The term that refers to the ability of organisms to react to changes in the environment is:

The correct answer is responsiveness.

Explanation:

All the organisms react to amendments in their environment. These reactions can take place due to heredity, by learned experience, or adaptation. Collectively, the tendency of the organism to react with the changes in the environment is termed as responsiveness.  

A response can be a spontaneous action, an instantaneous or decisive behavior. Evolution is a gradual, however, more persistent form of responsiveness.  

the sphincter muscles at the end of the digestive tract is the anus.