A) rarely anaerobic
B) anaerobic
C) purely aerobic
D) Both [a] and [b]
Correct Answer: D
Solution :
Yeast is a facultative aerobe. When yeast is grown in a well aerated (aerobic) nutrient medium, the sugar is completely oxidised in normal respiration. \[\underset{\text{glucose}}{\mathop{{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{12}}}{{\text{O}}_{\text{6}}}}}\,\text{+6}{{\text{0}}_{\text{2}}}\xrightarrow{{}}\text{6C}{{\text{O}}_{\text{2}}}\text{+6}{{\text{H}}_{\text{2}}}\text{O+}\,\text{Energy}\] But in anaerobic condition, sugar is converted into \[C{{O}_{2}}\] and ethyl alcohol \[({{C}_{2}}{{H}_{5}}OH)\] within the cytoplasm. \[\underset{\text{glucose}}{\mathop{{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{12}}}{{\text{O}}_{\text{6}}}}}\,\text{+Yeast}\xrightarrow{{}}\underset{\text{ehtyal}\,\text{alcohol}}{\mathop{\text{2}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}\text{OH+C}{{\text{O}}_{\text{2}}}\text{Energy}}}\,\]
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