In biological taxonomy, Domain is defined as a taxonomic category above which level, and what are the three domains?

• A. The second-highest rank below family
• B. A grouping that includes only unicellular organisms
• C. A taxonomic category above the kingdom level; the three domains are Archaea, Bacteria, and Eukarya
• D. A grouping only for plants

Answer: (C)

Domain is the highest major taxonomic rank used in the modern system, placed above the kingdom. There are three domains: Archaea, Bacteria, and Eukarya. This arrangement comes from genetic data, especially ribosomal RNA sequences, which show deep evolutionary splits. Archaea and Bacteria are prokaryotic, lacking a true nucleus, while Eukarya includes organisms with complex cells that have a nucleus—plants, animals, fungi, and many protists. This broader grouping reflects fundamental differences in cellular organization and genetics, offering a more accurate framework than older schemes. The other statements don’t fit because the domain level is not below the family, it’s not limited to unicellular organisms, and it’s not a grouping only for plants.