Anaerobic Respiration

Glucose ---> Pyruvate: Substrate level phosphorylation and reduction of NAD produce ATP and NADH in addition to Pyruvate

Pyruvate ---> Lactate: requires Lactate dehydrogenase to oxidise NADH to NAD which can then be recycled. 

If lactate (lactic acid) stays in the muscles, pH drops, causing a decrease in enzyme activity. The lactate may then go to the liver - some is broken down into Glucose, some into Pyruvate and Glycogen.

yeast - faculative anaerobic (live without oxygen)

Glucose ---> Pyruvate: ATP and NADH produced

Pyruvate ---> Ethanal + CO2: requires Pyruvate decarboxylase

Ethanal ---> Ethanol: requires Ethanol dehydrogenase to oxidise NADH to NAD , which is then recycled

(Alcohol is a non competitive inhibitor for enzymes in yeast -> above 13% concentration and yeast dies)