1. DIFFUSION & OSMOSIS

2. Diffusion: the gradual spreading out of molecules
Molecules spread from areas of high concentration to areas of low concentration

3. Osmosis: a special TYPE of diffusion
Osmosis is the diffusion of WATER through a membrane

4. 3 Types of Solutions: Hypertonic Solution:
Solution that has a lower concentration of water and a higher concentration of solutes than in the cell
Water moves from high to low so…
water will move out of the cell
Cell shrinks called PLASMOLYSIS

5. 3 Types of Solutions: 2. Hypotonic Solution:
Solution that has a higher concentration of water and lower concentration of solutes than in the cell
Water moves from high to low so…
water will move into the cell
Cell GROWS called CYTOLYSIS

6. 3 Types of Solutions: 3. Isotonic Solution:
Solution outside the cell has the same concentration of water as inside the cell
Water moves into and out of the cell at the same rate
No net gain or loss of water

7. WATER ALWAYS MOVES FROM HYPOTONIC TO HYPERTONIC

8. Cell membranes are….. Selectively Permeable (semi-permeable)
-some things can get in/out, others can’t
Analogy – like a screen on a window!

9. If you put a cell into a hypertonic solution,
There’s more water inside the cell
than there is outside the cell
Water will move out of the cell
94% water, 6% solutes
This will keep going on until the two
solutions are balanced
95% water, 5% solutes
If the cell loses water, it will
Shrink (plasmolysis)

10. If you put a cell into a hypotonic solution
There’s more water outside the cell
than there is inside the cell
95% water, 5% solutes
Water will move into the cell
94% water, 6% solutes
This will keep going on until the two
solutions are balanced
Cell takes in water, it will grow = cytolysis

12. Osmosis video

13. CHECK YOUR UNDERSTANDING
What happens to a cell in a HYPERTONIC solution?
What happens to a cell in a HYPOTONIC solution?
What happens to a cell in an ISOTONIC solution?
Explain, using osmosis terms, why you should never drink sea water
Explain, using osmosis terms, why leftover salad gets wilted if it already has salad dressing on it

14. Plant cells – don’t burst – protected by cell wall turgor pressure builds up

15. Single-celled pond creatures – don’t burst collect water into contractile vacuoles and spit it back out

16. How do cells get the stuff they need?
If they can’t get it by diffusion, they may have to use energy to collect certain molecules
ACTIVE TRANSPORT