The process that converts food to energy that the cell can use is called cellular respiration. This process happens in the mitochondria, often referred to as the "powerhouses of the cell".

Here's a simplified breakdown of how it works:

1. Glycolysis: The first stage breaks down glucose (a simple sugar) into pyruvate. This occurs in the cytoplasm of the cell.

2. Krebs Cycle (Citric Acid Cycle): Pyruvate is further broken down in the mitochondria, releasing electrons and producing some ATP (the cell's energy currency).

3. Electron Transport Chain: The electrons from the Krebs cycle are passed along a chain of molecules in the mitochondrial membrane. This process releases energy that is used to generate a lot more ATP.

Cellular respiration requires oxygen to function efficiently. The energy produced from this process is stored in the chemical bonds of ATP molecules, which are then used to power various cellular processes like muscle contraction, protein synthesis, and active transport.