The part of the autonomic nervous system that conserves energy is the parasympathetic nervous system.

Here's why:

* The parasympathetic nervous system is often called the "rest and digest" system. It promotes activities that conserve energy and restore the body, such as:

* Slowing heart rate

* Lowering blood pressure

* Stimulating digestion

* Contracting the bladder and stimulating urination

* Constricting the pupils

* The sympathetic nervous system, on the other hand, is the "fight or flight" system. It prepares the body for action and expends energy by increasing heart rate, blood pressure, and respiration.