The chemical reaction that breaks down starch to produce energy is called hydrolysis. This process involves the addition of water molecules to break the bonds between the glucose monomers that make up starch.

Here's how it works:

1. Enzymes: The process is initiated by enzymes like amylase (found in saliva and the pancreas).

2. Breaking Bonds: These enzymes catalyze the breaking of the glycosidic bonds between the glucose units in starch.

3. Water Addition: Water molecules are added to the starch molecule, allowing the bonds to break.

4. Simple Sugars: This process results in the formation of simpler sugars like maltose and glucose.

Glucose is then absorbed into the bloodstream and transported to cells where it is used in cellular respiration to produce energy (ATP).

Cellular respiration is a series of biochemical reactions that occur in the mitochondria of cells. This process converts glucose into ATP, which is the primary energy currency of cells.

Therefore, the breakdown of starch through hydrolysis and subsequent cellular respiration produces ATP, the energy molecule used by cells for various functions.