考研英语作文美文范例指南

　　考生们在考研英语的复习期间，要找到英语作文的写作方法，可以参考一些美文范例。小编为大家精心准备了考研英语作文美文参考资料，欢迎大家前来阅读。

考研英语作文美文范例指南

　　考研英语作文美文范例：盐与新陈代谢

　　Just how salt became so crucial to our metabolism is a mystery; one appealing theory traces our dependence on it to the chemist ry of the late Cambrian seas. It was there, a half billion years ago, that tiny metazoan organisms first evolved systems for sequestering and circulating fluids. The water of the early oceans might thus have become the chemical prototype

　　for the fluids of all animal life - the medium in which cellular operations could continue no matter how the external environment changed. This speculation is based on the fact that, even today, the blood serums of radically divergent species are remarkably similar. Lizards, platypuses, sheep, and humans could hardly be more different in anatomy or eating habits, yet the salt content in the fluid surrounding their blood cells is virtually identical. As early marine specics made their way to fresh water and eventually to dry land, sodium remained a key ingredient of their interior, if not their exterior,milieu. The most successful mammalian species would have been those that developed efficient hormonal systems for maintaining the needed sodium concentrations. The human body, for example, uses the hormones renin, angiotensin, and aldosterone to retain or release tissue fluids and blood plasma. The result, under favorable conditions, is a dynamic equilibrium in which neither fluid volume nor sodium concentration fluctuates too dramatically. But if the body is deprived of salt, the effects soon become dangerous, despite compensatory mechanisms.

　　全文翻译：盐与新陈代谢盐为何成为人类新陈代谢的关键是一个谜;一个富有吸引力的理论认为我们对盐的依赖可从寒武纪海洋的化学变化中得到线索。五亿年前，就是在那里，微小的后生动物首先进化成与外隔绝的循环液体系统。因此，早期海洋里的水可能是所有动物体内液体的化学原型--一个无论外界环境如何改变，其细胞活动仍将继续的环境。这个设想是建立这一事实基础上：即使是在今天，物种迥异的'众多动物血清非常相似。蜥蜴、鸭嘴兽、绵羊和人类，在解剖学和饮食习惯上完全不同，但细胞周围的液体中的盐含量却基本上是相等的。在海洋生物向淡水区域并最终向陆地移动的过程中，盐始终是它们生存环境--如果不是外部环境，其码也是内部环境中的关键成份。最高级的哺乳类动物为保持所需的盐浓度而进化出了高效的内分泌系统。例如，人体为了保留或释放组织液体和血浆而使用高血压蛋白原酶、血管紧张素、醛固酮等激素。这样在有利的环境下，液体与其中盐浓度之间形成的动态平衡，两者均不致出现大起大落。但如果身体里丧失了的盐分，尽管有各种的补偿机制，后果将马上极其危险。

　　考研英语作文美文范例：油和水

　　To understand the emulsifying process, we must first accept the scientific principle that oil and water do not naturally mix. Quite literally, they find each other's presence repulsive. A good illustration of this aversion is homemade oil and vinegar salad dressing.When you shake or beat your salad dressing, you do more than disperse the oil throughout the vinegar: you also break down the oil into droplets minute enough to remain temporarily suspended in the vinegar (which from now on we will call water, because that tart condiment is in effect mainly water). The second you stop agitating the dressing, the oil droplets start to combine into units too large to be suspended in the water, and thus slither their way upward, separating from the water in the process. The oil rises to the top and the water sinks because oil has a lower specific density than water. If you want a stable emulsion, you need an emulsifying agent which prevents the oil droplets from combining into larger units. Emulsifying agents occur naturally in many animal substances including egg yolks and milk. An emulsifying agent helps to keep the oil particles from combining in three basic ways. First, the agent coats the oil, serving as a physical barrier between the droplets. Second, it reduces the water's surface tension, which, in turn, reduces the water's ability to repulse oil. Third, the agent gives the surfaces of the oil droplets identical electrical charges; since like charges repel each other the

　　droplets repel each other.

　　全文翻译：油和水为理解乳化过程的发生，我们必须首先认识到这样一条科学原理：水和油不能自然混合，它们实实在在互相排斥。家制的油醋沙拉调料就是一个好例子。当你搅拌沙拉调料时，你不仅使油扩散到醋里，而且使油滴被搅得很小可以悬浮在醋中(自此我们改称它为水，因为事实上这种酸性调味品的主要成份就是水)。一旦你停止了搅动，油滴就会凝聚，大到再也不能悬浮在水中时，它们就向上滑动出来而与水分离了。因为油的密度小，所以油会浮在水上。如果想得到稳定的乳化，就需要一种乳化剂。它可以不让油形成大的油滴。自然界中，很多动物体中含有乳化剂，如蛋黄和牛奶。乳化剂可以从以下三方面阻止油滴凝聚。一、乳化剂包裹住油滴，在油滴间形成一道物质屏障。二、乳化剂降低水的表面张力，从而降低了水排斥油的能力。三、乳化剂使油滴表面带上了同种电荷，因为同种电荷互相排斥，油滴之间也相互排斥。