👉 In biology, unicellular organisms are those that lack a nucleus or other cell structure. They can be divided into two types: prokaryotes and eukaryotes. Prokaryotes are single-celled organisms without a nucleus, which means they cannot divide or reproduce independently. Examples of prokaryotic cells include bacteria, archaea, viruses, and some fungi. Prokaryotes lack a cell wall but do have membrane-bound organelles like ribosomes and mitochondria that