Viruses

Viruses ( the name viruses that means venom or poisonous fluid was given by Pasteur ) are intracellular obligately parasitic, self-replicating non cellular, sub microscopic organisms. They lack cellular organelles like ribosomes, mitochondria, etc. and make use of the protein synthesis machinery of the host cells.



Are Viruses Living or Non Living?

Viruses are the simplest and most primitive organisms. Hence, it is difficult to assign them any rank in the living kingdom. It is also not easy to define the features of viruses within the accepted framework of living beings. Hence it is better to regard them as an intermediate stage between living and non living. Some of the characters of living exhibited by viruses are as follows.

1. Viruses are living in the following respects.

1) viruses have genetic material ( DNA or RNA ).
2) They mutate.
3) They can be transmitted from one host to another.
4) They are capable of multiplication with in a host.
5) They react to heat, radiation and chemicals.

2. Viruses are non-living in the following respects.

1) They can be crystallized like an ordinary chemicals and stored in a bottle or test tube indefinitely.
2) Outside the host viruses are inert.
3) There is no cell wall, membrane or cytoplasm.
4) There are no cell organelles and there is no metabolism.
5) Sedimentation of viruses is according to their molecular weight like non living beings.

3. Some unique characters of viruses.

1) Presence of only DNA or RNA.
2) Capacity to produce from the sole nucleic acid.
3) They do not show cell division.



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