what organisms have a nucleus
It depends on the type of organism! One major group of organisms, the bacteria, do not have a nucleus in their cell. However they do have DNA, like other organisms. Bacteria belong to the kingdom Prokaryota, which means without a nucleus (literally, before the nucleus) All other organisms are eukaryotes: they do have a nucleus in their cells. Single-celled eukaryotes are classified as Protists or Protoctists. The protists range from very simple organisms to very complicated organisms, for example ciliates. Ciliates can have more than one nucleus in their cells.