select the part whose main job is to break down sugar and release energy that the cell can use.

The part of the cell whose main job is to break down sugar and release energy that the cell can use is the mitochondrion. Mitochondria are often referred to as the powerhouses of the cell because they take in nutrients, break them down, and create energy-rich molecules (ATP) through the process of cellular respiration. This energy is then available for the cell to perform various functions.