Exchange of Materials (B3.1)

Diffusion, osmosis, active transport and exchange of materials in the gut and lungs

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  • Exchange of Materials (B3.1)
    • Diffusion
      • The net movement of particles from a high concentration to a low concentration
        • Solute- solid
        • Solvent- liquid
      • The diffusion of water across a partially permeable membrane
        • A partially permeable membrane allows water through it because it has tiny holes in it that only the small water molecules can fit through
          • eg/ visking tubing
      • exchange systems need to...
        • ...have a large surface area so there is more space to diffuse on
        • ...be moist because the molecules must be in the same state
        • ...have a good blood supply because it keeps the concetration gradient steep
        • ....have a small distance for the molecules to travel so it occurs quicker
    • Osmosis
      • The diffusion of water across a partially permeable membrane
        • A partially permeable membrane allows water through it because it has tiny holes in it that only the small water molecules can fit through
          • eg/ visking tubing
      • When there is a low concentration of water in the cell, water moves through osmosis across the partially permeable membrane and into the cell
        • Water concentration must therefore me maintained as it could go the other way
      • Isotonic- the water concentration both inside and outside the cells are the same
        • Isotonic Sports drink contain the same amount of water, ions, and glucose as a healthy cell so it moves into the cell quicker without hurting it
          • You should not drink them unless doing sport because...
            • create stores of unused glucose as glycogen
            • Pancreas will have to work twice as hard to maintain blood sugar levels
              • Leads to diabetes
    • Active Transport
      • moving of substances against the concentration gradient. This requires energy from respiration
        • Made in the mitochondria
    • Exchange in the gut
      • Villi- finger like projections in the small intestines
        • large surface area for more area for diffusion to occur on
        • rich blood supply to keep the concentration gradient steep for efficient diffusion
        • think wall (only 1 cell thick) so there is only a short distance for diffusion
      • digestion
        • Physical digestion- teeth, gut movement
        • Chemical digestion- enzymes
    • Gas exchange in the lungs
      • thorax- chest cavity
      • diaphragm- muscle underneath the lungs which pulls down when breathing in
      • Alveoli- balloon like adaption of the lungs in which diffusion occurs
        • (1) air moves into the alveolus when breathing in
          • (2) blood flows into the alveolus in cappilaries (low in oxygen)
            • (3) oxygen diffuses from an area of high concentration(alveolus) to low concentration(blood)
              • (4) blood rich in oxygen flows out of the alveolus and person breathes out
              • in the same way carbon dioxide diffuses out of the blood
        • wall is only 1 cell thick so molecules have a small distance to travel
      • Rib cage- bones that protect the prgans in the chest such as the heart and lungs
      • Intercostle muscles- relax and contract to increase and decrease pressure in the lungs
        • this makes the air rush into the lungs for gas exchange- breathing in
          • higher pressure (outside the body) to lower pressure (inside the lungs)
  • Solute- solid

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