Most of the electrons removed from glucose by cellular respiration are used for which of the following processes?

• A. Reducing NAD⁺ to NADH in glycolysis and the citric acid cycle
• B. Producing a proton gradient for ATP synthesis in the mitochondria
• C. Driving substrate-level phosphorylation in glycolysis
• D. The second and third answers are correct.
• E. The first two choices are correct.

Answer: (E)

Verified step by step guidance

1. Understand that cellular respiration involves multiple stages where electrons are removed from glucose and transferred to electron carriers.
2. Recognize that NAD+ is an electron carrier that gets reduced to NADH during glycolysis and the citric acid cycle. This is a key step in capturing energy from glucose.
3. Identify that NADH carries electrons to the electron transport chain in the mitochondria, where these electrons are used to create a proton gradient across the inner mitochondrial membrane.
4. Acknowledge that the proton gradient is essential for ATP synthesis through oxidative phosphorylation, as protons flow back into the mitochondrial matrix via ATP synthase, driving the production of ATP.
5. Conclude that the electrons removed from glucose are primarily used to reduce NAD+ to NADH and to produce a proton gradient for ATP synthesis, making the first two choices correct.