Q5 - ATP-Dependent Na+ Efflux in the Squid Giant Axon
ATP is an important energy source for maintaining normal membrane potential in nerve cells. Figure 1 shows the result of an experiment demonstrating Na+ efflux from an isolated squid giant nerve axon after injecting a buffer solution (artificial cytoplasm) that contains radioactive 24Na+.
Figure 1.
Using the information and data, determine which of the statements are true or which are false.
A. This experiment should have been carried out under the condition with sufficient oxygen to maintain the activity of ATP production by mitochondria.
B. The efflux of 24Na+ observed in seawater without DNP indicates the leaking of Na ions out of the cell by nonspecific transportation.
C. Delayed decrease of 24Na+ efflux after using DNP reflects some amount of ATP storage inside the axon, including that being produced by glycolysis.
D. Active transport of sodium ions was estimated to increase internal sodium concentration by 10% in 50 min.
Question reproduced from IBO 2020, Theoretical Exam 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)