Bacteria able to metabolize with or without oxygen are called which term?

• A. Facultative Bacteria
• B. Aerobic Bacteria
• C. Anaerobic Bacteria
• D. Pathogens

Answer: (A)

Bacteria that can metabolize with or without oxygen have metabolic flexibility: they are facultative anaerobes. They use oxygen for energy when it’s available (aerobic respiration) and switch to anaerobic pathways like fermentation when oxygen is absent. This ability to adapt to different oxygen levels lets them thrive in diverse environments, which is why this term fits best. In contrast, strictly aerobic bacteria need oxygen, strictly anaerobic bacteria can’t tolerate oxygen and rely entirely on anaerobic processes, and pathogens describe disease-causing potential rather than how they metabolize oxygen. An example is E. coli, which grows well with oxygen but can also grow without it.