1. The Movement of Materials Across a Cell Membrane

2. Which materials must get into/out of a cell?
Food
Water
O2 (animal cell)
CO2 (plant cell)
Wastes
CO2 (animal cell)
O2 (plant cell)
excess water

3. How do materials get into/out of a cell?
DIFFUSION
The tendency for very small molecules to drift from where they are in greater concentration toward where they are in lesser concentration
Ex: perfume molecules diffusing across a room
diffusion “stops” when the concentrations equalize -

4. Diffusion (cont.)

5. Ex: The diffusion of CO2 across a cell membrane
water

6. - Osmosis is a special kind of diffusion -
the diffusion of water molecules across a cell membrane
- the laws of diffusion apply -

7. cell swells cell shrivels cell stays same cell in pure water
hypotonic solution
contains less dissolved substances than a cell does
hypertonic solution
contains more dissolved substances than a cell does
isotonic solution
contains the same concentration of dissolved substances as a cell
100%
70%
50%
70%
70%
70%
cell in pure water
cell in 50% water (50% salt) solution
cell in 70% water (30% salt) solution
cell swells
cell shrivels
cell stays same

8. Osmosis animation

9. QUIZ

10. 1 & 2
List two things that must constantly enter a plant cell in order for it to stay alive.

11. - 3 -
Besides the general term “waste”, name one thing that must constantly EXIT a plant cell in order for it to stay alive.

12. - 4 -
Osmosis Diffusion Hypotonic Isotonic Hypertonic Which term refers to the tendency for very small molecules to drift from one place to another because of their relative concentrations?

13. What will happen to this cell?
- 5 -
What will happen to this cell?
Shrink
Swell
Stay the same
70%
90%
cell in 90% water
cell will swell