A cell is having many parts in it, which help in proper functioning of our body as they help in releasing and storing of energy. all this is is maintained by mitochondria-power house of the cell. i think there is only one mitochondria in one cell. 

Theoretically "0". That is why mitochondrial DNA related diseases only come from mother. But, personally, I believe anything can happen in biology.
Mitochondria is present in the tail of the sperm whereas it is present inside the ovum. During fertilization only the head of the sperm fuses with the egg and not the tail. That's why mitochondrial diseases are inherited maternally and not paternally! That's the reason btw :)