Gas exchange

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  • Gas exchange
    • SA to Vol. ratio
      • Ficks law
      • Rate of exchange depends on SA in contact with the surroundings
      • SA/Vol.
        • As organisms get bigger, SA:Vol gets smaller
        • As organisms get bigger, exchange with surroundings gets harder
      • Heat
        • Small SA:Vol. ration slows heat loss, small organisms need high metabolism to generate more heat
    • Insects
      • Active, need to respire quickly
      • Network of tubes carry air directly to cells from spiracels which lead to tubes called tracheae, which branch into tracheoles
      • Trachioles are held open by chatin
      • Oxygen and water diffuses in, CO2 diffuses out
      • Trachioles can be ventilated using muscles to squeeze trachia
    • Fish
      • Gills
        • Composed of filaments, covered by lamellae containing capillaries. Large SA, small distance
        • Water flows over them so oxygen can diffuse in and Co2 can diffuse out
        • Covered by muscular flaps - opercula
      • Ventilation
        • One way - through mouth, out opercular valves
        • Inspiration
          • Mouth opens and muscles contract lowering buccal cavity, increases volume and decreases pressure, outside pressure closes peculiar valves, water flows in
        • Expiration
          • Mouth closes and muscles relax raising buccal cavity, decreases volume, increases pressure, peculiar valves open, water flows out
      • Counter Current flow
        • Blood and water flow past each other in different directions, so diffusion is always occurring, giving 80% uptake
    • Plants
      • Spongey mesophyll cells - irregular shaped, loosely packed spongey cells increase SA giving a large SA:Vol ratio
      • Gasses enter through stomata surrounded by guard cells
      • Water diffuses from xylem and mesophyll cells to air spaces in leaves
      • Water loss
        • Waterproof cutical made of lipids, moist air spaces, guard cells
      • Adaptaions
        • Paliside - thin cytoplasm, lots of chloroplasts
        • Mesophyll cells - loosely packed, lots of space
      • Photosynthasis increaces O2 in air spaces and decreces Co2, speeding diffussion


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