第一篇
TOPIC 细胞学发展史Cell Theory
讲细胞学整个理论的完善过程，涉及多位科学家的研究。先讲列文虎克发现细胞但仍延续旧理论很可惜(有题)。后面说到前人没有发现细胞的原因(有题)，又有个人终于发现细胞推翻前理论，并提出了一个假设(有题)。还提到了显微镜等科技进步。
解析：本文属生物学和历史学话题结合文章，重点围绕微生物内容考察。发展史类型文章重点要关注两点，第一是时间节点，第二是观点评价。由这两点可以得知文章前后之间的关联。
Cell theory
The cell was first seen by Robert Hooke in 1665. He examined (under a coarse, compound microscope) very thin slices of cork and saw a multitude of tiny pores that he remarked looked like the walled compartments a monk would live in. Because of this association, Hooke called them cells, the name they still bear. However, Hooke did not know their real structure or function. Hooke's description of these cells (which were actually non-living cell walls) was published in Micrographia. His cell observations gave no indication of the nucleus and other organelles found in most living cells.
The first person to make a compound microscope was Zacharias Jansen, while the first to witness a live cell under a microscope was Anton van Leeuwenhoek, who in 1674 described the algae Spirogyra and named the moving organisms animalcules, meaning "little animals". Leeuwenhoek probably also saw bacteria. Cell theory was in contrast to the vitalism theories proposed before the discovery of cells.
The idea that cells were separable into individual units was proposed by Ludolph Christian Treviranus and Johann Jacob Paul Moldenhawer. All of this finally led to Henri Dutrochet formulating one of the fundamental tenets of modern cell theory by declaring that "The cell is the fundamental element of organization".
The observations of Hooke, Leeuwenhoek, Schleiden, Schwann, Virchow, and others led to the development of the cell theory. The cell theory is a widely accepted explanation of the relationship between cells and living things. The cell theory states:
l All living things or organisms are made of cells and their products.
l New cells are created by old cells dividing into two.
l Cells are the basic building units of life.
The cell theory holds true for all living things, no matter how big or small. Since according to research, cells are common to all living things, they can provide information about all life. And because all cells come from other cells, scientists can study cells to learn about growth, reproduction, and all other functions that living things perform. By learning about cells and how they function, you can learn about all types of living things. Cells are the building blocks of life
Credit for developing cell theory is usually given to three scientists: Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow. In 1839, Schwann and Schleiden suggested that cells were the basic unit of life. Their theory accepted the first two tenets of modern cell theory (see next section, below). However, the cell theory of Schleiden differed from modern cell theory in that it proposed a method of spontaneous crystallization that he called "free cell formation". In 1855, Rudolf Virchow concluded that all cells come from pre-existing cells, thus completing the classical cell theory. (Note that the idea that all cells come from pre-existing cells had in fact already been proposed by Robert Remak; it has been suggested that Virchow plagiarised Remak.)
第二篇
TOPIC 经济大萧条
讲美国经济大萧条。按时间发展顺序讲，1929前情况，爆发以后情况，中间分两个阶段以及发生原因。然后讲公众对政府和经济的态度有改变，从对政府管控的否定态度转而希望政府干预。因为公众认为investment banker造成了这次危机crisis。
解析：本文属历史类话题，涉及内容是美国近代历史中非常著名的1929-33年经济大萧条。可以看到当涉及历史内容时，经济还是最主要的考察维度。本文结构属描述类文章，。关于大萧条相信很多同学尤其是学习经济金融相关专业的同学一定非常熟悉，下附简单介绍，结合学习了解。
The Great Depression
The Great Depression began in August of 1929, when the United States economy first went into an economic recession. Although the country spent two months with declining GDP, it was not until the Wall Street Crash of October, 1929 that the effects of a declining economy were felt, and a major worldwide economic downturn ensued. The market crash marked the beginning of a decade of high unemployment, poverty, low profits, deflation, plunging farm incomes, and lost opportunities for economic growth and personal advancement. Although its causes are still uncertain and controversial, the net effect was a sudden and general loss of confidence in the economic future.
The usual explanations include numerous factors, especially high consumer debt, ill-regulated markets that permitted overoptimistic loans by banks and investors, and the lack of high-growth new industries, all interacting to create a downw;lard economic spiral of reduced spending, falling confidence, and lowered production.
