Lecture Script:

Today, we are going to explore the concept of circadian rhythms in human biology. Circadian rhythms are 24-hour cycles that are part of the body's internal clock, running in the background to carry out essential functions and processes. One of the most important and well-known circadian rhythms is the sleep-wake cycle. This cycle is influenced by external cues like sunlight and temperature. For instance, exposure to natural light helps regulate the production of melatonin, a hormone that makes you feel sleepy. When the sun sets, melatonin levels increase, prompting the body to prepare for sleep. Conversely, exposure to bright light during the day can help improve alertness and mood. These rhythms are crucial because they regulate numerous bodily functions, including hormone release, eating habits, and digestion.

Key Points:

• Circadian rhythms are 24-hour cycles in the body’s internal clock.
• They play a key role in the sleep-wake cycle.
• External cues like sunlight influence these rhythms.
• Example: Sunlight affects melatonin production, impacting sleep.
• They regulate various functions such as hormone release and digestion.

Sample Answer:

The topic discussed is circadian rhythms, which are 24-hour cycles in our bodies. The main idea is that these rhythms are crucial for regulating essential functions, especially the sleep-wake cycle. For example, sunlight influences these cycles by affecting melatonin production, which helps us feel sleepy at night and awake during the day. Understanding these rhythms is important because they also regulate other bodily functions like hormone release and digestion. In conclusion, maintaining regular circadian rhythms is vital for overall health and well-being.

This structured content provides a comprehensive overview of circadian rhythms, ideal for a TOEFL Speaking Type 4 practice set, with an academic tone and clear organization using HTML tags.