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Aerobic and Anaerobic Respiration
In the presence of oxygen, glycolysis is followed by fermentation, the Krebs cycle and the electron transport chain. Glycolysis, fermentation, the Krebs cycle, and the electron transport chain make up a process called cellular respiration. Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen. Each of these four processes use and don’t use oxygen in several different ways.
Aerobic respiration is a metabolic process involving oxygen in the breakdown of glucose. Anaerobic respiration is a metabolic process that does not involve oxygen in the breakdown of glucose. Throughout the four processes of cellular respiration, oxygen is not always used. Cellular respiration itself requires oxygen, but its sub-processes all do not. If cellular respiration took place in just one step or process, all of the energy from the breakdown of the glucose would be released at once, and most of it would be lost in the form of light and heat.
Glycolysis is the first step of cellular respiration. Glycolysis itself is an anaerobic process. After a cell has completed glycolysis, and depending on the circumstances in which the cell finds itself, that cell can either move into the process of aerobic respiration and commence the citric acid cycle [Krebs cycle] or continue with less efficient anaerobic respiration in a process called fermentation. Fermentation releases energy from food molecules by producing ATP in the absence of oxygen. After the conversion of the molecules in fermentation, glycolysis is allowed to continue producing a steady supply of ATP. Because glycolysis didn’t require oxygen and its taking place in fermentation, fermentation is said to be an anaerobic process.
At the end of glycolysis, 90 percent of the chemical energy that was available in glucose still wasn’t used. To get the rest of the energy, cells turn to one of...