托福TPO45阅读Passage 2真题解析

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托福TPO45阅读Passage 2真题解析

Pollen, a powdery substance, which is produced by flowering plants and contains male reproductive cells, is usually carried from plant to plant by insects or birds, but some plants rely on the wind to carry their pollen. Wind pollination is often seen as being primitive and wasteful in costly pollen and yet it is surprisingly common, especially in higher latitudes. Wind is very good at moving pollen a long way; pollen can be blown for hundreds of kilometers, and only birds can get pollen anywhere near as far. The drawback is that wind is obviously unspecific as to where it takes the pollen. It is like trying to get a letter to a friend at the other end of the village by climbing onto the roof and throwing an armful of letters into the air and hoping that one will end up in the friend's garden. For the relatively few dominant tree species that make up temperate forests, where there are many individuals of the same species within pollen range, this is quite a safe gamble. If a number of people in the village were throwing letters off roofs, your friend would be bound to get one. By contrast, in the tropics, where each tree species has few, widely scattered individuals, the chance of wind blowing pollen to another individual is sufficiently slim that animals are a safer bet as transporters of pollen. Even tall trees in the tropics are usually not wind pollinated despite being in windy conditions. In a similar way, trees in temperate forests that are insect pollinated tend to grow as solitary, widely spread individuals.

2. Which of the following can be inferred from paragraph 1 about pollen production?

A.Pollen production requires a significant investment of energy and resources on the part of the plant.
B.The capacity to produce pollen in large quantities is a recent development in the evolutionary history of plants.
C.Plants in the tropics generally produce more pollen than those in temperate zones.
D.The highest levels of pollen production are found in plants that depend on insects or birds to carry their pollen.

正确答案：D
题目分析：本题考查定向需找细节信息并总结概括的能力。文章第一层讲了什么是pollen，pollen的转播途径:生物和风。第二层讲了wind传播的特点。第三层讲了什么地区的植物更倾向采用wind传播途径。A，B选项原文没有提到。C选项，不同地区比较的是哪个地区的植物更趋向风的传播，而不是比较pollen quantity。D选项原文中提到“wind pollination is often seen as being primitive”,推断出来wind的方式相对原始，动物传播途径相对high level。

3. According to paragraph 1, wind-pollinated trees are most likely to be found

A.in temperate forests
B.at lower latitudes
C.in the tropics
D.surrounded by trees of many different species

正确答案：A
题目分析：原文明确出现的信息“wind pollination is often seen as …common, especially in higher altitude ”

4. Paragraph 1 supports which of the following as the reason animals are a safer bet than wind as pollinators when the individual trees of a species are widely separated?

A.Animals tend to carry pollen from a given flower further than the wind does.
B.Animals serve as pollinators even where there is little wind to disperse the pollen.
C.An animal that visits a flower is likely to deliberately visit other flowers of the same species and pollinate them.
D.Birds and insects fly in all directions, not just the direction the wind is blowing at a given moment.

正确答案：C

5. In paragraph 1, the author compares pollen moved by wind with letters thrown off roofs in order to

A.explain why there are relatively few species of trees that depend on wind pollination
Bpare natural, biological processes with human social practices
C.make a point about the probability of wind-blown pollen reaching a tree of the same species
D.argue against the common assumption that the tallest trees are the most likely to employ wind pollination

正确答案：C
题目分析：用throw the letter in the air 的几率来类比wind pollination的几率。

Since wind-pollinated flowers have no need to attract insects or other animals, they have dispensed with bright petals, nectar, and scent. These are at best a waste and at worst an impediment to the transfer of pollen in the air The result is insignificant-looking flowers and catkins (dense cylindrical clusters of small, petalless flowers).

6. Paragraph 2 suggests that wind-pollinated plants do not have bright petals, nectar, and scent for which TWO of the following reasons? To receive credit, you must select TWO answers.

A.They interfere with pollination by wind.
B.They are easily damaged by wind.
C.They are unnecessary.
D.They reduce the amount of pollen that can be produced.

