Homeostasis is the regulation of the functions of some internal conditions as reaction to changes in the environment.
For example, although the external temparuture changes the matabolism is capable to keep the temperauture of the body constants through homeostasis.
That does not happen with the cold blooded animals. If you put a small frog very close to a hot ligthed bulb, its blood will not be able to keep it cool and it will dry completely.
Mitochondrion functions as the "power house of the cell". It provides to the cell with most of the cell's energy. It converts food to "useful" energy so that it can be utilized by the cell.
