Question

Concentration of $N{a}^{+}$ ions outside a nerve cell is $\sim 100$ times more than inside. The concentration of $K^{+}$ ions is more inside the cells. The levels of $N{a}^{+}$ ions and $K^{+}$ ions are maintained by

• A. Free diffusion of $N{a}^{+}$ ions and pumping of $K^{+}$ ions across the membrane.
• B. $N{a}^{+}$ and $K^{+}$ pumps in the membrane.
• C. Free diffusion of $K^{+}$ ions and pumping of $N{a}^{+}$ ions across the membrane.
• D. Water channels formed by lipids in the membrane.

Answer 1

Answer: (B)

$N{a}^{+}$ and $K^{+}$ pumps in the membrane.

Under physiological conditions, concentration of Na${}^{+}$ ions outside a nerve cell is approximately 100 times more than that in the intracellular fluid. In contrast, the concentration of K${}^{+}$ ions is more inside the cell than the extracellular fluid. This concentration gradient is maintained by the action of the enzyme Na${}^{+}$/K${}^{+}$-ATPase. The levels of ions are maintained by Na${}^{+}$ and K${}^{+}$ pumps in the membrane. Because of this, 2 K${}^{+}$ ions are pumped into the cell for every 3 Na${}^{+}$ ions pumps out of the cell.

Thus, the correct answer is option B.