Question

Which of the following has a larger electrochemical gradient across a cell's plasma membrane?

A. K+
B. Na+
C. Both K+ and Na+ have equal electrochemical gradients.
D. The electrochemical gradient depends on the specific conditions.

Answer 1

Na+ typically has a larger electrochemical gradient across a cell's plasma membrane than K+, as both the concentration and electrical gradients favor Na+ entry into the cell, which is not fully the case for K+.

Step-by-step explanation:

The student asked which ion, K+ or Na+, has a larger electrochemical gradient across a cell's plasma membrane. In living cells, Na+ tends to have a larger electrochemical gradient than K+. This is because the extracellular fluid typically has a higher concentration of Na+, and the cytoplasm of the cell is more negative due to negatively charged proteins and other molecules. The electrochemical gradient arises from the combination of the concentration gradient, which drives Na+ into the cell, and the electrical gradient, which also attracts positively charged sodium ions towards the negatively charged interior of the cell. Conversely, while the concentration gradient promotes the movement of K+ out of the cell, the electrical gradient attempts to draw K+ back in due to the negative charge inside the cell. Nonetheless, because Na+ has both gradients favoring its entry to the cell, it typically presents a larger electrochemical gradient than that of potassium.