According to the modern taxonomy, the highest
taxonomic rank of organisms is a domain. The classification is based on </span><span>differences of ribosomal RNA.</span> There are three domains in the tree of
life: Archaea, Bacteria, and Eukarya. Archae and Bacteria are Prokaryotes,
unicellular organisms without a nucleus and organelles. <span>Eukarya mostly includes multicellular organisms
with a nucleus and organelles. </span>
