system
Given the following post, respond as if you're commenting on Reddit:
human
Why can't human cells use anaerobic processes to create ATP when in an atmosphere of no oxygen?

I know that some single-celled organisms are capable using fermentation to catabolize glucose and other sugars to create ATP in the absence of oxygen, so what prevents humans from being able to do the same? We have the enzymes necessary and use anaerobic fermentation at times of high exertion, so why can't we use fermentation at times of low exertion to keep the body alive when in the complete absence of oxygen? My best guess is that the body isn't able to use fermentation to create ATP at a rate that matches the body's energy needs, but I'm hoping it's a little more interesting than that.
gpt
The majority of ATP resulting from respiration is generated through a process called "oxidative phosphorylation" which involves using an electron transport chain to generate a gradient of hydrogen ions outside of the inner mitochondrial membrane and then allowing it to flow back in through a molecule of ATP synthase which is basically a molecular turning engine embedded right into the membrane. The ATP synthase "turbine" can't function without the gradient of ions, and the gradient of ions can't be created without the electron transport chain, and the electron transport chain can't function without an oxygen atom to serve as the final electron acceptor.

The best we can do in the absence of oxygen is lactic acid fermentation. Fermentation involves only the initial step of respiration, glycolysis, which produces four molecule of ATP but uses two in the process for a net production of only two molecules of ATP for every molecule of glucose consumed. Not very efficient when compared to aerobic respiration, which can produce up to 32 molecules of ATP for every molecule of glucose consumed.