Humber Admissions Practice Test

Which cycle directly follows glycolysis in cellular respiration?

1. Electron transport chain

2. Calvin cycle

3. Krebs cycle

4. Fermentation

The correct answer is: Krebs cycle

The cycle that directly follows glycolysis in cellular respiration is the Krebs cycle, also known as the citric acid cycle or the tricarboxylic acid (TCA) cycle. After glycolysis, which takes place in the cytoplasm, the pyruvate produced is transported into the mitochondria. Here, it undergoes a transformation into acetyl-CoA, which then enters the Krebs cycle. This cycle is crucial as it processes acetyl-CoA to produce electron carriers, namely NADH and FADH2, which are essential for the next stage of cellular respiration, the electron transport chain. The Krebs cycle also releases carbon dioxide as a waste product and generates ATP, although in relatively smaller amounts compared to the electron transport chain. This sequence of events illustrates the integral role of the Krebs cycle in the broader context of energy production within the cell, linking glycolysis and the electron transport chain in a continuous pathway for energy metabolism. Other options, while related to cellular processes, do not directly follow glycolysis. The electron transport chain occurs after the Krebs cycle, the Calvin cycle is related to photosynthesis in plants, and fermentation is an alternative pathway that can occur when oxygen is not available, but it does not directly follow glycolysis