Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean? 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. Cells of each domain evolved proton pumps independently when oceans became more acidic. B. Proton pumps are an essential feature of all cell membranes. C. Proton pumps must have evolved before any living organisms were present on Earth. D. Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life.

The correct answer is A and D

Explanation:

According to Russell's conception that lies in natural proton gradients. He states that Four billion years ago, alkaline fluids bubbled to produce mildly acidic oceans (As CO2 levels were about a thousand times higher, and it reacts with H2O to form carbonic acid, rendering the oceans mildly acidic). Acidity is just a measure of proton concentration, higher in the oceans than in vent fluids. This difference has given rise to a natural proton gradient across the vent membranes that had the same polarity (outside positive) which is similar to the electrochemical potential as modern cells have. This might be the reason that last universal common ancestors of all the three domains have evolved proton pumps.