Final answer:
An organism that has reached equilibrium with its external environment is using ATP to maintain this state of equilibrium and is healthy and actively metabolizing.
Step-by-step explanation:
An organism that has reached equilibrium with its external environment is not dead or actively performing work, but rather it is using ATP to maintain this state of equilibrium. ATP is a molecule that provides energy for various cellular activities, including maintaining homeostasis and carrying out metabolic reactions. The organism is healthy and actively metabolizing because it is able to maintain a stable internal environment through the utilization of ATP.