Flavoproteins in anaerobic respirers can generate oxygen radicals. Oxygen radicals can also be generated in non-respiratory ways. Aerobic organisms must have these enzymes to survive. There still is not necessarily a good match between the energy-generating compounds used and the presence or absence of these enzymes. They oxidize compounds using oxygen and have protective enzymes.
Aerobic organisms can only live in an oxygenated habitat.
They oxidize compounds using oxygen, but have low levels of protective enzymes. Consequently, they are found in habitats with reduced oxygen levels. The oxidative reactions they carry out for ATP synthesis don't require oxygen, but they have enzymes to protect themselves from oxygen damage. It is a fermenter which produces lactate whether oxygen is present or not, and possesses peroxidase. It can live in the presence or absence of oxygen obligate anaerobes.