Question

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.

Answer 1

Proton pumps across all domains of organisms suggest they were present in the last universal common ancestor, supporting the idea that cells from all domains share an evolutionary origin in proton gradient utilization.

Step-by-step explanation:

The presence of proton pumps in all three domains of organisms — Bacteria, Archaea, and Eukarya — suggests a shared evolutionary origin. These proton pumps are integral to chemiosmosis and the generation of a proton motive force (PMF), which is fundamental for cellular processes like ATP synthesis. Considering the ubiquity and essential function of proton pumps, it is most likely that they were present in the last universal common ancestor (LUCA) of all three domains, and thus, option B (Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life) is the correct answer.