Which of the following structures is found in viruses?

Viruses are unique entities that differ significantly from living cells, and one of their defining features is the presence of a genome. The genome of a virus consists of its genetic material, which can be either DNA or RNA, and it contains the instructions necessary for the virus to replicate and produce new virus particles. This genetic material is encapsulated within a protein coat called a capsid, and sometimes surrounded by an additional lipid envelope, but the essential component is always the genome.

The presence of a genome is critical for viruses, as it allows them to take over the cellular machinery of a host organism to propagate themselves. This characteristic distinguishes viruses from other structures, such as cell membranes, which are found in living cells and are involved in enclosing cellular contents, and cell walls, which provide structural support and protection to many types of organisms including bacteria and plants. Plasma membranes also pertain to living cells and are not features of viruses. Thus, the genome is the fundamental element that is inherent to all viruses, providing them the capability to exist and replicate within host cells.