Direction: Read the following passage and answer the questions that follows.
There are three major ways in which different cells handle pyruvate (pyruvic acid) produced by glycolysis. These are lactic acid fermentation, alcoholic fermentation and aerobic respiration. Fermentation takes place under anaerobic conditions in many prokaryotes and unicellular eukaryotes. For the complete oxidation of glucose to $C{O}_2$ and $H_{2}O$ however, organisms adopt Krebs’ cycle which is also called as aerobic respiration. This required $O_2$ supply.
In fermentation, the incomplete oxidation of glucose is achieved under anaerobic conditions by sets of reactions where pyruvate is converted to $C{O}_2$ and ethanol. Other organisms like bacteria produce lactic acid from pyruvic acid. In animal cells also, like muscles during exercise, when oxygen is inadequate for cellular respiration, pyruvic acid is reduced to lactic acid. In both lactic acid and alcohol fermentation, not much energy is released. How many ATP molecules are produced when a molecule of glucose undergoes fermentation?