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Diffusion, Osmosis

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
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