The Stages of Cellular Respiration

 Stage 1: Glycolysis

Grooming Phase happens when pyruvate itself does not enter the citric acid cycle. A carboxyl group is removed from pyruvate and given off as a molecule of CO2. The two carbon compound remaining is oxidized while a molecule of NAD is reduced to NADH ; and a compound called coenzyme A , derived from a B vitamin, joins with the two carbon group to form a molecule called acetyl coenzyme A.
For each molecule of glucose that enters glycolysis, two molecules of pyruvate are produced. These are oxidized, and then two molecules of acetyl CoA enter the citric acid cycle.

Stage 2: 

The Krebs Cycle also known as the Citric Acid Cycle occurs in the mitochondrial matrix.

Stage 3: The Electron Transport Chain and Chemiosmosis