Final answer:
Viruses are extremely small collections of replicating genetic code that depend on other organisms, known as hosts, for their survival. They infect a host cell and use the host's replication processes to produce progeny virus particles.
Step-by-step explanation:
Virus is the term used to describe extremely small collections of replicating genetic code that depend on other organisms, known as hosts, for their survival.
Viruses are acellular, parasitic entities that are not classified within any domain because they are not considered alive. They have no plasma membrane, internal organelles, or metabolic processes, and they do not divide. Instead, they infect a host cell and use the host's replication processes to produce progeny virus particles.
Once inside the host cell, viruses use the cell's ATP, ribosomes, enzymes, and other cellular parts to make copies of themselves. The host cell makes a copy of the viral genetic material and produces viral proteins, which are then packaged into new viruses.