Respiration thet occurs in the absence of oxygen is called anerobic repiration. Certain bateria and microorganisms like yeast derive energy by anerobic respiration. In this type of repiration, in the absense of oxygen, 
glucose molecule is incolpletely broken down into ethyl alcohol or lactic acid and carbon dioxide. During this process, a small quantity of energy i released as shown down in equation below:
C₆H₁₂O₆ --> 2C₂H₅OH  + 2CO₂  + 2ATP.

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