What does a mitocondrion do

A mitochondria is basically the power house of the cell. It turns left over glucose into energy.

The mitochondria take fuel (glucose) and essentially burns it. The energy given off by oxidizing the fuel is harnessed by causing ions to move across a membrane, kind of like pumping water. The ions then flow down through a protein which synthesizes ATP much like the water then flows down through a dam to generate electricity.