What defines a living organism's ability to respond to its environment?

The ability of a living organism to respond to its environment is best defined by reactivity. Reactivity refers to how an organism interacts with external stimuli, such as changes in temperature, light, or the presence of other organisms. This ability enables organisms to make immediate adjustments or responses in order to survive and thrive in their surroundings.

For instance, when exposed to sudden temperature changes, many organisms will alter their behavior or physiological processes to cope with the new conditions. This immediate responsiveness is a fundamental characteristic of life and is essential for day-to-day survival.

In contrast, homeostasis pertains to the maintenance of a stable internal environment within an organism despite fluctuations in the external environment. Adaptation refers to the long-term evolutionary changes that enhance species' survival in response to environmental pressures over generations. Feedback mechanisms are processes that regulate biological functions, often involving a system of checks and balances within an organism. While all these concepts relate to how life interacts with its environment, reactivity specifically highlights the immediate and direct responses to environmental changes.