Which organelle is the site of ATP production and contains cristae formed by a folded inner membrane?

• A. Lysosomes
• B. Mitochondria
• C. Peroxisomes
• D. Golgi apparatus

Answer: (B)

ATP production happens mainly in mitochondria through oxidative phosphorylation. The key feature is the cristae, folds of the inner mitochondrial membrane that greatly increase surface area for the electron transport chain complexes and ATP synthase. As electrons pass along the chain, protons are pumped into the intermembrane space, creating a proton gradient that drives ATP synthesis when protons flow back into the matrix via ATP synthase. The matrix itself houses the enzymes of the TCA cycle, feeding electrons into the chain. Mitochondria also contain their own DNA and ribosomes, reflecting their evolutionary origin. Other organelles have different roles: lysosomes degrade macromolecules, peroxisomes perform fatty acid oxidation and detoxification, and the Golgi apparatus modifies and sorts proteins. The organized structure with cristae is what makes mitochondria the primary site of ATP production.