What does it mean if a microorganism is anaerobic?

A microorganism that is classified as anaerobic is one that can live and grow in environments devoid of oxygen. This characteristic is crucial for understanding the diverse ecosystems microorganisms can inhabit. Anaerobic organisms have adapted biochemical processes that allow them to generate energy without the need for oxygen. For example, they may rely on fermentation or anaerobic respiration to metabolize substrates and produce energy-rich compounds.

In contrast, the other options refer to different characteristics that do not apply to anaerobic microorganisms. The necessity for oxygen corresponds to aerobic microorganisms, which thrive in oxygen-rich environments. The reference to thriving in high temperatures pertains to thermophiles, a different classification based on temperature preference. Lastly, while some anaerobic microorganisms can indeed be harmful to humans, not all anaerobes are pathogenic; many play essential roles in various ecosystems and even in human health, such as in digestion.