From my understanding, alcohol fermentation takes place in yeast and lactate production takes place in humans.
These two pathways take place only when there is insufficient oxygen, because the other parts of metabolism (TCA cycle, ETC) can't take place as they happen in the mitochondria, which requires O2.
For alcohol fermentation, there is production of carbon dioxide while lactic acid fermentation does not produce carbon dioxide. CO2 is produced when there is an oxidation of one carbon molecule. So my main question is: since there is a lack of O2, how does yeast produces CO2 while humans do not?
Also, how does NAD+ recycle all the time when glycolysis is happening?