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Wind pllinatin
Pllen, a pwdery substance, which is prduced by flwering plants and cntains male reprductive cells, is usually carried frm plant t plant by insects r birds, but sme plants rely n the wind t carry their pllen. Wind pllinatin is ften seen as being primitive and wasteful in cstly pllen and yet it is surprisingly cmmn, especially in higher latitudes. Wind is very gd at mving pllen a lng way; pllen can be blwn fr hundreds f kilmeters, and nly birds can get pllen anywhere near as far. The drawback is that wind is bviusly unspecific as t where it takes the pllen. It is like trying t get a letter t a friend at the ther end f the village by climbing nt the rf and thrwing an armful f letters int the air and hping that ne will end up in the friend's garden. Fr the relatively few dminant tree species that make up temperate frests, where there are many individuals f the same species within pllen range, this is quite a safe gamble. If a number f peple in the village were thrwing letters ff rfs, yur friend wuld be bund t get ne. By cntrast, in the trpics, where each tree species has few, widely scattered individuals, the chance f wind blwing pllen t anther individual is sufficiently slim that animals are a safer bet as transprters f pllen. Even tall trees in the trpics are usually nt wind pllinated despite being in windy cnditins. In a similar way, trees in temperate frests that are insect pllinated tend t grw as slitary, widely spread individuals.
Since wind-pllinated flwers have n need t attract insects r ther animals, they have dispensed with bright petals, nectar, and scent. These are at best a waste and at wrst an impediment t the transfer f pllen in the air The result is insignificant-lking flwers and catkins (dense cylindrical clusters f small, petalless flwers).
Wind pllinatin des, f curse, require a lt f pllen. Birch and hazel trees can prduce 5.5 and 4 millin grains per catkin, respectively. There are varius adaptatins t help as much f the pllen g as far as pssible. Mst deciduus wind-pllinated trees (which shed their leaves every fall) prduce their pllen in the spring while the branches are bare f leaves t reduce the surrunding surfaces that “cmpete" with the stigmas (the part f the flwer that receives the pllen) fr pllen. Evergreen cnifers, which d nt shed their leaves, have less t gain frm spring flwering, and, indeed, sme flwer in the autumn r winter.
Pllen prduced higher in the tp branches is likely t g farther: it is windier (and gustier) and the pllen can be blwn farther befre hitting the grund. Mrever, dangling catkins like hazel hld the pllen in until the wind is strng enugh t bend them, ensuring that pllen is nly shed int the air when the wind is blwing hard. Weather is als imprtant. Pllen is shed primarily when the air is dry t prevent t much sticking t wet surfaces r being kncked ut f the air by rain. Despite these adaptatins, much f the pllen fails t leave the tp branches, and nly between 0.5 percent and 40 percent gets mre than 100 meters away frm the parent. But nce this far, significant quantities can g a kilmeter r mre. Indeed, pllen can travel many thusands f kilmeters at high altitudes. Since all this pllen is flating arund in the air, it is n wnder that wind-pllinated trees are a majr surce f allergies.
nce the pllen has been snatched by the wind, the fate f the pllen is bviusly up t the vagaries f the wind, but nt everything is left t chance. Windbme pllen is dry, runded, smth, and generally smaller than that f insect-pllinated plants. But size is a tw-edged swrd. Small grains may be blwn farther but they are als mre prne t be whisked past the waiting stigma because smaller particles tend t stay trapped in the fast-mving air that flws arund the stigma. But stigmas create turbulence, which slws the air speed arund them and may help pllen stick t them.
1. The wrd "drawback" in the passage is clsest in meaning t
ther side f the issue
bjectin
cncern
prblem
2. Which f the fllwing can be inferred frm paragraph 1 abut pllen prductin?
Pllen prductin requires a significant investment f energy and resurces n the part f the plant.
The capacity t prduce pllen in large quantities is a recent develpment in the evlutinary histry f plants.
Plants in the trpics generally prduce mre pllen than thse in temperate znes.
The highest levels f pllen prductin are fund in plants that depend n insects r birds t carry their pllen.
3. Accrding t paragraph 1, wind-pllinated trees are mst likely t be fund
in temperate frests
at lwer latitudes
in the trpics
surrunded by trees f many different species
4. Paragraph 1 supprts which f the fllwing as the reasn animals are a safer bet than wind as pllinatrs when the individual trees f a species are widely separated?
