Crossing Membranes

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  • Crossing Membranes
    • Passive Processes
      • Diffusion
        • The tendency to even out is diffusion
          • Gas/liquid molecules spread out from the high concentration
        • Is the net movement of molecules from a region of high concentration to a region of lower concentration down a concentration graident
        • No energy
        • The rate of diffusion is affected by:
          • Temperature
          • Concentration graident
          • Stirring/moving
          • Surface area
          • Distance
          • Size of molecule
    • Active Processes
      • The needs of the cell aren't always met by diffusion. Sometimes it may need more of a particular substancesin the cytoplasm than is present outside the cell or may need to move materials into or out of the cell more quickly than diffusion allows.
      • Active Transport
        • Refers to the movement of molecules or ion across membranes which uses ATP
        • Carrier proteins
          • Shape is complementryto the molecule they carry
        • Carry molecules against the concentration graident
      • Bulk Transport
        • Endocytosis
          • Which involves bringing materials into the cell
        • Exoctysis
          • Which involves moving material out of the cell
        • Possible because membranes can easily fuse, separate and 'pinch off'
        • Requires energy
          • Used to move the mebranes around to form the vesicles that are needed and to move the vesicles around the cell
    • Water
      • Water Potential
        • Is the measure of the concentration of water molecules thjat are able to diffuse.
      • Solute -  a substances that dissolves in a liquid
      • Solvent -  a liquid that dissolves substances
      • Solution - a liquid containing dissolved substances
  • Carry larger/charged molecules through membranes
    • Carrier proteins
      • Shape is complementryto the molecule they carry


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