What is something that causes an organism to act in a certain way?

The term that causes an organism to act in a certain way is known as a stimulus. A stimulus refers to any external or internal factor that elicits a reaction or response from an organism. For instance, when a bright light shines in a person's eyes, the sudden brightness can cause them to squint or close their eyes, which is a direct reaction to the stimulus of light.

This concept is fundamental in understanding behavior and physiological responses in living organisms. The stimulus can originate from various sources such as environmental changes, social interactions, or even internal bodily signals, prompting the organism to engage in a specific behavior or action in response to that stimulus.

Responses, reflexes, and behavior refer to the actions or reactions of the organism itself. While these terms are related to the organism's reaction, it is the stimulus that initiates the whole process. Understanding this relationship is essential for studying behavioral science and biology.