1.14 Passive Transport

Electrolyte – positive/negative ions dissolved in an aqueous solution

Simple Diffusion

Selectively permeable – allows only certain substances to pass through it• Many small, uncharged molecules (ex. H2O, O2, CO2, fatty

acids) pass through the cell membrane freely either through the P-lipid bilayer or through protein channels throughout the membrane

Simple diffusion – the movement of particles from an area of high concentration to an area of low concentration until particle concentration is equal• Doesn’t use any of the cell’s energy

Concentration gradient – a difference in concentration between 2 areas

Dynamic equilibrium – a state of balance where particles move in all directions at equal rates• [particles] remains the same on both sides of

the cell membrane

The rate of diffusion depends on the temperature and the [solute molecules] in the solution

• Molecules move faster at higher temperatures

• There are more molecules to balance things out at higher concentrations

Facilitated DiffusionFacilitated diffusion – the diffusion of solutes through a membrane assisted by proteins

Amino acids, carbohydrates, nucleic acids, and large lipids can’t move through the cell membrane• These substances need help getting through the

membrane – do so through membrane proteins

Different proteins act in different ways to help substances across the membrane

• A channel protein can provide a channel through which the particle can travel. Ions such as sodium and chloride cross the membrane in this way.

• A carrier protein can bind to the particle, transport it across the membrane, and release it. Large polar molecules such as glucose cross the membrane in this way.

OsmosisOsmosis – the net movement of water across a selectively permeable membrane from an area of high concentration to an area of low concentration

• High [H2O] = low [solute] (dilute)• Low [H2O] = High [solute] (concentrated)

Isotonic solution – solution where [solute] is equal

Hypertonic solution – has higher [solute]

Hypotonic solution – has low [solute]

Osmosis and Blood

Red blood cell cytoplasm and blood serum are isotonic

Osmosis doesn’t happen in red blood cells

When a patient receives an IV drip, the IV solution mixes with blood serum• If the IV solution given is hypotonic (low [solute]) it might

dilute the blood serum• Blood serum is hypotonic to RBC cytoplasm• Osmosis will occur into the RBC, causing it to fill with fluid

and burst (hemolysis)– May be fatal because the RBCs won’t be able to transport O2

If the IV solution is hypertonic (high [solute]), it will concentrate the blood serum• Blood serum is hypertonic to the RBC cytoplasm• Osmosis will occur out of the RBC, causing it to shrivel

(crenation)– Can be fatal because the shrivelled cells can stick to one

another and clog veins and arteries

Homework

• Pg. 64 #1-11