All cells need energy to live, grow and move. There are 3 major ways for animal cells to make the energy they need to survive. Glycolysis turns sugar into energy, the citric acid cycle uses the leftover molecules from glycolosis to make energy, and oxydative phosphorylation uses oxygen to create energy. Mitochondria are little organs within cells that can use oxygen to create energy in the form of a molecule called ATP (adenosine triphosphate). Mitochondria are extremely good at creating A LOT of energy, so cells that need a lot of energy to function could not survive without the large amounts of energy produced by mitochondria.

For more information on how cells make and store energy, check this website out:

The number of mitochondria in each cell depends on the type of cell it is and the amount of energy it needs. For instance, red blood cells do not have any mitochondria because they do not need much energy and can create energy using other metabolic pathways. On the other hand, a muscle cell requires a lot of energy and thus has hundreds or even thousands of mitochondria to keep up with its high energy demand. When mitochondria stop working properly then very serious diseases arise, which tells us that these tiny organelles are very important in the body. Did you know that mitochondria are thought to have once been single cell organisms that lived on their own?

Check out the following webpage for more details on the origin and function of mitochondria: