Which statement describes a facultative anaerobe most accurately?

Which statement describes a facultative anaerobe most accurately?

• A. It prefers an environment with oxygen, but may live without it.
• B. It requires an environment with no oxygen to grow.
• C. It cannot tolerate oxygen.
• D. It dies in the presence of oxygen.

Answer: (A)

Facultative anaerobes can grow with or without oxygen. They use aerobic respiration when oxygen is available to generate more energy, and when oxygen is absent they switch to fermentation or anaerobic respiration to keep growing. They also have enzymes like catalase and superoxide dismutase to neutralize reactive oxygen species, which lets them survive in oxygen-rich conditions. This flexibility makes the statement describing them as preferring an environment with oxygen, but able to live without it, the best description. It wouldn’t fit to say they require no oxygen—that would describe obligate anaerobes. Saying they cannot tolerate oxygen or that they die in its presence would also be incorrect for facultative anaerobes, since they tolerate and often thrive in the presence of oxygen.

Facultative anaerobes can grow with or without oxygen. They use aerobic respiration when oxygen is available to generate more energy, and when oxygen is absent they switch to fermentation or anaerobic respiration to keep growing. They also have enzymes like catalase and superoxide dismutase to neutralize reactive oxygen species, which lets them survive in oxygen-rich conditions. This flexibility makes the statement describing them as preferring an environment with oxygen, but able to live without it, the best description. It wouldn’t fit to say they require no oxygen—that would describe obligate anaerobes. Saying they cannot tolerate oxygen or that they die in its presence would also be incorrect for facultative anaerobes, since they tolerate and often thrive in the presence of oxygen.