1. Functions of Cell (Plasma) Membrane
Protective barrier
Regulate transport in & out of cell (selectively permeable)
Allow cell recognition
Provide anchoring sites for filaments of cytoskeleton

2. Cell membranes help organisms maintain homeostasis by controlling what substances may enter or leave the cells.

3. Photograph of a Cell Membrane

4. Membrane Components 3) Proteins (peripheral and integral)
3) Proteins (peripheral and integral)
1) Phospholipids
2) Cholesterol

5. Phospholipids Make up the cell membrane
Contains 2 fatty acid chains that are hydrophobic
Head is hydrophilic & contains a –PO4 group & glycerol

6. FLUID MOSAIC MODEL
FLUID- because individual phospholipids and proteins can move side-to-side within the layer, like it’s a liquid.
MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.

7. Cell Membrane Polar heads are hydrophilic “water loving”
Nonpolar tails are hydrophobic “water fearing”
Makes membrane “Selective” in what crosses

8. Semipermeable Membrane
Small molecules and larger hydrophobic molecules move through phospholipid bilayer easily.
Examples: O2, CO2

9. Semipermeable Membrane
Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own.

10. Check Point
The cell membrane can be described as “selectively permeable”. What does that mean?
What are the components of the cell membrane?
Draw and label a phospholipid. Explain how the different parts make a cell selectively permeable.
What types of molecules can easily pass through the cell membrane? Give an example.
What types of molecules cannot move easily through the cell membrane? Give an example.

11. Passive Transport: the movement of substances across a cell membrane without the use of cell energy (ATP) down a concentration gradient
Diffusion
Simple Diffusion
Facilitated Diffusion
Osmosis

12. Concentration Gradient

13. Simple Diffusion
The movement of molecules from an area of high concentration to an area of low concentration (high  low)
Molecules tend to “spread out”
Requires no energy
Molecules that can dissolve in lipids (hydrophobic) can diffuse through the membrane
Very small molecules that are not lipid soluble can also diffuse through the membrane (EX: O2 and CO2 )

14. Facilitated Diffusion
Carrier proteins “help” molecules across the membrane down the concentration gradient
Molecules that use facilitated transport:
Polar molecules (amino acids)
Some large molecules (glucose)
Charged molecules (ions)

15. The carrier protein transports the molecule across the cell membrane
A molecule outside the cell binds to a carrier protein on the cell membrane
The carrier protein transports the molecule across the cell membrane
The molecule is released from the carrier protein inside the cell

16. Osmosis The diffusion of water molecules across a cell membrane
High concentration  low concentration
Watch the animation:

17. SOLUTES SUCK Rule for Osmosis
If the area outside the cell has more salt—then water will be sucked out of the cell

18. Cells in Different Solutions
“Iso” means the same
Solutes are in equilibrium

19. “Hypo” = less
Cells may burst or “lyse”

20. “Hyper” = more Cell will shrink or die, plants wilt
Q: Why is it dangerous to drink salt water?