Which of the following statements is true regarding the presence of alcohol within the human body?

• A. Alcohol cannot cross the blood-brain barrier.
• B. Alcohol is primarily metabolized in the liver by the enzyme alcohol dehydrogenase.
• C. Alcohol is stored in fat cells for long-term energy use.
• D. Alcohol is excreted unchanged in large amounts through urine.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the question and identify the key concepts involved. The problem is asking about the behavior and metabolism of alcohol in the human body, specifically focusing on its interaction with the liver, fat cells, blood-brain barrier, and excretion.
2. Step 2: Recall the biological process of alcohol metabolism. Alcohol is primarily metabolized in the liver by the enzyme alcohol dehydrogenase, which converts ethanol into acetaldehyde, a toxic intermediate, and then into acetate, which can be further processed for energy.
3. Step 3: Evaluate the statement about alcohol crossing the blood-brain barrier. Alcohol is a small, non-polar molecule, which allows it to easily cross the blood-brain barrier and affect the central nervous system, leading to its intoxicating effects.
4. Step 4: Analyze the statement about alcohol being stored in fat cells. Alcohol is not stored in fat cells for long-term energy use. Instead, it is metabolized and used immediately for energy or excreted from the body.
5. Step 5: Examine the statement about alcohol excretion. Alcohol is not excreted unchanged in large amounts through urine. Only a small percentage of alcohol is excreted unchanged through breath, sweat, and urine; the majority is metabolized in the liver.