The ability of an organism to detect and respond to environmental changes is called sensitivity or irritability.

Here's why:

* Sensitivity: This term highlights the organism's ability to perceive changes in its surroundings. It emphasizes the organism's capacity to "sense" the environment.

* Irritability: This term emphasizes the organism's ability to react to stimuli, often in a way that helps it survive.

Both terms are used to describe the same fundamental property of living things - the ability to interact with their environment.