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Movement of Molecules: Diffusion, Osmosis, and Active Transport

This chapter discusses the movement of molecules through diffusion, osmosis, and active transport, including the roles of capillary hydrostatic pressure and filtration. It also covers the concepts of osmotic pressure, tonicity, and membrane transports. Examples and explanations are provided for each process.

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Movement of Molecules: Diffusion, Osmosis, and Active Transport

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  1. Unit III: Lively MoleculesMovement of Molecules Chapter 3 – pp 101 - 109

  2. Capillary hydrostatic pressure (CHP) Filtration Amino acid Blood protein • Particles are driven through a selectively permeable membrane by water • Moves material between cells not thru • Examples: coffee filter, blood capillaries Glucose Ions Interstitial fluid Small solutes Hydrogen bond Water molecule Endothelial cell 1 Endothelial cell 2

  3. Diffusion and Osmosis • Simple Diffusion • Passive transport • Random motion of solutes • Rates depend on: • Temperature • Size of the molecule • Distance • Concentration gradient • how a cell acquires nutrients and gets rid of wastes

  4. Diffusion • Down gradient • Eventually becoming uniform • Brownian Motion – random motions of microscopic particles caused by collisions with moving molecules • Example: a drop of dye in water

  5. Diffusion and Osmosis • Osmosis • Special type of diffusion: • the diffusion of water molecules across a semi-permeable membrane

  6. Diffusion and Osmosis • Osmosis • Osmotic pressure = Hydrostatic pressure to halt osmosis • Osmotic pressure is proportional to the solute concentration • Example:

  7. Diffusion and Osmosis • Osmosis • Example: Red blood cells placed in a drop of distilled water will swell and burst • Explanation: The distilled water is hypotonic to the RBC’s cytoplasm (a) Hypotonic

  8. Diffusion and Osmosis • Osmosis • Example: Red blood cells placed in a drop of highly concentrated salt solution will shrivel up • Explanation: The salt solution is hypertonic to the RBC’s cytoplasm

  9. Diffusion and Osmosis • Osmosis • Example: Red blood cells placed in a drop of blood plasma – no change. • Explanation: The blood plasma is isotonic to the RBC’s cytoplasm

  10. Diffusion and Osmosis • Osmosis • Osmolarity – total solute concentration in an aqueous solution • Tonicity – description of how the solution effects a cell • Example situation: giving large volume of fluid during blood loss or dehydration. • Osmolarity starts the same but ECF is ______________ • Ions (thus water) moves in to ICF to equilibrate ↑ osmolarity • Administer: ________________

  11. Other Membrane Transports • Carrier – Mediated Transport • Cell membrane is essential • Employ transport proteins/carriers • Specificity • Saturation Transport maximum (Tm) Rate of solute transport (molecules/sec passing through plasma membrane) Concentration of solute

  12. Carrier – Mediated Transport Facilitated Diffusion • Down gradient • No ATP used

  13. Carrier – Mediated Transport Active Transport • Up gradient • ATP energy required to change carrier • Examples: • sodium-potassium pump • bring amino acids into cell • pump Ca2+ out of cell

  14. Carrier – Mediated Transport Active Transport Sodium-Potassium Pump • Needed because Na+ and K+ constantly leak through membrane • One ATP utilized to exchange three Na+ pushed out for two K+ brought in to cell

  15. Carrier – Mediated Transport Active Transport Sodium-Potassium Pump Sodium ion Glucose molecule + • Regulation of cell volume • Heat production • Maintenance of a membrane potential • Secondary active • transport (No ATP used) Na+–K+ pump CYTOPLASM +

  16. Vesicular Transport • Transport large particles or fluid droplets through membrane in vesicles • Endocytosis – • phagocytosis – • pinocytosis – • receptor mediated endocytosis – • Exocytosis – Bacterium Pseudopodium Phagocytosis Lysosome Golgi apparatus Exocytosis

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