Cellulose is found throughout the cell walls of paint cells cellulose makes cell walls rigid which indicates that cellulose is a

It is a protective layer that is a type of certain glucosidic bonds

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.