2. Systematics of Living Organisms - part 06 - Acellular organisms

 

2. Systematics of Living Organisms - part 06 - Acellular organisms


Acellular organisms :
a.Viruses :
  • Viruses were named so by Louis Pasteur; considering the meaning, Venom or poison. 
  • These obligate parasites were given the name 'virus' by M. J. Beijernek, after observation that they were able to migrate in an agar gel. 
  • Thus, being and infectious soluble agent, he called the filtrate as 'contagium vivum fluidum'. 
  • It was scientist Stanley who demonstrated that viruses are inert outside the host cell and can be crystallised. 
  • They are made up of proteins.
  • Viruses lack their own cell machinery.
  • They have protein coat (capsid) around nucleic acid strand, thus considered to be acellular organisms. 
  • Viruses are inactive outside a host cell; but once they enter their specific host cell, they take charge of cellular machinery of host cell and duplicate themselves. 
  • Viruses thus can be called infectious nucleoprotein particles.
Types of viruses :
  • As per genetic material, viruses are grouped as DNA or RNA viruses.
Do u know?
  • Viruses have either DNA or RNA as their genetic material but never DNA as well as RNA.
  • Protein coat called capsid is made up of smaller units, the capsomeres. 
  • Capsomeres are arranged in polyhedral or helical forms. 
  • Capsid protects genetic material.
  • The genetic material in viruses is either single-stranded RNA or single or doublestranded RNA or double-stranded DNA.
  • Viruses that infect bacterial cells are calledbacteriophages which normally have doublestranded DNA.
  • Viruses cause disorders like leaf curling, yellowing, mosaic formation etc. in plants. 
  • You have heard of foot and mouth disease in animals or swine flu which are viral diseases. 
  • Small pox, mumps, herpes to common cold,viruses are the causative agents of many diseases in humans. 
  • The list includes AIDS too!
b. Viroids : 
  • Potato spindle tuber disease was found to be caused by single stranded RNA which lacks protein coat. 
  • T. O. Diener in 1971 reported that this is low molecular weight RNA and smaller in size than viruses. 
  • These infectious RNA strands are called viroids.

c. Lichens : 

  • Lichen is co-existence of algae and fungifor mutual benefit. 
  • Algal member, the phycobiont as it is called, mostly belongs to cyanobacteria (blue-green algae) or green algae. 
  • Fungal member is called mycobiont.
  • 2. Systematics of Living Organisms - part 06 - Acellular organisms

  • Acellular organisms :
  • a.Viruses :
  • Viruses were named so by Louis Pasteur; considering the meaning, Venom or poison. 
  • These obligate parasites were given the name 'virus' by M. J. Beijernek, after observation that they were able to migrate in an agar gel. 

  • Thus, being and infectious soluble agent, he called the filtrate as 'contagium vivum fluidum'. 
  • It was scientist Stanley who demonstrated that viruses are inert outside the host cell and can be crystallised. 
  • They are made up of proteins.
  • Viruses lack their own cell machinery.
  • They have protein coat (capsid) around nucleic acid strand, thus considered to be acellular organisms. 
  • Viruses are inactive outside a host cell; but once they enter their specific host cell, they take charge of cellular machinery of host cell and duplicate themselves. 
  • Viruses thus can be called infectious nucleoprotein particles.
  • Types of viruses :
  • As per genetic material, viruses are grouped as DNA or RNA viruses.
  • Do u know?
  • Viruses have either DNA or RNA as their genetic material but never DNA as well as RNA.
  • Protein coat called capsid is made up of smaller units, the capsomeres. 

  • Capsomeres are arranged in polyhedral or helical forms. 
  • Capsid protects genetic material.
  • The genetic material in viruses is either single-stranded RNA or single or doublestranded RNA or double-stranded DNA.
  • Viruses that infect bacterial cells are called bacteriophages which normally have doublestranded DNA.
  • Viruses cause disorders like leaf curling, yellowing, mosaic formation etc. in plants. 
  • You have heard of foot and mouth disease in animals or swine flu which are viral diseases. 
  • Small pox, mumps, herpes to common cold, viruses are the causative agents of many diseases in humans. 
  • The list includes AIDS too!
  • b. Viroids : 
  • Potato spindle tuber disease was found to be caused by single stranded RNA which lacks protein coat. 
  • T. O. Diener in 1971 reported that this is low molecular weight RNA and smaller in size than viruses. 
  • These infectious RNA strands are called viroids.

  • c. Lichens : 


  • Lichen is co-existence of algae and fungi for mutual benefit. 
  • Algal member, the phycobiont as it is called, mostly belongs to cyanobacteria (blue-green algae) or green algae. 
  • Fungal member is called mycobiont.
  • They are excellent example of symbiosis. 
  • The algal component of lichens provides food to fungal part while fungus provides shelter to alga and also absorbed water and minerals to alga. 
  • The association is intense and it is difficult to identify them as separate living beings.
  • Though found in extreme environments like snow clad poles, lichens are sensitive to pollution. 
  • They are not found in polluted regions, hence are considered as pollution indicators. 
  • Lichens also play important role in soil formation by using specific acid productions.
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  • They are excellent example of symbiosis. 
  • The algal component of lichens provides food to fungal part while fungus provides shelter to alga and also absorbed water and minerals to alga. 
  • The association is intense and it is difficult to identify them as separate living beings.
  • Though found in extreme environments like snow clad poles, lichens are sensitive to pollution. 
  • They are not found in polluted regions, hence are considered as pollution indicators. 
  • Lichens also play important role in soil formation by using specific acid productions.

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