小編寄語：英語四級六級考試，閱讀是不可或缺的一大部分，生詞多，理解難，時間少，是不少考生抱怨的問題。要想在考場上做好閱讀理解，必須在平常多閱讀，掌握新詞匯，提高閱讀速度。而滬江小編就為大家準備了閱讀材料系列，供大家練習(xí)。

我們的這個閱讀系列旨在為大家提供一些閱讀材料，不一定跟四六級考試的難度、篇幅、內(nèi)容完全一樣。對于很多童鞋糾結(jié)這是四級還是六級范圍的閱讀，其實沒有必要。如果大家覺得比較簡單，就當作泛讀材料了解了解，認識幾個新單詞或新表達方式也不錯。如果大家覺得這些材料理解上有難度，不妨當做挑戰(zhàn)自己的拔高訓(xùn)練，希望大家都有進步^^

【今日推薦閱讀】

NASA-Funded Research Discovers Life Built With Toxic Chemical

NASA-funded astrobiology research has changed the fundamental knowledge about what comprises all known life on Earth.?

Researchers conducting tests in the harsh environment of Mono Lake in California have discovered the first known microorganism on Earth able to thrive and reproduce using the toxic chemical arsenic. The microorganism substitutes arsenic for phosphorus in its cell components.?

"The definition of life has just expanded," said Ed Weiler, NASA's associate administrator for the Science Mission Directorate at the agency's Headquarters in Washington. "As we pursue our efforts to seek signs of life in the solar system, we have to think more broadly, more diversely and consider life as we do not know it."

This finding of an alternative biochemistry makeup will alter biology textbooks and expand the scope of the search for life beyond Earth. The research is published in this week's edition of Science Express.

Carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur are the six basic building blocks of all known forms of life on Earth. Phosphorus is part of the chemical backbone of DNA and RNA, the structures that carry genetic instructions for life, and is considered an essential element for all living cells.

Phosphorus is a central component of the energy-carrying molecule in all cells (adenosine triphosphate) and also the phospholipids that form all cell membranes. Arsenic, which is chemically similar to phosphorus, is poisonous for most life on Earth. Arsenic disrupts metabolic pathways because chemically it behaves similarly to phosphate.?

"We know that some microbes can breathe arsenic, but what we've found is a microbe doing something new -- building parts of itself out of arsenic," said Felisa Wolfe-Simon, a NASA Astrobiology Research Fellow in residence at the U.S. Geological Survey in Menlo Park, Calif., and the research team's lead scientist. "If something here on Earth can do something so unexpected, what else can life do that we haven't seen yet?"

The newly discovered microbe, strain GFAJ-1, is a member of a common group of bacteria, the Gammaproteobacteria. In the laboratory, the researchers successfully grew microbes from the lake on a diet that was very lean on phosphorus, but included generous helpings of arsenic. When researchers removed the phosphorus and replaced it with arsenic the microbes continued to grow. Subsequent analyses indicated that the arsenic was being used to produce the building blocks of new GFAJ-1 cells.?

The key issue the researchers investigated was when the microbe was grown on arsenic did the arsenic actually became incorporated into the organisms' vital biochemical machinery, such as DNA, proteins and the cell membranes. A variety of sophisticated laboratory techniques was used to determine where the arsenic was incorporated.

The team chose to explore Mono Lake because of its unusual chemistry, especially its high salinity, high alkalinity, and high levels of arsenic. This chemistry is in part a result of Mono Lake's isolation from its sources of fresh water for 50 years.?

The results of this study will inform ongoing research in many areas, including the study of Earth's evolution, organic chemistry, biogeochemical cycles, disease mitigation and Earth system research. These findings also will open up new frontiers in microbiology and other areas of research.

"The idea of alternative biochemistries for life is common in science fiction," said Carl Pilcher, director of the NASA Astrobiology Institute at the agency's Ames Research Center in Moffett Field, Calif. "Until now a life form using arsenic as a building block was only theoretical, but now we know such life exists in Mono Lake."?

The research team included scientists from the U.S. Geological Survey, Arizona State University in Tempe, Ariz., Lawrence Livermore National Laboratory in Livermore, Calif., Duquesne University in Pittsburgh, Penn., and the Stanford Synchroton Radiation Lightsource in Menlo Park, Calif.?

NASA's Astrobiology Program in Washington contributed funding for the research through its Exobiology and Evolutionary Biology program and the NASA Astrobiology Institute. NASA's Astrobiology Program supports research into the origin, evolution, distribution, and future of life on Earth.

文章內(nèi)容講解及閱讀技巧介紹戳這里>>

【內(nèi)容簡介】

文章第一段以一句話簡潔宣布美國宇航局有了科學(xué)新發(fā)現(xiàn)。

接著，文章描述了美國宇航局這項發(fā)現(xiàn)的意義。

然后，文章也介紹了已知生命的六大基本構(gòu)建元素，而這次新發(fā)現(xiàn)的細菌的成分如何。詳細解釋了為什么這是一項全新發(fā)現(xiàn)，并引用了美國宇航局研究員的話語告訴我們這項微生物的不同之處以及生命的未知神奇。

最后，文章詳細介紹了這次發(fā)現(xiàn)的微生物以及該研究成果將來的應(yīng)用領(lǐng)域。