Organisms can he divided into those whose cells do not have a nucleus, the single celled “prckaryotes” (Greek: pro = before; karyon = nucleus), and those whose cells have a nucleus, the single- or multi-celled “eukaryotes” (Greek: eu = good or normal; karyon = nucleus). Prokaryotes include species of bacteria (eubacteria) and archaea (archaebacteria), the latter being a bacteria- like group sometimes found in extreme environments (e.g. hot springs). Eukaryotes (eukarya) include all species of animals and plants, hoth singlecelled (protozoa, protophyta) and multi-celled (metazoa, metaphyta).
Exons and Introns