Fish

• Why can't fish use their bodies as an exchange surface?


  Waterproof, impermeable outer membrane

  Small SA:V
• Two main features of a fish gas transport system

  Gills

  Lamellae
• Gills

  Supported by arches

  Multiple projections of gill filaments
• Lamellae

  Increase SA

  Blood and water flow across them in opposite directions (countercurrent exchange system)
• Explain the process of gas exchange in fish

  Fish opens its mouth to enable water to flow in and then closes its mouth to increase pressure

  Water passes over the lamellae and the oxygen diffuses into the bloodstream

  Waste CO2 diffuses into the water and flows back out of the gills
• How does the countercurrent exchange system maximise oxygen absorbed by the fish?

  Maintains a steep concentration gradient

  Keeps rate of diffusion constant along the whole length of gill

  Blood will always have a lower oxygen concentration
• Explain how the counter-current principles allows efficient oxygen uptake in fish

  Blood and water flow in opposite directions

  Diffusion gradient is maintain along the length of lamella
• Label a diagram of a fish gill


  ...
• Describe and explain the advantage of the counter-current principles allows efficient in gas exchange across a fish gill

  Water and blood flow in opposite directions

  Maintains diffusion gradient of oxygen/oxygen concentration is always higher in water

  Consistent diffusion along the length of lamellae