Which of the following is the best evidence for a three-domain system in biological classification?

• A. Differences in ribosomal RNA (rRNA) sequences among Bacteria, Archaea, and Eukarya
• B. Ability to perform photosynthesis
• C. Similarities in body plans among multicellular organisms
• D. Presence of a nucleus in all living cells

Answer: (A)

Verified step by step guidance

1. Understand the concept of the three-domain system in biological classification. This system divides life into three domains: Bacteria, Archaea, and Eukarya, based on fundamental differences in cellular and molecular characteristics.
2. Recognize that ribosomal RNA (rRNA) sequences are highly conserved and play a critical role in protein synthesis, making them ideal for studying evolutionary relationships among organisms.
3. Learn that differences in rRNA sequences are used to distinguish between the three domains because they reflect evolutionary divergence at the molecular level.
4. Evaluate the other options provided in the question. The ability to perform photosynthesis, similarities in body plans, and the presence of a nucleus are not universal or fundamental enough to serve as evidence for the three-domain system.
5. Conclude that differences in rRNA sequences among Bacteria, Archaea, and Eukarya are the best evidence for the three-domain system, as they provide a molecular basis for classification and reflect evolutionary history.