Q60. Which assertion about viruses is generally incorrect?
[CGPSC 2021 Prelims, held 13 February 2022]
(A) A virus may possess DNA or RNA
(B) RNA viruses can mutate comparatively quickly
(C) Most DNA viruses necessarily contain single-stranded DNA
(D) Viruses lack independent cellular metabolism
Answer: (C) Most DNA viruses necessarily contain single-stranded DNA
Explanation: Many DNA viruses carry double-stranded DNA, so claiming they are usually single-stranded is misleading. Viral genomes may be DNA or RNA, single- or double-stranded. Mutation rates vary considerably; many RNA viruses evolve rapidly because of replication characteristics.
Q59. What was the volume of a single Covishield vaccine dose in the examined vaccination schedule?
[CGPSC 2021 Prelims, held 13 February 2022]
(A) 1.0 mL
(B) 2.0 mL
(C) 0.5 mL
(D) 1.5 mL
Answer: (C) 0.5 mL
Explanation: The standard Covishield dose used in the programme was 0.5 mL by intramuscular injection. Covishield employs an adenovirus-vector platform to express the SARS-CoV-2 spike antigen. Dose schedules and recommendations should follow the contemporary national programme or product label.
Q58. Which disease in the following group is bacterial rather than viral?
[UPSC NDA (I) 2022]
(A) AIDS
(B) Dengue
(C) COVID-19
(D) Typhoid
Answer: (D) Typhoid
Explanation: Typhoid is caused by Salmonella Typhi, a bacterium transmitted commonly through contaminated food or water. AIDS, dengue and COVID-19 are caused by HIV, dengue virus and SARS-CoV-2 respectively. The difference matters because antibiotics target bacteria, not viruses directly.
Q57. Which groups can normally grow on a cell-free artificial medium: bacteria, fungi and viruses?
[UPSC CSE Prelims 2021]
(A) Bacteria and fungi only
(B) Fungi and viruses only
(C) Bacteria and viruses only
(D) All three
Answer: (A) Bacteria and fungi only
Explanation: Many bacteria and fungi grow on suitable artificial culture media because they possess their own cellular metabolism. Viruses must infect susceptible living cells to replicate. Laboratory virology commonly uses cell cultures, embryonated eggs or other living systems rather than nutrient agar alone.
Q56. Assess the claims:
Adenoviruses have single-stranded DNA whereas retroviruses have double-stranded DNA;
Adenoviruses can cause colds whereas HIV is a retrovirus.
[UPSC CSE Prelims 2021]
(A) First only
(B) Second only
(C) Both
(D) Neither
Answer: (B) Second only
Explanation: The first statement reverses the usual genome types: adenoviruses possess double-stranded DNA, while HIV is an RNA retrovirus. The second is correct. Some adenoviruses cause respiratory illness, and retroviruses copy their RNA into DNA using reverse transcriptase.
Q55. ACE2 attracted attention in relation to which subject?
[UPSC CSE Prelims 2021]
(A) GM crop markers
(B) Satellite navigation
(C) Wildlife tracking
(D) Entry and spread of certain coronaviruses
Answer: (D) Entry and spread of certain coronaviruses
Explanation: Angiotensin-converting enzyme 2 is a receptor used by SARS-CoV-2 to enter many susceptible cells. The viral spike protein attaches to it as part of the entry process. ACE2 also performs normal physiological functions independently of infection.
Q54. What is the official name of the virus that causes COVID-19?
[WBCS Prelims 2021]
(A) SARS-CoV-2
(B) COVID-19 virus
(C) nCOVID-19
(D) Coronavirus disease 2019
Answer: (A) SARS-CoV-2
Explanation: SARS-CoV-2 is the name of the virus, while COVID-19 is the disease it causes. The distinction matters: virus naming follows taxonomic conventions, whereas diseases receive separate public-health names. SARS-CoV-2 is related to the coronavirus associated with SARS.
Q53. Which disease among cholera, AIDS, cold and dengue is not viral?
[RRB NTPC CBT-I, 14 March 2021]
(A) Cholera
(B) AIDS
(C) Common cold
(D) Dengue
Answer: (A) Cholera
Explanation: Cholera is caused by the bacterium Vibrio cholerae and commonly spreads through contaminated water. AIDS results from HIV, colds from several respiratory viruses and dengue from dengue virus. Pathogen classification is the central distinction in this question.
Q52. Japanese encephalitis virus most directly damages which organ?
[RPSC RAS Prelims 2021]
(A) Skin
(B) Red blood cells
(C) Brain
(D) Lungs
Answer: (C) Brain
Explanation: Japanese encephalitis is inflammation of the brain associated with Japanese encephalitis virus. It is transmitted mainly through Culex mosquitoes, with pigs and water birds important in the transmission cycle. Severe illness may involve seizures, altered consciousness and neurological injury.
Q51. Which virus causes the historically widespread disease smallpox?
[UPSC NDA (II) 2021]
(A) Adenovirus
(B) Variola virus
(C) Coxsackievirus
(D) Aichi virus
Answer: (B) Variola virus
Explanation: Smallpox was caused by variola virus, an orthopoxvirus. Worldwide vaccination campaigns stopped naturally occurring transmission, allowing WHO to declare eradication in 1980. It should not be confused with chickenpox, which is caused by varicella-zoster virus.
