Advanced Placement (AP) Biology 2026 – 400 Free Practice Questions to Pass the Exam

The correct answer is paracrine signaling, which involves a cell releasing signaling molecules that diffuse through the extracellular space and affect nearby target cells. This type of signaling is crucial for a variety of processes, including cell growth, differentiation, and immune responses, allowing cells in close proximity to communicate effectively and coordinate their activities.

In paracrine signaling, the signal molecules act locally rather than traveling long distances, which distinguishes it from other types of signaling. For instance, autocrine signaling refers to a cell signaling itself or responding to its own signals, which does not involve nearby cells. Juxtacrine signaling involves direct contact between neighboring cells, meaning the signaling occurs through interactions that require cell-to-cell contact rather than diffusible signals. Synaptic signaling is specific to nerve cells and involves the release of neurotransmitters across a synapse to influence adjacent neurons.

In summary, paracrine signaling is characterized by the release of molecules that affect only nearby cells, facilitating local communication within tissues.