Which organelle is the site of cellular respiration?

• A. Ribosome
• B. Golgi apparatus
• C. Mitochondrion
• D. Nucleus

Answer: (C)

Cellular respiration primarily takes place in the mitochondria because this organelle houses the main pathways that generate ATP. After glycolysis in the cytoplasm, pyruvate enters the mitochondria and is converted to acetyl‑CoA, feeding the Krebs cycle. The Krebs cycle releases energized electrons that are carried by NADH and FADH2 to the electron transport chain in the inner mitochondrial membrane. As these electrons flow through the chain, a proton gradient drives ATP synthase to produce ATP. Oxygen serves as the final electron acceptor, forming water at the end of the chain. Because the key energy-producing steps are organized here, the mitochondrion is the primary site of cellular respiration. Other organelles have different roles: ribosomes synthesize proteins, the Golgi apparatus packages and modifies them, and the nucleus houses genetic material, not energy production.