Question

Diseases like polio and chickenpox are caused by
(a) Bacteria
(b) Fungi
(c) Viruses
(d) Worms

Answer 1

Hint: Polio and chickenpox are caused by the members of the group which also cause mumps, common cold, etc in humans. The members of this group have not been placed under any kingdom from the Whittaker five- kingdom system.

Complete Answer:
Diseases like polio and chickenpox are caused by viruses. Polio is caused by poliovirus and chicken[ox is caused by the varicella- zoster virus. Viruses are obligate parasites who have non- cellular structures i.e. their basic unit is not a cell. They have an inert crystalline structure when present outside a living cell and behave like non- living things. But once they enter a living cell, they take over the machinery of the host cell to replicate themselves. Viruses are smaller than bacteria as they can pass through bacteria- proof filters.

Additional information: Let us look at the structure of a virus in detail.
- Virus is made up of only protein and nucleic acid which can be RNA or DNA i.e. nucleoprotein.
- The protein coat known as capsid is responsible for protecting the nucleic acid and is made up of small units known as capsomeres.
- The nucleic acid of the virus is its genetic material and it is infectious in nature.
- Generally, plant infecting viruses have single- stranded RNA, and animal infecting viruses have double- stranded RNA or double- stranded DNA.
So, the correct option is ‘(c) Viruses’.

Note:
- The term virus was given by Dmitri Ivanowsky in 1892 to indicate that it was a poisonous fluid or venom that caused the tobacco mosaic disease.
- The extract of this poisonous fluid was taken from the tobacco plant and used to infect healthy plants by M.W.Beijerinck.
- He called the fluid ‘Contagium vivum fluidum’ which means infectious living fluid.