As a result of what process occurring in mitochondria is ATP synthesized?

ATP is synthesized in the process of energy metabolism, or dissimilation. Let’s consider an example of an animal cell.
Stage I – preparatory. It flows in the digestive organs. The starch breaks down to glucose, producing a small amount of energy that is dissipated as heat.
Stage II – oxygen-free. It flows in the cytoplasmic matrix. Glucose breaks down to 2 PVC molecules and 2 ATP molecules.
Stage III – oxygen. It flows in the mitochondria. PVCA decomposes to CO2, H2O and 36 ATP molecules.