Which are the three biological domains?

• A. Prokaryotes and Eukaryotes
• B. Bacteria, Archaea, Eukarya
• C. Bacteria, Archaea, Protista
• D. Plants, Animals, Fungi

Answer: (B)

Grouping life into three domains reflects deep evolutionary relationships shown by genetic data. The world’s organisms are divided into Bacteria, Archaea, and Eukarya because comparisons of ribosomal RNA and other molecular features reveal three distinct lineages that diverged long ago. Bacteria and Archaea are both prokaryotes (lacking a nucleus), but their genetic machinery, cell chemistry, and other molecular traits are different enough to place them in separate domains. Archaea, interestingly, share more in common with Eukarya in how their transcription and translation work, yet they differ in membrane lipids and some cell wall components from both Bacteria and Eukarya. Eukarya includes all organisms with a true nucleus and membrane-bound organelles, such as plants, animals, fungi, and many protists. The other options mix higher-level domains with kingdoms or cell-type groupings (like Protista or Plants/Animals/Fungi) and don’t capture the broad evolutionary divisions that the three-domain system represents.