An organism that respires using oxygen when it is present but can switch to an alternative anaerobic pathways when it is absent is a(n)________.

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Facultative anaerobes are organisms that can use oxygen for respiration when it is present but can switch to alternative anaerobic pathways when oxygen is not available. Examples of facultative anaerobes include E. coli and yeast. Aerotolerant anaerobes (A) do not use oxygen for respiration but can tolerate its presence. Obligate aerobes (B) require oxygen for respiration, while obligate anaerobes (E) cannot survive in the presence of oxygen. Microaerophiles (D) require low levels of oxygen for growth and respiration.

An Organism That Respires Using Oxygen When It Is Present