Biology Nervous Coordination MDCAT 2018
PMDC Verified Question 78 of 86
How many sodium ions are pumped out in response to two potassium ions transported into the membrane?
A
4
B
1
C
2
D
3
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: 3
Concept:

The resting membrane potential is actively maintained by an electrogenic pump powered by ATP.

Solution:

  • The Sodium-Potassium Pump (\(\text{Na}^+/\text{K}^+\) ATPase) utilizes one molecule of ATP to actively transport 3 \(\text{Na}^+\) ions out of the cell while simultaneously bringing 2 \(\text{K}^+\) ions into the cell. This 3:2 ratio maintains the negative charge inside the membrane.


Why other options are incorrect:

  • Options 1, 2, and 4 do not reflect the strict stoichiometric 3:2 ratio characteristic of this fundamental cellular pump.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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