Which term refers to microscopic organisms that are typically single-celled and lack a nucleus?

• A. Virus
• B. Protozoa
• C. Bacteria
• D. Fungi

Answer: (C)

This item tests how we classify microscopic life by cellular structure, focusing on whether there is a nucleus. Bacteria are prokaryotes, meaning they are microscopic and typically single-celled organisms that lack a membrane-bound nucleus. Their DNA sits in a nucleoid region rather than a true nucleus, and they don’t have membrane-bound organelles, which sets them apart from organisms with nuclei.

Protozoa are single-celled but have a true nucleus, making them eukaryotes. Fungi are also eukaryotic and mostly multicellular (though some yeasts are single-celled) and they possess nuclei. Viruses aren’t cells at all and lack cellular organization, so they don’t fit the idea of a single-celled organism with or without a nucleus.

So, the term that describes microscopic organisms that are typically single-celled and lack a nucleus is bacteria.