Caffeine is a(n) __________ of adenosine that blocks its receptors from activation.

• A. Inhibitor.
• B. Antagonist.
• C. Agonist.
• D. Activator.

Answer: (B)

Verified step by step guidance

1. Understand the role of adenosine in the body: Adenosine is a neurotransmitter that typically promotes sleep and relaxation by binding to its receptors in the brain.
2. Identify the function of caffeine: Caffeine is known to increase alertness and reduce the feeling of tiredness.
3. Determine how caffeine interacts with adenosine receptors: Caffeine binds to adenosine receptors without activating them, preventing adenosine from binding and exerting its effects.
4. Define the term 'antagonist': In biochemistry, an antagonist is a substance that binds to a receptor and blocks or dampens the biological response, without triggering the receptor's typical action.
5. Conclude that caffeine acts as an antagonist: Since caffeine blocks adenosine from binding to its receptors and does not activate them, it is classified as an antagonist.