In the past, Earth has experienced only one mass extinction.

False. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty.

However, many organisms have developed strategies to carry out metabolism without oxygen, or can switch from aerobic to anaerobic cell respiration when oxygen is scarce. During cellular respiration, some living systems use an organic molecule as the final electron acceptor.

Explanation:

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