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1、 为了帮助大家高效备考托福， 为大家带来托福 TPO45 阅读 Passage2 原文文本+题目+答案 解析，希望对大家备考有所帮助。 Wind pollination 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
2、.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 drawba
3、ck 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 friends garden.For the relatively few
4、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 t
5、ree 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
6、 in temperate forests that are insect pollinated tend to grow as solitary,widely spread individuals. 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 tran
7、sfer of pollen in the air.The result is insignificant-looking flowers and catkins(dense cylindrical clusters of small,petalless flowers). Wind pollination does,of course,require a lot of pollen.A Birch and hazel trees can produce 5.5 and 4 million grains per catkin,respectively.B There are various a
8、daptations to help as much of the pollen go as far as possible.C 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 t
9、hat receives the pollen)for pollen.D Evergreen conifers,which do not shed their leaves,have less to gain from spring flowering,and,indeed,some flower in the autumn or winter. Pollen produced higher in the top branches is likely to go farther:it is windier(and gustier)and the pollen can be blown fart
10、her 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 s
11、ticking 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.
12、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. Once the pollen has been snatched by the wind,the fate of the pollen is obviously up to the vagaries
13、 of the wind,but not everything is left to chance.Windborne 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 part
14、icles 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. Paragraph 1 Pollen,a powdery substance,which is produced by flowering plants and contains male reproductive cells,is u
15、sually 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
16、;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
17、 armful of letters into the air and hoping that one will end up in the friends 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
18、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
19、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. 1.The word“drawback“in paragraph 1 is closest in meaning to A.other side of the issue B.ob
20、jection C.concern D.problem 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 e
21、volutionary 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. 3.According to paragraph 1,wind-pollinated trees are most likely to
22、 be found A.in temperate forests B.at lower latitudes C.in the tropics D.surrounded by trees of many different species 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 t
23、end 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
24、 all directions,not just the direction the wind is blowing at a given moment. 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 B.compare natural,biological proce
25、sses 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 Paragraph 2 Since wind-pollinated flowers have no need to attract
26、 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 su
27、ggests 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
28、 that can be produced. Paragraph 3 Wind pollination does,of course,require a lot of pollen.A Birch and hazel trees can produce 5.5 and 4 million grains per catkin,respectively.B There are various adaptations to help as much of the pollen go as far as possible.C Most deciduous wind-pollinated trees(w
29、hich 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.D Evergreen conifers,which do not shed their leaves,have less to gai
30、n from spring flowering,and,indeed,some flower in the autumn or winter. 7.The word“respectively”in paragraph 3 is closest in meaning to A.over time B.separately C.in that order D.consistently 8.According to paragraph 3,why do most deciduous wind-pollinated trees produce their pollen in the spring? A
31、.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 treesstigmas C.Because they do not have enough energy to produce new leaves and pollen at the same time D.In order to ta
32、ke advantage of the windiest time of year Paragraph 4 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
33、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 lea
34、ve 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 a
35、ir,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 g
36、row 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. 10.The word“significant“in paragraph 4 is closest in meaning to A.sufficient B.considerable C.increasing D.small 11
37、.The phrase“no wonder“in paragraph 4 is closest in meaning to A.unsurprising B.understandable C.well-known D.unfortunate Paragraph 5 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.Windborne pollen
38、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
39、 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 e
40、ssential 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 grain speed and ar
41、e 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. 13.Look at the four squaresthat indicate where the following sentence could be added to the passage. This level of volume is important to ensure that at lea
42、st some of the pollen reaches target tree,but dispersing the pollen is crucial as well. Where would the sentence best fit?Click on a squareto add the sentence to the passage. 14.Directions:An introductory sentence for a brief summary of the passage is provided below.Complete the summary by selecting
43、 the THREE answer choices that express the most important ideas in the passage.Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage.This question is worth 2 points. Drag your answer choices to the spaces where
44、they belong.To remove an answer choice,click on it. To review the passage,click VIEW TEXT Some plants depend on the wind to carry their pollen. Answer Choices A.Because there are few trees in temperate forests,it is safer to transport pollen by insects or birds. B.Wind pollination is a safe reproduc
45、tive strategy for trees in temperate forests where there are only a few dominant species and,therefore,many individuals of the same species. C.Wind pollination requires production of a large amount of pollen,which must be released at the right time and under the right conditions to extend its range.
