[Campbell Biology P.990] If, hypothetically, blood and water flowed in the same direction co... | Practice Question
If, hypothetically, blood and water flowed in the same direction concurrently over the fish gills, what would be the most likely consequence regarding oxygen exchange?
A: Oxygen transfer efficiency would increase significantly due to a sustained high partial pressure gradient throughout the entire gill.
B: Oxygen would diffuse from water to blood only at the beginning of the gill, quickly reaching equilibrium and limiting further O2 uptake.
C: The fish would be able to extract more than 80% of the dissolved O2 from the water, surpassing the efficiency of countercurrent exchange.
D: The partial pressure of oxygen in the blood would steadily decrease as it moves through the gill, hindering oxygen delivery to tissues.
Explanation
In concurrent flow, substances move in the same direction. This means that the partial pressure gradient would rapidly diminish as the two fluids approach equilibrium, leading to a much lower overall transfer efficiency compared to countercurrent exchange.