Final answer:
The statement that viruses can contain either DNA or RNA, but not both, is true, making the distinction between DNA viruses and RNA viruses. These acellular entities require host cell machinery to replicate and are not considered living organisms. They are visible under an electron microscope due to their small size.
Step-by-step explanation:
The statement "Viruses can contain either DNA or RNA, but not both" is true. Viruses have evolved to carry either DNA or RNA in their virion structures as the genetic material, but not both simultaneously. This allows for a simple categorization into DNA viruses and RNA viruses. DNA viruses replicate their genome using the host cell's machinery, while RNA viruses carry their own enzymes for replication because host cells typically do not support direct replication of RNA genomes.
Additional points related to viruses include: Viruses are acellular organisms, meaning they lack cells, and cannot replicate on their own. Instead, they must infect a host cell and use its machinery to produce new viral particles. Moreover, viruses are not considered living organisms because they cannot maintain cellular processes independently. Many viruses are difficult to visualize with a light microscope due to their small size, and instead, they can often only be seen under an electron microscope.