In 1892 this became the first virus to be discovered.

• A. Bacteriophage
• B. Tobacco mosaic virus
• C. Influenza virus
• D. Rhinovirus

Answer: (B)

The main idea is that viruses were shown to be infectious agents smaller than bacteria, revealed by filtration experiments. In 1892, tobacco mosaic disease in tobacco plants was studied, and the disease could be transmitted by sap that had been filtered through a very fine filter that trapped bacteria. Yet the filtrate still caused disease, indicating an ultrafine infectious agent. This led to the identification of the tobacco mosaic virus, the first virus described. Later scientists coined the term virus to describe such agents. The other viruses listed were discovered later—bacteriophages infect bacteria, influenza virus was identified in the 1930s, and rhinovirus in the 1950s—so tobacco mosaic virus is the earliest.