What are the different steps of aerobic respiration?

Respiration can be broken down into four main stages: glycolysis, the link reaction, the Krebs cycle (or citric acid cycle), and the electron transport chain. Glycolysis is the process through which glucose is broken down through a series of reactions to produce two molecules of pyruvate, 2 molecules of ATP, and 2 molecules of NADH. This is the step that takes place in both aerobic and anaerobic respiration because it does not require oxygen to produce the 2 ATP molecules.The link reaction is then used for pyruvate oxidation. Each pyruvate molecule produced in glycolysis is coverted to a two-carbon molecules bound to Coenzyme A; this molecules is known as acetyl Coenzyme A. This process releases carbon dioxide and another molecule of NADH. The acetyl Coenzyme A molecules are then combined with a four-carbon molecule in the Krebs cycle. Through a series of redox reactions, as much energy from these molecules as possible is harvested in the form of NADH and FADH₂.The final stage of aerobic respiration is the electron transport chain, also known as oxidative phosphorylation. This utilises proteins and organic molecules found in the inner membrane of mitochondria; electrons are passed from one member of the chain to the next through a series of redox reactions. NADH and FADH₂ are used to donate the electrons at the start of the chain, allowing these to return to previous reactions to pick up more electrons. The electrons then pass through the chain, from higher energy to lower energy levels, releasing energy. Some of this energy is used to pump H⁺ ions into the intermembrane space to establish an electrochemical gradient. As H⁺ ions flow down their gradient and back into the mitochondrial matrix, they pass through an enzyme known as ATP synthase which harnesses the flow of ions to produce ATP. At the end of the chain, electrons are transferred to O₂ molecules to form 2 molecules of O^-; these combine with the H⁺ ions that have flowed into the matrix to produce water and to maintain the electrochemical gradient.