Psychology is a broad discipline, essentially spanning subject matter from biology to sociology. Biology studies the structures and functions of living organisms. Psychologists study the intersection of two critical relationships: 1) the biology of brain function and behavior and 2) the relationship between the environment and behavior. Psychologists use scientific methods, carefully observing, experimenting, and analyzing both human and animal behavior, physiology, and mental processes. Psychologists conduct both basic and applied research, serve as consultants to communities and organizations, diagnose and treat people, work in industry and government, and teach future psychologists and other students.