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MCAT Biology Question — Infection

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

A. lacks membrane-bound organelles

B. cannot reproduce in acellular culture

C. has a length of 1μm, about the size of a mitochondrion

D. contains DNA

Click for Explanation

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).

A. lacks membrane-bound organelles, incorrect, Both viruses and bacteria lack membrane-bound organelles.

B. cannot reproduce in acellular culture, correct. Viruses require host cells in order to reproduce.

C. has a length of 1μm, about the size of a mitochondrion, incorrect, This is the size of a bacterium.

D. contains DNA, incorrect, Both bacteria and viruses may contain DNA.

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