托福听力课外资料练习：科学美国人60秒细菌基本构成元素相关内容分享

2017年07月18日17:42 来源：小站整理: 参与（2）阅读（3376）

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在托福听力考试的备考过程中，科学美国人60秒相信大家一定用得比较多，那么大家平时是如何利用这个课外资料的呢?这里小编整理了科学美国人60秒：细菌基本构成元素相关的内容分享，大家一起来学习一下吧。

科学美国人60秒听力练习：细菌基本构成元素

科学美国人60秒英文文本

A bacterium has been discovered that can substitute arsenic for phosphorus in fundamental life chemistry. Christopher Intagliata reports

Life on Earth requires six basic ingredients—carbon, hydrogen, nitrogen, oxygen, sulfur and phosphorus. Those six elements are the building blocks for DNA and RNA, along with proteins and fats. Which means they're essential for life—as we know it. But it might be time to update that list. Because scientists have found a bacterium that can do without phosphorus—live on arsenic instead.

The researchers had a hunch a bug like this might exist, because arsenic has some chemical properties in common with phosphorus. So they collected mud from California's Mono Lake, where the waters are naturally salty, and laced with arsenic. Back in the lab, they cultured microbes from that mud. But instead of adding phosphorus to the cultures to help the bugs grow, they added varying levels of arsenic.

One bacterial strain continued to thrive. And tests confirmed that the organisms compensated for the lack of phosphorus by building their DNA with arsenic instead. The research appears in the journal Science. [Felisa Wolfe-Simon et al., "A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus"]

This is the first known life form that seems to be able to swap out one of life's fundamental building blocks with another element. So for astrobiologists hunting for life in space, don’t rule out places filled with poison.