Which group of microorganisms is composed only of hereditary material wrapped in a protein covering?

The correct choice is viruses because they are unique among microorganisms in that they consist solely of genetic material—either DNA or RNA—enclosed in a protein coat known as a capsid. This simplistic structure allows them to infect host cells and replicate, but outside of a host, they cannot carry out any metabolic processes or reproduce independently.

In contrast, bacteria are more complex cells that contain both hereditary material and cellular machinery necessary for metabolic functions. Fungi are multicellular or unicellular organisms that possess a defined cellular structure with membranes and organelles, allowing them to perform a wide range of biological functions. Protozoa are also single-celled organisms with complex cellular structures that can reproduce and metabolize independently. Thus, only viruses exhibit the characteristic of being composed solely of genetic material surrounded by a protein covering, making them distinct from the other listed microorganisms.