The respiratory processes of mitochondria create the greatest yield of ATP but the molecule is synthesised outside the organelle as well by glycolysis. This process creates 2 molecules of ATP when the food sources glucose or glycerol are broken down to pyruvate which is then phosphorylated by 2 enzymes, PGK and pyruvate kinase.

This answer depends on where in the body the cell in question is located because some cell types are more active than others and have different energy demands. Generally speaking their numbers can range from less than a hundred to several thousand. As well as this, their size and shape can vary from small spheres of a few nanometers in diameter to the more traditional elongated shape of 1 micrometer in diameter and 7 micrometers in length.

Mitochondria can be seen in many distributions within a cell. In many cases they can be seen freely placed in cells especially in non-motile types. In a more specialised cell such as a sperm cell they can be found in large numbers localised around the mid section where the tail attaches. This is because the tail needs lots of energy to enable the sperm to "swim". It has also be shown that, although mitochondria may look randomly distributed, they are actually attached on fibrils of the cell's cytoskeleton. 

This arrangement is typical of bacterial genomes and reflects the endosymbiont theory where mitochondria are thought to have originated from a single bacterium. The circles of genetic material in bacteria are referred to as plasmids. The fact that the DNA is arranged in a circle means that there are no open ends to the genetic sequence producing a stable complex.

It is extremely difficult to diagnose a mitochondrial disease so the process is very expensive, invasive and time consuming. The diagnosis process involves testing many functions such as metabolism in the subject's major bodily fluids. Complete neurological and physical examinations are practised as well as of course checking family history. Further tests such as DNA sequencing or MRI are performed based upon what type of symptoms the patient exhibits.

As mentioned, there are no known cures for mitochondrial diseases. Patients must manage their symptoms in order to reduce their severity and delay the further development of the disease. Vitamin or enzyme treatment is often prescribed in order to promote the correct functioning of mitochondria. As well as this, a dietician may help to identify foods which are high in antioxidants or alternatively antioxidant therapy may be used. This is to reduce the level of the damaging oxidative particles produced by mitochondria called free radicals.