Which organelle is primarily responsible for providing energy in the form of ATP?

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

Answer: (B)

Energy production in cells happens mainly in the mitochondria, where cellular respiration converts nutrients into ATP. The bulk of ATP comes from oxidative phosphorylation, which occurs as electrons move through the inner mitochondrial membrane’s electron transport chain and protons are pumped across it. This proton gradient powers ATP synthase to convert ADP and inorganic phosphate into ATP. Glycolysis in the cytoplasm starts the process, and the citric acid cycle in the mitochondrial matrix feeds high-energy electrons into the chain, but the actual ATP yield comes from the mitochondrial membrane system. Other organelles have different roles: the nucleus stores genetic information, ribosomes synthesize proteins, and the Golgi apparatus processes and ships those proteins.