Ace the CVS Pharmacy Exam 2025 - Your Prescription for Success!

The ion that exhibits the largest concentration gradient across the cell membrane is calcium. This is due to the fact that calcium ions usually exist in much higher concentrations outside of the cell compared to the inside. In a typical physiological state, the extracellular concentration of calcium is typically around 1-2 mM, while the intracellular concentration is maintained at a significantly lower level, often around 100 nM.

This steep gradient is crucial for various cellular processes, including muscle contraction, neurotransmitter release, and various signaling pathways. The large difference between the extracellular and intracellular concentrations of calcium creates a strong driving force for calcium to enter the cell when channels open, contributing to physiological responses.

In contrast, sodium also has a higher concentration outside the cell, but not as pronounced as that of calcium. The concentration of potassium is usually higher inside the cell, and while chloride and other ions can also have gradients, they do not reach the extreme disparity seen with calcium. Therefore, calcium represents the ion with the most substantial concentration gradient across the cell membrane, making it key in many cell signaling processes.