UPSC Prelims 2013 Q93: Science & Technology – Health & Diseases
Which 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.
- (a) 1 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (a) 1 only
Explanation
Properties of viruses
| Statement | Verdict | Fact |
|---|---|---|
| 1. Viruses lack enzymes necessary for the generation of energy | Correct | They have no metabolism of their own; they use the host cell's machinery |
| 2. Viruses can be cultured in any synthetic medium | Incorrect | They grow only in living cells: tissue culture, eggs or animals |
| 3. Viruses are transmitted from one organism to another by biological vectors only | Incorrect | They also spread through air, water, food, contact and blood |
Viruses at a glance:
| Feature | Detail |
|---|---|
| Structure | DNA or RNA (never both) inside a protein coat |
| Outside a cell | Inert; can even be crystallised |
| Nature | Obligate intracellular parasites |
| Antibiotics | Do not work on them |
How viruses spread:
| Route | Example |
|---|---|
| Vector | Dengue, by the Aedes mosquito |
| Air | Influenza, measles |
| Water and food | Hepatitis A, polio |
| Blood and body fluids | HIV, Hepatitis B |
Answer: (a) 1 only.
Why each option is right or wrong
- (a) CORRECT. Only statement 1 is true: viruses lack energy-generating enzymes.
- (b) Incorrect. Viruses cannot grow in a synthetic medium, and vectors are not the only route.
- (c) Incorrect. Statement 3 is false; viruses spread by many routes.
- (d) Incorrect. Statements 2 and 3 are false.
Key point
Viruses: DNA or RNA in a protein coat; no metabolism; grow only in living cells; spread by air, water, contact, blood and vectors.
Remember
Viruses: no energy enzymes, need living cells.
Common mistakes
- Thinking viruses grow on nutrient agar like bacteria.
- Accepting 'only' in statement 3.
- Believing antibiotics cure viral diseases.
Exam tip
Bacteria grow on a plate; viruses need a living cell.
Sources
- NCERT Class XI — Biology, Ch 2 (Biological Classification: Viruses, Viroids and Lichens)
- NCERT Class XII — Biology (Human Health and Disease)