Question 55

Glycolysis produces pyruvate.

The stage of cellular respiration that produces pyruvate is glycolysis. This process occurs in the cytoplasm of the cell and breaks down glucose into two molecules of pyruvate.

A) Krebs cycle

The Krebs cycle, also known as the citric acid cycle, is a series of reactions that occurs in the mitochondria after glycolysis. It does not produce pyruvate; rather, it utilizes the pyruvate generated from glycolysis to produce energy-rich molecules like NADH and FADH2.

B) Electron transport chain

The electron transport chain is the final stage of cellular respiration and takes place in the inner mitochondrial membrane. It does not produce pyruvate; instead, it uses electrons from NADH and FADH2 to generate ATP. Pyruvate is already formed before this stage.

C) Glycolysis

Glycolysis is the process that breaks down glucose into two molecules of pyruvate, which is why it is the correct answer. This anaerobic process occurs in the cytoplasm and is the first step of cellular respiration, leading to further energy production in subsequent stages.

D) Calvin cycle

The Calvin cycle is a part of photosynthesis, not cellular respiration. It takes place in the chloroplasts of plant cells and is responsible for synthesizing glucose from carbon dioxide and water. Therefore, it does not produce pyruvate.

Conclusion

Glycolysis is definitively the correct answer as it is the only stage of cellular respiration that directly produces pyruvate from glucose. The other options, including the Krebs cycle, electron transport chain, and Calvin cycle, either utilize pyruvate produced from glycolysis or relate to different metabolic processes entirely.