cell membrane transport

• diffusion?

  net movement of molecules from a region of high concentration to a region of low concentration down a concentration gradient

  • passive, doesn't require energy
  • molecules move until equilibrium is reached- no net change in number of molecules
• what factors affect the rate of diffusion?

  • temperature
  • steepness of concentration gradient
  • surface area of membrane
  • type/size of molecule entering/exiting
  • thickness of membrane
  • membrane permeability of molecule
• facilitated diffusion?

  same as diffusion just involving carrier/channel proteins for moving polar/larger molecules (larger than carbon dioxide)
• osmosis?

  movement of water molecules from a solution with a higher concentration of free water molecules to a lower concentration with free water molecules moving down a concentration gradient through a PPM.
• active transport?

  moving molecules against a concentration gradient from a lower -> higher concentration

  • requires ATP
  • channel/carrier proteins involved
• exocytosis/endocytosis (bulk transport?)

  • exo: molecules enclosed in vesicle transported out of the cell when vesicle fuses with surface and releases content
  • endo: membrane bulged inwards, wraps around particle and pinches off to form a vesicle inside the cell.

  requires energy to form vesicles