Proton Pumps Are Used in Various Ways by Members of Every

Multiple Choice

Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this fact most probably mean?

A) Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life.
B) The high concentration of protons in the ancient atmosphere must have necessitated a pump mechanism.
C) Cells of each domain evolved proton pumps independently when oceans became more acidic.
D) Proton pumps are necessary to all cell membranes.