Water and ions

Leonard B. Kirschner

It is commonly believed that living cells developed in the ocean, although it is impossible to obtain unequivocal evidence for this. Whatever the ancestral home, it seems likely that the basic chemical composition of cells has been stable through a billion or more years of evolution. The major osmotically active intracellular cation in most animal, plant, and microbial cells is K+, with Na+ and Cl– ions present at lower, usually much lower concentration. The main anionic component is polyvalent protein with some charge contributed by smaller organic anions like ATP.

Fonte: Kirschner, L. B. 1991. In: Prosser, C. L. ed. Environmental and metabolic animal physiology. NY, Wiley.