Classification and Cladistics · Paper 1 — Free Biology HL Practice Questions

A microorganism isolated from a hydrothermal vent at 85 °C is found to be prokaryotic, with cell walls lacking peptidoglycan, membrane lipids containing isoprenoid chains linked to glycerol by ether bonds, and an RNA polymerase with subunit complexity comparable to that of eukaryotes. To which domain does this organism belong?

Carl Woese's 1977 analysis of ribosomal RNA (rRNA) nucleotide sequences revealed that methanogenic prokaryotes from anaerobic swamp sediments were as genetically distant from typical bacteria such as Escherichia coli as they were from eukaryotes such as humans. This finding led Woese to propose a three-domain classification system. Which of the following best explains why rRNA sequence comparison was the most appropriate tool for identifying such deep evolutionary divergences?