Question

A virus is also known as parasite because it
A. Harms its host
B. Cannot reproduce outside its host
C. Kills its host
D. Both A and B
E. All of the above

Answer 1

Hint: Viruses are acellular obligate parasites. A virus benefits from its host by taking the metabolites from its host to multiply. Parasitism is an association in which one organism benefits at the cost of the other.

Complete answer:
Viruses can survive outside the host in the environment but they require a host cell to reproduce and replicate. Thus it is called an obligate parasite. They can exist on their own but cannot generate further generations without a host cell. When a host cell dies, the viruses cannot replicate further and thus are not anymore infectious.
A parasite uses metabolites from the host and uses them for its own metabolism and replication. During this process, the virus may lead to the destruction of the host cell. Thus the virus benefits from the host and in turn, the host is harmed. A virus invades the host system. There are lytic viruses that lyse the host cell. These viruses harm the host cells and may also kill it.
Thus, all the options are correct and the correct answer is Option E.

Note:
Bacteriophages are viruses that infect bacteria. These bacteriophages are also brought to use by humans to fight against certain bacterial diseases. A virus can be both living and nonliving. If a virus is present outside a host, it is nonliving. If a virus attaches itself to a host, it becomes living. A virus is just a genetic material, that is either a DNA or an RNA surrounded by a layer of capsid, a protective protein. This capsid is not present in all viruses.