46、 D.Most wind-pollinated trees are deciduous because evergreen needles compete with the stigma for pollen,making wind pollination uncertain. E.Wind-pollinated plants usually have small petalless flowers which often grow in catkins that produce a very fine-grained pollen. F.Wind-pollinated trees must
47、grow in regions that are only moderately windy because strong winds will blow the tiny pollen grains past the stigma. 参考译文 风媒传粉 开花植物产生的花粉包含雄性繁殖细胞，通常被昆虫或鸟类从一株植物携带到另一株植 物，还有一些植物依靠风来传播花粉。风媒传粉通常被看成是一种原始的并且浪费珍贵花粉 的传播方式，但它却出乎意料的常见，特别是在高纬度地区。风是一种非常好的长距离传播 花粉的方式;花粉可以被吹到几百千米远， 而只有鸟类可以在同样的距离范围内得到附近任意 地点的花粉。这种
48、方式的缺点就是，风不能准确的把花粉传递到特定的地方。这就好比想把 信交给村子另一边的一个朋友，你爬到房顶上，将一堆信扔到空中，希望有一封能够落在这 个朋友的花园里。当一片仅由几种树种组成且在花粉传播的范围内存在很多同种的树组成的 温带森林里，风媒传粉是一个稳赚不赔的赌博。这就好比如果村子里的很多人都从房顶上往 外扔信，你的朋友很容易就会得到一封。但相对而言，在热带地区，每个树种的数量较少， 并且分布的很分散，所以风媒传粉的成功性很小以至于动物才是更稳妥的传播方式。即使在 热带地区的高大树木通常都不会使用风媒传粉，尽管处在多风情况中。同样的，温带森林中 通过昆虫传播花粉的树木也倾向于稀疏分布。
49、因为风媒传粉的花不需要吸引昆虫或其他动物，它们摒弃了鲜艳花瓣、花蜜和香气。这 些特征至多是一种浪费，而在最坏的情况下可能阻碍空气中花粉的传播。所以就产生了不太 容易被发现的花和柔荑花序(很多没有花瓣的小花所组成的圆柱形的花穗)。 当然，风媒传粉需要大量的花粉。白桦树和榛子树的每个柔荑花序分别能产生 550 万和 400 万的花粉粒。还有很多种类的适应性能力能够帮助尽可能多的花粉传播到尽可能远的地 方。大部分通过风媒传播花粉而又每年落叶的树木会在春天产生花粉，这个时候，枝条没有 叶子，所以不会阻挡柱头(花中接受花粉的部分)接收到花粉。四季常青的针叶树，不会落叶， 相比之下会从春季、秋季和冬季的花中获得更少的花粉。 在顶端枝条上产生的花粉可能传播的更远：这个位置风更大(更多阵风)，所以花粉在落 到地面之前会被吹得更远。 此外， 悬挂着的柔荑花序会收住花粉， 直到风力足够强大把它弯折， 使得花粉进入空气中。天气同样很重要。花粉一般在空气很干燥的时候落下来，空气干燥可 以让花粉无法粘在潮湿的表面，也不会被雨点打落。尽管有这些适应性存在，很多的花粉还 是不能离开顶端枝条，并且只有大约 0.5%到 40%的花粉会传播到 100 米以外的距离。但是一 旦到达了这么远的距离， 大量的花粉就能传播到 1000 米或更远的地方。 确实， 在高纬度地区， 花粉能够传播几