What Are Viruses?
Measles, the flu, and even the common cold are examples of viruses. Viruses are extremely unique in that they do not fit into any of the five kingdoms. They do not contain any of the basic parts that all organisms of the five kingdoms share. The only characteristic that viruses share with organisms is the ability to reproduce. Viruses are basically infectious agents that have the ability to take over cells' functions.
In order to reproduce, a virus must be exposed to a host cell. Once a virus is introduced to the body, they inject their DNA into a host cell. This injection causes the host cell to abandon its previous function and perform the same functions of the virus. When you have a virus, you usually show some type of symptoms, e.g. coughing and a runny nose. Symptoms are a result of cells being taken over by the virus. Once a virus begins to take over cellular activity, it is very hard to stop.
Viruses are a very controversial topic. Some scientists believe that viruses are not living creatures because they contain no cells, do not eat, and they do not perform many of the functions that living things perform. Viruses do reproduce, however, and this one fact is good enough for some scientists to believe that viruses are indeed alive.