What are the four phases of cellular respiration?

• A. Glycolysis, citric acid cycle, electron transport chain, and oxidative phosphorylation
• B. Glycolysis, pyruvate oxidation, citric acid cycle, and oxidative phosphorylation
• C. Fermentation, glycolysis, aerobic respiration, and anaerobic respiration
• D. Oxidative phosphorylation, pyruvate oxidation, Krebs cycle, and glycolysis

Answer: (B)

The four phases of cellular respiration are glycolysis, pyruvate oxidation, the citric acid cycle (also known as the Krebs cycle), and oxidative phosphorylation.

Glycolysis occurs in the cytoplasm and breaks down glucose into two molecules of pyruvate, generating a small amount of ATP and electron carriers (NADH). Pyruvate oxidation follows, where each pyruvate is converted into acetyl-CoA, releasing carbon dioxide and producing more NADH. The citric acid cycle takes place in the mitochondria, where acetyl-CoA is further oxidized, leading to the production of ATP, GTP, NADH, and FADH2 while releasing additional carbon dioxide. Lastly, oxidative phosphorylation occurs in the inner mitochondrial membrane, where the electrons from NADH and FADH2 are transferred through the electron transport chain, creating a proton gradient that ultimately drives ATP synthesis through ATP synthase.

This correct answer captures all essential steps involved in aerobic cellular respiration, illustrating the complete pathway from glucose to ATP production.