Which two domains are composed exclusively of unicellular organisms?

• A. Archaea and Eukarya
• B. Bacteria and Eukarya
• C. Eukarya and Protista
• D. Bacteria and Archaea

Answer: (D)

Verified step by step guidance

1. Understand the concept of domains: In biology, the three domains of life are Archaea, Bacteria, and Eukarya. These domains classify all living organisms based on their cellular structure and genetic characteristics.
2. Recall the characteristics of Archaea: Archaea are unicellular organisms that lack a nucleus and are prokaryotic. They are often found in extreme environments, such as hot springs or salt lakes.
3. Recall the characteristics of Bacteria: Bacteria are also unicellular and prokaryotic organisms. They lack a nucleus and are found in a wide variety of environments, including soil, water, and inside other organisms.
4. Understand the characteristics of Eukarya: Eukarya includes organisms with eukaryotic cells, which have a nucleus and membrane-bound organelles. While some eukaryotes are unicellular (e.g., certain protists), the domain Eukarya also includes multicellular organisms like plants, animals, and fungi.
5. Conclude that the two domains composed exclusively of unicellular organisms are Bacteria and Archaea, as Eukarya includes both unicellular and multicellular organisms.