What stage of cellular respiration produces the most ATP? A. Electron transport chain B. Glycolysis C. Krebs cycle D. Fermentation
The Correct Answer and Explanation is:
Correct Answer: A. Electron transport chain
The electron transport chain (ETC) is the stage of aerobic cellular respiration that produces the most ATP. This process takes place in the inner mitochondrial membrane and relies on the energy carried by electrons from NADH and FADH₂, which are produced during earlier stages such as glycolysis and the Krebs cycle.
The ETC works by passing these high-energy electrons through a series of protein complexes embedded in the membrane. As electrons move along the chain, energy is released and used to pump protons (H⁺ ions) from the mitochondrial matrix into the intermembrane space. This creates a proton gradient, which stores potential energy, similar to water behind a dam.
Eventually, the protons flow back into the matrix through ATP synthase, a protein that acts like a molecular turbine. This flow of protons provides the energy needed to convert ADP into ATP. This specific process of ATP production using a proton gradient is called chemiosmosis.
Oxygen plays a vital role here. It acts as the final electron acceptor at the end of the chain and combines with electrons and protons to form water. Without oxygen, the ETC cannot operate, and cells must rely on far less efficient anaerobic processes like fermentation.
In total, the ETC can produce about 32 to 34 molecules of ATP per glucose molecule, which is much higher than glycolysis (2 ATP) or the Krebs cycle (2 ATP). Fermentation does not involve the ETC and produces only 2 ATP per glucose molecule.
In summary, the electron transport chain is the most efficient stage of cellular respiration in terms of ATP production. It uses the energy from electrons carried by NADH and FADH₂, creates a proton gradient, and drives the synthesis of ATP through ATP synthase.
