To maintain homeostasis, which components must be functional?

• A. Receptor, control center, and effector
• B. Glands, hormones, and targets
• C. Muscle, bone, and nerve
• D. Heart, lungs, and brain

Answer: (A)

Maintaining homeostasis relies on a three-part loop: a receptor to sense changes, a control center to interpret the signal and decide on a response, and an effector to carry out that response and restore balance. When something in the body deviates from the set point—like a rise in temperature—receptors pick up the change, the control center (often in the brain) compares it to the normal value, and the effectors (such as sweat glands or blood vessels) enact actions to bring the condition back toward the set point. If any part of this chain is missing or not functioning, the body cannot detect the change, decide how to respond, or implement the response, so homeostasis is disrupted. The other options describe broader systems or components, but they do not by themselves constitute the complete sensing–processing–responding loop required to keep the internal environment stable.