True or False. At the end of the electron transport chain, hydrogen combines with carbon dioxide to form water.
The correct answer and explanation is :
False.
At the end of the electron transport chain (ETC) in cellular respiration, hydrogen does not combine with carbon dioxide to form water. Instead, oxygen acts as the final electron acceptor and combines with hydrogen ions (protons) and electrons to form water (H₂O).
The electron transport chain is the final stage of aerobic respiration and takes place in the inner mitochondrial membrane. It consists of a series of protein complexes and electron carriers, such as NADH and FADH₂, which donate electrons to the chain. As electrons move through these complexes, they help pump protons into the intermembrane space, creating a proton gradient. This gradient drives ATP synthesis via ATP synthase, producing ATP, the main energy currency of the cell.
At the end of the chain, the electrons must be removed to keep the process going. Oxygen, which is highly electronegative, acts as the final electron acceptor. It combines with the electrons and free hydrogen ions (H⁺) to form water:
[
O₂ + 4e⁻ + 4H⁺ → 2H₂O
]
Carbon dioxide (CO₂) is actually produced earlier in cellular respiration, particularly during the Krebs cycle (citric acid cycle), when carbon atoms from glucose are released as CO₂. However, CO₂ does not participate in the ETC or the formation of water.
If oxygen were not available to accept electrons, the ETC would halt, preventing ATP production and leading to anaerobic conditions, where cells rely on fermentation for energy instead. This is why oxygen is critical for efficient ATP production in aerobic organisms.