What term describes an automatic body response to a stimulus?

The term that describes an automatic body response to a stimulus is "reflex." A reflex is a quick, involuntary response to a specific stimulus, such as pulling your hand away from a hot surface or the knee-jerk reaction when the patellar tendon is tapped. Reflexes are fundamental for survival, allowing individuals to react swiftly without requiring conscious thought.

The other options do not encapsulate the concept of an automatic response in the same way. An impulse typically refers to a sudden urge to act, which may not necessarily involve an immediate physical response to a stimulus. Reaction can suggest a more conscious process involving decision-making, whereas instinct refers to inherent tendencies or behaviors that are often complex and not merely physical responses to a stimulus. Reflexes, therefore, uniquely identify that immediate and automatic nature of body responses to particular stimuli.