Advanced Placement (AP) Biology Practice Exam

Juxtacrine signaling is best described as:

1. A signal that can travel long distances

2. A type of signaling requiring physical contact between cells

3. A process that affects cells in a local area

4. Signaling through the bloodstream

The correct answer is: A type of signaling requiring physical contact between cells

Juxtacrine signaling refers to a form of cell communication in which signals are transmitted between cells that are in direct contact with one another. This signaling is characterized by the need for physical interaction and often involves the binding of membrane-bound ligands on one cell to receptors on an adjacent cell. This type of signaling is crucial in processes such as embryonic development and immune responses, where cellular interactions are pivotal for proper function and regulation. The concept highlights the importance of proximity in juxtacrine signaling, distinguishing it from other types of signaling such as paracrine (involving nearby cells without direct contact) or endocrine signaling (which involves hormones traveling through the bloodstream over long distances). This direct cell-to-cell communication allows for precise and immediate responses, making it essential for various biological processes.