(a) : Saccharomyces converts starch or sugars to pyruvic acid through EMP pathway. Then this pyruvic acid is converted to acetaldehyde and finally to ethyl alcohol in the absence of oxygen. This entire process is called fermentation.
C6H12O6→2CH2COCOOH→2C2H5OH+2CO2
This released carbon dioxide makes the dough to rise and gives spongy nature to bread.