1. A cell's membrane ​is selectively permeable. (aka semi-permeable)
The cell membrane

2. Permeable means things can pass through it.
Selectively permeable means the cell membrane "selects" (chooses) 
​what it permits to enter the cell and 
​what it "allows" to leave the cell.
Selective means "picky", the membrane chooses what it 
​allows to enter/exit the cell.
Permeable means things can pass through it.

3. The ball rolls down the hill
WITHOUT ANY EFFORT...
It requires NO energy!

4. That is Passive Transport!
The ball rolls down the hill WITHOUT 
​ANY EFFORT...It requires NO energy
Passive Transport: means the movement of 
​substances without the use of energy.

5. DIFFUSION is a type of passive transport.
Diffusion occurs because molecules 
​move naturally (without energy) 
​from areas where there are more 
​of them (high concentration) to areas where there are fewer of 
​them (low concentration).

6. INTO or OUT?

7. THE RULES OF DIFFUSION:
Diffusion occurs when....
1. The molecules move from high concentration 
​ to low concentration
2. The cell membrane is selectively permeable
 (if it is not permeable...nothing will get in or 
​ out)
3. The molecules are small enough to fit 
​ through the openings (pores) in the cell 
​ membrane

8. Fresh fruits and vegetables are often 
​sprayed with water at the supermarket. 
​Explain why.

9. Roads are sometimes salted to melt ice.
How does the salt affect the plants growing alongside the road?

10. In the hospital, people are often given an IV of Saline (salt) solution.
Why not just give them an IV of Distilled (pure) water?

11. BUT... What if the cell needed to move molecules AGAINST the concentration gradient?
It would have to use ENERGY!

12. Plasma Membrane Made of: Lipids Proteins Carbohydrate Chains
Fluid Mosaic Model
Plasma Membrane
Cell Membrane
Double Layered
(Phospholipid Bi-layer)
Controls what Enters
and or Leaves the
Cell (except for
Water and Air)
Semi-Permeable