The process that converts food into energy is called cellular respiration. It's a complex series of chemical reactions that occur in the cells of all living organisms. Here's a simplified breakdown:

1. Digestion: Food is broken down into smaller molecules (like glucose) that can be absorbed by the body.

2. Glycolysis: Glucose is broken down in the cytoplasm of the cell, producing a small amount of ATP (adenosine triphosphate), the main energy currency of the cell.

3. Krebs Cycle (Citric Acid Cycle): This cycle takes place in the mitochondria, the powerhouses of the cell. It further breaks down the products of glycolysis and releases electrons.

4. Electron Transport Chain: These electrons are passed along a chain of molecules in the mitochondria, releasing energy that is used to create a lot of ATP.

In short, the mitochondria are the organelles primarily responsible for converting food into energy.

Here's an analogy: Imagine food as a log. Cellular respiration is like a series of machines that break the log down into smaller pieces, extracting energy along the way. The final product is a usable form of energy (ATP) that can be used by the cell to carry out its various functions.