It’s not a deer/deer single/plural situation with mitochondria, if that is what you are getting at. The word mitochondria is not singular. To replace mitochondria with lion in your analogy doesn’t work because mitochondria is a plural word. Neither “Lions is the king of the jungle” nor “The lions is the king of the jungle” is correct. The singular version of mitochondria is mitochondrion. “The mitochondrion is the powerhouse of the cell” and “Mitochondria are the powerhouse of the cell” both work and could be the phrase, just like "The lion is the king of the jungle " and “Lions are the king of the jungle” are both grammatically correct.