Which group shows better growth in the presence of oxygen but can also grow without it?

• A. Microaerophiles
• B. Facultative anaerobes
• C. Aerotolerant anaerobes
• D. Obligate anaerobes

Answer: (B)

Organisms that can switch between energy pathways depending on oxygen availability show the ability to grow well with oxygen but also survive without it. When oxygen is present, aerobic respiration yields the most ATP, fueling faster growth. If oxygen disappears, these organisms can shift to anaerobic metabolism (such as fermentation or anaerobic respiration), still producing enough energy to grow, though usually at a slower rate. This combination of preferences and flexibility defines facultative anaerobes. In contrast, microaerophiles need lower levels of oxygen and don’t thrive with normal air, so they wouldn’t exhibit better growth in oxygen-rich conditions. Aerotolerant anaerobes don’t rely on oxygen for growth and aren’t advantaged by its presence, while obligate anaerobes are harmed by oxygen and require its absence to grow.