During which step of cellular respiration is the most ATP produced?
The Correct Answer and Explanation is:
Correct Answer:
The most ATP is produced during the electron transport chain (ETC) step of cellular respiration.
Explanation:
Cellular respiration is the process by which cells break down glucose to produce energy in the form of adenosine triphosphate (ATP). It occurs in three main steps: glycolysis, the Krebs cycle (also known as the citric acid cycle), and the electron transport chain. Each step plays a different role in harvesting energy from glucose.
- Glycolysis happens in the cytoplasm of the cell. It breaks down one molecule of glucose into two molecules of pyruvate. This step produces a small amount of ATP—specifically, a net gain of 2 ATP molecules per glucose molecule.
- The Krebs cycle takes place in the mitochondrial matrix. It processes the pyruvate produced in glycolysis and generates high-energy electron carriers such as NADH and FADH₂. This cycle produces 2 ATP molecules per glucose molecule.
- The electron transport chain (ETC) occurs in the inner membrane of the mitochondria. Here, the NADH and FADH₂ produced in the previous steps donate electrons to the chain. As electrons move through the proteins of the ETC, energy is released and used to pump protons across the mitochondrial membrane. This creates a gradient called the proton motive force.
The movement of protons back into the mitochondrial matrix through an enzyme called ATP synthase powers the production of ATP from ADP and inorganic phosphate. This process is known as chemiosmosis.
The electron transport chain produces the most ATP—approximately 34 ATP molecules from one molecule of glucose. When combined with the ATP produced from glycolysis and the Krebs cycle, the total yield of cellular respiration is about 36 to 38 ATP molecules, depending on the cell type and conditions.
Thus, the electron transport chain is the most energy-productive phase of cellular respiration.
