Eli5 why do we CONSTANTLY need oxygen?


Surely we can switch off for a little while like a half hour and be fine why does everything just immediately fail if we don’t get oxygen? It’s such a design flaw. What is it actually doing to me that is so necessary I need it constantly?

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The natural processes going on in living cells require energy, accessing that energy uses oxygen and converts it into carbon dioxide, no oxygen and the individual cells die, if enough cells die the body dies.

Your body’s energy to live comes from oxidizing carbon. That’s why you eat carbon rich foods (carbs and fats) and breath in oxygen and breathe out carbon dioxide. It’s not too different from to very slow, controlled burning of the food. Just like a fire without oxygen the fire stops, without oxygen all the processes that represent your life stop, too.

Fire is rapid oxidation. Rust is slow oxidation. Oxygen is the molecule that breaks down various compounds. As such, oxygen is necessary for our body to regulate (accelerate or slow down) our biochemical reactions (like breaking down food, extracting and converting proteins, etc). These processes are constantly running and require oxygen. Now, some animals evolved to hold their breath for extended periods of time, but that usually comes at slower metabolism. Humans, as land-dwelling animals, never evolved the mechanism of manual regulation of metabolism, therefore we need constant supply of oxygen to stay alive, as even just a couple minutes of oxygen starvation is enough for cells in our brains to start dying off. Animals never evolve organs or abilities without a real need, as those things require energy and resources to maintain. That’s why humans didn’t evolve the ability to hold our breath for extended period of time, fish didn’t evolve extra limbs for walking (just in case they need to), and cave animals are losing eyes over time.

This actually raises in interesting question. Anaerobic bacteria exist and predate aerobic metabolism. So is our aerobic metabolism necessary for complex, multi-cellular life or just “it happened that way because it happened that way”?