2011年职称英语理工类完形填空练习题(8)

　　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.
　　奇妙的网 (C)
　　蜘蛛网对蜘蛛来说不仅仅是家，它们还是奇妙的引虫入网的陷阱。世界最棒的织网者可能是Goldern Orb Weaver的蜘蛛。雌性的Orb Weaver可以织出很细的丝，连被捕的昆虫都看不见。但却是坚韧得可以将一只飞入网中的鸟缠住而不弄断。
　　那么蜘蛛网为何有如此强的力度呢？有一种网丝有超强的弹力，叫做蜘蛛的避敌丝。当雌性的蜘蛛准备编织蛛网的幅条和框架时，它就用腿从一个空的喷嘴里勾出轻飘飘的丝线，放到肚子里面。避敌丝不粘，因此蜘蛛可以沿着它来回活动编织，从而来编织网的标志性螺旋。
　　与某些种类的蜘蛛不同，它不用每天织新网，只要网不破，就能一直用下去，有时一用就两年。柔软如丝的蛛丝的强度比相同重量的钢丝大五倍。同时可以承受的力度比一种高强度的防弹衣的人工材料大三倍多。同时由于它有很强的张力，或者说一种能够抵住被弄断的往下的拉力。一根单线可以伸长至比原始长度长40%以上，然后重新弹回至原来的长度，还像新的一样。没有一种人造纤维可以与它相媲美。
　　因此，生产者们强烈要求蛛丝也就不足为奇了。在消费这一方面，人们强烈要求的是高质量的运动服和永不脱丝的长袜。试想一下另外如降落伞绳索和吊桥上的绳索。如果有稳定的蛛丝的供应，它将是一个价值上亿的产业，但问题是怎么样才能生产出稳定的蛛丝呢？试图以养蛛场收获蛛丝是行不通的，因为生长在那块地方的节肢动物有可能会吞掉它们的这些“邻居”。
　　现在，生物工艺公司“Nexifa”的科学家们正在研制一种仿制Goldorn Orb避敌丝的人工丝。第一步骤：从蜘蛛身上抽取制丝的基因，然后，将这些基因植入山羊的卵细胞中。由这些卵细胞发育生的雌山羊会在羊奶中分泌一种带丝的蛋白质。“Nexia”公司总裁吉弗利·特纳说：“这些幼山羊不须任何我们的帮助就可以将制丝基因遗传过去。”“Nexia”继续在完善它的制丝过程。但是他们希望这种人造蜘蛛丝能尽快地吸引住顾客，就像真正的蛛丝抓住昆虫一样。是因为它对天体有影响，而不是它可以被看到或测出。
　　但是在宇宙中最具决定性力量的是“暗能量”。天文学家说，这是一种引起宇宙中星系以越来越快的速度分开的力量。
　　有一位科学家说，很明显，暗物质和暗能量之间开展了一场万有引力间的拔河比赛，最后，暗能量获胜。