Which of the following is true about eukaryotic organisms?

• A. They include bacteria
• B. They include archaea
• C. They include protozoa
• D. They include viroids

Answer: (C)

Eukaryotic organisms are those with a true nucleus and membrane-bound organelles, which distinguishes them from prokaryotes. Protozoa are single-celled eukaryotes, meaning each organism has a defined nucleus and organelles such as mitochondria, placing them squarely in the eukaryotic group. Bacteria and archaea lack a nucleus and other membrane-bound organelles, so they are prokaryotes, not eukaryotes. Viroids are tiny infectious RNA molecules without a cellular structure, so they’re not organisms at all. Therefore, protozoa are the true example of eukaryotic organisms in this set.