Prelims 2013 · archive
MediumWhich of the following statements is/are correct?
- 1.Viruses lack enzymes necessary for the generation of energy
- 2.Viruses can be cultured in any synthetic medium.
- 3.Viruses are transmitted from one organism to another by biological vectors only.
Select the correct answer using the codes given below.
Answer & explanation
Answer: (a) 1 only
Viruses are obligate intracellular parasites. They have no energy-generating machinery of their own and borrow the host cell's, so statement 1 is correct. For the same reason they replicate only inside living cells and cannot be grown in a lifeless synthetic medium. They also spread by air, contact, blood and other routes, not only through biological vectors.
- ✓ 1. A virus depends wholly on the host cell's machinery and metabolism, including its energy supply. It has no energy-generating enzyme system of its own.
- ✗ 2. Viruses can replicate only in living cells, so laboratories grow them in cell cultures (and in living hosts such as eggs or animals). A cell-free synthetic medium cannot support them, unlike many bacteria.
- ✗ 3. Vectors are only one route. HIV spreads through sexual contact, contaminated blood and needles, and from mother to child. The common cold virus spreads through droplets and shared utensils. None of these needs a biological vector.
- ✗ (c) This option pairs the correct statement 1 with the wrong statement 3, which says vectors are the only mode of transmission.
- ✗ (d) Statements 2 and 3 are both wrong, so all three cannot be correct.
Remember · Viruses are obligate intracellular parasites. They have no metabolism or energy machinery of their own, grow only in living cells, and spread by many routes, not only vectors.
📘 Read it in NCERT: Class 12 Biology, Ch 7 (practise this chapter)
Sources
- Viruses and intracellular bacterial pathogens reprogram host cell metabolism (Frontiers; NIH PMC) ↗ “Viruses are obligate intracellular parasites and their reproduction entirely relies on the host cell machinery for the synthesis of viral components such as nucleic acids, proteins and membranes.”
- Cultivation of viruses, Textbook of Medical Virology (NIH PMC) ↗ “Viruses can only replicate in living cells. For studies of the growth of viruses and for the production of virus components, it is, therefore, necessary to have access to cells cultivated in the laboratory.”
- NCERT Class 12 · Biology, Chapter 7 “Transmission of HIV-infection generally occurs by (a) sexual contact with infected person, (b) by transfusion of contaminated blood and blood products, (c) by sharing infected needles as in the case of intravenous drug abusers”
Question: UPSC Civil Services (Preliminary) 2013, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·