Part of a cell where catabolism primarily occurs: cell membrane nucleus mitochondria genes endoplasmic reticulum

The answer is mitochondria. Catabolisms involves the prices of breaking down bigger molecules into smaller molecules. It is the opposite of anabolism which is the building of bigger molecules from small ones. In the mitochondria, molecules (pyruvate) are broken down (in a series of redox reactions) in the Krebs cycle to produce ATP.