There are three theories about the origin of mitochondria.
1. De novo origin: According to this theory, amino acids and lipids combine to form mitochondria. This doctrine is not accepted at present.
2. Cell membrane or endoplasmic origin: According to scientist Morison (1966), vesicles are formed from endoplasmic reticulum or cell membrane and mitochondria are formed from vesicles. This doctrine is now defunct.
3. Mitochondrial origin: According to this theory, during cell division, old mitochondria divide to form new mitochondria. The new mitochondria quickly change shape and move to other parts of the cell. It grows rapidly and divides to increase the number of cells to meet more energy.