Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 7

Sodium Ion Transport. A marine protozoan is known to pump sodium ions outward by a simple ATP-driven Na + pump that operates independently of potassium ions. The intracellular concentrations of ATP, ADP, and P, are 20, 2, and 1 mM, respectively, and the membrane potential is -75 mV.
(a)Assuming that the pump transports three sodium ions outward per molecule of ATP hydrolyzed, what is the lowest internal sodium ion concentration that can be maintained at 25°C when the external sodium ion concentration is 150 mM
(b)If you were dealing with an uncharged molecule rather than an ion, would your answer for part a be higher or lower, assuming all other conditions remained the same Explain.