托福听力

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Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about a fascinating adaptation in desert plants, specifically the saguaro cactus. The saguaro, which is native to the Sonoran Desert, has evolved several strategies to survive extreme heat and drought. First, its accordion-like pleats allow it to expand and contract as it stores and uses water. After a heavy rain, the saguaro can absorb hundreds of gallons of water, swelling to accommodate the liquid. During dry periods, it slowly uses this stored water, and the pleats shrink. Another key adaptation is its shallow, widespread root system. These roots extend far from the plant, sometimes as far as the cactus is tall, to capture moisture from even light rainfalls. Additionally, the saguaro has a thick, waxy coating on its skin that reduces water loss through evaporation. Finally, its growth pattern is slow but steady; a saguaro may only grow a few inches in its first decade. This slow growth allows it to allocate energy efficiently, ensuring survival in a resource-limited environment. So, these combined features make the saguaro a superb example of desert adaptation.