[Solved] When a recipient cell acquires a piece of naked DNA from the environment,it is called A)conjugation. B)transformation. C)transduction. D)transfection. Serotonin: A chemical messenger in the brain crucial for maintaining stable mood, as well as promoting feelings of contentment and joy. Peripheral Nervous System: The part of the nervous system outside the brain and spinal cord, which connects the central nervous system to limbs and organs. Sympathetic Nervous System: Part of the autonomic nervous system that prepares the body for physical activity by increasing heart rate, constricting blood vessels, and raising blood pressure. Parasympathetic Nervous System: The division of the autonomic nervous system that calms the body, conserving its energy.