2015年10月25日
第一篇：
题材划分：植物类文章
主要内容：
年轮对考古学家很有用，年轮的形成受很多因素的影响。科学家利用一种方法能抽取树干的核心，以获取信息。
有时候，借助一块地方的一大片树木可以确定比单一树木的年轮更广的时间范围。但是，年轮法有他的局限所在。比如，有些年份年轮会消失不见，有些树木的年轮形成会受气候环境影响，最后讲述，科学家们通过一些方法减少了误差。
解析：整体文章结构清晰，对比清楚，考生只要抓住各段主旨即可。学生如果有这方面的背景知识也可帮助做题。
相似TPO练习推荐：
TPO22- Spartina
TPO25- The Evolutionary Origin of Plants
相关文章：
Spartina alterniflora, known as cordgrass, is a deciduous, perennial flowering plant native to the Atlantic coast and the Gulf Coast of the United States. It is the dominant native species of the lower salt marshes along these coasts, where it grows in the intertidal zone (the area covered by water some parts of the day and exposed others).
These natural salt marshes are among the most productive habitats in the marine environment. Nutrient-rich water is brought to the wetlands during each high tide, making a high rate of food production possible. As the seaweed and marsh grass leaves die, bacteria break down the plant material, and insects, small shrimplike organisms, fiddler crabs, and marsh snails eat the decaying plant tissue, digest it, and excrete wastes high in nutrients. Numerous insects occupy the marsh, feeding on living or dead cordgrass tissue, and redwing blackbirds, sparrows, rodents, rabbits, and deer feed directly on the cordgrass. Each tidal cycle carries plant material into the offshore water to be used by the subtidal organisms.
Spartina is an exceedingly competitive plant. It spreads primarily by underground stems; colonies form when pieces of the root system or whole plants float into an area and take root or when seeds float into a suitable area and germinate. Spartina establishes itself on substrates ranging from sand and silt to gravel and cobble and is tolerant of salinities ranging from that of near freshwater (0.05 percent) to that of salt water (3.5 percent). Because they lack oxygen, marsh sediments are high in sulfides that are toxic to most plants. Spartina has the ability to take up sulfides and convert them to sulfate, a form of sulfur that the plant can use; this ability makes it easier for the grass to colonize marsh environments. Another adaptive advantage is Spartina’s ability to use carbon dioxide more efficiently than most other plants.
These characteristics make Spartina a valuable component of the estuaries where it occurs naturally. The plant functions as a stabilizer and a sediment trap and as a nursery area for estuarine fish and shellfish. Once established, a stand of Spartina begins to trap sediment, changing the substrate elevation, and eventually the stand evolves into a high marsh system where Spartina is gradually displaced by higher-elevation, brackish-water species. As elevation increases, narrow, deep channels of water form throughout the marsh. Along the east coast Spartina is considered valuable for its ability to prevent erosion and marshland deterioration; it is also used for coastal restoration projects and the creation of new wetland sites.
Spartina was transported to Washington State in packing materials for oysters transplanted from the east coast in 1894. Leaving its insect predators behind, the cordgrass has been spreading slowly and steadily along Washington’s tidal estuaries on the west coast, crowding out the native plants and drastically altering the landscape by trapping sediment. Spartina modifies tidal mudflats, turning them into high marshes inhospitable to the many fish and waterfowl that depend on the mudflats. It is already hampering the oyster harvest and the Dungeness crab fishery, and it interferes with the recreational use of beaches and waterfronts. Spartina has been transplanted to England and to New Zealand for land reclamation and shoreline stabilization. In New Zealand the plant has spread rapidly, changing mudflats with marshy fringes to extensive salt meadows and reducing the number and kinds of birds and animals that use the marsh.
Efforts to control Spartina outside its natural environment have included burning, flooding, shading plants with black canvas or plastic, smothering the plants with dredged materials or clay, applying herbicide, and mowing repeatedly. Little success has been reported in New Zealand and England; Washington State’s management program has tried many of these methods and is presently using the herbicide glyphosphate to control its spread. Work has begun to determine the feasibility of using insects as biological controls, but effective biological controls are considered years away. Even with a massive effort, it is doubtful that complete eradication of Spartina from nonnative habitats is possible, for it has become an integral part of these shorelines and estuaries during the last 100 to 200 years.
第二篇
题材划分：地质类文章
主要内容：
人类对于地球表层的东西知道的很多，但是对于地球内部的事情知之甚少。获得信息的几个途径就是在地面采样，采样底下来的岩石。
后来人类发现了一种方法能测量地球内部-heat flux法，后面具体叙述了这个方法，原理拿了个热汤做比较，热的东西和冷的东西会形成对流，有热量辐射。
解析：
就文章题材而言，是考生相对不是很陌生的话题，就阅读而言存在一些专业词汇，过程比较复杂，选项干扰比较大，考生只要放好心态即可。
相似TPO练习推荐：
TPO7- The Geologic History of the Mediterranean
TPO25- The surface of Mars
第三篇
题材划分： 生物类文章
主要内容：
海洋生物的分布
生命起源于海洋。但是海洋内的生物多样性比陆地低。下面开始介绍在海洋的生物中，上层下层都有比较多的生物，中层比较少。原因是中部海洋有很少的障碍，生物不用去向各种方向进化以适应功能。
科学家们后来才发现，底层生物的多样性原来也是很大的。有很多藏在泥巴里的小生物他们没有研究到。
解析：
话题比较轻松，理解起来也比较容易，并没有什么特别难或者陌生的单词，注意把握好文章的结构，不要过度在意文中出现的专业词汇即可。
相似TPO练习推荐：
TPO17—Animal Signals in the Rain Forest
TPO 4-Deer Populations of the Puget Sound
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