Which type of organism requires oxygen for growth and is harmed by its absence?

• A. Facultative anaerobe
• B. Aerotolerant anaerobe
• C. Obligate aerobe
• D. Obligate anaerobe

Answer: (C)

Organisms that require oxygen for growth rely on aerobic respiration to generate most of their ATP. Oxygen acts as the final electron acceptor in the electron transport chain, yielding a high energy output that these microbes depend on. They also possess enzymes to detoxify reactive oxygen species, which would otherwise damage cellular components; without oxygen, energy production collapses and growth stops or cells die.

Other types either can switch to energy production without oxygen or tolerate oxygen without needing it. Facultative anaerobes can use oxygen when it’s available but can ferment or respire anaerobically in its absence. Aerotolerant anaerobes don’t use oxygen and aren’t harmed by it. Obligate anaerobes, in contrast, are harmed by oxygen and rely entirely on anaerobic metabolism.