What effect does elevated alertness have on the body?

Elevated alertness leads to increased readiness to react because it heightens an individual's awareness and responsiveness to their environment. When a person is alert, their sensory perception sharpens, and cognitive functions are enhanced, allowing for quicker decision-making and reaction times. This heightened state is essential, especially in critical situations where prompt action is necessary.

In contrast, the other options describe states typically associated with lower levels of alertness. Improved digestion often occurs in relaxed states where the body is not under stress. Increased relaxation inherently suggests a calming effect that would counteract elevated alertness. Similarly, a reduction in stress levels is generally associated with a relaxed state of being, rather than one characterized by high alertness, which often comes with increased tension and preparedness to respond. Therefore, the option reflecting an increase in readiness to react aligns best with the physiological and psychological effects of being in an alert state.