趣谈英语：咖啡因的那些事-Caffeine Is A Natural Pesticide

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caffeine: a drug found in some plants, including coffee seeds and tea leaves

pesticide: a substance that keeps insects or harmful materials away from a plant

alert: awake and paying attention

ward off: to keep away something harmful

Caffeine Is A Natural Pesticide

Caffeine wakes us up and helps us stay alert. Many people rely on a caffeine kick a few times a day. In fact, coffee and tea are the most popular beverages in the world, making caffeine the most popular drug. Caffeine is found in the seeds, leaves, and fruit of certain plants. Have you ever wondered why caffeine exists in coffee seeds and tea leaves? Studies have shown that caffeine is a natural pesticide. It gives off a bitter odour to ward off or kill insects that come to feed on it. While caffeine is generally safe for humans, it can be toxic to pets and should be kept away from cats, dogs, and birds.