The cell organelle that converts food energy into cellular energy is the mitochondrion.

Here's why:

* Mitochondria are the powerhouses of the cell. They are responsible for carrying out cellular respiration, a process that breaks down glucose (a type of sugar) and other food molecules in the presence of oxygen to produce ATP (adenosine triphosphate).

* ATP is the primary energy currency of cells. It provides the energy needed for all cellular activities, including muscle contraction, protein synthesis, and active transport.

So, while food provides energy, the mitochondria are the ones that actually convert it into a usable form for the cell.