Final answer:
The parasympathetic nervous system is responsible for digestion and conserving energy as it controls 'rest and digest' activities.
Step-by-step explanation:
When the body's organ systems are directed towards digestion and conserving energy, the parasympathetic nervous system is in control. The autonomic nervous system, which the parasympathetic division is a part of, operates without conscious control and regulates internal organs and glands to maintain homeostasis. Unlike the sympathetic nervous system that prepares the body for stress-related activities, the parasympathetic nervous system manages activities associated with rest and digest functions, reducing the heart rate and increasing digestion abilities.