Each pyruvate molecule that enters the mitochondria produces 3 CO2 molecules.

Here's why:

* Pyruvate Oxidation: When pyruvate enters the mitochondria, it undergoes a series of reactions called pyruvate oxidation, where it is converted to acetyl-CoA. This process releases one CO2 molecule.

* Krebs Cycle: Acetyl-CoA then enters the Krebs cycle (also known as the citric acid cycle), where it is further broken down. During the Krebs cycle, two more CO2 molecules are released.

Therefore, the total number of CO2 molecules produced from one pyruvate is 1 (from pyruvate oxidation) + 2 (from the Krebs cycle) = 3 CO2 molecules.