2017 考博英语 阅读题源经济学人文章每日精析（十三）

考博英语阅读大部分博士研究生招生院校都使用《经济学人》杂志文章作为题源，考博信息网|http://www.kaoboinfo.com教育考博频道为考博生们将其中的文章进行深度分析，希望能提高大家的考博英语阅读水平，读懂长难句。

Waste not, want not勿浪费，勿奢侈

One fish’s excretions are another’s vital resource垃圾是放错地方的资源

Oct 29th 2016 | From the print edition2016年10月29日 | 摘自印刷版

Is that ammonia I sniff我闻到的是氨气吗

Ammonia：n. 氨

AMMONIA is as repulsive to most marine animals as it is to land-lubbing ones—and for good reason. It is extremely toxic. But there is an exception. Far from being repelled by ammonia, sharks are actually attracted to it. The longtime assumption has been that this is because it is a waste product, voided into the water by fish and other creatures, that signals the presence of potential prey. But Chris Wood and Marina Giacomin of the University of British Columbia, in Vancouver, think there may be more to it than this. As they describe in the Journal of Experimental Biology, they suspect that for sharks, ammonia is itself a useful resource.

有充分的理由证明，无论是对大多数海洋动物或者是陆生动物来说，氨气都是非常令人讨厌的。并且它毒性很强，不过也有例外，比如鲨鱼就不讨厌氨气，并且十分喜欢它。对此，长时间以来有一个假说：因为氨气是废气，鱼类和其他生物都会在水中排放它，这也使得氨气成为了潜在猎物存在的信号。不过来自温哥华英属哥伦比亚大学的Chris Wood 和 Marina Giacomin却认为事实远非如此。他们在《实验生物学期刊》发表了论文，文中论述到他们怀疑对鲨鱼来说，氨气本身就是一种有用的资源。

Repulsive：adj. 排斥的;令人厌恶的

All animals make ammonia. It is a compound of nitrogen and hydrogen produced by the breakdown of amino acids, the building blocks of proteins. Marine creatures can flush it directly into the sea (fish do so through their gills), since it is soluble in water. Land animals often add carbon and oxygen to convert it into urea, which is far less toxic, and store the result in solution in a bladder, for periodic evacuation. Sea creatures can make urea too, though—and in sharks this molecule, which they synthesise in their gills, plays a crucial role in stabilising the salinity of their tissues.

所有的生物体内都会生成氨气。它是氨基酸(组成蛋白质的基石)分解出的氮和氢化合物。因为氨气溶于水，所以海洋生物能直接把它排放到海里(鱼类通过鱼鳃排放)。陆生动物通常会通过添加碳元素和氧元素合成尿素(其毒性远没有氮气强)之后，将它们通常储存在膀胱中，并且会定期地排放出体外。海洋生物也能生成尿素，这种分子在平衡鲨鱼身体组织中盐分的稳定方面发挥了重要的作用。

Compound：n. 化合物;混合物amino acid：氨基酸bladder：n. 膀胱evacuation：n. 排泄

Dr Wood and Ms Giacomin knew from the work of others that sharks forced to swim in water containing unnaturally high concentrations of ammonia absorb the chemical into their gills, convert it into urea and then expel that urea back into the water. The presumptionwas that this was an anti-poisoning mechanism. That, though, is a slightly odd idea. In the wild, unconfined by an experimenter’s tank, it would surely be simpler and safer for a shark to swim away from the dangerous area and avoid the problem altogether. The two researchers therefore wondered if what had been seen in these previous experiments was really an accidental consequence of something else. Given urea’s role in shark salinity-stabilisation (a role which it does not play in other groups of fish), they wondered if the animals’ eagerness to find water with lots of ammonia in it was as much to do withreplenishing their urea supplies as with locating prey. They therefore decided to run some experiments of their own.

Wood博士和Giacomin小姐从别人的研究中得知，鲨鱼会迫使自己在氨气浓度高的地方游动，它们会用鳃吸收氨气，然后将其转化成尿素排出体外。因此两个研究员想知道，先前实验的是否只是某个偶然事件的造成的。考虑到尿素在鲨鱼体内充当着稳定盐分的角色(这在别的鱼类中是不存在的)两个研究员怀疑动物寻找含有大量氨的水域是来补充体内尿素而非定位猎物。因此他们自己亲自做些实验。

Presumption：n. 推测Replenish：v. 补充

To this end, they exposed ten Pacific spiny dogfish (a type of small shark easily maintained in the laboratory) to ammonia concentrations ranging from 100 micromoles per litre (μmol/l), a level commonly found in the wild, to 1,600 μmol/l, an unnaturally high level, while monitoring the water’s chemistry closely.

为此，他们将十头太平洋白斑角鲨(这是一个小型鲨鱼种类，容易在实验室养殖)放在了氨浓度是100μmol/l(一般的海水氨气浓度)到1600μmol/l(实验的氨气浓度)的水中，并且密切监测水中的化学成分。

To this end：为了这个目的spiny dogfish：白斑角鲨

Whatever the initial level of ammonia, they found, that substance’s concentration began declining almost as soon as the sharks were put into the tank. The animals were, indeed, absorbing it. They were not, though, automatically excreting the resulting urea. Levels of this in the water rose only when the dogfish were exposed to ammonia concentrations of 800 μmol/l or more. And a closer look at the animals’ gills and blood confirmed that they were retaining urea.

他们发现，无论是起始氨气浓度是多少，其浓度从鲨鱼放入水槽那一刻就开始下降。鲨鱼确实在吸收氨气。尽管它们不以尿素的形式排泄出来。只有当白斑角鲨被放在800μmol/l或以上的氨气浓度水中时，水里的氨气浓度才会上升。并且仔细检测动物的鳃和血液后，证实它们的确保留着尿素。

All this makes perfect sense. The importance of urea to shark physiology means they have to make it from something. Amino-acid breakdown, the alternative source of its central element, nitrogen, requires otherwise-valuable proteins. Calculations performed by Dr Wood and Ms Giacomin suggest dogfish swimming in ammonia-rich waters would be able to scavenge from those waters almost a third of the nitrogen they need to make urea. Thatadds up to a tidy saving in protein. So, sharks may well be driven by appetite to swim towards places where their prey have been releasing large amounts of waste ammonia. But, contrary to past theories, the appetite that takes them there may really be for the waste itself.

所有这一切完全合情合理。尿素对于鲨鱼生理机能的重要性意味着它们不得不在从其他地方获取氨气。中心元素氮的另一来源是氨基酸水解(还需要别的珍贵蛋白质)。Wood博士和Giacomin小姐通过计算得出，白斑角鲨在富含氨元素的水中游动可能能够吸收水中大概三分之一的氮用来制造尿素，并将其储存在蛋白质中。所以，鲨鱼可能更倾向于在那些猎物释放了大量氨的地方游动。不过，与过去结论相反的是，驱使它们到那里去的可能真是其他动物排出的废气。

Scavenge：vt. 以……为食add up：v. 合计