A series of electron carrier proteins that shuttle high-energy electrons during ATP-generating reactions describes which component?

• A. Electron Transport Chain
• B. Photosystems
• C. Calvin Cycle
• D. ATP Synthase

Answer: (A)

The main idea being tested is the electron transport chain, a series of electron carrier proteins that shuttle high-energy electrons during ATP-generating reactions. In aerobic respiration, NADH and FADH2 donate electrons into this chain embedded in the inner mitochondrial membrane. As electrons move through the chain, their energy is used to pump protons across the membrane, creating a proton gradient. That gradient powers ATP synthase to synthesize ATP from ADP and inorganic phosphate. The chain ultimately transfers electrons to oxygen, forming water. This description precisely matches the electron transport chain. Photosystems are light-harvesting units in photosynthesis, not the series of carriers that directly drives ATP production in respiration; the Calvin Cycle fixes carbon dioxide into sugars; ATP synthase is the enzyme that uses the proton gradient to make ATP, not the chain of carriers itself.