What two allele combinations (parents) would you have to cross to get offspring that have the following probabilities:

50% Bb, 25% BB, 25% bb (75% brown eyes, 25% blue eyes)?

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.