The organelle where energy is released from broken down molecules is the mitochondrion.

Here's why:

* Cellular Respiration: Mitochondria are the sites of cellular respiration, the process that converts glucose (sugar) into usable energy in the form of ATP (adenosine triphosphate).

* Krebs Cycle and Electron Transport Chain: The Krebs cycle and electron transport chain, the key stages of cellular respiration, occur within the mitochondria.

* ATP Production: The electron transport chain, in particular, is responsible for producing the majority of ATP.

Let me know if you'd like more information about the process of cellular respiration!