Which of the following best describes the electron transport chain? A Electrons are pumped across a membrane by active transport. B Acetyl CoA is fully oxidized to CO2. C Hydrogen atoms are added to CO2 to make an energy-rich compound. D Glucose is broken down to a three-carbon compound in preparation for the citric acid cycle. E Electrons are passed from one carrier to another, releasing a little energy at each step.

Sourav PanDecember 12, 2024

Answered step-by-step

The correct answer is:

E. Electrons are passed from one carrier to another, releasing a little energy at each step.

Explanation:

• In the electron transport chain (ETC), electrons from NADH and FADH2 are passed through a series of protein complexes (such as NADH dehydrogenase, cytochrome c reductase, and cytochrome c oxidase). As electrons move through these carriers, they release small amounts of energy, which is used to pump protons (H+^++) across the inner mitochondrial membrane, establishing a proton gradient. This energy is ultimately used to produce ATP.

Why the other options are incorrect:

• A (Incorrect): Electrons are not directly pumped across the membrane; instead, the energy from the electrons is used to pump protons across the membrane.
• B (Incorrect): Acetyl CoA is fully oxidized to CO2 in the citric acid cycle, not the electron transport chain.
• C (Incorrect): Hydrogen atoms are not added to CO2 in the electron transport chain. CO2 is a byproduct of the citric acid cycle.
• D (Incorrect): Glucose is broken down into pyruvate during glycolysis, not in preparation for the citric acid cycle.