孙晶楠：托福TPO25阅读第三篇(原文+翻译)

　　文/孙晶楠

　　作者简介：北京新航道学校托福阅读主讲，大学英语四、六级写作主讲。 美国Syracuse University交流生，专业英语八级，英语语言文学及人力资源管理双学位，曾担任高校专业英语讲师，并获得高校教师资格证书，专业技术职称，翻译专业资格证书，以及“全国高校中青年骨干教师”称号。对英语学习有独到的见解，擅长在课堂中融入中西方文化知识。理智，风趣。深信“care and diligence bring luck”。

　　ETS发布了TPO25和TPO26，TPO25篇和第二篇的阅读我都给大家翻译并且分享了，剩下的第三篇阅读：The Evolutionary Origin of Plants，本文中笔者继续为大家奉上，希望广大同学参考译文的准备考试。

　　TPO25READING THREE

　　The Evolutionary Origin of Plants

　　The evolutionary history of plants has been marked by a series of adaptations. The ancestors of plants were photosynthetic single-celled organisms that gave rise to plants presumably lacked true roots, stems, leaves, and complex reproductive structures such as flowers. All of these features appeared later in the evolutionary history of plants. Of today’s different groups of algae, green algae are probably the most similar to ancestral plants. This supposition stems from theclose phylogenetic (natural evolutionary) relationship between the two groups. DNA comparisons have shown that green algae are plants’ closest living relatives. In addition, other lines of evidence support the hypothesis that land plants evolved from ancestral green algae used the same type of chlorophyll and accessory pigments in photosynthesis as do land plants. This would not be true of red and brown algae. Green algae store food as starch, as do land plants and have cell walls made of cellulose, similar in composition to those of land plants. Again, the good storage and cell wall molecules of red and brown algae are different.

　　Today green algae live mainly freshwater, suggesting that their early evolutionary history may have occurred in freshwater habitats. If so, the green algae would have been subjected to environmental pressures that resulted in adaptations that enhanced their potential to give rise to land-dwelling or organisms.

　　 The environmental conditions of freshwater habitats, unlike those of ocean habitats, are highly variable.  Water temperature can fluctuate seasonally or even daily and changing level of rainfall can lead to fluctuations in the concentration of chemical in the water or even to period in which the aquatic habitat dries up. Ancient fresh water green algae must have evolved features that enable them to withstand extremes of temperature and periods of dryness.  These adaptations served their descendant well as they invaded land.

　　The terrestrial world is green now, but it did not start out that way. When plants first made the transition ashore more than 400 million years ago, the land was barren and desolate, inhospitable to life. From a plant ’s evolutionary view point, however, it was also a land of opportunity, free of competitors and predators and full of carbon dioxide and sunlight (the raw materials for photosynthesis, which are present in far higher concentrations in air than in water). So once natural selection had shaped the adaptations that helped plants overcome the obstacles to terrestrial living, plants prospered and diversified。

　　When plants pioneered the land, they faced a range of challenges posed by terrestrial environments. On land, the supportive buoyancy of water is missing, the plant is no longer bathed in a nutrient solution, and air tends to dry things out. These conditions favored the evolution of the structures that support the body, vessels that transport water and nutrients to all parts of plant, and structures that conserve water. The resulting adaptations to dry land include some structural features that arose early in plant evolution; now these features are common to virtually all land plant.来源：北京新航道托福 They include roots or root like structures, a waxy cuticle that covers the surfaces of leaves and stems and limits the evaporation of water, and pores called stomata in leaves and stems that allow gas exchange but close when water is scarce, thus reducing water loss. Other adaptations occurred later in the transition to terrestrial life and now wide spread but not universal among plants. These include conducting vessels that transport water and minerals upward from the roots and that move the photosynthetic products from the leaves to the rest of the plant body and the stiffening substance lignin, which support the plant body, helping it expose maximum surface area to sunlight. These adaptations allowed an increasing diversity of plant forms to exploit dry land. Life on land, however, also required new methods of transporting sperm to eggs. Unlike aquatic and marine forms, land plants cannot always rely on water currents to carry their sex cells and disperse their fertilized eggs. So the most successful groups of land plants are those that evolved methods of fertilized sex cell dispersal that are independent of water and structures that protest developing embryos from drying out. Protected embryos and waterless dispersal of sex cells were achieved with the origin of seed plans and the key evolutionary innovations that they introduced: pollen, seeds, and later, flowers and fruits。

