The organelle that breaks down food and turns it into energy for cell use is the mitochondrion.

Here's how it works:

* Food is broken down: The process of breaking down food (glucose) begins in the cytoplasm through glycolysis. This produces a small amount of ATP (energy) and pyruvate.

* Pyruvate enters the mitochondrion: Pyruvate moves into the mitochondrion, where it's further broken down in the Krebs cycle (also known as the citric acid cycle). This cycle produces more ATP and electron carriers (NADH and FADH2).

* Electron transport chain: The electron carriers deliver their electrons to the electron transport chain located in the mitochondrial inner membrane. This chain uses the energy from the electrons to pump protons across the membrane, creating a concentration gradient.

* ATP production: The protons flow back across the membrane through a protein called ATP synthase, which uses the energy from their movement to produce ATP, the primary energy currency of the cell.

So, the mitochondrion is like the cell's power plant, converting the energy stored in food into a usable form for all cellular activities.