Which of these is not a response to internal stimuli? A. drinking when thirsty
B. eating when hungry
C. breathing hard when exercising because of a drop in oxygen levels
D. wearing sunglasses to protect eyes from UV rays

Long term continuous groundwater monitoring, especially with warning systems and anthropic activity monitors

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.