Final answer:
The correct option is D. Constantly compares input signals to the setpoint.
A control loop in homeostasis, utilizing negative feedback, constantly compares inputs to a set point and adjusts through effectors to maintain balance. Sensors detect deviations and the control center orchestrates the response to ensure the variable stays within a normal range.
Step-by-step explanation:
In a control loop, such as the negative feedback mechanism in homeostasis, a controller does not operate without a set point; rather, it constantly compares input signals to the setpoint. The controller's task is to maintain the variable within a normal range. The set point is a crucial reference value in the loop.
When the value of the variable deviates from the set point, the sensor, also known as a receptor, detects this change and sends data to the control center. The control center then assesses these signals and, if necessary, sends a corrective signal to the effector, such as a gland or muscle, to adjust the variable back towards the set point and maintain overall system balance. This ensures that any deviation is corrected, keeping the variable within its normal range.
An example of this would be body temperature regulation where the skin and brain work together to detect changes and initiate responses to heat or cool the body, maintaining a stable internal environment.