II. MEMBRANES
A. Structure
1. Phospholipid bilayer
2. Protein “islands”
3. Selectively permeable
B. Movement across membrane
1. Diffusion [concentration gradient]
High concentration to low concentration
2. Osmosis
Diffusion of water across cell membrane
a. Osmotic pressure
Tendency of water to move by osmosis
b. Osmolality {solutes – milliosmoles/volume}
c. Tonicity [solution, solvent]
-Isotonic
-Hypotonic
-Hypertonic
3. Facilitated diffusion = Passive transport
Diffusion along membrane protein carriers
4. Filtration
Solutions move across membrane by hydrostatic pressure; influenced by molecule size
5. Active transport
Movement against concentration gradient requiring metabolic energy
Na/K Pump (3 Na out/2 K in)
6. Endocytosis, Phagocytosis, Exocytosis
Processes taking in or discharging particles while maintaining the integrity of the cell membrane