Question

A public health microbiologist needs to identify an unknown organism found in a water sample. She examines its cellular structure and finds it has no membrane-bound nucleus but does have a cell wall. Based on modern classification systems, which domain does this organism belong to?
Question 2 options:

Either Bacteria or Archaea, because it lacks a membrane-bound nucleus (prokaryotic)

Eukarya, because it has a cell wall like plants and fungi

Cannot be determined without knowing whether it causes disease in humans

Protista, because it was found in a water sample and might be unicellular

Answer 1

Either Bacteria or Archaea, because it lacks a membrane-bound nucleus (prokaryotic).

Explanation: Modern classification uses three domains. Absence of a membrane-bound nucleus indicates a prokaryote, which places it in either Bacteria or Archaea. Eukarya and Protista are eukaryotic (have nuclei), and disease-causing ability is irrelevant to domain assignment.