Why do all Krebs cycle reactions occur twice for each molecule of glucose that undergoes respiration?

Answer: This is because 2 pyruvate molecules were produced in Glycolysis, and each must be metabolize to extract one ATP molecule each contained.

In addition to produced required number of reduced Co-enzymes for Electron Transport Chain (ETC) reactions to take place for ATP production

It must also be twice/glucose molecule to generate required volume of oxygen for decaboxylation, because the oxygen in the reaction came from. from. redox and not from the atmosphere.

Therefore the both the link reaction and the kreb. cycle

must occur twice to produce mandatory 2 ATPs, and generate the required amount of reduced Co Enzymes NADH and FADH2 for ETC (electron transport Chain) to occur.

The Krebs cycle reaction occurs twice because glucose produces two molecules of Pyruvate and then two acetyl CoA.

Explanation:

The citric acid cycle goes around twice for each molecule of glucose that enters cellular respiration because there are two pyruvates from the single glucose molecule and thus, two acetyl CoA is produced per glucose which is the starting molecule in the Krebs cycle.