Mitochondria

Mitochondria are the sites of cellular respiration, generating ATP from the catabolism of sugars, fats, and other fuels in the presence of oxygen. They convert energy to forms that cells can use for work. Mitochondria are in almost all eukaryotic cells, outside of the endoplasmic reticulum. They have a smooth outer membrane and a folded inner membrane, called cristae. The cristae present ample surface area for the enzymes that synthesize ATP. The area enclosed by the cristae is called the mitochondrial matrix, which is a fluid-filled space with DNA, ribosomes, and enzymes.  They can move, change shape, and divide by themselves. They look like beans, leaves, or even a piece of meat.