1. Cell Function – Cells and their Environment

2. Molecules are always moving
Molecules move randomly and bump into each other and other barriers

3. Diffusion
Movement of molecules from an area of high concentration to an area of lower concentration (down a concentration gradient).
Continues until equilibrium is reached.

4. Diffusion

5. Concentration Gradient
100% - high
0 % - lower

6. Diffusion
Occurs without control or energy use – it is called Passive Transport
Affected by:
Size of molecules
Size of pores in a membrane
Temperature
Stirring

8. Simple Diffusion

9. LAB – Diffusion Dialysis tubing – simulates a cell membrane Starch
Water
glucose
Water
Iodine
What will happen to the starch?
glucose?
iodine ?
WHY?

10. Cell Membranes are Semipermeable
Let some molecules pass through and not others.
Small molecules pass through – ex: water
Large molecules can’t pass through – ex: proteins and complex carbohydrates

12. How long does diffusion continue?
Until equilibrium is reached:
This means there will be an equal distribution of molecules throughout the space – this is why odors smell strong at first, then seem to disappear

13. Osmosis – A Special kind of Diffusion
Diffusion of water across a selectively permeable membrane
Cytoplasm is a solution of water and solutes (stuff dissolved in the water).
Water moves into and out of cells because of the different concentrations of the solutes.
Different kinds of cells react differently to osmosis, depending on the solution they are in:

14. Hypertonic Solution – More water inside cell than outside
Plasmolysis
Plasmolysis
Cells shrink and die

15. Iso-osmotic Solution – same concentration of water inside and outside cell
Animal cell
Plant cell
No net gain or loss of water

16. Hypotonic Solution – more water outside cell than inside
Cytolysis – cell swells and bursts
Builds up turgor pressure – cell becomes stiff, keeping plant upright