What does "homeostasis" refer to in biological systems?

Homeostasis refers to the ability of organisms to maintain a stable internal environment despite changes in external conditions. This concept is crucial for the survival of living organisms, as it allows them to regulate various physiological processes, such as temperature, pH, hydration, and nutrient levels.

For example, humans maintain a core body temperature around 98.6°F (37°C) through mechanisms like sweating or shivering, depending on whether they are too hot or too cold. Similarly, plants can regulate water loss through transpiration and adjust their metabolic rate according to environmental conditions.

The other options pertain to different biological processes. Reproduction involves the ability of organisms to produce offspring but does not specifically address internal stability. The response to external stimuli focuses more on how organisms react to their environment rather than how they maintain internal equilibrium. The mechanisms of cellular respiration relate specifically to the process of converting food into energy and do not encompass the broader regulation of internal conditions. Thus, the emphasis on maintaining a stable internal environment makes the second choice the correct answer.