Advanced Placement (AP) Biology Practice Exam

Which of the following describes local regulators?

1. Chemical signals that travel long distances through the bloodstream.

2. Chemical signals that act on the secreting cell.

3. Chemical signals that diffuse over short distances.

4. Chemical signals that coordinate systemic responses.

The correct answer is: Chemical signals that diffuse over short distances.

Local regulators are indeed characterized as chemical signals that diffuse over short distances. They are typically released by cells and have effects on neighboring cells within the immediate environment. This local action is crucial for processes such as paracrine signaling, where a cell communicates with nearby cells to coordinate local responses, or autocrine signaling, where a cell influences its own activity. In this context, local regulators are pivotal for cellular communication in tissues, allowing for quick and localized responses to changes in the environment or in cellular conditions. Examples include growth factors, neurotransmitters, and prostaglandins, which all exert their effects within a limited range. The other descriptions do not align with the definition of local regulators. While some chemical signals do travel long distances through the bloodstream, that describes hormones rather than local regulators. The notion that they act solely on the secreting cell pertains to autocrine signals but does not encompass the broader category of local regulators that can influence neighboring cells. Finally, the concept of coordinating systemic responses is indicative of hormones that operate on a larger scale compared to the localized action of local regulators.