Answer:
presence or absence of a nucleus
Explanation:
These classification of organisms into broad domains is based on the present or absence of nucleus in the cell of an organism.
The archaea are prokaryotes and they lack a distinct cellular nuclei.
Bacteria are similar to archaea but bacteria have only one RNA polymerase
Eukarya have true nucleus and membrane bound organelles .
So, the variations in their cells are used to classify organisms into the broad categories
