The compound that starts all three versions of cellular respiration is glucose.

Here's why:

* Cellular respiration is the process by which living organisms break down glucose to release energy in the form of ATP.

* Glycolysis, the first stage of cellular respiration, directly uses glucose as its starting material.

* The Krebs Cycle and Electron Transport Chain (the remaining stages) utilize pyruvate, a product of glycolysis, which is derived from glucose.

So, regardless of whether we're talking about aerobic, anaerobic, or fermentation, the process always begins with the breakdown of glucose.