Which of the following correctly lists the sequence of steps as energy is extracted from glucose during cellular respiration?

• A. Glycolysis → Krebs cycle (Citric Acid Cycle) → Electron Transport Chain
• B. Glycolysis → Electron Transport Chain → Krebs cycle
• C. Electron Transport Chain → Glycolysis → Krebs cycle
• D. Krebs cycle → Glycolysis → Electron Transport Chain

Answer: (A)

Verified step by step guidance

1. Understand that cellular respiration is the process by which cells extract energy from glucose to produce ATP, the energy currency of the cell.
2. Recall the three main stages of cellular respiration: Glycolysis, the Krebs cycle (Citric Acid Cycle), and the Electron Transport Chain (ETC). These stages occur in a specific sequence to efficiently extract energy.
3. Glycolysis is the first step, occurring in the cytoplasm, where glucose is broken down into two molecules of pyruvate, producing a small amount of ATP and NADH.
4. The Krebs cycle (Citric Acid Cycle) is the second step, occurring in the mitochondrial matrix. Here, pyruvate is further broken down, generating more NADH and FADH2, which are electron carriers.
5. The Electron Transport Chain (ETC) is the final step, occurring in the inner mitochondrial membrane. Electrons from NADH and FADH2 are transferred through protein complexes, creating a proton gradient that drives ATP synthesis via chemiosmosis.