AP BIOLOGY

Detailed explanation-1: -The three-domain system presumes that eukaryotes are more closely related to archaea than to bacteria and are sister group to archaea, thus, it treats them as separate domain.

Detailed explanation-2: -Scientists thought for a long time that Bacteria and Archaea were the most closely related domains of life, since they both consist of unicellular organisms. However, recent genome sequencing evidence suggests that Archaea and Eukarya are actually the most closely related domains.

Detailed explanation-3: -In fact, Archaea and Eukarya form a monophyletic group, not Archaea and Bacteria. These relationships indicate that archaea are more closely related to eukaryotes than to bacteria, even though superficially archaea appear to be much more similar to bacteria than eukaryotes.

Detailed explanation-4: -Bacteria encompass two domains: eubacteria and archaea. Eubacteria and archaea have very different cell walls. They are also distinguished by their DNA-the DNA of archaea has histone proteins while that of eubacteria does not.

Detailed explanation-5: -The inferred composite trees reveal that archaebacteria are more closely related to eukaryotes than to eubacteria for all the cases.