Which acellular infectious agent requires a host cell to survive and replicate?

• A. Prion
• B. Bacteriophage
• C. Viroid
• D. Virus

Answer: (D)

Verified step by step guidance

1. Understand the definition of an acellular infectious agent: these agents lack cellular structure and cannot carry out metabolic processes independently.
2. Review the characteristics of each option: Prions are infectious proteins without nucleic acids; Bacteriophages are viruses that infect bacteria; Viroids are small infectious RNA molecules without a protein coat; Viruses are acellular agents composed of nucleic acid and protein that require a host cell to replicate.
3. Identify which agent requires a host cell to survive and replicate by considering their replication mechanisms: Prions and viroids do not have typical replication machinery and rely on host processes differently, while viruses must enter a host cell to use its machinery for replication.
4. Recognize that bacteriophages are a type of virus that specifically infect bacteria, so they also require a host cell, but the broader category is viruses in general.
5. Conclude that the acellular infectious agent that requires a host cell to survive and replicate is a virus, as it depends entirely on host cellular machinery for reproduction.