Glycolysis followed by the production of ethanol or lactate and the regeneration of NAD in anaerobic respiration.

The first stage of respiration is the same in aerobic and anaerobic respiration; glycolysis. This is because it does not involve oxygen so is not hindered if it is not present.

Two ATP are used to add phosphate groups to glucose, creating phosphorolated glucose. This splits into two molecules of triosephosphate which has phosphate removed by ADP and is reduced byv NAD to make pyruvate.

By doing these things the cell has a net gain of 2ATP and so has respired, but with a much lower energy yield than aerobic respiration.

Usually at this stage NADH would go on to the Krebs cycle, lose its hydrogen, and become NAD again, ready to take part in some more glycolysis. However there is no oxygen, so there is no Krebs cycle, this would mean that NAD was not avalible because it was all NADH.

To solve this problem the pyruvate takes the hydrogen from the NADH making it NAD again. Pyruvate and hydrogen can make one of two things: ethanol + carbon dioxide or lactic acid.

In some plants and in yeast ethanol and CO2 are produced, and in animals it's lactate.