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. NOTE: (*tonic = solute. [High] solute means [low] water)
Solutions on the outside of a cell (in its environment) can be described based on how they affect the cell:
Hypertonic
“Above Strength”
Cell Shrinks
The solution outside the cell has a [higher] of solutes than inside
Water moves OUT of cell
Hypotonic
“Below Strength”
Cell Swells
The solution outside the cell has a [lower] of solutes than inside
Water moves INTO the cell
Isotonic
“Same Strength”
Cell stays the same
the solution outside the cell has the [SAME] of solutes than inside
Water moves EQUALLY in/out of the cell
NOTE: (*tonic = solute. [High] solute means [low] water)
"HYPER" = HIGH; "HYPO" = LOW; "ISO" = equal or same.

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

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

11. VISUALIZE ISOTONIC What will happen a) no net movement
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

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. Let’s do some math!
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?

15. Osmotic Pressure
Driven by differences in solute concentration, the net movement of water into or out of a cell produces a force known as 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… Conditions Water will… Environment is...
Solute concentration in the environment is equal to that in the cell
Solute concentration in the environment is greater than the cell
Solute concentration in the environment is less than the cell
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. Animal cell (blood cell)
Show what happens to plant and animal cells subjected to isotonic, hypertonic, and hypotonic solutions in the environment:
Conditions
Plant Cell (leaf cell)
Animal cell (blood cell)
Environment
Before
After
Solute concentration in the environment is equal to that in the cell:
Isotonic solution
Solute concentration in the environment is greater than the cell:
Hypertonic Solution
Solute concentration in the environment is less than the cell:
Hypotonic Solution

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?