What is a virus?
A virus is a micro-organism that can not grow or reproduce outside of a living cell. It typically consists of a nucleic acid molecule in a protein coat, but may have other components such as a tail or a membrane envelope.
You can read more about viruses here.
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How do we find viruses?
The first virus was discovered in 1892. Leaves from a tobacco plant affected by Tobacco Mosaic Disease, were mashed up and the sap was filtered. People knew that bacteria (the smallest form of life known then) would not pass through the filter, but the filtered sap could still infect other plants. They called the infectious agent Tobacco Mosaic Virus (TMV). Since then, many other viruses have been discovered.
Viruses are too small to see with even the most powerful light microscopes. To see viruses, we need to use an electron microscope, which uses a beam of electrons to take images. To read more about electron microscopes, click here.