CVS Practice Test

What equation helps describe the chemical equilibrium of the cell for a specific ion?

1. Nerst equation

2. Gibbs equation

3. Henderson-Hasselbalch equation

4. Van der Waals equation

The correct answer is: Nerst equation

The Nernst equation is essential for understanding the chemical equilibrium of specific ions within a cell. It provides a quantitative relationship between the concentration gradient of an ion across a membrane and the electrical potential difference that balances that gradient. This equation allows one to calculate the equilibrium potential (also known as the reversal potential) for a given ion, which is critical for understanding how ions contribute to the membrane potential of cells, particularly in neurons and muscle cells. The Nernst equation takes into account the charge of the ion and the concentrations of the ion on both sides of the membrane. This relationship is crucial for predicting how changes in ion concentration can affect cell function, particularly in terms of how neurons fire and the general excitability of cells. In contrast, the Gibbs equation is more relevant to thermodynamics and energy changes in chemical reactions but does not specifically address ion transport across membranes. The Henderson-Hasselbalch equation deals with the pH of buffer solutions and acid-base equilibria, rather than ion equilibrium. The Van der Waals equation describes the behavior of real gases, accounting for interactions between molecules, but does not pertain to ionic equilibria within biological systems. Thus, the Nernst equation is the most appropriate for describing chemical equilibrium for specific ions