Which organelle's inner membrane houses the electron transport chain and contains cristae?

• A. Mitochondria
• B. Nucleus
• C. Golgi apparatus
• D. Endoplasmic reticulum

Answer: (A)

The organelle in question is the mitochondrion. Its inner membrane houses the electron transport chain and contains cristae, the folds that dramatically increase surface area. The electron transport chain is a series of protein complexes embedded in this inner membrane, and ATP synthase sits there too. As electrons move through the chain, protons are pumped into the space between the inner and outer membranes, creating a gradient. When protons flow back through ATP synthase, it drives the production of ATP. The cristae provide the large surface area essential for housing all these components and enabling efficient energy production. Other listed organelles don’t carry out this chain of events: the nucleus stores genetic material; the Golgi apparatus and endoplasmic reticulum are involved in processing, modifying, and shipping proteins and lipids rather than producing ATP through respiration. So the mitochondrion is the correct organelle.