Brownian movement - random mov't of molecules in biological systems

• occurs due to collisions between molecules
• molecules' mov't can't directly be seen, but mov't after collisions can be seen

diffusion - directional mov't of molecules down a gradient

• from areas of high concentration, heat, pressure to areas of low concentration, heat, pressure
• rate determined by steepness of gradient and characteristics of the molecules
• temperature/pressure usually constant in most biological systems
• selective (differentiable) permeability - ability of cell membranes to decide what moleules can pass through it; selects based on size, charge, solubility
• polar molecules - positive/negative charged areas
• nonpolar molecules - no local areas of charge
• small nonpolar molecules pass through the membrane most easily
• dialysis - separation of dissolved substances by using their unequal diffusions

osmosis - diffusion of water across a differentially permeable membrane

• follows rules of diffusion, except w/ water
• hypotonic - solution w/ lower solute concentration than surrounding environment
• hypertonic - solution w/ higher solute concentration than surrounding environment
• isotonic - 2 solutions w/ equal solute concentration
• water moves from hypotonic to hypertonic areas
• even in isotonic solutions, water still moves, but concentrations stay the same

water potential - effects of concentration/pressure from cell walls

• increased by high water concentration/pressure
• decreased by high solute concentration, low pressure
• water flows from areas of high water potential to areas of low water potential

lysis - destruction of cell by influx of water

• animal cells lack cell walls, bursts more easily than plant cells
• hemolysis - lysis of red blood cells
• crenation - shriveling of cells
• plasmolysis - shrinking of plant cytoplasm, where cell membrane pulls away from cell wall in plants