Active transport is the process in which a substance is transferred from a region of lower concentration to one of higher concentration. This is a non spontaneous process and must be coupled to a spontaneous process, such as the hydrolysis of ATP. The concentrations of K+ ions in the blood plasma and in nerve cells are 15 mM and 400 mM, respectively (1 mM = 1 × 10-3M). Use Equation (18.13) to calculate ∆G for the process at the physiological temperature of 37°C: