Passive and active transport of ions across biological membranes

2 Passive and active transport of ions across biological membranes 

Nature has devised complex strategies for controlling the flow of ions across cell membranes, some of which are thermodynamic and others kinetic. Here we consider thermodynamic aspects of ion transport. 

With a better understanding of how ions behave in solution, we are now prepared to discuss their behavior in cells. The concepts developed in the previous sections can be applied to the aqueous environment inside and outside cells. But we also need to know how ions traverse cell membranes and how such transport controls important biological processes, such as the synthesis of ATP and neuronal activity. 

The thermodynamic tendency to transport a species A through a biological cell membrane is partially determined by an activity gradient across the membrane, which results in a difference in molar Gibbs energy between the inside and the 

The equation implies that transport into the cell of either neutral or charged species is thermodynamically favorable if out or, if we set the activity coefficients to 1, if [A]in [A]o f An ion also needs to cross a membrane potential difference that arises from differences in Coulomb repulsions on 

---

PASSIVE AND ACTIVE TRANSPORT OF IONS ACROSS BIOLOGICAL MEMBRANES 187... 

---