Gas Exchange: Fish

Question 1

Explain how the gills of fish are adapted for gas exchange:

Answer 1

1. Gills made of many filaments covered with many lamellae
   ○ Increase surface area for diffusion
2. Thin lamellae wall / epithelium
   ○ So short diffusion distance between water / blood
3. Lamellae have a large number of capillaries
   ○ Remove O2 and bring CO2 quickly so maintains
   concentration gradient

Question 2

Counter current flow:

Answer 2

1. Blood and water flow in opposite directions through/over lamellae
2. So oxygen concentration always higher in water (than blood near)
3. So maintains a concentration gradient of O2 between water and blood
4. For diffusion along whole length of lamellae

Question 3

Why is parallel flow not used?

Answer 3

If parallel flow, equilibrium would be reached so oxygen wouldn’t diffuse into blood along the whole gill plate.