1. Lab 6
Diffusion/osmosis

2. Intro to Lab 6

3. Solutions Molecules (solutes) dissolved in a liquid (solvent)
All molecules are constantly in motion
Molecules in solution move randomly
Random motion causes mixing

4. Brownian Motion
Random tendency of ALL molecules to move due to their inherent kinetic energy.
Kinetic energy: energy of motion

5. Concentration Gradient
Concentration is the amount of solute in a solvent
Concentration gradient:
more solute in one region of a solvent than in another

6. Concentration gradients
Concentrations of some key ions are very different on the inside versus the outside of cells creating a gradient
IN:
[Na+] = low
[K+] = high
[Ca2+] = very low
[Cl-] = low
OUT:
[Na+] = high
[K+] = low
[Ca2+] = low
(blood, interstitial fluid)

7. Passive transport: Diffusion
Due to: random motion and collision of molecules
Movement “down” a concentration gradient (from area of high concentration to area of low concentration)
Occurs until a dynamic equilibrium is reached

8. Diffusion – solid in water

9. Animation

10. What factors Affect Diffusion Rates?
Distance
Molecule size
Temperature
Gradient
Electrical force

11. What can/can’t diffuse through the cell membrane?

12. Lab exercise 6 Transport
Activities 6.1 – 6.4
1 Brownian motion – view in scope up front
2 Diffusion of a liquid – view demo
4 Dialysis – I’ll start it, come and look later

13. Exercise 4. Dialysis Starch + iodine = purple
Purple will be inside or outside bag

14. Osmosis Osmosis is the net diffusion of water across a membrane.
Osmosis only occurs when solutes cannot cross a selectively permeable membrane (no diffusion) so the solvent, water, crosses instead

15. Osmosis = Water Movement
Water molecules diffuse across membrane toward solution with more solutes
Volume increases on the side with more solutes
Can think of it like diffusion of water: water moves from an area in which it is more concentrated (less solute) to area where it is less concentrated (more solute)

16. Osmosis

17. How Osmosis Works
More solute molecules = lower concentration of water molecules
Key to osmosis: membrane must be freely permeable to water, selectively permeable to solutes.
(i.e. some solutes must be impermeable. Otherwise, diffusion would occur)

18. Osmosis in cells

19. Osmosis Isotonic  cell ok
Hypotonic  Swelling or hemolysis (burst). Like in the bathtub
Hypertonic  crenation (shrinkage)

20. Osmosis Osmosis is the net “diffusion” of water across a membrane.
Osmosis only occurs when solutes cannot cross a selectively permeable membrane (no diffusion) so the solvent, water, crosses instead
Osmotic Pressure = a pulling force exerted by the side with more solutes that pulls water in.

21. Egg lab
Eggs are very large single cells, allow us to measure osmosis easily
We will place eggs into solutions of unknown concentration to determine what type of solution each is (hypertonic, isotonic, hypotonic)
What will happen to the egg if the solution is hypertonic and why? What about hypotonic?

22. Lab 6 Assignment
Lab Exercise #6 Parts: B
C:1,2,4 D