The hexose monophosphate shunt, also known as the pentose phosphate pathway (PPP), is an alternative metabolic pathway to glycolysis. It serves multiple functions in the cell, one of which is the generation of reducing power in the form of NADPH, which is required for various biosynthetic processes and antioxidant defense mechanisms.

One of the key reactions in the hexose monophosphate shunt is the oxidative phase, which involves the conversion of glucose-6-phosphate (G6P) to ribulose-5-phosphate (R5P) while generating two molecules of NADPH. In this process, one molecule of CO2 is released for each NADPH generated.

Let's compare this to glycolysis, the main pathway for glucose metabolism. Glycolysis involves the conversion of glucose to pyruvate, generating a small amount of ATP and NADH in the process. However, glycolysis does not release any CO2 molecules directly.

So, when we compare the number of CO2 molecules evolved in the hexose monophosphate shunt and glycolysis:

- In the hexose monophosphate shunt, one molecule of CO2 is released for each NADPH generated during the oxidative phase.
- In glycolysis, no CO2 molecules are directly released.

Therefore, the number of CO2 molecules evolved in the hexose monophosphate shunt is more than glycolysis. This is because the hexose monophosphate shunt specifically generates NADPH and requires the release of CO2 as a byproduct during the oxidative phase.

It's important to note that the hexose monophosphate shunt is not solely responsible for glucose metabolism. Glycolysis is the primary pathway for glucose metabolism, generating ATP and pyruvate. The hexose monophosphate shunt acts as a parallel pathway, providing NADPH and other metabolites required for various cellular processes.

In glycolysis there is no decarboxylation, but in pentose phosphate pathway there is a liberation of 1 co² during conversion of phosphogluconic acid to RUMP