Which of the following is an example of a prokaryotic cell?

A prokaryotic cell is defined by the absence of a membrane-bound nucleus and other membrane-bound organelles. Prokaryotes are unicellular organisms that fall into two main categories: bacteria and archaea. Among the options presented, a bacterium is the best representation of a prokaryotic cell, as it is a unicellular organism that contains genetic material, ribosomes, and a plasma membrane, but lacks a defined nucleus.

In contrast, fungi are eukaryotic organisms characterized by their complex cellular structure that includes a nucleus and membrane-bound organelles. Viruses are not classified as cells; they are acellular infectious agents that require host cells to replicate and do not exhibit characteristics typical of living cells. Protozoa, like fungi, are also eukaryotic organisms that contain a nucleus and other organelles. Therefore, the bacterium stands out as the only prokaryotic example among the choices provided.