Which statement accurately describes the rock layers?
layer 8 is older than layer 1.
layer 3 is younger than layer 6.
layer 7 and layer 4 are the same relative age.
layer 2 and layer 9 are the same relative age.

What's the yellow wallpaper?

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.