How many times does the Krebs cycle turn for each glucose molecule?

The Krebs cycle, also known as the citric acid cycle, turns twice for each glucose molecule that undergoes cellular respiration. This is because each glucose molecule is broken down into two molecules of pyruvate during glycolysis, which then enter the mitochondria. Each pyruvate is converted into acetyl-CoA before entering the Krebs cycle.

As the Krebs cycle processes one acetyl-CoA at a time, and since each glucose yields two acetyl-CoA molecules, the cycle must complete two full turns to oxidize both acetyl-CoA molecules. Each turn of the cycle generates important energy-carrying molecules such as NADH and FADH2, as well as ATP, which are critical for the subsequent steps in cellular respiration, particularly the electron transport chain.

Therefore, the answer that indicates the Krebs cycle turns twice aligns perfectly with the metabolic pathway's mechanics.