1. Movement Across the Membrane
Chapter 6, Section 3

2. Diffusion
The net movement of molecules from areas of high concentration to low concentration
Only the random motion of molecules is required-
No Energy!!
In a fluid, molecules will diffuse until equilibrium (or balance) is reached.

3. Passive Transport
Diffusion of substances across a selectively permeable membrane
Carbon dioxide and oxygen freely diffuse across the membrane
Water will also pass across the membrane, but often needs the help of a protein

4. Facilitated Diffusion
A process in which a transport protein provides a pathway or channel for molecules to pass across the membrane

5. Osmosis
The diffusion of water across a selectively permeable membrane

6. Osmosis and Osmotic Pressure
Hypotonic Solutions have
a LOW salt concentration
relative to the cell
Isotonic Solutions have a salt concentration EQUAL
to the cell
Hypertonic Solutions have
a HIGH salt concentration
relative to the cell

7. How do cells deal osmotic pressure?
Cell Wall- prevents plant cells from bursting
Contractile Vacuoles- pump out excess water
Bathe cells in isotonic/blood solutions
Kidneys/Gills remove excess water from blood

8. Active Transport
Movement against the concentration gradient that REQUIRES ENERGY!!
Exs: protein pumps and transport of large molecules

9. Transport of Large Molecules
ENDOCYTOSIS
Takes material into
the cell within vesicles
EXOCYTOSIS
Vesicle fuses with
plasma membrane and
spills contents outside
the cell

10. A Summary: Side by Side