Define homeostasis.

• A. The maintenance of stable internal conditions in an organism or cell.
• B. The development of new traits over generations.
• C. The breakdown of glucose to produce energy.
• D. The movement of ions across membranes.

Answer: (A)

Homeostasis is the maintenance of stable internal conditions in an organism or cell. It keeps factors like temperature, pH, fluid and ion balance, and nutrient levels within narrow limits even when the external environment changes. When a deviation occurs, sensors and control systems trigger responses—such as sweating to cool down or conserving water to maintain blood volume—so cellular processes keep running smoothly. Other ideas describe evolution (traits changing over generations), metabolism (breaking down glucose for energy), or membrane transport (moving ions across membranes). While related to biology, they are not the definition of maintaining stable internal conditions.