Question

Viruses are called obligate parasites because

• A. Viruses must carry out their reproduction by parasitizing a host cell
• B. They cannot multiply outside a living cell
• C. They can only replicate inside of a specific host
• D. All of the above

Answer 1

The correct option is D All of the above

Virus, is a nucleoprotein entity which is able to utilize the synthetic machinery of a living cell of another organism for its multiplication which does not involve the growth and the division. Pasteur coined the term virus before its scientific discovery. The virus cannot grow on non living culture medium. It requires living cells for its metabolism and multiplication.
The virus is an obligate parasite as it is inert outside the host cell. An inert virus is called the Virion. A Biosynthetic machinery is absent. There is no system to liberate energy. A virus does not grow. It does not divide or reproduce like typical organisms without host machinery.
It multiplies by independent formation of its parts using host machinery and then assembly of parts to produce virus particles. A virus lacks irritability and motility. It requires a vector for transfer from one host to another.
So the correct option is 'All of the above'.