Movement of Substances

Movement of Substances

1. Types

   • Passive
     • Does not require energy
     • Move ↓ conc. gradient
     • Eg.
       • Diffusion
       • Osmosis
   • Active
     • Requires energy
     • Move against / up conc. gradient

2. Diffusion

   • NET movement of particles frm a region of HIGH conc. to LOW conc.
     • Down conc. gradient
       • Conc. gradient
         • Diffeence in conc. btw 2 regions
         • Steeper grad.
           • ↑ rate of diffusion
   • Factors affecting RATE
     • Conc. gradient
       • Steeper
         • ↑ rate
     • Temperature
       • ↑
         • ↑ energy level of molecules
           • ↑ rate
     • Size of particles
       • ↓
         • ↓ energy required to move particles
           • ↑ rate
     • Thickness of membrane
       • Thin
         • ↓ distance for particles to travel
           • ↑ rate
       • May be unapplicable
         • Diffusion does not require a membrane
   • Eg.
     • Animal cells
       • Partially permeable membrane
         • Allow some substances through
       • Eg.
         • Lungs
           • Alveolus separated frm capillaries by a thin membrane
           • Diffusion
             • Gas exchange across membrane
         • Small intestines
           • Epithelium of villus
             • One-celled thick
               • ↑ of diffusion
                 • Digested food molecules into bloodstream
     • Practical Application
       • Kidney Dialysis
         • Diffusion
           • Wastes products removed frm blood through artificial membrane in machine
             • Blood cells & large molecules retained

3. Osmosis

   • NET movement of WATER molecules frm a region of ↑ WATER POTENTIAL to ↓ w.p
     • Across a PARTIALLY PERMEABLE MEMBRANE
       • Water potential
         • Tendency for water molecules to move frm 1 place to other
         • Eg.
           • Dilute solution
             • ↑ water molecules per unit vol than a concentrated soln
   • Plants
     • Tugor pressure

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