State two characteristics that permit the classification of microbes into domains.

cell wall structure/composition / whether the cell wall contains peptidoglycan;
size of / 70S or 80S ribosomes;
(base sequence in) ribosomal RNA/rRNA;
whether there are introns;
whether there are histone proteins;
membrane structure / ether or ester bonds (in membrane lipids);

This posed few problems for well-prepared candidates, though (a) and (b) were not known by all.