Question

Gas exchange in fish is fairly efficient because:

A. oxygen concentrations in water are higher than oxygen concentrations in air, making it easy for oxygen to diffuse from water into the blood.

B. water with very high oxygen content flows in the same direction as blood with very low oxygen content, maintaining a small but consistent difference in oxygen content that encourages continuous diffusion of oxygen from water to blood.

C. blood and water flow in opposing directions, maintaining a small but consistent difference in oxygen content that encourages continuous diffusion of oxygen from water to blood.

D. water with very high oxygen content flows past blood with very low oxygen content, which results in rapid diffusion of oxygen into the blood due the large difference in the partial pressure of oxygen.

Answer 1

In fishes efficient gaseous exchange occurs due to a mechanism called counter current oxygen exchange mechanism. In this mechanism the water flows in the opposite direction to the blood in the gills. By this method the blood is exposed to oxygen for longer time. As the low oxygen blood come into the gills, the oxygen start diffusing to blood from high oxygen concentration water and as the blood reaches the end of the gill, it becomes saturated with oxygen.

So, correct answer is (C) blood and water flow in opposing directions, maintaing a small but consistent difference in oxygen content that encourages continous diffusion of oxygen fron water to blood.

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