1. Diffusion and Osmosis
Lab 2 Background

2. Membranes Phospholipid bilayer containing embedded proteins
Fatty acids limit the movement of water because of their _______________.
Hydrophobic nature.

3. Water
Passes freely through the membrane by osmosis or through aquaporins.
Moves from areas of high potential/high [water] to low potential of low [water].
* In walled cells, osmosis is affected by [solute] & resistance to water movement in the cell by the cell wall (known as Turgor Pressure).

4. Ions
Move through protein channels

5. Larger Molecules
Ex. Carbohydrates
Use transport proteins

6. Diffusion Simplest form of movement
Solute move from areas of high [solute] to areas of low [solute]
Does not require energy input
*ATP and protein carriers called Pumps are required to move solute from areas of low [] to areas of high [].

7. Diffusion
Molecular weight is inversely related to the rate of diffusion
Non-directional
Increases as kinetic energy increases (for example via increase in temperature)
At equilibrium, diffusion reaches a dynamic equilibrium not static equilibrium.

8. Solute concentrations
Hypertonic- high [solute]; low water potential
Hypotonic- low [solute]; high water potential
Isotonic- equal water potentials
The above 3 terms are used to describe solutions separated by selectively permeable membranes
These terms are used to describe solute concentration.
How does solute reduce free water in a system?
Which way will water move through a selectively permeable membrane in the above solutions?

9. Homeostasis
Cells must maintain their internal environments and control solute movement
Why?

10. Water Potential
As water moves out of the cell, the cell shrinks or undergoes crenation.
As water moves into the cell, it may eventually burst or lyse.
In walled cells (fungal & plant), the cell wall prevents the cell from bursting as water enters but pressure builds up inside the cell and affects the rate of osmosis.
Stopped here with 5th period (09/27/13)

11. Water Potential
Measures the tendency of water to move from 1 compartment to another
Is the free energy/mole of water
Represented by the Greek letter psi ____.
= pressure potential (+ve or –ve) + solute potential (aka osmotic potential)
*pressure potential = exertion of pressure
* Solute potential = [solute]

12. Calculating Solute Potential
Solute potential ____= -iCRT
i=ionization content
C= molar concentration
R= pressure constant =
liter bars/mole-K
T= temp in K (273 + degree Celcius)
* Bar- a metric measure of pressure and is the same as 1 atmosphere at sea level

13. Hints Water potential ____of pure water =0
Water potential ____of a solution = -ve value
Why?
*Summary videos:
Solutes in the solution decreases the water potential.
Stopped here: 2nd P (09/27/13)

14. Practice
Calculate the solute potential of a 0.1M NaCl solution at 25 degree Celcius. If the concentration of NaCl inside the plant cell is 0.15M, which way will the water diffuse if the cell is placed into the 0.1M NaCl solution?
What must turgor pressure equal if there is no net diffusion between the solution and the cell?
1. Solute potential of the solution= -4.9 ; water potential = 0 + (-4.9)= -4.9
Solute potential in the cell= -7.4; water potential = 3 + (-7.4)= -4.4
-4.4 is a higher value than -4.9, inside the cell has a higher water potential than outside the cell, therefore water will move down its concentration gradient into the cell.
2. Turgor pressure must = 2.5 for there to be no next movement of water

15. Part 1
Think-pair-share: discuss with your lab partners the answers to the questions under getting started on pgs. S54-S55.
Conduct Step 1
Conduct Step 2 & answer the questions
* Cut 3 square blocks of agar (1cm, 2cm & 3cm)
*Don’t forget to record your rate of diffusion.

16. Part 2
Think-pair-share: discuss with your lab partners the answers to the questions under getting started on pgs. S56-S57.
Set up your experiment- you should 5 cups, don’t forget to label your cups with what solution is inside tube and what soln is outside
Get initial weight; after 30 mins and after 24hrs.

17. Dialysis Videos
re=related
re=related

18. Elodea Video

19. Part 3 Think-pair-share: answer question in Step 1 S58-S59.
Skip Step 2
Design and Conduct your investigation (use potato pieces of the same size however you may vary the type of potato)
Leave overnight
Answer questions on S59
Rank solutions from lowest to highest solute concentrations
Rank solutions from lowest to highest water potential.