The most prominent roles of mitochondria are to produce the energy currency of the cell, ATP (i.e., phosphorylation of ADP), through respiration, and to regulate cellular metabolism. The central set of reactions involved in ATP production are collectively known as the citric acid cycle, or the Krebs cycle. However, the mitochondrion has many other functions in addition to the production of ATP.
Mitochondria are the power house of a cell. These produce the energy to cell in form of ATP.
These also help in cellular respiration of cell.
Usually a cell have 100-150 mitochondria. We can observe the mitochondrian’s unique internal structure through only electron microscope