You are on a fishing trip at the beach with your friends. While you are waiting

Question

You are on a fishing trip at the beach with your friends. While you are waiting for any action on your line, you start to talk about whether it would be easier to get enough oxygen if you were a fish swimming in the salty water than it is for you breathing air. Which one of the following points would NOT be one that you would add to the conversation? A You calculate the partial pressure of oxygen as the % of oxygen in air multiplied by the atmospheric pressure B Gills of fish and lungs in humans both use countercurrent exchange mechanisms to maximise the extraction of oxygen into the blood C In the alveoli in the lungs, humans only need to extract about 25% of the oxygen from inhaled air D The partial pressure of oxygen is about 160 mmHg both in air and in water exposed to air E There is less oxygen dissolved in water in tropical seas than in a river in a cold climate

Explanation / Answer

B. Gills of fish and lungs in humans both use countercurrent exchange mechanisms to maximize the extraction of oxygen into the blood.

All the other options are correct.
Human does not possess countercurrent exchange mechanism for respiration. Only fish gills use countercurrent mechanism for the exchange of gases. Both fish gills and alveoli of human lungs provide a large respiratory surface but humans have specialized respiratory organs i.e lungs which provide two-way ventilation system. Fishes have one-way ventilation system (water flows through the gills in one direction), the countercurrent mechanism maximizes the concentration difference between the blood and water, thereby maximizes the efficiency of the diffusion of gases.

In humans, countercurrent mechanism is found in the kidney.

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