Which of the following is NOT true of proteins? a. they form muscle, skin and hair
b. they are found in food
c. they are a main source of energy
d. they are sensitive to pH and temperature

Hold on to his or her beliefs even if there is no evidence for those beliefs.

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.