📘 IAS Prelims 2025 — GS-I Q.49 | Classroom Explanation

(Basic Science | Virology)

📌 Question

Q.49) 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

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✅ Correct Answer: (d) None

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🧑‍🏫 Classroom Explanation

This question probes fundamental virology concepts that UPSC frequently revisits, especially to test absolute statements like “no”, “never”, “all”.

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🔍 Statement-wise Analysis

❌ Statement I: Incorrect

• Viruses are abundant in ocean waters.
• Marine viruses, especially bacteriophages, are the most numerous biological entities in the oceans.
• They:

• Survive for extended periods in seawater
• Regulate microbial populations
• Drive marine nutrient cycles (viral shunt)

➡️ Hence, viruses do survive in ocean waters.

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❌ Statement II: Incorrect

• Bacteriophages (phages) are viruses that infect bacteria.
• They are found in:

• Oceans
• Soil
• Human gut
  • Applications:
• Phage therapy (alternative to antibiotics)

➡️ Hence, viruses do infect bacteria.

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❌ Statement III: Incorrect

• Viruses actively manipulate host cell transcription.
• Mechanisms include:

• Hijacking host RNA polymerase
• Suppressing host genes
• Activating viral gene expression

• This manipulation is essential for:

• Viral replication
• Immune evasion

➡️ Hence, viruses do change cellular transcriptional activity.

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🧮 UPSC-Style Elimination

Statement	Correct?
I	❌
II	❌
III	❌

➡️ Correct statements = 0

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🎯 Final Answer

✅ Correct Answer: (d) None

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📦 High-Value Prelims Add-Ons (Info Box)

🧠 One-Line Memory Hook

Viruses are everywhere, infect everything, and hijack host genes.

⚠️ UPSC Trap Alert

• Absolute words like “no”, “never”, “all” are usually wrong in biology.
• Viruses are:

• Ubiquitous
• Diverse
• Highly interactive with host machinery

🔗 Current Affairs Link

• Marine virology is key to:

• Climate models
• Carbon cycling
• Ocean productivity

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