Question

what happens to the carbon atom during fermentation

Answer 1

After glycolysis, fermentation occurs and acts on the two pyruvates. The 2 pyruvates is then converted into lactate in human muscle cells, ethanol in alcohol yeast) to make NAD+ for glycolysis.

Carbon is oxidized (cellular respiration)
carbon is reduced (lactate fermentation)

Answer 2

http://www.meadmadecomplicated.org/figures/fermentation.gif