Where glucose is broken down into smaller molecules to produce energy. The second part of the process takes place in the

Mitochondria

Explanation:

Glucose in an energy molecule contained in carbohydrate food substances. The end product of the digestion of carbohydrate is glucose which is broken down to produce energy.

The sequence of breakdown of glucose is as follows; In the first step, 6-carbon glucose is broken down into two molecules of  3-carbon pyruvic acid. This occurs in the cytoplasm of the cell. It is an anaerobic process.

In the second step which occurs in the mitochondrion, each of the molecules of pyruvic acid is now oxidized to carbon dioxide and water and energy is produced in the process.