Final answer:
Organisms without oxygen access use alternative metabolic pathways such as anaerobic processes like fermentation, to produce ATP for their energy needs, employing strategies that trace back to early anaerobic life forms.
Step-by-step explanation:
Organisms that can survive without oxygen harvest energy through alternative pathways to cellular respiration, which relies on oxygen. Anaerobic metabolism evolved approximately 3.8 billion years ago when the atmosphere lacked oxygen. This form of metabolism still exists today in many microorganisms, which employ various methods to acquire metabolic energy. These organisms use anaerobic processes like fermentation that only utilize the glycolysis part of cellular respiration. Some prokaryotes even have unique metabolic pathways that do not rely on cellular respiration at all. Furthermore, organisms like chemoautotrophs can make food without light, and photoheterotrophs utilize light to gain energy without relying on oxygen.
Throughout evolution, metabolic pathways have diverged, with specialized enzymes developing to enable organisms to better adapt to their environments. Although the specific mechanisms may differ, the underlying goal for all organisms is the same: to harvest energy from their environment and convert it to ATP to support cellular functions when oxygen is not available.