高中英语听力mp3下载：海洋生物有趣的睡觉习惯

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高中英语听力mp3下载：海洋生物有趣的睡觉习惯

Marine Animals Have Interesting Sleeping Habits

Many people know that marine mammals, like whales, porpoises and dolphins, breathe air, like we do. But, many people don’t know that marine mammals have developed some interesting sleeping habits in order to accommodate their regular trips up to the surface for air. Today, A Moment of Science looks at what its like to sleep with the fishes. No Sleep Tonight

Unlike our own breathing, which does not require

conscious effort, marine mammals must consciously go to the surface of the water to breathe through a blowhole on top of their heads. Because of this, marine mammals don’t sleep for a solid 8 hours a night, the way we do.

Some marine mammals sleep while swimming. Whales nap for brief periods while swimming alongside an alert friend who guides them. In fact, young whales must sleep alongside their mother because the mother’s slipstream actually pulls the calf along： it will sink if the mother stops. Dolphin

Other marine mammals, like dolphins, sleep while floating on the surface of the water or take short catnaps while floating below the surface. Researchers claim that while marine mammals sleep their brain is always partially alert. Aside from these brief naps, dolphins are active most of the night.






Of course, marine mammals are equipped to handle

underwater sleeping. They have proportionately larger lungs, exchange air more fully at each breath, and carry more oxygen in their blood than we do, so they can hold their breath long enough to sleep with the fishes. 海洋生物有趣的睡觉习惯

绝大部分人都知道些海洋哺乳动物，比如鲸鱼，鼠海豚和海豚。它们和我们一样都要呼吸空气。但是绝大部分人都不知道这些哺乳动物已经养成了一些有趣的睡眠习惯，以配合来回水面呼吸空气。今天，科学一刻将探究一下，这些哺乳动物是如何像鱼类一样睡觉的。 今夜无眠

与人类“无意识”呼吸不同，这些动物必须到水面，通过头顶的气孔，实行“有意识”的呼吸。所以，它们不像我们，每晚能够稳定的睡上八小时。

有些海洋哺乳动物边睡觉边游动。对于鲸鱼，只要有同伴放风，并引导着，他们就会边游边打会个盹。实际上，幼鲸必须在母鲸身边睡觉，因为母鲸游动时产生的水流能够推动幼崽向前：如果母鲸停止游动，幼崽就会沉下去。 海豚

而其它海洋哺乳动物，像海豚，睡觉的时候是浮在水面上，打盹的时候就浮在水面下。研究表明，海洋哺乳动物睡觉时，他们部分大

脑依然保持警觉。海豚在晚上，除了打盹，其余时间都处于活跃状态。 当然，也有些海洋哺乳动物具备水下睡觉的水平。相对应地，他们的肺都很大，每次呼吸都能换进更多的空气。他们的血液中的含氧量就比我们的高，这样他们就能长时间屏息，像鱼类一样睡觉。

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