Question

Given below are two statements, one is labelled as Assertion (A) and other labelled as Reason (R).
Assertion (A): Viruses are molecular parasites.
Reason (R): Viruses depend on host for their basic functions like replication.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Remember that viruses lack ribosomes and metabolic enzymes.
Without a host's translational machinery, they cannot produce proteins or replicate, making them the ultimate molecular parasites.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Viruses exist on the border between living and non-living systems.
They are acellular particles lacking a metabolic system, cytoplasm, or ribosomes, and are entirely dependent on host cell machinery to complete their life cycle.

Step 2: Detailed Explanation:
Assertion (A) describes viruses as "molecular parasites."
This is a biologically accurate description because, outside a living host cell, a virus is simply an inert macromolecular assembly of nucleic acids and proteins.
Unlike cellular parasites, they do not possess any independent metabolic pathways, cellular organelles, or ribosomes.
They function strictly at the molecular level, injecting their genetic material to manipulate host molecular processes, making Assertion (A) true.
Reason (R) states that viruses depend on the host for basic functions like replication, transcription, and translation.
Because they lack the enzymatic machinery to synthesize their own proteins or duplicate their genomes independently, they must hijack the host's enzymes, ribosomes, tRNAs, and energy reserves.
This complete dependence on host cellular machinery for genetic replication and protein synthesis is the exact reason why they are defined as obligate intracellular molecular parasites.
Therefore, both statements are true, and the Reason serves as the correct explanation of the Assertion.

Step 3: Final Answer:
Both (A) and (R) are true and (R) is the correct explanation of (A).