Classify the following according to whether they are inputs or outputs of the electron transport chain: 19 NADH Input of electron transport chain Output of electron transport chain 0.19 points FADH eBook Print References FAD NADH ATP ADP H2O Reset McGraw-Hill Location Prev 19 of 52 Next
The Correct Answer and Explanation is:
The electron transport chain (ETC) is the final stage of cellular respiration, occurring in the inner mitochondrial membrane. It plays a crucial role in ATP production by using electron carriers to generate a proton gradient, which drives ATP synthesis.
Classification of Inputs and Outputs
Inputs of the Electron Transport Chain:
- NADH – A high-energy electron carrier that donates electrons to Complex I.
- FADH₂ – Another electron carrier that donates electrons to Complex II.
- ADP + Pi – Used in ATP synthesis.
- Oxygen (O₂) – The final electron acceptor, combining with electrons and hydrogen ions to form water.
Outputs of the Electron Transport Chain:
- ATP – The primary energy currency produced through oxidative phosphorylation.
- H₂O – Formed when oxygen accepts electrons and combines with hydrogen ions.
- NAD+ – Regenerated after NADH donates electrons.
- FAD – Regenerated after FADH₂ donates electrons.
Explanation
The electron transport chain is a series of protein complexes (I–IV) embedded in the inner mitochondrial membrane. NADH and FADH₂, generated during glycolysis and the Krebs cycle, provide high-energy electrons to the chain. NADH donates electrons to Complex I, while FADH₂ donates to Complex II. These electrons are transferred through a series of redox reactions, gradually releasing energy.
This energy is used to pump protons (H⁺) across the membrane, creating an electrochemical gradient. The accumulation of H⁺ in the intermembrane space establishes a high-energy state, driving the movement of protons back into the mitochondrial matrix through ATP synthase. This movement powers the conversion of ADP and inorganic phosphate (Pi) into ATP.
Oxygen serves as the terminal electron acceptor, combining with electrons and protons to form water. Without oxygen, electrons would be unable to continue moving, halting ATP production. The regeneration of NAD+ and FAD ensures the continuation of glycolysis and the Krebs cycle.
Ultimately, the electron transport chain maximizes ATP yield, making cellular respiration highly efficient. This process is essential for sustaining biological functions, especially in energy-demanding tissues such as muscles and the brain.