正确答案：AC
题目分析： 题目考察信息的同意改写。主要说对于风授粉的植物，不需要用花瓣和香味吸引昆虫，花瓣还会阻碍划分传播到空气中。这些原因导致花朵不明显。

Wind pollination does, of course, require a lot of pollen. ■ Birch and hazel trees can produce 5.5 and 4 million grains per catkin, respectively. ■There are various adaptations to help as much of the pollen go as far as possible. ■ Most deciduous wind-pollinated trees (which shed their leaves every fall) produce their pollen in the spring while the branches are bare of leaves to reduce the surrounding surfaces that “compete" with the stigmas (the part of the flower that receives the pollen) for pollen. ■ Evergreen conifers, which do not shed their leaves, have less to gain from spring flowering, and, indeed, some flower in the autumn or winter.

8.According to paragraph 3, why do most deciduous wind-pollinated trees produce their pollen in the spring?

A.To avoid competing with evergreen conifers, which flower in the fall or winter
B.So that the leaves of the trees receiving the pollen will not prevent the pollen from reaching the trees' stigmas
C.Because they do not have enough energy to produce new leaves and pollen at the same time
D.In order to take advantage of the windiest time of year

正确答案：B
题目分析：事实细节题。本段讲了为了使花粉传播得更远，植物有几个方面的进化：春天开花，原因是 reduce the surrounding surfaces that “compete" with the stigmas。

Pollen produced higher in the top branches is likely to go farther: it is windier (and gustier) and the pollen can be blown farther before hitting the ground. Moreover, dangling catkins like hazel hold the pollen in until the wind is strong enough to bend them, ensuring that pollen is only shed into the air when the wind is blowing hard. Weather is also important. Pollen is shed primarily when the air is dry to prevent too much sticking to wet surfaces or being knocked out of the air by rain. Despite these adaptations, much of the pollen fails to leave the top branches, and only between 0.5 percent and 40 percent gets more than 100 meters away from the parent. But once this far, significant quantities can go a kilometer or more. Indeed, pollen can travel many thousands of kilometers at high altitudes. Since all this pollen is floating around in the air, it is no wonder that wind-pollinated trees are a major source of allergies.

9. According to paragraph 4，which of the following is NOT an adaptation that helps ensure that pollen travels as far as possible?

A.Pollen-producing flowers and catkins are located at or near the top of the tree.
B.Trees grow at least 100 meters away from each other.
C.Dangling catkins release pollen only when the wind is blowing hard.
D.Pollen is not released during rain storms or when the air is damp.

正确答案：B

Once the pollen has been snatched by the wind, the fate of the pollen is obviously up to the vagaries of the wind, but not everything is left to chance. Windbome pollen is dry, rounded, smooth, and generally smaller than that of insect-pollinated plants. But size is a two-edged sword. Small grains may be blown farther but they are also more prone to be whisked past the waiting stigma because smaller particles tend to stay trapped in the fast-moving air that flows around the stigma. But stigmas create turbulence, which slows the air speed around them and may help pollen stick to them.

12. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

A.Because smaller particles tend to stay trapped in the fast moving air, they are blown much farther than other grains.
B.Smaller particles are trapped by the stigma when fast-moving air flows past it.
C.Small particles that are whisked past the waiting stigma gain speed and are often trapped in the fast-moving air.
D.While smallness helps pollen travel farther, it also makes it more likely to be blown past the stigma.

正确答案：D

Wind pollination does, of course, require a lot of pollen. ■ Birch and hazel trees can produce 5.5 and 4 million grains per catkin, respectively. ■There are various adaptations to help as much of the pollen go as far as possible. ■ Most deciduous wind-pollinated trees (which shed their leaves every fall) produce their pollen in the spring while the branches are bare of leaves to reduce the surrounding surfaces that “compete" with the stigmas (the part of the flower that receives the pollen) for pollen. ■ Evergreen conifers, which do not shed their leaves, have less to gain from spring flowering, and, indeed, some flower in the autumn or winter.

13. Look at the four squares [■] that indicate where the following sentence could be added to the passage.
This level of volume is important to ensure that at least some of the pollen reaches target tree, but dispersing the pollen is crucial as well.
Where would the sentence best fit? Click on a square [■] to add the sentence to the passage.

正确答案：B 

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