1. Membrane Permeability
hydrophobic, nonpolar molecules can cross with ease
examples: CO2 & O2
hydrophilic molecules have difficulty passing through the hydrophobic core of the lipid bilayer
examples: water & glucose
transport proteins help hydrophilic substances cross
channel proteins create hydrophilic tunnels (ex: water passes thru aquaporins)
carrier proteins shuttle molecules across

2. Passive Transport
diffusion – movement of molecules from area of high concentration to area of low concentration (down concentration gradient)
occurs spontaneously so no energy is required

3. Osmosis the diffusion of water
water diffuses from a region of lower solute concentration to a region of higher solute concentration until equilibrium is reached

4. Tonicity
the ability of a solution to cause a cell to gain or lose water
isotonic solution will cause no net movement of water into or out of a cell
hypertonic solution (higher solute concentration than cell) will cause water to move out of the cell & cell will shrink/shrivel
hypotonic solution (lower solute concentration than cell) will cause water to move into the cell & cell will burst (lyse) if no cell wall is present

5. turgidity is healthy for non-woody plants because it helps keep the plant upright
plasmolysis will cause plants to wilt & possibly die

6. Facilitated Diffusion
diffusion with the help of transport proteins
channel protein – provides a tunnel for molecules to move through
(ex) gated ion channel – opens & closes with a chemical or electrical stimulus
carrier protein – translocates molecules across the membrane by changing shape when a solute binds to it

7. Active Transport
movement of molecules across a membrane from low to high concentration (against concentration gradient)
requires energy (ATP)
involves carrier proteins
(ex) sodium-potassium pump
other examples:
cotransport
exocytosis
endocytosis

8. Ion Pumps create membrane potential = the voltage across a membrane
cytoplasm is negative in charge compared to the extracellular fluid
creates an electrical force that helps drive ion movement (cations will move in & anions will move out)
therefore, ions diffuse down their electrochemical gradient
examples of electrogenic pumps:
in animals: sodium-potassium pump
in plants, fungi, & bacteria: proton pump

9. Cotransport coupling of active transport with passive transport
example:
proton pump moves H+ ions against their concentration gradient causing them to build up outside the cell
as the H+ ions diffuse back into the cell (down their
electrochemical gradient)
thru a cotransport protein, energy is released that drives the uptake of another molecule

10. Exocytosis
bulk transport of molecules OUT of a cell via vesicles

11. Endocytosis bulk transport of molecules INTO a cell via vesicles
3 types:
phagocytosis (cellular “eating”)
pinocytosis (cellular “drinking”)
receptor-mediated endocytosis