Which organelle is called the powerhouse of the cell?

Mitochondria.
This is what it looks like:
The mitochondria is the main site of chemiosmosis.
This is a process by which a large amount of ATP molecules are made in the last stage of respiration, known as The Electron Transport Chain .
The ATP molecules are the energy currency of the cell. Whenever any of the cell’s bodies require energy to function, they take that energy from ATP molecules.
That is how energy from the food we eat is transferred to cells in our bodies: Through ATP.
Since mitochondria are the main site of ATP synthesis, hence they produce most of the power required by the body and they are termed as the powerhouse of the cell.
The mitochondria is an exceptionally unique organelle. It holds the distinction of being the ONLY organelle in animal cells that makes its own DNA. The only other place where this happens is the nucleus.
Mitochondria is also crucial for our understanding of how life evolved on our planet earth. Scientists believe that the ancient ancestors of mitochondria were the first prokaryotes that inhabited the planet.
If this organelle is so amazing, you should definitely know more about it since it works 24/7 to give you energy 🙂
A stellar animation about how mitochondria make ATP here!
Over here you can explore the structure of mitochondria at an even deeper level.