2015年職稱英語考試理工類完形填空二級文章(5)

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　　2015年職稱英語考試理工類完形填空二級文章(5)

　　Wonder Webs

　　Spider webs are more than homes, and they are ingenious traps. And the world’s best web spinner may be the Golden Orb Weaver spider. The female Orb Weaver spins a web of fibers thin enough to be invisible to insect prey, yet __1_tough_ enough to snare a flying bird without breaking.

　　The secret of the web’s strength? A type of super-resilient __2_silk_ called dragline. When the female spider is ready to __3_weave_ the web’s spokes and frame, she uses her legs to draw the airy thread out through a hollow nozzle in her belly. Dragline is not sticky, so the spider can race back and forth along __4_it_ to spin the web’s trademark spiral.

　　Unlike some spiders that weave a new web every day, a Golden Orb Weaver __5_reuses_ her handiwork until it falls apart, sometimes not for two years. The silky thread is five times stronger than steel by weight and absorbs the force of an impact three times better than Kevlar, a high-strength human-made __6_material_ used in bullet-proof vests. And thanks to its high tensile strength, or the ability to resist breaking under the pulling force called tension, a single strand can stretch up to 40 percent longer than its original _7_length_ and snap back as well as new. No human-made fiber even comes _8_close_.

　　It is no __9_wonder_ manufacturers are clamoring for spider silk. In the consumer pipeline: High-performance fabrics for athletes and stockings that never run. Think parachute cords and suspension bridge cables. A steady __10_supply_ of spider silk would be worth billions of dollars ? but how to produce it? Harvesting silk on spider farms does not __11_work_ because the territorial arthropods have a tendency to devour their neighbors.

　　Now, scientists at the biotechnology company Nexia are spinning artificial silk modeled after Golden Orb dragline. The __12_first_ step: extract silk-making genes from the spiders. Next, implant the genes into goat egg cells. The nanny goats that grow from the eggs secrete dragline silk proteins in their __13_milk_. “The young goats pass on the silk-making gene without __14_any_ help from us,” says Nexia president Jeffrey Turner. Nexia is still perfecting the spinning process, but they hope artificial spider silk will soon be snagging customers __15_as fast as_ the real thing snags bugs.

　　奇妙的網(wǎng)

　　蜘蛛網(wǎng)對蜘蛛來說不僅僅是家，它們還是奇妙的引蟲入網(wǎng)的陷阱。世界最棒的織網(wǎng)者可能是Goldern Orb Weaver的蜘蛛。雌性的Orb Weaver可以織出很細的絲，連被捕的昆蟲都看不見。但卻是堅韌得可以將一只飛入網(wǎng)中的鳥纏住而不弄斷。

　　那么蜘蛛網(wǎng)為何有如此強的力度呢?有一種網(wǎng)絲有超強的彈力，叫做蜘蛛的避敵絲。當雌性的蜘蛛準備編織蛛網(wǎng)的幅條和框架時，它就用腿從一個空的噴嘴里勾出輕飄飄的絲線，放到肚子里面。避敵絲不粘，因此蜘蛛可以沿著它來回活動編織，從而來編織網(wǎng)的標志性螺旋。

　　與某些種類的蜘蛛不同，它不用每天織新網(wǎng)，只要網(wǎng)不破，就能一直用下去，有時一用就兩年。柔軟如絲的蛛絲的強度比相同重量的鋼絲大五倍。同時可以承受的力度比一種高強度的防彈衣的人工材料大三倍多。同時由于它有很強的張力，或者說一種能夠抵住被弄斷的往下的拉力。一根單線可以伸長至比原始長度長40%以上，然后重新彈回至原來的長度，還像新的一樣。沒有一種人造纖維可以與它相媲美。

　　因此，生產(chǎn)者們強烈要求蛛絲也就不足為奇了。在消費這一方面，人們強烈要求的是高質量的運動服和永不脫絲的長襪。試想一下另外如降落傘繩索和吊橋上的繩索。如果有穩(wěn)定的蛛絲的供應，它將是一個價值上億的產(chǎn)業(yè)，但問題是怎么樣才能生產(chǎn)出穩(wěn)定的蛛絲呢?試圖以養(yǎng)蛛場收獲蛛絲是行不通的，因為生長在那塊地方的節(jié)肢動物有可能會吞掉它們的這些“鄰居”。

　　現(xiàn)在，生物工藝公司“Nexifa”的科學家們正在研制一種仿制Goldorn Orb避敵絲的人工絲。第一步驟：從蜘蛛身上抽取制絲的基因，然后，將這些基因植入山羊的卵細胞中。由這些卵細胞發(fā)育生的雌山羊會在羊奶中分泌一種帶絲的蛋白質�！癗exia”公司總裁吉弗利?特納說：“這些幼山羊不須任何我們的幫助就可以將制絲基因遺傳過去。”“Nexia”繼續(xù)在完善它的制絲過程。但是他們希望這種人造蜘蛛絲能盡快地吸引住顧客，就像真正的蛛絲抓住昆蟲一樣。是因為它對天體有影響，而不是它可以被看到或測出。

　　但是在宇宙中最具決定性力量的是“暗能量”。天文學家說，這是一種引起宇宙中星系以越來越快的速度分開的力量。

　　有一位科學家說，很明顯，暗物質和暗能量之間開展了一場萬有引力間的拔河比賽，最后，暗能量獲勝。