Single-celled protists in the guts of animals thrive without mitochondria

> I'm too busy burning my oxygen to figure it out

Your mitochondria are doing that so your brain doesn't have to spend attention on it. And its not very clear whether they are "you" or your symbiotes.

Oxymonads are oxymonoids in the category of enterofauna, of course

Following links from the article, we may find that mitochondria are usually integral to several other processes besides oxygen metabolism. So, it's not surprising to find that protists in anaerobic environments don't need their mitochondria to process (usually) absent oxygen.

But it was surprising to find these protists producing iron-sulfur complexes without the aid of mitochondria. And, able to break down glycine and serine to form folic and then formic acid, and methionine, which normally happens within mitochondria.

Nothing in biology is as simple as "X does Y, and nothing else", and rarely "X, and nothing else, does Y". There seems to be no benefit to simplicity in biology, which makes the near-universality of the genetic code the more astonishing. ("Near", because minor variations occur even there.)

There is in the small intestine, and close to the epithelium in the large intestine