Industries that suffered the most included construction, agriculture as dust-bowl conditions persisted in the agricultural heartland, shipping, mining, and logging as well as durable goods like automobiles and appliances that could be postponed. The economy reached bottom in the winter of 1932–33; then came four years of very rapid growth until 1937, when the Recession of 1937 brought back 1934 levels of unemployment.
The Depression caused major political changes in America. Three years into the depression, Herbert Hoover lost the 1932 presidential election to Franklin Delano Roosevelt in a sweeping landslide. Roosevelt's economic recovery plan, the New Deal, instituted unprecedented programs for relief, recovery and reform, and brought about a major realignment of American politics.
The Depression also resulted in an increase of emigration of people to other countries for the first time in American history. For example, some immigrants went back to their native countries, and some native US citizens went to Canada, Australia, and South Africa. It also resulted in the mass migration of people from badly hit areas in the Great Plains and the South to places such as California and the North, respectively (see Okies and the Great Migration of African Americans). Racial tensions also increased during this time. By the 1940s immigration had returned to normal, and emigration declined. A well-known example of an emigrant was Frank McCourt, who went to Ireland, as recounted in his book Angela's Ashes.
The memory of the Depression also shaped modern theories of economics and resulted in many changes in how the government dealt with economic downturns, such as the use of stimulus packages, Keynesian economics, and Social Security. It also shaped modern American literature, resulting in famous novels such as John Steinbeck's "The Grapes of Wrath" and "Of Mice and Men".
第三篇
TOPIC Poikilotherm
先介绍三类动物，恒温、变温和时而恒温时而变温。后面讲变温动物怎么调节体温，以及体型大小与体温的关系，比如温度低的时候动物会freeze，用蛇举很多例子。
解析：本文属生物学话题，围绕动物体温展开描述，重点围绕变温动物进行阐述。动物学一直是
poikilotherm
A poikilotherm is an organism whose internal temperature varies considerably. It is the opposite of a homeotherm, an organism which maintains thermal homeostasis. Usually the variation is a consequence of variation in the ambient environmental temperature. Many terrestrial ectotherms are poikilothermic. However some ectotherms remain in temperature-constant environments to the point that they are actually able to maintain a constant internal temperature (i.e. are homeothermic). It is this distinction that often makes the term "poikilotherm" more useful than the vernacular "cold-blooded", which is sometimes used to refer to ectotherms more generally. Poikilothermic animals include types of vertebrate animals, specifically fish, amphibians, and reptiles, as well as a large number of invertebrate animals. The Naked mole rat is the only mammal that is currently thought to be poikilothermic.
For an important chemical reaction, poikilotherms may have four to ten enzyme systems that operate at different temperatures. As a result, poikilotherms often have larger, more complex genomes than homeotherms in the same ecological niche. Frogs are a notable example of this effect, though their complex development is likely more important.
Because their metabolism is variable and generally below that of homeothermic animals, sustained high-energy activities like powered flight in large animals or maintaining a large brain is generally beyond poikilotherm animals. The metabolism of poikilotherms favors strategies such as sit-and-wait hunting over chasing prey for larger animals with high movement cost. As they do not use their metabolisms to heat or cool themselves, total energy requirement over time is low. For the same body weight, poikilotherms need a half to a tenth of the energy of homeotherms.
It is comparatively easy for a poikilotherm to accumulate enough energy to reproduce. Poikilotherms at the same trophic level often have much shorter generations than homeotherms: weeks rather than years. Such applies even to animals with similar ecological roles such as cats and snakes.
This difference in energy requirement also means that a given food source can support a greater density of poikilothermic animals than homeothermic animals. This is reflected in the predator-prey ratio which is usually higher in poikilothermic fauna compared to homeothermic ones. However, when homeotherms and poikilotherms have similar niches, and compete, the homeotherm can often drive poikilothermic competitors to extinction, because homeotherms can gather food for a greater fraction of each day.
Poikilotherms succeed in some habitats, such as islands and hot deserts, or distinct bioregions (such as the small bioregions of the Amazon basin). These biomes often do not have enough food to support a viable breeding population of homeothermic animals. In these habitats, poikilotherms such as large lizards, crabs and frogs supplant homeotherms such as birds and mammals.