Genetic variation can arise in a number of different ways the picture below shows an example that occurs during meiosis

C. crossing over This is because each gene have a piece of each other Hope this helped=)

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.