STAGES OF CELLULAR RESPIRATION
First stage
glycolysis, the six-carbon sugar molecule (glucose) breaks down into 2 three-carbon molecules (pyruvic acid). The energy of the broken bonds is captured, yielding two molecules of ATP.
Second stage
the Krebs cycle, the three-carbon molecules resulting from glycolysis are broken down into carbon dioxide molecules. Both glycolysis and the Krebs cycle make ATP and NADH an electron carrier that donates electrons.
Third stage
the electron transport chain, oxygen is combined with the hydrogen atoms of NADH to make water. During electron transport, energy is continuously captured to make ATP. Because the process requires oxygen, it is sometimes called oxidative phosphorylation.