托福听力

🎧 听力原文

Narrator: Listen to part of a lecture in a biology class. Professor: Today we're going to talk about a fascinating adaptation in desert plants, specifically the saguaro cactus. As you know, deserts are harsh environments with extreme temperatures and scarce water. The saguaro has evolved several strategies to survive. First, its accordion-like pleats allow it to expand and store water when it rains, and then slowly contract as it uses that water during dry periods. Second, its shallow, wide-spreading root system can quickly absorb surface moisture from brief rain showers. But perhaps the most surprising adaptation is its growth rate. You might think that in such a dry place, plants would grow quickly when water is available. However, the saguaro grows very slowly—only about an inch per year in its first decade. This slow growth is actually an advantage because it allows the plant to invest energy in developing a strong, thick outer skin that reduces water loss. Also, the saguaro doesn't produce its first flowers until it's about 50 to 75 years old. This delayed reproduction ensures that the plant has enough stored water and energy to support the flowers and fruits, which are crucial for attracting pollinators like bats and birds.