Nursing Entrance Exam (NEX) Practice Exam

The correct choice is protozoans because they are a group of unicellular eukaryotic organisms, meaning they possess a defined nucleus within their cells. This characteristic distinguishes them from prokaryotic organisms, such as monerans, which do not have a nucleus. Protozoans come in various forms and can exhibit diverse locomotion methods, including flagella and cilia.

Monerans are primarily made up of bacteria and archaea, which are also unicellular but lack a nucleus, making this option incorrect. Fungi, although they can be unicellular (like yeast), are typically multicellular and belong to a different kingdom, thus making them unsuitable. Spermatozoa, or sperm cells, while also unicellular, are specialized cells involved in reproduction and do not fit the broader classification of organism groups like protozoans.

In summary, protozoans are uniquely characterized as unicellular organisms with a nucleus, fitting the criteria set forth in the question.