Which of the following microorganisms are classified as noncellular?

The correct answer is based on the understanding of cellular structure in microorganisms. Viruses are classified as noncellular because they lack the cellular machinery that defines living organisms. They do not have a cellular structure, and instead, they consist of genetic material (DNA or RNA) surrounded by a protein coat, and sometimes an additional lipid envelope.

Viruses cannot carry out metabolic processes on their own and are dependent on a host cell for replication and reproduction. This reliance on host cells for their life cycle is a key factor that distinguishes them from other microorganisms such as bacteria, fungi, and protozoa, all of which are composed of one or more cells and exhibit characteristics typically associated with living organisms, including the ability to metabolize energy and reproduce independently.

Thus, in the context of the classification of microorganisms, viruses stand out as noncellular entities, while bacteria, fungi, and protozoa are all cellular forms of life.