Lippincott Microbiology Practice Exam 2025 - Free Microbiology Practice Questions and Study Guide

The major characteristics of viruses highlight their unique nature compared to other forms of life. Viruses are considered acellular entities; they do not possess a cellular structure, which is a fundamental characteristic that distinguishes them from other living organisms. Unlike bacteria, fungi, and other microorganisms that are made up of cells, viruses are composed of genetic material encased in a protein coat, and sometimes a lipid envelope.

Viruses are obligate intracellular parasites, meaning they require a host cell to replicate. Once a virus infects a suitable host, it hijacks the cellular machinery of the host to produce new viral particles. This reliance on host cells for replication is a cornerstone of viral biology and defines their inability to carry out metabolic processes independently.

In contrast, the other choices present characteristics that do not accurately describe viruses. They are not multicellular and cannot replicate on their own, nor do they contain multiple chromosomes or ribosomes, which are necessary for independent protein synthesis. Furthermore, they cannot reproduce through binary fission, which is a method typical of many prokaryotes like bacteria. Thus, the aspects outlined in the correct response are central to understanding the defining traits of viruses.