Passive Transport: Diffusion and Osmosis Chapter 7; ; Pgs Objective: I can correctly predict which molecules will go where, based on permeability and concentration gradients.

Plasma Membrane is Selectively Permeable Certain materials can directly pass through  Small nonpolar molecules can penetrate straight through bilayer (easiest to do so) CO 2 and O 2 …but what about sugar and others…? How do they get into/out of cell? LARGE MOL. (polar/nonpolar) small molecule (polar) small molecule (nonpolar) Easiest Small nonpolar Small polar Large (polar/non) Hardest

Plasma Membrane is Selectively Permeable Transport proteins (integral proteins)  Allow certain molecules/materials to pass through protein into the cell Will discuss specific examples later…  Overall  plasma membrane = selectively permeable But what direction do these molecules/ materials move? How know?

Concentration The amount of solute compared to water  Solute = substance dissolved in water Examples: sugar, salt, kool-aid, etc.  Determine concentration by ratio of molecules  Blue = water molecule; Red = kool-aid

Concentration Gradient Difference in concentration  Pointed down (toward low concentration) If concentrations are equal, then there is no concentration gradient

Diffusion Movement of solute from area of high concentration to area of low concentration Movement down theconcentration gradient Results from normal, natural, random movement of molecules

Diffusion across membrane Diffusion requires NO energy  Type of passive transport  Which way will diffusion move the solute molecules? Dynamic Equilibrium: No “net” movement: equal movement back and forth

Diffusion In Action Some depictions show no water  2 solutes… Red = oxygen molecule White = carbon dioxide molecule  Both small enough (and nonpolar) to get through plasma membrane

Osmosis Movement of water from an area of low solute concentration to an area of high solute concentration  “Diffusion of water” Form of passive transport Water can flow into/out of cell through channel proteins called aquaporins Move water from area of high conc. of water to area of low conc. of water

Osmosis moves water  From area of low SOLUTE conc. to high  From area of high WATER conc. to low (when aquaporins only allows water through) If diffusion COULD work…

Osmotic Pressure Strong enough to push water up against gravity Maintains turgor pressure (keeps plants rigid)

3 Types of Osmotic Solutions All end in “-tonic”  tonicity: Ability of a solution (outside the cell) to cause a cell to gain/lose water  Isotonic  Hypotonic  Hypertonic

Isotonic solution Solution has same concentration outside of cell as inside of cell Water flows equally in both directions (dynamic equilibrium) Cell does not change size “iso” = equal

Hypotonic Solution Solution has LOWER concentration outside of cell than inside of the cell Water flows into the cell (to dilute) Cell expands in size (can burst!) “hypo” = low If diffusion COULD work…

Hypertonic Solution Solution has HIGHER concentration outside of cell than inside of the cell “hyper” = high Water flows out of the cell (to dilute) Cell shrinks If diffusion COULD work…

Comparing and Contrasting Diffusion and Osmosis DiffusionOsmosis Passive transport (requires no energy) MovessoluteMoveswater Moves from high (solute) concentration to low concentration Moves from low (solute) concentration to high concentration

Osmoregulation (animal cells) Regulating/controlling water balance If an animal cell is placed in a environment, it could lyse (burst)… Animal cell will try to pump out water …sounds like? Contractile vacuole (found in paramecium) hypotonic

Osmoregulation (plant cells) Hard cell wall prevents bursting/lysing  Hypotonic  Turgid (plant is upright) from Turgor Pressure: most desired in plants  Isotonic  Flaccid (wilting): not ideal…  Hypertonic  Plasmolysis: cell shrinks and plasma membrane pulls away from wall (dying!)

Facilitated Diffusion Passive Transport (no energy needed)  Requires the help (facilitation) of proteins Especially for large/polar molecules (H 2 O/ions/glucose) Two types of transport proteins  Channel Proteins Acts like a fitted slot with a hydrophilic interior Some are gated channels, like ion channels Ex. Aquaporin (for water)  Carrier Proteins Binds to solute and changes shapes to move across Can saturate, which limit how much passes

Hydrophilic region in the middle 8/student/animations/membrane_transport/in dex.html /student_view0/chapter2/ani mation__how_facilitated_diffusion_work s.html