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Plant virus :

1. Capsid: It is only external boundary.
2. Genetic material: RNA
3. Nucleic acid strand: Single stranded
4. Nature of nucleic acid: Linear
5. Infection: Enter through wound or pore

Animal virus :

1. Capsid: In addition to capsid envelope is also present.
2. Genetic material: DNA
3. Nucleic acid strand: Double stranded
4. Nature of nucleic acid: Linear or Circular
5. Infection: Enter through phagocytosis

Many theories put farwarded regarding the nature of the viruses out of them the viral theory is the most accepted theory. 

According to it

1. Virus is a granular structure which can not be seen by normal microscope. They can not be isolated by bacterial filter.
2. They can not be cultured in artificial (dead) medium.
3. They cause specific symptoms in their host cells. They respond to temperature and humidity.

features :

1. Nature of Nucleic acid – RNA or DNA
2. Symmetry of the capsid (virus)
3. Molecular weight of the virus
4. Shape and size (Dimensions) of the viruses
5. Presence or absence of envelope

• They are minute structures and can be studied with the help of electron microscope.
• Size : The normal size of virus is 10 to 200 nM. The size may be upto 300 pM. The plant viruses are smaller than the animal viruses.
• Shape : They have different shapes such as roughly spherical (pleiomorphic) eg.-Influenza virus, mumps virus, Icosahedral eg – Herpes virus, Helical eg -TMV etc.
• Chemical Composition : The fundamental structure of all the viruses is similar. Each virus consists of central core of DNA or RNA which is bounded by a protein covering. The base pairs (nucleotides pairs) varies from 1000 to 2,50,000. But it is constant in a specific virus

Term virus originated from Greek Work Virus which means venom or poisnous fluid or toxin molecule. They can’t be separated using bacterial filtre because they are smaller than the bacteria. Chemically, they are nucleic acid bounded by protein capsule.

Discovery of Virus:

• The credit of virus discovery goes to D.J. Ivanowsky (1892). He discovered virus while working on mosaic infected tabacco leaves. F. Twort (1915) and F.d. Herelle (1917) independently discovered the bacteriaophages.
• According to Luria & Dornel (1968), they are the unit in which genome is a nucleic acid. They replicate in the host cell using the cellular facilities to form special particles called virons. They granules are capable to transmit virus genome into other cells.
• According to Matthews (1970), virus consists of one or more templet of nucleic acid (DNA or RNA) which exhibt hereditary characters.
  features of viruses :

1. Nature of Nucleic acid – RNA or DNA
2. Symmetry of the capsid (virus)
3. Molecular weight of the virus
4. Shape and size (Dimensions) of the viruses
5. Presence or absence of envelope.
6. Number of chromomeres in the caspid
7. Diameter of coiled nucleocaspid and number of cuboid capsomeres.
8. Diamter of nucleic acid coiling.
9. Interacellular multiplication
10. Process of virus transmission.

Polio, Small pox

iving proterties of virus :

1.  The viruses respond to chemicals, heat, light, radiations etc.
2.  They exhibit antigenic properties.
3.  Their hereditary material is DNA or RNA.
4.  They can multiple only in living host cells.
5.  They have capacity to infect host cells and are host specific.

non-living proterties of virus :

1. They can be crystallized easily.
2. They are not able to perform metabotic activities.
3. They do not respire.
4. Normally, they lack enzymes.
5. They don’t have cellular structures.

The answer is Tobacco Mosaic Virus

The answer is (b) Unicellular
 

The answer is (c) Nucleoprotein