FISH

• why do fish have a specialised internal gas exchange system

  have a waterproof (gas tight) outer coating and a small surface area to volume ratio
• what are fishes specialised internal gas exchange organ

  gills
• what are gill filaments


  small divisions of the gills in fish that extend off of the gill arch
• what are gill lamella the site of

  gas exchange
• what are the three adaptations of the gill lamellae


  -increases surface area of gills

  -constant bloody supply from capillaries

  -short diffusion distance
• what is the benefit of the gill lamellae having a good blood supply


  maintains a steep concentration gradient for carbon dioxide
• what is the benefit of a short diffusion distance in the gill lamellae


  oxygen/carbon dioxide can diffuse directly from lamellae to bloodstream/water
• where does the counter current exchange happen

  the gill lamellae
• explain the counter current exchange

  1. blood with low oxygen concentration passes into capillaries of gill lamellae
  2. blood passes through gill lamellae where oxygen diffuses into water from blood
  3. oxygen rich blood now passes out of the gill lamellae and leaves gills
• what happens if blood and water had a parallel flow


  they would meet equilibrium, diffusion would stop and only 50% of oxygen can diffuse from water to blood
• why is the counter-current flow more efficient 


  as equilibrium is never reached so there is always a steep concentration gradient for oxygen and 80% of oxygen in water can diffuse into blood
• how do fish respire

  1. mouth opens, operculum closes
  2. buccal floor lowers so buccal cavity volume increases and pressure decreases, forcing water in
  3. mouth closes
  4. buccal floor raises so volume decreases, pressure increases
  5. operculum opens and water is forced out through the gills