fish gas exchange

• In the gill lamella of fish, water flows in the opposite direction to blood, this is called a counter current exchange system
• countercurrent exchange increases efficiency as it reduces the amount of oxygen that leaves the blood without being used
• The counter current exchange system maintains a concentration gradient for diffusion
• In a counter current system oxygen always diffuses from water, into the blood
• explain gas exchange in fish:

  • fish opens mouth and water flows in, mouth is then closed to increase pressure
  • water passes over the lamellae, and o2 diffuses into the bloodstream
• describe and explain how fish maintain a flow of water over their gills

  1. mouth opens, operculum shuts

  2. floor of mouth lowered

  3. water enters due to decreased pressure / increased volume

  4. mouth closes, operculum opens

  5. floor raised results in increased pressure / decreased volume

  6. high / increased pressure forces / pushes water over gills
• how is the fish adapted for efficient gas exchange?

  1. Large surface area provided by lamellae / filaments increases diffusion area/makes diffusion efficient

  2. Thin epithelium / short distance between blood and water

  3. Water and blood flow in opposite directions / countercurrent

  4. maintains concentration gradient along entire length of gill

  5. Circulation replaces blood saturated with oxygen

  6. Ventilation replaces water (as oxygen removed)