Carl Woese’s major taxonomic contribution Carl Woese and colleagues are best known for establishing which overarching classification framework based on ribosomal RNA comparisons?

Introduction / Context:
Taxonomy has evolved with molecular biology. Carl Woese revolutionized systematics by comparing small subunit ribosomal RNA sequences across organisms, revealing deep evolutionary divisions that were not apparent from morphology alone. This question asks you to identify his signature contribution to biological classification.

Given Data / Assumptions:

• Woese’s work used rRNA as a molecular chronometer.
• Findings supported a new high-level grouping above kingdoms.
• The resulting framework is now foundational in microbiology and evolution.

Concept / Approach:

The three-domain system partitions life into Bacteria, Archaea, and Eukarya. It highlights that archaea are not just unusual bacteria but a distinct lineage, often more closely related to eukaryotes in information-processing machinery. This classification supplanted earlier two-empire systems and complements, rather than replaces, kingdom-level groupings.

Step-by-Step Solution:

Verification / Alternative check:

Modern phylogenies and textbooks universally present the three-domain framework, reflecting Woese’s legacy.

Why Other Options Are Wrong:

• Five kingdom system: Proposed by Whittaker, not Woese.
• Prokaryote-eukaryote system or plant-animal system: Earlier, simplistic schemes not aligned with rRNA evidence.
• Eight-kingdom system: Not Woese’s signature model.

Common Pitfalls:

• Confusing domains with kingdoms; domains are above kingdoms in rank.
• Thinking archaea are bacteria; molecular data separate them clearly.

Final Answer:

the three domain system