How do facultative anaerobes function under oxygen-free conditions?

Facultative anaerobes are versatile organisms that can thrive in both the presence and absence of oxygen. Under oxygen-free conditions, they utilize fermentation as their primary mode of energy production. This process allows them to break down glucose (or other organic molecules) to generate ATP without relying on oxygen.

In environments lacking oxygen, these organisms switch from aerobic respiration to fermentation pathways. During fermentation, they partially oxidize their substrates, producing energy along with byproducts such as lactic acid or ethanol, depending on the type of facultative anaerobe and the substrates available. This adaptability is key to their survival in varying environmental conditions, enabling them to exploit different ecological niches effectively.

The other possibilities do not accurately depict the behavior of facultative anaerobes. They do not cease all metabolic activity when oxygen is unavailable; rather, they have alternative pathways for generating energy. They also do not convert oxygen into carbon dioxide, as that process is associated with aerobic respiration, which they can use when oxygen is present. Lastly, facultative anaerobes do not require assistance from other microbes to thrive in oxygen-free environments; they have the metabolic flexibility to function independently.