Energy in organisms is called
a) organelles
b) metabolism
c) homeostasis
d) cells

A) organelles are the "organs of a cell" B) metabolism is an organism's energy C) homeostasis is a status of balance or equilibrium in an organism D) I'm pretty sure you know what a cell is

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.