Animals tend t carry pllen frm a given flwer further than the wind des.
Animals serve as pllinatrs even where there is little wind t disperse the pllen.
An animal that visits a flwer is likely t deliberately visit ther flwers f the same species and pllinate them.
Birds and insects fly in all directins, nt just the directin the wind is blwing at a given mment.
5. In paragraph 1, the authr cmpares pllen mved by wind with letters thrwn ff rfs in rder t
explain why there are relatively few species f trees that depend n wind pllinatin
cmpare natural, bilgical prcesses with human scial practices
make a pint abut the prbability f wind-blwn pllen reaching a tree f the same species
argue against the cmmn assumptin that the tallest trees are the mst likely t emply wind pllinatin
6. Paragraph 2 suggests that wind-pllinated plants d nt have bright petals, nectar, and scent fr which TW f the fllwing reasns? T receive credit, yu must select TW answers.
They interfere with pllinatin by wind.
They are easily damaged by wind.
They are unnecessary.
They reduce the amunt f pllen that can be prduced.
7. The wrd "respectively” in the passage is clsest in meaning t
ver time
separately
in that rder
cnsistently
8.Accrding t paragraph 3, why d mst deciduus wind-pllinated trees prduce their pllen in the spring?
T avid cmpeting with evergreen cnifers, which flwer in the fall r winter
S that the leaves f the trees receiving the pllen will nt prevent the pllen frm reaching the trees' stigmas
Because they d nt have enugh energy t prduce new leaves and pllen at the same time
In rder t take advantage f the windiest time f year
9. Accrding t paragraph 4，which f the fllwing is NT an adaptatin that helps ensure that pllen travels as far as pssible?
Pllen-prducing flwers and catkins are lcated at r near the tp f the tree.
Trees grw at least 100 meters away frm each ther.
Dangling catkins release pllen nly when the wind is blwing hard.
Pllen is nt released during rain strms r when the air is damp.
10. The wrd "significant" in the passage is clsest in meaning t
sufficient
cnsiderable
increasing
small
11. The phrase “n wnder" in the passage is clsest in meaning t
unsurprising
understandable
well-knwn
unfrtunate
12. Which f the sentences belw best expresses the essential infrmatin in the highlighted sentence in the passage? Incrrect chices change the meaning in imprtant ways r leave ut essential infrmatin.
Because smaller particles tend t stay trapped in the fast mving air, they are blwn much farther than ther grains.
Smaller particles are trapped by the stigma when fast-mving air flws past it.
Small particles that are whisked past the waiting stigma gain speed and are ften trapped in the fast-mving air.
While smallness helps pllen travel farther, it als makes it mre likely t be blwn past the stigma.
13. Lk at the fur squares [] that indicate where the fllwing sentence culd be added t the passage.
This level f vlume is imprtant t ensure that at least sme f the pllen reaches target tree, but dispersing the pllen is crucial as well.
Where wuld the sentence best fit? Click n a square [] t add the sentence t the passage.
14. Directins: An intrductry sentence fr a brief summary f the passage is prvided belw. Cmplete the summary by selecting the THREE answer chices that express the mst imprtant ideas in the passage. Sme sentences d nt belng in the summary because they express ideas that are nt presented in the passage r are minr ideas in the passage. This questin is wrth 2 pints.
Drag yur answer chices t the spaces where they belng. T remve an answer chice, click n it.
T review the passage, click VIEW TEXT
Sme plants depend n the wind t carry their pllen.
Answer Chices
Because there are few trees in temperate frests, it is safer t transprt pllen by insects r birds.
Wind pllinatin is a safe reprductive strategy fr trees in temperate frests where there are nly a few dminant species and, therefre, many individuals f the same species.
Wind pllinatin requires prductin f a large amunt f pllen, which must be released at the right time and under the right cnditins t extend its range.
Mst wind-pllinated trees are deciduus because evergreen needles cmpete with the stigma fr pllen, making wind pllinatin uncertain.
Wind-pllinated plants usually have small petalless flwers which ften grw in catkins that prduce a very fine-grained pllen.
Wind-pllinated trees must grw in regins that are nly mderately windy because strng winds will blw the tiny pllen grains past the stigma.