UPSC Prelims 2021 Q70: Science & Technology – Health & Diseases
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (b) 2 only
Explanation
Adenoviruses vs Retroviruses
| Feature | Adenovirus | Retrovirus (HIV) |
|---|---|---|
| Genome type | Double-stranded DNA (dsDNA) | Single-stranded RNA (ssRNA) |
| Envelope | Non-enveloped | Enveloped |
| Enzyme | DNA polymerase | Reverse transcriptase (RNA to DNA) |
| Diseases | Common cold, conjunctivitis, gastroenteritis | AIDS (HIV), leukemia (HTLV) |
| Genome size | Medium (~36 kb) | Small (~10 kb) |
Checking the statements:
| Statement | Claim | Verdict | Detail |
|---|---|---|---|
| 1 | Adenoviruses = ssDNA; Retroviruses = dsDNA | FALSE (reversed) | Adenoviruses are dsDNA; Retroviruses are ssRNA. |
| 2 | Common cold sometimes caused by adenovirus; AIDS by retrovirus | TRUE | Adenoviruses cause common cold, conjunctivitis, gastroenteritis. HIV (a retrovirus) causes AIDS. |
Only statement 2 is correct. Answer: (b).
Answer: (b) 2 only.
Why each option is right or wrong
- (a) Incorrect. Statement 1 is completely reversed - adenoviruses are dsDNA (not ssDNA); retroviruses are ssRNA (not dsDNA).
- (b) CORRECT. Only statement 2 is correct - adenoviruses cause common cold (among other rhinoviruses, coronaviruses); HIV (a retrovirus) causes AIDS. Statement 1 has the genome types completely reversed.
- (c) Incorrect. Statement 1 is factually wrong.
- (d) Incorrect. Statement 2 is a well-established fact.
Key point
Adenovirus = double-stranded DNA (dsDNA), non-enveloped. Retrovirus (HIV) = single-stranded RNA (ssRNA), enveloped, uses reverse transcriptase. Adenoviruses cause common cold; HIV causes AIDS. Statement 1 is REVERSED.
Remember
Adenoviruses have DOUBLE-stranded DNA genomes and Retroviruses have SINGLE-stranded RNA genomes (statement 1 is reversed and WRONG). Common cold is sometimes caused by adenoviruses and AIDS is caused by a retrovirus (HIV) - statement 2 is correct. Answer: (b) 2 only.
Common mistakes
- Confusing DNA and RNA virus classifications. Adenovirus is DNA (dsDNA); Retrovirus is RNA (ssRNA).
- Not knowing common cold is caused by MULTIPLE viruses: rhinoviruses (~50%), coronaviruses, adenoviruses, RSV, parainfluenza.
- Missing that Covishield uses a chimpanzee adenovirus VECTOR (harmless) - because adenovirus is well-studied and safe.
Exam tip
Virus classification by genome: DNA (Herpesvirus, Adenovirus, Poxvirus, HPV, Hep B), RNA (Influenza, Coronavirus, HIV, Ebola, Rabies, HCV). Retroviruses = ssRNA + reverse transcriptase (converts RNA to DNA to integrate into host genome).
Sources
- NCERT Class XII Biology - Chapter 8: Human Health and Disease
- ICMR-NIV - Viral Genome Classification Guidelines