Biology Regents Practice Exam

Which change is an example of a response to a stimulus?

1. The pupil of an eye decreases in size in bright light

2. A leaf absorbs sunlight in the morning

3. The water level of a pond rises on a rainy day

4. A dead tree decays after many years

The correct answer is: The pupil of an eye decreases in size in bright light

The answer provided is a clear example of a response to a stimulus because it describes a physiological reaction that occurs in response to a specific environmental condition. In this case, bright light serves as the stimulus, and the pupil of the eye decreasing in size is the body's response to that stimulus. This process, known as the pupillary light reflex, is a protective mechanism that helps regulate the amount of light that enters the eye, allowing for optimal vision and preventing damage to the retina from excessive light. In contrast, when a leaf absorbs sunlight in the morning, this is a part of the process of photosynthesis and does not occur as a direct response to a variable stimulus—rather, it is an ongoing biological process. The rising water level of a pond on a rainy day is a natural physical occurrence due to the influx of rainwater and does not involve a direct response or adaptation from living organisms. A dead tree decaying over time is a process that is a result of the natural lifecycle and decomposition, unrelated to an immediate stimulus in the environment.