STOP 10. The Sphase stands for synthesis, which means to make or build something more complex out of
simpler parts. Scientists know that during the Sphase DNA is being made in the nucleus of the
cell. Why do you think the cell needs to make more DNA at this time in the cell cycle?

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.