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?

(a) Only one
(b) Only two
(c) All the three
(d) None ✓ UPSC's answer

Why the answer is (d)

• Statement I is wrong: the oceans hold an estimated 10^30 viruses — mostly bacteriophages — making them the most abundant biological entities on Earth; a litre of seawater contains billions.

• Statement II is wrong: viruses that infect bacteria, the bacteriophages, are well known and are even being explored as 'phage therapy' against antibiotic-resistant infections.

• Statement III is wrong: viruses routinely hijack the host cell's machinery and alter its gene transcription to produce viral proteins; some (e.g. HPV, HIV) integrate into the host genome and change its expression.

• Each absolute claim ('no virus can…') is refuted by well-established biology.

• None of the statements is correct, option (d).

Why the other options are wrong

(a) Only one: No statement is correct: each is contradicted by marine virology, bacteriophages and viral gene regulation.
(b) Only two: None of the three statements holds.
(c) All the three: All three are false absolute claims.

Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2025, held on 25 May 2025. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.