The electron transport chain is the final stage of aerobic respiration. It is a series of electron carrier proteins embedded in the inner mitochondrial membrane (cristae).1. Reduced NAD and reduced FAD, from glycolysis, the link reaction and the Krebs cycle, deliver hydrogen atoms to the chain and are reoxidised to NAD and FAD.
2. Each hydrogen atom splits into a proton (H+) and an electron.
3. The electrons pass from carrier to carrier in a series of redox reactions: each carrier is reduced when it gains an electron and oxidised when it passes it on. The electrons lose energy at each step.
4. Some carriers use this energy to pump protons from the matrix into the intermembrane space, building up a proton gradient that is used to make ATP.
5. At the end of the chain, oxygen is the final electron acceptor. It combines with electrons and protons to form water:4H+ + 4e− + O2 → 2H2O 
Without oxygen, electrons cannot leave the chain, so the carriers stay reduced and the chain stops. Reduced NAD then cannot be reoxidised, and the Krebs cycle and link reaction stop too.Reduced FAD passes its electrons to a carrier further along the chain than reduced NAD does, so fewer protons are pumped and less ATP is made from each reduced FAD.Poisons such as cyanide inhibit the final carrier (cytochrome oxidase), stopping the chain; cells then quickly run out of ATP.
2. Each hydrogen atom splits into a proton (H+) and an electron.
3. The electrons pass from carrier to carrier in a series of redox reactions: each carrier is reduced when it gains an electron and oxidised when it passes it on. The electrons lose energy at each step.
4. Some carriers use this energy to pump protons from the matrix into the intermembrane space, building up a proton gradient that is used to make ATP.
5. At the end of the chain, oxygen is the final electron acceptor. It combines with electrons and protons to form water:
Without oxygen, electrons cannot leave the chain, so the carriers stay reduced and the chain stops. Reduced NAD then cannot be reoxidised, and the Krebs cycle and link reaction stop too.Reduced FAD passes its electrons to a carrier further along the chain than reduced NAD does, so fewer protons are pumped and less ATP is made from each reduced FAD.Poisons such as cyanide inhibit the final carrier (cytochrome oxidase), stopping the chain; cells then quickly run out of ATP.