Final answer:
The major organization that represents BOTH the scientific and professional branches of psychology in the United States is the American Psychological Association (APA). The APA is the largest organization of psychologists in the world and has several divisions representing various specialties within psychology.
Step-by-step explanation:
The major organization that represents BOTH the scientific and professional branches of psychology in the United States is the American Psychological Association (APA).
The APA is the largest organization of psychologists in the world and its mission is to advance and disseminate psychological knowledge for the betterment of people.
The APA has several divisions representing a wide variety of specialties within psychology.