Osmosis

1. Osmosis

2. Osmosis… • …is the diffusion of water molecules • …happens across a semi-permeable membrane

3. ONLY WATER • Water is a small but extremely important molecule that makes up most of the liquid part of the cytoplasm in living things. • Deals ONLY with the diffusion of WATER • The molecules (in this case, water - not solute molecules) will tend to move from an area of high (water)concentration to an area of low(water)concentration until equilibrium is reached.

5. OSMOSIS: FACILITATED DIFFUSION OF WATER ACROSS A CELL MEMBRANE Why would water molecules normally have a hard time getting across the cell membrane? The inside of a cell’s lipid bilayer is hydrophobic (water hating) Click me!

6. Aquaporins • Most cells have special water channel proteins • Known as – Aquaporins • Allow H2O to pass right through them by facilitated diffusion. • This EXTREMELY important process is = OSMOSIS

7. By knowing the concentrations of solute and solvent on the inside and outside of a cell, we can predict the direction of osmosis and the result on the cell. • Solutions on the outside of a cell can be described based on how they affect the cell • hypERtonic • hypOtonic • isotonic

8. Solutions on the outside of a cell (in its environment) can be described based on how they affect the cell: NOTE: (*tonic = solute. [High] solute means [low] water) "HYPER" = HIGH; "HYPO" = LOW; "ISO" = equal or same.

9. Cell with 2% solute, 98% solvent Beaker with 3% solute, 97% solvent What will happen? a) net movement of water _______of cell b) cell will ________ c) solution is hypertonic to the cell VISUALIZE HYPERTONIC H2O H2O H2O AFTER BEFORE

10. Cell with 2% solute, 98% solvent Beaker with 1% solute, 988% solvent What will happen? a) net movement of water _______of cell b) cell will ________ c) solution is hypotonic to the cell VISUALIZE HYPOTONIC H2O H2O H2O AFTER BEFORE

11. Cell with 2% solute concentration, 98% solvent Beaker = 2% solute, 98% solvent What will happen a) no net movement b) cell won’t change in size c) solution = isotonic to the cell VISUALIZE ISOTONIC

12. Common mistakes when discussing hyper-, hypo-, and isotonic solutions • The solutions are named for the concentrations of the SOLUTES • The substance that moves to balance the solute concentration is the WATER • The solutes to not “pull” or “suck” the water across the membrane – the water simply diffuses from where it is in high concentration to low concentration

13. Solute and solvent concentrations can be expressed as percentages of the entire solution. • When added together, the solute and solvent concentrations must equal 100%. • A solution with a 10 % solute concentration has a 90% solvent concentration.

14. What is the solvent concentration of a solution with a 3% concentration of solute? What is the solvent concentration of a solution with a 15% concentration of glucose? What is the solute concentration of a solution with 98% solvent? What is the solute concentration of a solution with 75% water? Let’s do some math!

15. Driven by differences in solute concentration, the net movement of water into or out of a cell produces a force known as osmotic pressure Osmotic Pressure

16. Almost always hypertonic… • Because cells contain a variety of solutes such as: • sugars, proteins, salts, etc. • they are almost always hypertonic • (*the environment = HYPOtonic!) to fresh water; • as a result, a typical cell exposed to fresh water will tend to swell up quickly from the entering water. • This may in fact cause an animal cell to swell like an overinflated balloon.

17. Plant cells contain a central vacuole which stores excess water - shrinking and swelling as water enters or exits the cell. Plant cells wouldn't generally burst thanks to their protective cell walls. • In fact, most cells in large organisms are not in contact with fresh water on a regular basis - rather, they tend to be bathed in blood or other isotonic fluids which have solute concentrations approximately equal to themselves. • Cells which are plump and rigid in hypotonic environments are called turgid; when a cell shrinks in a hypertonic environment this is called plasmolysis

18. Fill in… Move in and out in equal amounts No net movement Isotonic to the cell Cell is isotonic to its environment Move OUT of the cell The Cell Shrinks Hypertonic to the cell Cell is hypotonic to its environment Move INTO the cell The Cell Swells Hypotonic to the cell Cell is hypertonic to its environment

19. Some more practice!

20. Show what happens to plant and animal cells subjected to isotonic, hypertonic, and hypotonic solutions in the environment:

22. APPLY what you have learned about osmosis… • Why do doctor’s use a saline solution in an IV drip?

23. APPLY what you have learned about osmosis… • Why would salt kill plants?

24. APPLY what you have learned about osmosis… • Why do restaurants put out free salty snacks such as peanuts, pretzels or chips?