1. March 19, 2010 What is the point of a cell membrane?
What is the difference between a prokaryote and a eukaryote?

2. Demo w/ Food Coloring
If I add in one drop of food coloring, draw what the beaker will look like at time 0 sec.
Use “x” to represent molecules of food coloring
PREDICT what it will look like after 30 sec
Draw your prediction
PREDICT what it will look like in 15 min

3. Demo w/ Food Coloring Why does it happen like this?
(30 sec) Food coloring molecules are heavier than water, so fall to bottom.
Molecules like to be spread out
Since they are always moving, they bump into each other and they don’t like it.

4. Demo w/ Food Coloring How does this relate to cells?
Particles need to get into and out of cells
When there is too much waste inside, they want to spread out so need to leave the cell!
When there is not enough nutrients (ex. Glucose, oxygen) in the cell, it needs to enter!
Cell membrane controls enter/exit of things

5. Important Information Relating to Discovery of Cells
Discovery of cells goes along with developments of microscope
1590 = Janssen make compound microscope (more than one lens)
1667 Hooke = studies cork under microscope
Calls compartments “cells” since they look like jail cells
1675 Leeuwenhoek = “father of microscope”
Discovered bacteria and microscopic animals (zooplankton)

6. Statements of Cell Theory
Plant Cells
Statements of Cell Theory
All living things are made of cells
Cells are the basic building blocks of life.
Schleiden and Schwann (1840ish)
New cells are made from pre-existing cells
One cell grows and splits into two
Virchow (1858)
Bacteria Cell
Cell reproducing

7. Ideas for Cell Membrane
Danielli & Dawson (1935)
Lipids on inside, proteins on outside
Singer & Nicolson (1970)
current model

8. Cell Membrane Currently known as the Fluid Mosaic Model
“Fluid” because it moves
“mosaic” because it is made of many different parts
Mosaic is usually connected with art, many small parts making up a bigger image, such as the frog above
EVERY cell has one! (even if there is a cell wall, like in plants.)
Prokaryotes & Eukaryotes
Sometimes called the plasma membrane

9. Cell Membrane Protects the cell Composed of mainly
Allows only some things in (like glucose for energy) and some things out (like wastes), based on need of cell
We say it is selectively permeable
Composed of mainly
Lipids
Proteins
Also have some carbohydrates (for recognition) and cholesterol (for stability)

10. Lipids of Cell Membrane
Phospholipids
Phosphate head
Likes water
Called Hydrophillic – “hydro” = water, “phillic” = loving
Lipid tails
Don’t like water (imagine: oil, a lipid, and water do not mix!)
Hydrophobic – “hydro” = water, “phobic” = fear

11. Lipids Form a lipid bilayer (2 layer)
Outside of cells = lots of water
Inside of cells = lots of water
So tails face toward each other, heads face toward water
Some small molecules can make it in between phospholipids
PASSIVE transport (doesn’t use energy)

12. Proteins of Cell Membrane
External (peripheral)
Sit on outside of membrane
Serve as receptors for the cell, receive chemical messages from outside
Channels
allow molecules that wouldn’t mix with lipid tails thru
Not much bigger than space between phospholipids
PASSIVE transport (doesn’t use energy)
Pumps
Allow ions thru (charged atoms)
Force things thru, even if they don’t want to
ACTIVE transport (uses energy!)

13. Cell Membrane
Draw a picture of a cell membrane in your notes. Label phospholipid, lipid bilayer, protein channel, protein pump, hydrophobic, and hydrophillic regions

14. Why would molecules move without being forced to?
They get crowded
Move from high concentration (where there’s a lot of them) to low concentration (where there’s not as many of them)
Remember: all molecules are constantly moving. When they bump into each other, they move away. More bumping = more likely to be pushed/move away.

15. Why would molecules move without being forced to?
Will continue to move until equal amounts of molecules on both sides of membrane
Called dynamic equilibrium
When equilibrium is reached, they don’t stop moving. Instead, one molecule goes in
and one comes out.

16. Why would molecules move without being forced to?
Movement from high to low concentration is called diffusion
Form of PASSIVE transport, b/c energy isn’t required
Occurs between
phospholipids
(diffusion)
& in channel
proteins (called
facilitated diffusion)

17. Passive Transport
Label on your cell membrane picture where diffusion and facilitated diffusion occur

18. What happens if molecules are too big to move across membrane?
Sometimes water will move to help even out concentration
Move from high water concentration to low water concentration (just like diffusion)
Diffusion of water is called OSMOSIS

19. Factors that Affect Diffusion Lab
Be careful!
2 bottles of SAME color!
150 – 200 mL of water is fine, make sure you have same amount of water in each beaker.