Question

Which one of the following statements about viruses is correct?
A. Viruses possesses their own metabolic system
B. All viruses contain both RNA and DNA
C. Viruses are obligate parasites
D. Nucleic acid of viruses is known as capsid

Answer 1

Viruses are microscopic infectious agents. A virus is a small/ microscopic infectious agent. They replicate only inside the living cells of other organisms (hosts). They can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.

Complete answer:
All viruses are obligate parasites, i.e., they lack metabolic machinery of their own to generate energy or to synthesize proteins, hence they depend on the host cells to carry out these vital functions.All viruses contain either DNA or RNA as genetic material, but not both. Retroviruses have RNA, but in entering the host the genetic material converts into DNA. Hepatitis C virus, dengue virus, zika virus, etc. are some examples of RNA viruses.
The protein coat of the virus is known as a capsid. It is made up of several subunits known as
capsomeres.

Therefore, Option C: Viruses are obligate parasites

Note:
Apart from obligate parasites, there are facultative parasites. They may resort to parasitic
activity, but they do not absolutely rely on any host for the completion of its life cycle. Some
examples of facultative parasitism include species of fungi, such as family members of the genus Armillaria. Apart from viruses, there are viroids that are the smallest infectious pathogens known. They are composed solely of a short strand, circular, single-stranded RNA that has no protein coating (unlike viruses having capsid). All known viroids are inhabitants of higher plants. Most of them cause diseases that are usually contagious.Bacteriophages are viruses that affect and kill bacteria by interfering with their metabolic processes. Recently they are used as a mode of antibacterial as several strains of bacteria worldwide are showing increased resistance to antibiotics.