krebs cycle
The pyruvate molecules from glycolysis next enter the matrix of a mitochondrion. That's where the second stage of cellular respiration takes place. This stage is called the Krebs cycle . During this stage, two more molecules of ATP are produced. Other energy-storing molecules are also produced to be used to make more ATP in stage 3 . The Krebs cycle requires oxygen. Anything that needs oxygen is described as aerobic . The oxygen combines with the carbon from the pyruvate molecules. This forms carbon dioxide, a waste product.