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MCAT Biology Question — Virus vs. Bacterium

  • by Allison Chae
  • Apr 16, 2014
  • MCAT Biology, MCAT Blog, MCAT Question of the Day

An infectious agent is probably a virus instead of a bacterium if it:


  1. Lacks membrane-bound organelles
  2. Cannot reproduce in acellular culture
  3. Has a length of 1μm, about the size of a mitochondrion
  4. Contains DNA




Viruses possess DNA or RNA but not both, require a host cell’s reproductive machinery in order to reproduce, and have a size 10-100nm. For the MCAT: eukaryotic cell > bacterium (roughly size of mitochondrion) > virion (roughly size of protein,  roughly 100x smaller than bacterium, 1000x smaller than eukaryotic cell, cannot be seen with optical microscope).


  1. Lacks membrane-bound organelles, incorrect, Both viruses and bacteria lack membrane-bound organelles.
  2. Cannot reproduce in acellular culture, correct. Viruses require host cells in order to reproduce.
  3. Has a length of 1μm, about the size of a mitochondrion, incorrect, This is the size of a bacterium.
  4. Contains DNA, incorrect, Both bacteria and viruses may contain DNA.


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