why is mitochondria known as the powerhouse of the cell?
Mitochondria are called power house of the cell because they release energy in the form of ATP for the metabolic functions of the cell by aerobic respiration. So, almost all the energy received or required by the cell is generated by mitochondria and hence it is called powerhouse of the cell i.e. the place form where power is derived or taken.
Mitochondria are sometimes described as "cellular power plants," because they generate most of the cell's supply of ATP, used as a source of chemical energy. The number of mitochondria in a cell varies widely by organism and tissue type. Many cells possess only a single mitochondrion, while others can contain several million mitochondria. Although most of a cell's DNA is contained in the cell nucleus, mitochondria have their own independent genomes. According to the endosymbiotic theory, mitochondria are descended from free-living prokaryotes.