Where does the 'C' in exhaled CO₂ mostly come from?

Question

When a human being exhales CO₂, what is, by the numbers, the main source of carbon atoms exiting the body in this way? I mean what class of cells, or which tissues are the biggest on a pie chart of where carbon atoms breathed out in the form of CO₂ molecules came from?

Answer 1

One molecule of CO2 comes from the oxidation of pyruvate (3 carbon molecule) to acetyl CoA (two carbon molecule). Two other molecules of CO2 are produced during the Krebs (Citric Acid) cycle. Each glucose is split into two molecules of pyruvate during glycolysis. Therefore each glucose yields six molecules of CO2.

Answer 2

The carbon does not come from tissue. It comes from glucose via cellular respiration.

Answer 3

See previous answer supplying chemical equation of cellular respiration. C comes from the glucose. Look at the equation.

Answer 4

Cellular respiration:

C6H12O6 + 6O2 → 6H2O + 6 CO2

The carbon comes from sugar.