The Krebs cycle is a series of reactions that occur in the mitochondria and result in the formation of ATP and other molecules which undergo further reactions to form more ATP. Cellular respiration can be divided into four sequences. The first sequence is glycolysis, it breaks down one glucose molecule into two pyruyate molecules. The transition takes place in the matrix of mitochondria and refers to the onset of aerobic respiration. The process takes place if there is enough oxygen in the mitochondria. However, if there is not enough oxygen in the mitochondria, it could lead to fermentation. Transition reactions take place in the pyruvate molecule. In transition reactions, two hydrogen electrons and one carbon dioxide are removed from the pyruvate and added to coenzyme A. This is where the Krebs cycle, also known as the citric cycle, is ready for the acetyl Co-A. The first Krebs cycle was postulated in 1937 by Hans Krebs, it represents the process by which cells produce energy during the breakdown of energy-rich molecules. The Krebs cycle is composed of o...