What adjustments would clearly make countercurrent exchange more efficient in extracting oxygen from water running through fish gills?
a. hemoglobin with a greater affinity for oxygen
b. proportionally larger gills to body size
c. better ventilation
d. slower heart rate
e. warmer water
The correct answer and explanation is:
The correct answer is a. hemoglobin with a greater affinity for oxygen.
Countercurrent exchange is a mechanism in which blood and water flow in opposite directions across fish gills, maximizing the diffusion of oxygen from water into the blood. The efficiency of this process depends on maintaining a strong gradient between the oxygen concentration in the water and that in the blood. In this setup, the greater the difference in oxygen levels between the two, the more oxygen the blood can absorb from the water.
Having hemoglobin with a greater affinity for oxygen helps increase this gradient. Hemoglobin is the protein in red blood cells that binds oxygen, and its ability to effectively capture oxygen from the water is vital for efficient gas exchange. When hemoglobin has a higher affinity for oxygen, it can more readily bind oxygen at the lower concentrations present in the water, ensuring that as much oxygen as possible is transferred from the water to the blood.
While proportionally larger gills to body size (b) could provide more surface area for gas exchange, it does not directly influence the efficiency of oxygen uptake in the context of countercurrent exchange. Similarly, better ventilation (c) may help move oxygenated water through the gills faster, but the key factor in maximizing oxygen absorption is the interaction between the blood’s oxygen-carrying capacity and the oxygen concentration gradient.
A slower heart rate (d) or warmer water (e) would likely have negative effects. A slower heart rate would reduce the rate at which oxygenated blood is circulated through the fish, decreasing oxygen uptake. Warmer water reduces the solubility of oxygen, making it harder for the fish to extract sufficient oxygen from the water.
Thus, adjusting hemoglobin to have a higher oxygen affinity is the most effective way to enhance the efficiency of countercurrent exchange in fish gills.