosis:Osmosis: Movement of WATER from an area of more water (H) to an area of less water (L)Movement of WATER from an area of more water (H) to an area of less water (L) Water moves OPPOSITE of other molecules!Water moves OPPOSITE of other molecules!

4. How does osmosis work? Across a SEMI-PERMEABLE membraneAcross a SEMI-PERMEABLE membrane Only certain molecules, like water, can move freely across the membraneOnly certain molecules, like water, can move freely across the membrane Water molecules move from HIGH to LOWWater molecules move from HIGH to LOW They want to BALANCE OUT a solutionThey want to BALANCE OUT a solution Therefore, water moves OPPOSITE of other moleculesTherefore, water moves OPPOSITE of other molecules

5. Example of OsmosisExample of Osmosis #1 Example of Osmosis Condition #1: More Water outside of cellCondition #1: More Water outside of cell Inside cell = 98% Water, 2% saltInside cell = 98% Water, 2% salt Outside cell = 100% Water, 0% saltOutside cell = 100% Water, 0% salt Water moves into cell, salt moves out to balance CELL SWELLS or BURSTS! 98%L 100%H

6. Example of Osmosis #2 Condition #2: More water inside of cellCondition #2: More water inside of cell Inside cell: 98% Water, 2% SaltInside cell: 98% Water, 2% Salt Outside cell: 95% Water, 5% SaltOutside cell: 95% Water, 5% Salt Water moves out of cell, salt moves in to balance CELL SHRIVELS! 98%H 95%L

7. Osmotic Pressure Cells behave differently when placed in different solutions!Cells behave differently when placed in different solutions! This is due to OSMOSIS!This is due to OSMOSIS! Most cells are ~ 98% water!Most cells are ~ 98% water! Three types of osmotic pressure:Three types of osmotic pressure: HypotonicHypotonic HypertonicHypertonic IsotonicIsotonic

8. Hypotonic Condition Cell is placed in 100% waterCell is placed in 100% water Solution outside of cell has MORE water, less of other materials (i.e., salt)Solution outside of cell has MORE water, less of other materials (i.e., salt) Therefore, solution is below strength (hypo)Therefore, solution is below strength (hypo) CLICK HERE FOR DEMO! CLICK HERE FOR DEMO! 98% Water ENTERS cell 100% CELL SWELLS!

9. Hypertonic Condition Cell is placed in 95% waterCell is placed in 95% water Solution outside of cell has LESS water, more of other materials (i.e., salt)Solution outside of cell has LESS water, more of other materials (i.e., salt) Therefore, solution is above strength (hyper)Therefore, solution is above strength (hyper) CLICK HERE FOR DEMO! CLICK HERE FOR DEMO! Water LEAVES cell 98% 95% CELL SHRINKS!

10. Isotonic Condition Cell is placed in 98% waterCell is placed in 98% water Solution outside of cell has SAME water, same amount of other materials (i.e., salt)Solution outside of cell has SAME water, same amount of other materials (i.e., salt) Therefore, solution is equal strength (iso)Therefore, solution is equal strength (iso) Water moves equally; Equilibrium exists 98% CELL STAYS THE SAME!