The Behavior of Electrolytes in Valonia.

Abstract

The accumulation¹ of strong electrolytes in living cells presents a problem of peculiar interest. An example of this is afforded by Valonia macrophysa. The large multinuclear cell of this marine alga consists of a very thin protoplasmic membrane, inside of which is a large central vacuole filled with sap, and outside of which lies a cell wall imbibed with sea water. It is a very striking fact that the sap inside of this very thin film of protoplasm has a concentration of K about forty times as great as that in the sea water which bathes the outside of the film.²

This can be explained if we assume that the protoplasm is impermeable³ (or nearly so) to K⁺ and OH^- but that KOH enters in the form of undissociated molecules. This does not require the assumption that molecules of KOH exist as such in the sea water. We assume rather that K⁺ and OH^-, striking the surface of the protoplasm, which is presumably non-aqueous, associate to form KOH which then passes through the non-aqueous layer (for the sake of simplicity we will assume for the moment that the entire protoplasm consists of a single non-aqueous layer⁴) and dissociates in the sap inside. Equilibrium will be reached when as many molecules of KOH enter the external surface in unit time as enter the internal surface.

Since the pH value of the sap is about 5.8, while that of the sea water is about 8.2, it is evident that the concentration of OH⁻ is about 250 times as great in the sea water as in the sap, and that, in consequence, there must be at equilibrium a much higher concentration of K⁺ in the sap than in the sea water, to ensure that as many molecules of KOH enter the internal protoplasmic surface, as enter the external surface.