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Q25 - Ion Transport Across the Freshwater Fish Gill Epithelium

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Comparative Osmoregulation & Excretion

In the gills of freshwater teleost fishes, the blood plasma is separated from the freshwater by a thin epithelium so that the blood plasma tends to lose ions such as Na+ and Cl- to the ambient water across the gill epithelium and H2O tends to enter the plasma from the ambient water across the gill epithelium. There are transport mechanisms by which inorganic ions and water cross the gill epithelium and they help to maintain the difference in the ion composition between the plasma and the ambient water. Figure Q.25 shows the transportation of four ions across the gill epithelium.

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. Inhibition of the Cl- pump leads to an increase in blood pH.
B. An increase in CO2 produced by catabolism leads to an increase in Na+ and Cl- transports across the epithelium cell.
C. A substance blocking the electron transport chain causes a decrease of Na+ influx, but does not affect HCO3- outflux at the gill epithelium.
D. During alkalosis, the epithelial cell increases the synthesis of a key Cl-/HCO3- countertransport protein.
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Question reproduced from IBO 2016, Theoretical Paper A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)