OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What defines a stimulus in a biological context?

1. A change in behavior

2. A change in the environment

3. A response to an action

4. A fixed biological condition

The correct answer is: A change in the environment

A stimulus in a biological context is specifically defined as a change in the environment that can provoke a response from an organism. This could include various factors such as temperature changes, light intensity, or the presence of chemicals, which can trigger sensory receptors and lead to a physiological response. Option B is fundamental because it highlights that stimuli are external or internal signals that organisms detect, which then leads to a series of reactions or behaviors. For instance, the heat from a flame (stimulus) may cause an individual to move their hand away to avoid pain. In contrast, the other options do not accurately encompass what a stimulus is. A change in behavior is an effect that occurs after a stimulus has been detected and acted upon, a response to an action also arises after the initial detection of a stimulus rather than defining it, and a fixed biological condition does not involve change or variability that typically characterizes a stimulus.