Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean?
A) Proton pumps must have evolved before any living organisms were present on Earth.
B) Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life.
C) The high concentration of protons in the ancient atmosphere must have necessitated a pump mechanism.
D) Cells of each domain evolved proton pumps independently when oceans became more acidic.
E) Proton pumps are necessary to all cell membranes.

Question

Quizplus · Accepted Answer

Since proton pumps are used by members of every domain of organisms, it is most probable that the use of proton gradients across a membrane was present in the common ancestor of all three domains of life. This suggests that proton pumps evolved early in the history of life and have played a key role in the evolution of all forms of life.

Proton Pumps Are Used in Various Ways by Members of Every