"It was Krebs who discovered how these individual reactions are linked to each other in a cyclic process. He brought us a clear understanding of the essential principle of how the released energy is used for the building up processes which take place within the cell."

The ferris wheel is one model for how the citric acid cycle (Krebs cycle) works. 

Coenzyme A escorts a molecule of acetyl (obtained from glycolysis) into the cycle, just as the ride operator escorts riders onto the ferris wheel.  Instead of getting into a car, the acetyl molecule is transferred to a "carrier" molecule to form citric acid.  As this combined molecule completes the cycle, the "passenger" is broken apart and pieces "fly off" and away from the cycle.  The "car" returns empty, ready to pick up another "passenger." Some of the "flying pieces" are high-energy electrons that are escorted to the ETS by coenzymes and their energy eventually transferred to ATP.

Although the explosion is now thought to have been caused by lightning that set off an explosive powdered aluminum coating on the skin of the balloon, this disaster was originally thought to be primarily an explosion of hydrogen gas --thus effectively ending the age of the H₂ zeppelins. 

In aerobic cellular respiration, H₂ produced in the mitochondria (ETS) is oxidized immediately before it can build up to an explosive amount.  Thus the need for O₂.