Step-by-step explanation:
The carbon dioxide breathed out is a by-product of the process of cell respiration, as is water. In this process, energy is produced in the mitochondria of cells. This energy is our physical "life force". Both oxygen and glucose are required for this. Glucose contains carbon. That's where the carbon in carbon dioxide comes from. Glucose plus oxygen produces carbon dioxide, water and energy. When this process stops, the cell dies.