Osmosis

1. Osmosis

2. Experiment showing osmosis • What is osmosis? • What is water potential? • Water potential of sucrose solution • Water movement across a differentially permeable membrane • Osmosis and plant cells • Osmosis and red blood cells

3. 30 minutes later Experiment showing osmosis

4. What is osmosis? • The net movement of water molecules across a differentially permeable membrane from a less concentrated solution to a more concentrated solution • The net movement ofwater moleculesacross adifferentially permeable membrane from aregion ofhigher water potential toa region oflower water potential

5. What is water potential? • The probability of water molecules moving through a membrane from each side of the differentially permeable membrane • Value as the concentration of solutes  (i.e. as the concentration of water molecules ) • Distilled water: water potential = 0greatest water potential • Solutions: water potential < 0 (-ve value)

6. Water potential (arbitrary unit) + 0 - Concentration of sucrose solution (M) Water potential of sucrose solution 0

7. low water potential high water potential net movement of water molecules water molecule sucrose molecule Water movement across a differentially permeable membrane

8. Osmosis and plant cells When young plant cells are immersed in • distilled water they become turgid, bigger and heavier

9. Osmosis and plant cells When young plant cells are immersed in • concentrated sucrose solution they become soft, smaller and lighter

10. Osmosis and red blood cells When red blood cells are immersed in • distilled water they burst and release red pigments

11. Osmosis and red blood cells When red blood cells are immersed in • concentrated sucrose solution they shrink

12. Summary • Osmosis: the net movement of water molecules across a differentially permeable membrane down a water potential gradient • Effect of osmosis