the main difference between organisms of the domains Bacteriaand Archea and organisms of the domain Eukarya?

Answer 1

Bacteria and Archaea are prokaryotic - they have no nucleus and no membrane-bound organelles.

Eukarya are eukaryotic - they have cells with nuclei and membrane-bound organelles such as mitochondria, vacuoles, Golgi apparatus, e.r., etc.

There are other differences, but that's the main one.