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.

Question

Quizplus · Accepted Answer

The fact that proton pumps are used in all three domains of life suggests that the ability to generate proton gradients across a membrane was present in the common ancestor of all three domains. This is supported by the theory of endosymbiosis, which suggests that the first eukaryotic cell arose through the fusion of two different prokaryotic cells, one of which was likely an ancestor of modern-day bacteria and the other an ancestor of modern-day archaea.

Proton Pumps Are Used in Various Ways by Members of Every