Question

Question 11 Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.

Class XI Biology Chapter - Biological Classification Page 28

Answer 1

Viruses are sub-microscopic infectious agents that can infect all living organisms. A virus consists of genetic material surrounded by a protein coat. The genetic material may be present in the form of DNA or RNA.

Most of the viruses, infecting plants, have single stranded RNA as genetic material. On the other hand, the viruses infecting animals have single or double stranded RNA or double stranded DNA.

Bacteriophages or viruses infecting bacteria mostly have double stranded DNA. Their protein coat called capsid is made up of capsomere subunits. These capsomeres are arranged in helical or polyhedral geometric forms.

A.I.D.S, small pox, mumps, and influenza are some common examples of viral diseases.


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Answer 2

Answer:

Virus is a group of ultramicroscopic , non-cellular , highly infectious agent that multiply only intracellularly - inside leaving host cells without involving growth and division. Outside the host cell , they are inert particles. They are nucleoproteins having one or more nuclic acid molecule , either DNA or RNA , encased in a protective coat of protein or lipoprotein. A virus consists of two parts - nucleoid and capsid an envelope and few enzymes are present in some cases :-

1) Nucleoid

2) Capsid

3) Envelope

4) Enzymes.