1. Cell Membranes Osmosis and Diffusion

2. Functions of Membranes
1. Protect cell
2. Control incoming and outgoing substances
3. Maintain ion concentrations of various substances
4. Selectively permeable - allows some molecules in, others are kept out

3. Phospholipid Bilayer

4. Fluid Mosaic Model

5. Blood-Brain Barrier
Allows some substances into the brain, but screens out toxins and bacteria
Substances allowed to cross include:
water, CO2, Glucose, O2, Amino Acids, Alcohol, and antihistamines. HIV and bacterial meningitis can cross the barrier.

6. Solutions Solutions are made of solute and a solvent
Solvent - the liquid into which the solute is poured and dissolved. We will use water as our solvent today.
Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes.

7. Methods of Transport Across Membranes
1. Diffusion
2. Osmosis
3. Facilitated Diffusion
4. Active Transport

8. Methods of Transport Across Membranes
1. Diffusion -passive transport - no energy expended
2. Osmosis - Passive transport of water across membrane
3. Facilitated Diffusion - Use of proteins to carry polar molecules or ions across
4. Active Transport- requires energy to transport molecules against a concentration gradient – energy is in the form of ATP

9. Diffusion
Movement of molecules from an area of high concentration to an area of low concentration.
Movement from one side of a membrane to another, un-facilitated

10. Diffusion

11. Osmosis

12. Tonicity is a relative term
Hypotonic Solution - One solution has a lower concentration of solute than another.
Hypertonic Solution - one solution has a higher concentration of solute than another.
Isotonic Solution - both solutions have same concentrations of solute.

13. Plant and Animal Cells put into
various solutions

14. Types of Transport

15. Today’s Lab
We are using dialysis tubing as the cell membrane - It is selectively permeable
The solute is either the eosin starch solution or the sugar solution
What is the solvent?

16. Membrane Permeability
Solute is eosin-starch-chloride solution
Solvent is Water
Indicator for presence of starch is IKI
Starch is made of amylose and amylopectin – amylopectin is insoluble
Iodine is not very soluble in water, but with KI it forms a I3- (triiodine ion) which is soluble.
I3- combines with the amylose and the starch molecule turns blue-black.

17. Elmhurst College Website
Test for Starch
Elmhurst College Website

18. Test for Chloride ions
Indicator for presence of chloride ions is silver nitrate, AgNO3
A white precipitate, AgCl, forms if chloride is present.

19. Test for Sulfate ions
Indicator for the presence of sulfate ions is Barium chloride, BaCl
Barium sulfate, BaSO4 - forms a white precipitate
BaCl + NaSO > BaSO4 + NaCl

20. Living Cells
Beet cubes will be used to see the result of boiling and adding alcohol to a live membrane.
Yeast cells are used to see effects of heat
Fern gametophytes are used to see result of putting live cells in solutions of varying tonicity

21. Osmosis We will make an osmometer to see osmosis
Sugar solution in a dialysis tube is used to simulate a cell membrane.
Various concentrations of solute may be used around the room.

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