Some organisms can create a sodium motive force by pumping sodium ions across a membrane using the energy of an electron transport system. In order for this sodium motive force to provide useful energy for the cell, the organism must contain .

an Na+ driven synthase

Explanation:

Some organism have sodium driven synthase which actively transport the sodium ions across the cell membrane with the help of energy of electron transport chain.

In most bacteria, there are antiporters that are used to exchange sodium ions with proton which is driven by electrochemical proton potential. So these organisms converts proton motive force into sodium motive force.

In humans also there are antiporter called sodium-potassium pumps which use ATP energy to transport sodium out of the cell.

your answer is "the 1950's"