VIRUSES, VIROIDS AND LICHENS

Pasteur coined the term virus, which means Venom / poison.

Virus: The viruses are non-cellular organisms that are characterized by having an inert crystalline structure outside the living cell.

a)It is made of a outer protein coat and a centre genetic material (RNA / DNA). 

b) Viruses also contain genetic material, that could be either RNA or DNA. No virus contains both RNA and DNA.

 c)A virus is a nucleoprotein and the genetic material is infectious.

d)  Virus that infect plants have single stand RNA and those infect animals have either single or double

RNA or double stranded DNA.

e) Viruses cause disease like mumps, small pox, herpes, influenza and AIDS to animals. In plants the symptoms can be mosaic formation, leaf rolling, and curling, yellowing, dwarfing and stunted growth. 

 

Bacteriophages are viruses that infect the bacteria.

 Viroids:  It is a  infectious agent which is smaller than virus . It causes Potato spindle tuber disease. It has only a free RNA and lacked the protein coat, so named as viroid.

It was discovered by T.O.Diener

Lichens  :They are symbiotic association between algae and fungi.

 Phycobiont is algal component, which prepare food for fungi and 

Mycobiont  is a fungal  component, which provide shelter and absorb mineral nutrients and water for its partner.