Mitochondria What Are Mitochondria? Mitochondria are tiny structures inside your cells often called the “energy factories”  of the body. Nearly every human, animal, and plant cell contains them—sometimes in the hundreds or even thousands. Highly active cells, like muscle cells, require more energy and therefore contain more mitochondria than less active cells like skin cells. All living things are made up of cells, and inside each cell are specialized structures called organe