Which of the earth’s subsystems is directly affected by burning fossil fuels? geosphere hydrosphere biosphere atmosphere

Burning fossil fuels puts pollution into the air, meaning you're affecting the atmosphere. 

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.