Advanced Placement (AP) Biology Practice Exam

What is a local regulator in cellular signaling?

1. A molecule that influences distantly located cells

2. A molecule that affects nearby cells where it is secreted

3. A chemical that binds to membrane receptors

4. A phosphatase that reverses signaling effects

The correct answer is: A molecule that affects nearby cells where it is secreted

A local regulator in cellular signaling is described as a molecule that affects nearby cells where it is secreted. This is a key aspect of how local signaling operates within tissues. Local regulators, such as neurotransmitters or growth factors, are often released into the extracellular space and act on adjacent cells, facilitating communication and coordination of biological responses in localized areas. This mechanism allows for quick and efficient signaling between cells in close proximity, which is vital for processes like synaptic transmission in neurons or autocrine signaling where cells respond to substances they have released themselves. In contrast, the other choices pertain to different aspects of cellular signaling. For instance, a molecule influencing distantly located cells describes endocrine signaling, which involves hormones traveling through the bloodstream to target organs. Chemical binding to membrane receptors relates to the specificity of signaling responses but doesn't define the local nature of the regulator. Lastly, phosphatases are enzymes that remove phosphate groups from proteins, involved in reversing the effects of signaling pathways rather than defining what a local regulator is. Understanding these distinctions clarifies the unique role local regulators play in cellular communication.