The absence of leaves obligate anaerobes susceptible to killing by oxygen.

The answer in the space provided is superoxide dismutase, it is because if the superoxide dismutase is absent which is considered to be an enzyme, this will likely cause the oxygen into poisoning the obligate anaerobes and to lead it from being killed.

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs

a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.