Asked in PMC Practice Test 9 (2021) 2021Moderate

Which of the following is an exception to cell theory?:

Correct answer: B. Viruses

  • A. Bacteria
  • B. Viruses
  • C. Protists
  • D. Protozoans

Explanation

Viruses are an exception to cell theory since they are within the boundary of living and non-living. Non-living characteristics include the fact that they are not cells, have no cytoplasm or cellular organelles, and carry out no metabolism on their own; therefore, must replicate using the host cell's metabolic machinery which is against cell theory. Living characteristics included the presence of genome and protein.

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About Viruses

Viruses are acellular infectious particles made of genetic material enclosed by a protein capsid, sometimes with a lipid envelope. Their replication depends on a host cell and may follow lytic or lysogenic cycles, so viral structure and reproduction differ fundamentally from those of cellular organisms such as bacteria.

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