What is the role of an agonist in receptor activity?

• A. Blocks receptor activity
• B. Binds and produces a response
• C. Increases receptor numbers
• D. Decreases receptor sensitivity

Answer: (B)

An agonist plays a critical role in receptor activity by binding to a receptor and eliciting a biological response. This binding can stimulate a direct action through activating the receptor's signal transduction pathways, leading to a physiological effect. For instance, when an agonist binds to a neurotransmitter receptor, it may mimic the action of the natural ligand, such as a neurotransmitter, resulting in effects like increased heart rate or muscle contraction.

This binding is essential for initiating or enhancing the response within a target cell. In contrast, the other options describe different interactions or modifications that do not align with the function of an agonist. Blocking receptor activity pertains to antagonists, which inhibit receptor function rather than activate it, while increasing receptor numbers and decreasing receptor sensitivity refer to cellular adaptations rather than immediate agonist activity. Thus, the primary role of an agonist is to bind and produce a response, making this option the correct answer.