Question 55

Glycolysis produces pyruvate.

Glycolysis is the stage of cellular respiration that breaks down glucose into two molecules of pyruvate, which is a key intermediate in cellular metabolism.

A) Krebs cycle

The Krebs cycle, also known as the citric acid cycle, occurs after glycolysis and primarily processes acetyl-CoA to produce energy carriers like NADH and FADH2. It does not produce pyruvate; rather, it uses pyruvate that has already been generated in glycolysis.

B) Electron transport chain

The electron transport chain is the final stage of cellular respiration where electrons are transferred through a series of proteins to create ATP. It does not involve the production of pyruvate and occurs after glycolysis and the Krebs cycle, using products generated from these earlier stages.

C) Glycolysis

Glycolysis is the correct answer as it directly converts glucose into pyruvate, producing a small amount of ATP and NADH in the process. This stage is essential for cellular respiration as it initiates the breakdown of glucose.

D) Calvin cycle

The Calvin cycle is part of photosynthesis, not cellular respiration. It synthesizes glucose from carbon dioxide and does not involve the production of pyruvate, making it irrelevant to the question.

Conclusion

Glycolysis is definitively the stage of cellular respiration that produces pyruvate, while the other options refer to processes that either occur later in respiration or are unrelated to the breakdown of glucose. The Krebs cycle and electron transport chain utilize pyruvate, and the Calvin cycle pertains to photosynthesis, solidifying glycolysis as the only correct choice.