Water flow improves in the aftermath of a forest fire because rain always puts out fires.
no living organisms survive fires, decreasing demand.
they clear the land, allowing more water to flow over it.
much of the water in a local watershed will be used to fight the fire.

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.