How did the carbon atom get into cellular respiration

During cellular respiration the molecule takes in oxygen and glucose. In glycolysis, the six-carbon sugar, glucose, is broken down into two molecules of three-carbon molecule called pyruvate.

Carbon atoms are converted into metabolites like acetic acid, lactic acid, aldehydes, etc via the action of different bacteria. In the process of fermentation or cellular respiration, carbon atoms are cleaved into three carbon molecule called pyruvate then eventually forming into metabolites.