Mitochondria are often referred to as the powerhouse of the cell. They are small structures within a cell that are made up of two membranes and a matrix. The membrane is where the chemical reactions occur and the matrix is where the fluid is held. Mitochondria are a part of eukaryotic cells.
The main job of mitochondria is to perform cellular respiration. This means it takes in nutrients from the cell, breaks it down, and turns it into energy. This energy is then in turn used by the cell to carry out various functions.