2. Cellular Homeostasis – the plasma membrane
Semi-permeable or Selectively permeable
2 methods used in crossing the membrane – active and passive
Active transport requires the use of ATP. Which organelle provides this high-powered molecule for the cell?
Passive transport uses the principles of diffusion to cross the membrane and does not require the use of ATP.

3. Facilatated Diffusion
The random movement of molecules from an area of high concentration to an area of low concentration.
Facilatated Diffusion
Diffusion, from high to low concentration, using an integral protein carrier (examples: amino acids or glucose).

4. Active Transport
Movement is against the concentration gradient (low to high concentration).
Requires a protein carrier and the use of ATP. ATP is used by the carrier to modify the shape of the protein.
Example: Sodium-Potassium Pump; endocytosis, exocytosis.

5. Active Transport

6. Endocytosis Exocytosis
Process in which a portion of the plasma membrane engulfs a large substance and then pinches off the membrane. (cell eating)
Exocytosis
A process where a vesicle fuses with the outer plasma membrane as secretion of the contents occur. (waste)