Saturday 12 December 2015

VIRUS, VIROIDS AND LICHEN

* virus, viroids and lichen are acellular organism which have no place in five kingdom classification.
* VIRUS- viruses are non-cellular organism. they have inert crystalline structure outside the living                       body.
                 -when they invert living cell they take over the machinery of the host cell to replicate                            themselves and kill the host cell.
                 -D.J.IVANOWSKY(1892) named virus means poisonous fluid.
                 -M.W.BEIJERINEK(1898) discovered TMV(tobacco mosaic virus)
                 -W.M.STANLEY (1935) showed that virus could be crystallised and crystals consist                              largely of proteins.
                 -viruses are obligate parasites.
                 -it contain genetic material DNA or RNA.
                 -Bacteriophages or bacterial viruses are usually have double strand DNA.
                 -the protein coat of virus of capsid, made up of small subunits called capsomeres protect                       the nucleic acid.
                 -these capsomere are arranged in helical or polyhedral geometric form.
                 -disease caused by virus are AIDS, mumps,small pox etc.
                                                                                                                                           
BACTERIOPHAGE
TMV


*VIROIDS- T.O.DIENER discovered a new infectious agent smaller than virus
                   - it was a free RNA
                   - it lacked the protein coat.
                   - RNA of viroid had low molecular weight.



* LICHENS -  association of algae and fungus is calledlichen.
                      - algal component is called phycobiont and fungal component as mycobiont.
                      - algae prepare food for fungus and fungus provide shelter and absorb mineral and                                 water from soil.




                                                                                                                                page-17           

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