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2019年08月15日 18:08:38
新托福阅读背景知识:植物适应沙漠 ,托福阅读想要拿到高分,大家在复习的过程中,还是需要多进行各种知识的储备。今天介绍的是新的托福阅读的背景知识,这样能够更好地了解托福阅读的文章内容。
新托福阅读背景知识:植物适应沙漠 ,托福阅读想要拿到高分,大家在复习的过程中,还是需要多进行各种知识的储备。今天介绍的是新的托福阅读的背景知识,这样能够更好地了解托福阅读的文章内容。
Plant adaptation to the desert(背景材料)
Cactus adaptations.
The secret to the superior endurance of cacti lies in their adaptations. Over millions of years, through natural selection, only the strongest and best adapted species survived.
As you know, it is very dry in the desert. Plants that adapt to this are known as xerophytes (from zeros, dry and python, plant). There are plants that avoid the dry season by sprouting from seed just after the spring rain and growing very fast so that by the time the dry season comes, they have already produced a lot of seeds and died. These seeds lie on the soil for the dry season and sprout again in spring and the cycle repeats. Other xerophytes simply drop their leaves and stay dormant for the winter. But there is another special type of xerophytes which stores water in its fleshy tissues. Such plants are called succulents (from success, juicy). The cactus is a typical example of a succulent.
If you cut a cactus open, you see a juicy, slimy tissue. This is where the moisture is stored for the dry season. The part between the middle circle (and pith) and just under the very green part of the plant (or palisade parenchyma) just under the skin is allocated for the storage of water and food for the plant. This is a type of spongy parenchyma and can take up to 85% of the plant's volume. This is a major adaptation in the desert. Because the plant remains completely alive during the dry season and there is no need for it to dry up and lose everything, makes it possible for the plant to grow to large sizes. Another advantage is that the plant retains supplies (in the form of starch) for the winter so that it can flower right away in spring without accumulating more supplies (as most plants need to do in spring). The whole purpose of storing supplies for the winter is mostly to energize flowering in spring but it also lets the cactus start growing much sooner.
Flowering plants breathe and transpire (evaporate water from their surface) through closeable microscopic pores called stoats on the leaves or stems. To do this, their pores have to be open. In most plants these are open all day and on warm nights. But for cacti this is inconvenient as in daytime it is very hot and thus the plant would lose a lot of water through evaporation. So the cactus must close them in the daytime. But then it cannot breathe or photosynthesize (the process where sugars are made from carbon dioxide and water and releasing oxygen using the sun's energy). Succulents have an adaptation to that. Their stoats are closed during the day and are open at night, when it is not that hot and store carbon dioxide in its tissues as crass lean acid and then turn it back to carbon dioxide in the daytime. This process is called crass lean acid metabolism or CAM and it is a very smart way of respiring in the desert.
If we look at the outside of the plant, we notice that there is a tough leathery skin covering the plant, we can also notice the presence of ribs and spines and sometimes fur. These are all very smart adaptations. They serve mainly for surviving heat but are also used as defense.
The tough leathery skin is very impermeable to water, thus reducing evaporation from the surface of the plant. This skin often has a layer of plant wax on it which is often lightly colored (Pilosocereus azures is an example of a plant with such wax), white or blue. This reflects light and also reduces evaporation from the inside.
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常用的托福口语,赶紧学习起来~~ 1 I& 39;manofficeworker 我是上班族。 2 Iworkforthegovernment 我在政府机关做事。
1、篇幅:请大家务必要把作文的长度保持在300字以上,最好能有400字左右。2、文体格式(style):是不是按照ETS所要求的论文体(academic)来写的。
其实一战托福,我的心里十分忐忑。3月1号第一次考,当时上考场非常紧张,觉得椅子坐着都不舒服,拿着鼠标的手一直在抖,软件操作还出了问题,阅读都是在紧张的心情中看的。
托福考试的听说读写四个部分,对于大部分考生来说,大概最难的就是需要输出的口语和写作了,所以我先从这两部分讲起吧。
你好,我是某培训机构的老师,我的一个学生的例子或许能给你很多启发。姓名:周同学年龄:19成绩:阅读29、写作26、听力24、口语23阅读:托福的阅读其实并不难。