การฟัง TOEFL

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Listen to part of a lecture in a biology class. The professor is discussing animal communication. Professor: So we've talked about visual signals and auditory signals in animal communication. Today, I want to focus on chemical communication, specifically pheromones. Pheromones are chemical substances released by an animal that affect the behavior or physiology of others of the same species. One classic example is the alarm pheromone in ants. When an ant is injured, it releases a chemical that alerts nearby ants, causing them to become aggressive and attack. Another example is the sex pheromone in moths. Female moths release a specific chemical to attract males, sometimes from miles away. Interestingly, pheromones can also influence development. In honeybees, the queen produces a pheromone that suppresses the development of ovaries in worker bees, ensuring that only the queen reproduces. So, pheromones are not just for immediate behavior changes; they can have long-term physiological effects as well. Now, let's consider how researchers study these chemicals. They often use gas chromatography to identify the exact compounds, and then test them in controlled experiments. But it's tricky, because animals may respond to mixtures of chemicals rather than single ones.