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 3 options:

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

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

Cannot be determined without knowing whether it causes disease in humans

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

Answer 1

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

(You could distinguish Bacteria vs Archaea further by tests such as Gram staining/peptidoglycan detection, membrane lipid chemistry, or 16S rRNA sequencing.)