1. Testing the Squeeze Model
Diffusion and Osmosis

2. Review Goal: How does lead get into our cells? 3 Models Egg experiment
Squeeze
Channel
Active
Egg experiment
Test to see if squeeze model works with real cell membranes

3. Squeeze Model = Passive Transport
No energy required
Molecules move from area of HIGH to LOW concentration

4. Passive Transport: Diffusion
The process of random movement toward equilibrium
At equilibrium, particles continue to move, but there is no net change in distribution

5. Diffusion

6. Solute moves down the concentration gradient (from HIGH to LOW)
Diffusion is the net movement of a substance from regions of high concentration to regions of low concentration
Solute moves down the concentration gradient (from HIGH to LOW)

7. Diffusion Examples A membrane is not needed for diffusion
Food coloring
A membrane is not needed for diffusion
Diffusion causes many substances to move across a cell membrane but NO ENERGY IS NEEDED

8. Egg Experiment Results
With your group,
Analyze the data table
What happened in the egg experiment?
Draw a Model explaining the results

9. Data Table Oil No Very Large None 150 Glucose Large 90 5 DDT High 100
Substance
Charge of molecule
Size of molecule
Toxicity of molecule
Outside the egg at
Start (mL)
Inside egg after 24hrs
(per mL)
Oil No
Very Large
None
150
Glucose
Large 90 5
DDT
High
100 10
Carbon Monoxide
Small
110
Water
Iodine
Low 99
Calcium
Yes
Modify your egg experiment models based on the new information in the table.
Individually explain and justify the changes you have made in response to the complex data table.

10. Egg Experiment Results
What happened in the egg experiment
The water crossed the membrane, the oil did not
Why did the water move from the cup into the egg?
Why did the water move from the egg into the oil?

11. Membrane properties affect the diffusion of solutes

12. Small molecules (H2O) and lipid soluble, hydrophobic molecules (O2, CO2) move through easily
Molecules that pass through the phospholipid bilayer easily:
Hydrophobic molecules (oil soluble): O2, N2
Nonpolar: benzene
Small uncharged polar molecules: H2O, CO2, urea, glycerol

13. Ions, hydrophilic molecules larger than water, and large molecules such as proteins cannot move through the membrane on their own.
Molecules that don’t pass through the phospholipid bilayer easily
Large uncharged: glucose
Polar molecules: sucrose
Ions (charged): H+, Na+, Cl-, Mg 2+, HCO3, K+Ca 2+

14. Membrane properties affect the diffusion of solutes
3 characteristics of a molecule that determine the permeability of the membrane to that substance:
Polarity (hydrophobic vs. hydrophilic)
Charge (charged vs. uncharged)
Size (large vs. small)

15. What about Lead?!
Is it possible that lead can just squeeze through the membrane?
It is toxic….
It is small….
AND
It is ______________

16. OSMOSIS
Another form of passive transport

17. Egg Experiment Results
Osmosis (water diffusion)
Water diffuses from a region of high concentration to one of low concentration.
Move across the membrane until equilibrium is reached.

18. Descriptions of Solutions (in comparison to another)
Isotonic Solution
Equal [solute] in both solutions
Hypertonic Solution
Higher [solute] in the solution
Hypotonic Solution
Lower [solute] in the solution

19. Cell in Isotonic Solution
10% NaCl 90% H2O
ENVIRONMENT
CELL
NO NET MOVEMENT
10% NaCl
90% H2O
What is the direction of water movement?

20. Osmosis: Isotonic
Isotonic- special equilibrium case where there is no net movement of water
Hypotonic:A condition in which the inside of the animal or plant cell has a higher solute concentration than its environment.
Osmosis causes a net flow of water into the cell, causing swelling and expansion.
This swelling may cause cells without a rigid cell wall to burst.
Hypertonic:A condition in which the environment has a higher solute concentration than inside the animal or plant cell.
Osmosis pressure causes water to flow out of the cells and causing the cell to shrink

21. Cell in Hypotonic Solution
10% NaCl 90% H2O
CELL
20% NaCl
80% H2O
What is the direction of water movement?

22. Osmosis: Hypotonic Solution
Hypotonic- a condition in which the environment has a lower solute concentration than inside the animal or plant cell.
Water flows into the cell, causing swelling
Swelling = breakage
Hypotonic: A condition in which the inside of the animal or plant cell has a higher solute concentration than its environment.
Osmosis causes a net flow of water into the cell, causing swelling and expansion.
This swelling may cause cells without a rigid cell wall to burst.
Hypertonic: A condition in which the environment has a higher solute concentration than inside the animal or plant cell.
Osmosis pressure causes water to flow out of the cells and causing the cell to shrink
Swollen

23. Cell in Hypertonic Solution
15% NaCl 85% H2O
ENVIRONMENT
CELL
5% NaCl
95% H2O
What is the direction of water movement?

24. Osmosis: Hypertonic Solution
Hypertonic- a condition in which the environment has a higher solute concentration than inside the animal or plant cell.
Water flows out of cell into environment, cell shrinks
Hypotonic: A condition in which the inside of the animal or plant cell has a higher solute concentration than its environment.
Osmosis causes a net flow of water into the cell, causing swelling and expansion.
This swelling may cause cells without a rigid cell wall to burst.
Hypertonic:A condition in which the environment has a higher solute concentration than inside the animal or plant cell.
Osmosis pressure causes water to flow out of the cells and causing the cell to shrink

25. Osmosis

26. Osmosis in Red Blood Cells
Isotonic
Hypotonic
Hypertonic

27. Cytolysis & Crenation Crenation Cytolysis Cyto = cell Plasm=
Lysis = break
Crenation
Cytolysis

28. Plasmolysis vs. Turgid in Plant Cells

29. Osmosis With the egg in water: With the egg in oil:
The water solution is hypotonic.
Water will move into the egg until it becomes swollen
With the egg in oil:
The oil solution is hypertonic
Water will move out of egg into the oil.
Oil

30. Let’s Practice Some Problems