OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What is one example of a stimulant?

1. Heroin

2. Alcohol

3. Caffeine

4. Marijuana

The correct answer is: Caffeine

Caffeine is a classic example of a stimulant, a substance that increases activity in the central nervous system. It enhances alertness, reduces fatigue, and can improve concentration and focus. Caffeine achieves these effects by blocking adenosine receptors in the brain, which normally promote sleep and relaxation. As a result, when you consume caffeine, such as in coffee or tea, you can experience increased energy levels and heightened mental acuity. In contrast, the other substances listed have different classifications. Heroin is classified as an opioid and is known for its depressant effects on the nervous system, leading to pain relief and a sense of euphoria, but also significant sedation. Alcohol is also a depressant that primarily inhibits central nervous system activity, resulting in relaxation and impaired function. Marijuana has complex effects but is often categorized as having both depressant and hallucinogenic properties, rather than being classified strictly as a stimulant.