A culture of bacteria is fed glucose containing radioactive carbon and is then examined. During the citric acid cycle, radioactive carbon would first appear in:

-During citric acid cycle or Krebs cycle, radioactive carbon will be first appear in citric acid

Explanation:

During cellular respiration, glucose is first converted into pyruvate molecules by the process of glycolysis. These pyruvate molecules go for oxidative decarboxylation, during which acetyl co-enzyme A (acetyl CoA) is formed along with removal of carbon dioxide.

The acetyl co-enzyme enters to the next step in cellular respiration or citric acid cycle or Krebs cycle. The first step of citric acid cycle is formation of citric acid by joining of acetyl CoA and oxaloacetate.

As citric acid is first molecule formed during citric acid cycle, radioactive carbon would be first appear in citric acid.