What are Viruses & its Types in Biology

Viruses & its Types in Biology


Virus is Latin word which means poison.




Viruses were discovered by lwanowsky in 1892 from infected leaves of tobacco.


Living or Non-living:


They have characteristics of living and non-living things. When they enter in the body of living organisms they reproduce like living things. But when they are outside of the body they form crystals like non-living things.


Size & Shape:


Their size is from 0.01m to 0.3m. They are rounded, rod shaped, polyhedral and tadpoles in shape.




They are chemically alike and have two parts:


  1. i) An outer coat of protein. This coat determines the shape of virus. It consists of two parts Head & Tail.


  1. ii) An inner core of DNA or RNA. DNA is present in head region. Animal viruses contain DNA and plant viruses have RNA.




They cannot prepare their own food. All viruses are parasites and obtain food from host.




They reproduce when they enter in the body of host.




  1. i) In plants virus cause many diseases. For example ring spot in many plants. Yellow in sugar beet and mosaic in tobacco, potato and tomato etc.


  1. ii) In animals virus cause mouth and food diseases. Cowpox in horses and cows.


iii) In human virus cause cold, influenza, smallpox, polio, hepatitis, cancer and AIDs etc.


Sources of Transmission:


  1. i) Through droplets due to coughing.


  1. ii) Through droplets due to sneezing.


iii) Through physical contact.


  1. iv) By air and contaminated water and food.


  1. v) By re-use of already used syringes.


  1. vi) By un-sterilized surgery equipments


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