Final answer:
Oxygen is toxic to obligate anaerobes. Organisms that are obligate anaerobes will die when exposed to atmospheric levels of oxygen. They use molecules other than oxygen as terminal electron acceptors.
Step-by-step explanation:
Oxygen is toxic to A) obligate anaerobes. Organisms that are obligate anaerobes will die when exposed to atmospheric levels of oxygen. They use molecules other than oxygen as terminal electron acceptors. For example, Clostridium perfringens bacteria, which are commonly found in soil, are obligate anaerobes, and infection by them causes gas gangrene.