1. Cell Membranes

2. The cell membrane’s purpose is to control what goes in and what goes out of a cell
The cell membrane also provides protection and support

3. The Lipid Bilayer
The cell membrane is made up primarily of two sheets of lipids called the lipid bilayer
In addition to lipids, some carbohydrates and proteins are embedded in the bilayer. Because of these embedded molecules we refer to the lipid bilayer as a fluid mosaic.

6. Concentration
How does a cell membrane control what enters and exits a cell?
The concentration of the liquids on either side of the membrane is the key.

7. Concentration is the measure of the amount of “stuff” (solutes) in any given amount of a solvent.
Concentration = mass of solute / volume of solvent.
8 grams of an salt in 2 liter of water gives us a concentration of 4 g/L.

8. Which of these is more concentrated for sugar?
2 gallon of iced tea with one spoonful of sugar
3 gallons of iced tea with two spoonfuls of sugar

9. Which of these is more concentrated for sugar?
3 gallons of iced tea with two spoonfuls of sugar

10. Diffusion

11. Diffusion Diffusion is the random spreading out of molecules
In diffusion molecules move from areas of high to areas of low concentration

13. The cell membrane is only permeable to some substances
The cell membrane is only permeable to some substances. It is selectively permeable.
Diffusion can only occur across a cell membrane if that membrane is permeable to the solute in question.

14. Osmosis
Cell membranes usually permeable to water, so a special kind of diffusion called osmosis can occur.
Osmosis is diffusion of water.
Osmosis moves water from high concentration of water to low concentrations of water.

15. Concentration of Water
If a water solution is highly concentrated for a solute, it has a low concentration of water.

16. Which of these is more concentrated for iced tea?
2 gallon of iced tea with one spoonful of sugar
3 gallons of iced tea with two spoonfuls of sugar

17. Which of these is more concentrated for iced tea?
2 gallon of iced tea with one spoonful of sugar

18. Where will salt move?

19. Where will water move?

20. Transport
When substances move across a cell membrane we call it transport
There are 2 types of transport
Passive
Active

21. Passive Transport
No energy
Moves from high to low concentration

22. Facilitated Diffusion
Special protein channels allow substances to pass through a membrane
High to low concentration

24. Active Transport Uses energy Requires transport protein
Low concentration to high concentration

26. Tonicity
Hypotonic Solution – concentration is lower

27. Tonicity
Isotonic Solution – concentration is equal

28. Tonicity
Hypertonic Solution – concentration is higher

29. Why can’t we drink sea water?
Salt water is hypertonic to our cells

31. Water intoxication
Drinking extremely large amounts of water in a short time period can lead to death
Our cells are hypotonic to pure water