Without oxygen, cellular respiration grinds to a standstill, although glycolysis can continue to make some ATP anaerobically for a short time. When oxygen runs out, why does electron transport stop? Why do you thing the Krebs cycle stops?
When oxygen is present, it serves as the final electron acceptor in the process of cellular respiration. The electrons generated during glycolysis and the Krebs cycle are transferred to the electron transport chain (ETC), where they move through a series of protein complexes and carriers, ultimately leading to the reduction of oxygen to water. This transfer of electrons creates an electrochemical gradient that drives the synthesis of ATP.
When oxygen runs out, the electron transport chain stops because there is no longer any oxygen available to accept the electrons. The ETC relies on oxygen to function as the final acceptor in the electron transfer process. Without oxygen, the entire chain becomes unable to pass on the electrons, leading to a halt in the production of ATP via oxidative phosphorylation.
Similarly, the Krebs cycle stops when oxygen is absent because it depends on the availability of electron carriers such as NAD+ and FAD. During the Krebs cycle, NAD+ and FAD accept electrons from the breakdown of glucose and other molecules, becoming reduced to NADH and FADH2. These reduced forms of electron carriers are then used in the electron transport chain.
Without oxygen, the electron carriers NAD+ and FAD cannot be effectively regenerated, leading to their depletion within the Krebs cycle. As a result, the Krebs cycle cannot continue without a sufficient supply of electron carriers. This further halts the production of ATP, as the Krebs cycle generates high-energy electron carriers that fuel the ETC.
In summary, the electron transport chain and the Krebs cycle stop when oxygen runs out because both processes rely on oxygen as the final electron acceptor and depend on the regeneration of electron carriers. Without oxygen, the flow of electrons ceases, leading to a standstill in cellular respiration and ATP production.