51 Passive Transport

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5-1 Passive Transport
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• Passive transport - no energy input
• Diffusion
• movement of substances down a concentration
  gradient (from high to low)
• will occur until equilibrium exists
• some substances (oxygen, carbon dioxide, small
  molecules) can diffuse directly through the cell
  membrane

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• Osmosis
• diffusion of water
• Direction of Osmosis depends on concentration of
  solutes in the environment of the cell.
• Hypotonic lower concentration of solutes
  outside the cell
• Hypertonic higher concentration of solutes
  outside the cell
• Isotonic equal concentration of solutes inside
  and outside of cell

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• Effects of Osmosis
• Some unicellular organisms living in freshwater
  use contractile vacuoles to pump excess water out

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• Plant cells
• Turgor pressure take in water
• Plasmolysis lose water (wilt)
• Animal cells
• Cytolysis take in water (burst)
• Crenation lose water (shrink)

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• Facilitated Diffusion
• Substances diffuse across the cell membrane
  assisted by carrier proteins
• Diffusion Through Ion Channels
• Ions diffusion across the cell membrane through
  specialized channels