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

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

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

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

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

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

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

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

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

Exocytosis bulk transport of molecules OUT of a cell via vesicles

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