CO2 is made during the Krebs cycle, also known as the citric acid cycle, which is the third phase of cellular respiration.

Here's why:

* Glycolysis, the first stage, breaks down glucose into pyruvate, but doesn't produce CO2.

* The Krebs cycle takes pyruvate and further breaks it down, releasing CO2 as a byproduct. This is where the majority of CO2 in cellular respiration is produced.

* Electron transport chain, the final stage, uses electrons from previous stages to generate ATP, but doesn't produce CO2 directly.

So, while CO2 is a product of cellular respiration overall, it is specifically generated during the Krebs cycle.