　　TPO25 阅读第三篇文章参考译文：

　　植物的进化起源

　　植物的进化历史可以在一系列的适应性中表现出来。植物的祖先是具有光合作用的单细胞有机体，由此推测出植物可能缺少真正意义上的根，茎，叶子和复杂可再生的结构如叶子。所有的这些特征都是在植物进化历史的后期出现的。正如现在不同组群的藻类植物，绿藻类可能与原始植物最相像。这种推测源于这两组植物种类史(自然进化)的紧密关联。DNA对比已经显示出绿藻类与现存亲缘植物最接近。此外，另一方面的证据也支撑了陆地植物是由原始绿藻类植物进化而来的假设，因为她们与陆地植物一样在光合作用时使用相同类型的植物叶绿素和生物辅助色素。但是该假设对于红藻类和褐藻类就不成立了。绿藻就如陆地植物一样以植物浆液的形式储存养料，并且拥有由细胞膜形成的细胞壁，与陆地植物的形成相似。但是，红藻类植物和褐藻类植物养料存储和细胞壁分子却不相同。

　　现在绿色藻类植物主要生存在淡水中，那么就暗示着绿藻类植物早期进化历史就有可能发生在淡水环境中。如果是这样，绿藻类植物应该已经经历过了导致产生适应性的环境压力，增加了它们进化成为陆生植物或生物体的潜能。

　　淡水生物环境状况与海洋生物环境状况不相同，更容易发生变化。水温是随着季节发生波动，或者每天都发生变化，并且降雨量的变更也导致水中化学浓度的变化，甚至会发生一段时间水声环境枯竭的现象。古代淡水绿藻类具有能够使它们抵抗极端温度条件和干燥时期的进化特征。

　　现在的地球陆地是绿色的，但是在地球最初的时候却不是这样。当大约4亿年前，植物最初向陆地转换时，陆地还是贫瘠而孤寂的荒地不适合生物存活。然而，以一种植物的进化为观察点，陆地依然是一个机会之地，没有竞争者和捕食者并且充满了二氧化碳和阳光。(光合作用的原材料，其存在于空气中的浓度要比水中高的多。)因此一旦自然选择使植物形成适应性，那么这种适应性就会促使植物克服陆地生存的障碍，使其繁荣昌盛并形式各异。

　　当植物占领陆地，它们就将面临来自陆地生态环境的各种挑战。在陆地上，植物们失去了水的浮力，不能再浸泡在营养液(水)中，而空气似乎能将一切风干。所有外部条件都更有利于植物的组织结构为了支撑植株而进化，脉络将传输水分和养分给植株的各个部分并能够储存水分。为了适应干燥的陆地，在植物进化早期就呈现出了许多的植株结构特点，这些特点与目前的陆生植物相同。包括植物的根或根状结构和附着在植物茎叶表面的柔软和防止蒸腾失水的表皮层，此外表皮层上的气孔还可以进行气体交换但当植物缺水时气孔就会关闭来防止水分流失。地下生物在转换时也会产生另外的适应性并被广泛扩散，但在植物中却并不能通用。这些适应性包括能从根部向上传输水分和矿物质的脉络，它能够将光合作用产物从叶子传送到植株其他部位还能够传送粘稠的木质素，这种木质素可以支撑植株的身体并帮助它能够曝光于阳光下。

　　这些适应性使植物增强了形体的多样性使其能够在干燥的陆地繁衍生息。然而，陆地上的生物也需要一种全新的转换模式将精子转换成为卵子。与水生和海生植物不同，陆地植物不能依靠水流来运输它们的生殖细胞，也不能将受精卵分散出去。因此最成功的陆生植物能够产生不依靠水就能够使受精的卵细胞分散出去的方法和防止胚胎发育流失水分的结构。受保护的胚胎和无水的受精卵子都可以在孢子植物中获取并且它们进化的关键是引进的新方法：花粉，种子然后是花朵和果实。

　　上面就是关于托福TPO25阅读第三篇：The Evolutionary Origin of Plants(植物的进化起源)的原文及翻译，希望考生认真研究TPO真题，陆续我会为大家翻译余下的几篇，敬请关注。

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