Which is the name for a change in the environment that causes an organism to change its activity? a. brain b. parasite c. response d. stimulus

Stimulus is the name for a change in the environment that causes an organism to change its activity.

The answer to this is b

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.