Consider the following statements:
- I.No virus can survive in ocean waters.
- II.No virus can infect bacteria.
- III.No virus can change the cellular transcriptional activity in host cells.
How many of the statements given above are correct?
Answer & explanation
Answer: (d) None
None of the statements is correct, because each one is an absolute claim ("no virus can...") and a single counter-example disproves it. Viruses are abundant in seawater, bacteriophages infect bacteria, and many viruses take over the host cell's gene activity.
- ✗ I Viruses are the most abundant biological entities in the oceans, reaching up to about 10 crore (10^8) particles in every millilitre of seawater.
- ✗ II Bacteriophages are viruses that infect bacteria. NCERT describes how a phage attaches to a bacterium and its genetic material enters the bacterial cell.
- ✗ III An infected cell treats the viral genetic material as its own and makes more virus particles, so its gene activity is redirected. Many viruses actively shut off the host's own gene expression to help themselves multiply.
Remember · Viruses live in seawater, bacteriophages infect bacteria, and viruses reprogram host-cell gene activity, so 'no virus can...' statements are false.
📘 Read it in NCERT: Class 12 Biology, Ch 5 (practise this chapter) · Class 12 Biology, Ch 5 (practise this chapter)
Sources
- NCERT Class 12 · Biology, Chapter 5 “They worked with viruses that infect bacteria called bacteriophages. The bacteriophage attaches to the bacteria and its genetic material then enters the bacterial cell.”
- NCERT Class 12 · Biology, Chapter 5 “The bacterial cell treats the viral genetic material as if it was its own and subsequently manufactures more virus particles.”
- Marine Viruses: Key Players in Marine Ecosystems (Viruses, via NIH/PMC) ↗ “The discovery that viruses were the most abundant biological entities in oceanic marine environments”
- Shutoff of Host Gene Expression in Influenza A Virus and Herpesviruses (Viruses, via NIH/PMC) ↗ “The ability to shut off host gene expression is a shared feature of many viral infections, and it is thought to promote viral replication by freeing host cell machinery and blocking immune responses.”
Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·