Question

Viruses are best described as

• A. Prokaryotic cells
• B. Eukaryotic cells
• C. Independent living organisms
• D. Obligate intracellular parasites

Hint:

Viruses are often described as being on the border between living and non-living. \[ \boxed{\text{Outside host} \rightarrow \text{Non-living}} \] \[ \boxed{\text{Inside host} \rightarrow \text{Living}} \] Therefore, viruses are called obligate intracellular parasites.

Answer 1

The Correct Option is D

Concept: Viruses are acellular infectious agents composed of nucleic acid (DNA or RNA) surrounded by a protein coat called a capsid. They cannot reproduce independently and require a living host cell for replication.

Step 1: Understand the nature of viruses.
Viruses lack:
• Cytoplasm
• Ribosomes
• Cell organelles
• Independent metabolic machinery Therefore, they cannot perform life processes on their own.

Step 2: Why are they called obligate intracellular parasites?
Viruses must enter a host cell and use the host's machinery to:
• Replicate their genetic material
• Synthesize viral proteins
• Assemble new virus particles Without a host cell, viruses remain inactive.

Step 3: Eliminate incorrect options.

• Viruses are not prokaryotic cells.
• Viruses are not eukaryotic cells.
• They cannot live independently.
• They survive only inside host cells. Hence they are known as obligate intracellular parasites. Final Answer: \[ \boxed{Option (D) is correct \]