During aerobic respiration, electrons travel downhill in which sequence?

• A. glucose → NADH → electron transport chain → O\(_2\)
• B. O\(_2\) → NADH → glucose → electron transport chain
• C. glucose → electron transport chain → NADH → O\(_2\)
• D. NADH → glucose → electron transport chain → O\(_2\)

Answer: (A)

Verified step by step guidance

1. Understand the process of aerobic respiration: Aerobic respiration is a metabolic pathway where glucose is broken down to produce ATP, and electrons are transferred through a series of molecules to ultimately reduce oxygen (O\(_2\)).
2. Identify the starting point: Glucose is the initial molecule that undergoes oxidation during glycolysis, releasing electrons that are captured by NAD\(^+\) to form NADH.
3. Trace the electron flow: Electrons from NADH are transferred to the electron transport chain, a series of protein complexes embedded in the mitochondrial membrane.
4. Recognize the final electron acceptor: At the end of the electron transport chain, electrons are transferred to oxygen (O\(_2\)), which combines with protons to form water (H\(_2\)O).
5. Sequence the electron flow: The correct downhill sequence of electron travel during aerobic respiration is glucose → NADH → electron transport chain → O\(_2\).