Virus is a Latin word which means “poison”. Viruses are so small which can’t be seen with naked eye. To observe this organism we use microscopes or biological checks. Such things which can’t be seen with naked eyes and we use to microscopes to see it we can say that they are microbes or micro-organisms.

Viruses are of different shapes and of different sizes. Some are curvy, some are rod shaped and few are polyhedral like while are like tadpoles. According to structure viruses are not cellular but they are made up of nucleic harsh and proteins. Viruses have two layers the outer is called outer coat and made up of proteins and the inner is inner core and made up of DNA and RNA.

Viruses are considered as a link between living organisms and non-living organisms. They reproduce like living organisms and like non-living they are found in the form of crystals. All viruses are parasites and obtain their food from other living organisms. Viruses in living organisms are transmitted in a variety of ways like by air, contaminated water and food, through insects, droplets produce on coughing and sneezing and through contact.

Viruses produce many diseases in plants and animals. In humans viruses produce cold, small pox, polio, measles and influenza etc. viruses usually cause disease in the plants like tobacco, potato, tomato and cabbage etc.