The organelle that converts chemical energy in food into ATP for the cell to use is the mitochondrion.

Here's why:

* Mitochondria are often referred to as the "powerhouses" of the cell because they are responsible for cellular respiration.

* Cellular respiration is the process of breaking down glucose (a type of sugar found in food) in the presence of oxygen to generate ATP.

* ATP (adenosine triphosphate) is the main energy currency of cells. It's like a small, rechargeable battery that provides the energy needed for various cellular processes, such as muscle contraction, protein synthesis, and active transport.

So, in short, mitochondria take the energy stored in food and convert it into a usable form for the cell – ATP.