Which of the following is evidence of earth's age provided by fossils? fossils are found only in sedimentary rock. fossils range from simple to complex across rock layers. fossils formed gradually over time. fossils are found in rock above water.

Fossils range from simple to complex across rock layers.

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.