Which statement best describes homeostasis and provides an example of a negative feedback mechanism?

• A. Homeostasis is maintaining a stable internal environment; negative feedback (e.g., body temperature regulation) returns a variable toward the set point.
• B. Homeostasis is the body's response to injury; positive feedback completes the loop.
• C. Homeostasis is the process of metabolism; feedback is only hormonal.
• D. Homeostasis refers to growth and development, with no feedback.

Answer: (A)

Maintaining a stable internal environment through sensing deviations and correcting them is what homeostasis is all about, and negative feedback is the common mechanism that brings a variable back toward its set point. For example, body temperature is kept within a narrow range by a thermostat-style system: sensors detect changes, the brain (hypothalamus) processes the signal, and effectors such as sweat glands and blood vessels act to adjust heat loss or production. As temperature returns to normal, the corrective responses lessen and eventually stop—the deviation is reduced back toward the set point.

This aligns with the statement that homeostasis means a stable internal environment and that negative feedback returns a variable toward the set point. The other descriptions fall short: homeostasis isn’t merely a response to injury, and while some processes use positive feedback, they don’t restore the original value and thus aren’t typical homeostatic mechanisms. Homeostasis isn’t limited to metabolism or hormones alone, and it isn’t about growth and development without feedback.