Question: when pyruvate is a reactant in cellular respiration?
Answer: If you're looking at cellular respiration as a general three step process (glycolysis, Krebs/Citric Acid cycle, ETC) pyruvate is a reactant for the Krebs/ Citric Acid cycle. However, a more detailed description of respiration includes a step between glycolysis and the Krebs cycle called pyruvate oxidation.