Advanced Placement (AP) Biology Practice Exam

What characterizes paracrine signaling?

1. Signals act on the secreting cell itself.

2. Signals act on neighboring cells.

3. Signals require blood to travel long distances.

4. Signals induce a systemic response throughout the body.

The correct answer is: Signals act on neighboring cells.

Paracrine signaling is characterized by the action of signals on neighboring cells. In this type of signaling, cells release signaling molecules into the local environment that affect nearby target cells, allowing for communication and coordination within tissues and organs without requiring the signals to enter the bloodstream. This localized effect is crucial for processes such as tissue development, immune responses, and the regulation of cellular activities in a specific area. The other options do not accurately describe paracrine signaling. For instance, signals that act on the secreting cell itself pertain to autocrine signaling, where a cell influences itself. The requirement of blood for signals to travel long distances relates to endocrine signaling, which involves hormones that must enter the circulatory system to reach distant targets. Lastly, signals inducing a systemic response throughout the body aligns more closely with endocrine signaling, particularly where hormones have widespread effects, rather than the localized effects seen in paracrine signaling.