Which of the following is the smallest type of pathogen that grows in living cells?

• A. Prions
• B. Fungi
• C. Bacteria
• D. Viruses

Answer: (D)

Verified step by step guidance

1. Understand the types of pathogens listed: Prions, Fungi, Bacteria, and Viruses. Each represents a different category of infectious agents with distinct characteristics.
2. Recall the size and complexity of each pathogen type. Fungi are eukaryotic organisms, generally larger and more complex. Bacteria are prokaryotic cells, smaller than fungi but still cellular. Prions are infectious proteins without nucleic acids, smaller than cells but not considered living organisms.
3. Recognize that viruses are acellular entities composed of genetic material (DNA or RNA) enclosed in a protein coat, and they require living host cells to replicate, making them smaller than bacteria and fungi.
4. Compare the relative sizes: Viruses are smaller than bacteria and fungi, and although prions are smaller than viruses, prions are not considered pathogens that grow or replicate in living cells in the traditional sense—they cause disease by inducing misfolding of host proteins.
5. Conclude that among the options, viruses are the smallest type of pathogen that actively grow and replicate inside living cells.