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Passive Transport

diffusion - mov't of molecules from higher to lower concentration 

  • continues until concentration is uniform
  • allows certain polar molecules to enter through the channels
  • inner, polar lining of channels allow polar molecules to enter
  • each channel is selectively permeable, only allowing certain molecules to pass through
  • ions need transport proteins to move in/out of the cell
  • ion channels - have hydrated interiors so that ions never come in contact w/ nonpolar fatty acids
    • voltage and concentration determine direction of ions
  • carriers - brings substances across the membrane by binding to them at 1 end and releasing them out the other
    • depends on the concentration gradient of the substance being transported
    • performs facilitated diffusion (either specific, passive, or saturated)
    • certain red blood cell proteins transfers different molecules in different directions
    • glucose transporter - adds phosphate group to glucose to keep internal glucose levels low; used by red blood cells to attract more glucose molecules
  • saturation - occurs when all the protein carriers are used up; transport rate can no longer increase

osmosis - both water/solutes move from higher to lower concentrations 

  • aquaporins - specialized channels for water
  • water moves towards area of more concentrated solutes to form hydration shells
  • osmotic concentration - concentration of all solutes in a solution
    • hyperosmotic - solution w/ higher concentration
    • hypoosmotic - solution w/ lower concentration
    • isosmotic - solutions w/ equal concentrations
    • water flows towards hyperosmotic region
  • hydrostatic pressure - pressure of cytoplasm pushing out against the cell membrane; tends to drive water out of the cell
  • osmotic pressure - pressure needed to stop the mov't of water across the membrane; tends to drive water into a cell

maintaining equilibrium - important to have balance between pressures 

  • animals need to keep isosmotic conditions more than plants/fungi due to lack of cell walls
  • extrusion - used by single-celled eukaryotes w/ vacuoles
    • vacuole collects water from the cell, pumps it out by contracting rhythmically
  • isosmotic solutions - some animals use their environment to adjust internal solute concentration
    • ocean organisms' internal conditions match that of seawater
    • blood contains protein albumin to raise solute concentration of liquid blood to match that of the cells
  • turgor pressure - internal hydrostatic pressure
    • makes plants rigid by pressing against the membrane/cell wall
    • maintains shape of plants
Subject X2: 

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