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Passage 20 (20/63)
Species interdependence in nature confers many benefits on the species involved, but it can also become a point of weakness when one species involved in the relationship is affected by a catastrophe.Thus, flowering plant species dependent on insect pollination, as opposed to self-pollination or wind pollination, could be endangered when the population of insect-pollinators is depleted by the use of pesticides.
In the forests of New Brunswick, for example, various pesticides have been sprayed in the past 25 years in efforts to control the spruce budworm, an economically significant pest. Scientists have now investigated the effects of the spraying of Matacil, one of the anti-budworm agents that is least toxic to insect-pollinators.(Q4,as we can see that Matacil is the least toxic, the other kinds of pesticide are able to harm more plants) They studied Matacil’s effects on insect mortality in a wide variety of wild insect species and on plant fecundity, expressed as the percentage of the total flowers on an individual plant that actually developed fruit and bore seeds.(Q5) They found that the most pronounced mortality after the spraying of Matacil occurred among the smaller bees and one family of flies, insects that were all important pollinators of numerous species of plants growing beneath the tree canopy of forests. The fecundity of plants in one common indigenous species, the red-osier dogwood, was significantly reduced in the sprayed areas as compared to that of plants in control plots where Matacil was not sprayed. This species is highly dependent on the insect-pollinators most vulnerable to Matacil. Thecreeping dogwood, a species similar to the red-osier dogwood, but which is pollinated by large bees, such as bumblebees, showed no significant decline in fecundity.(Q3) Since large bees are not affected by the spraying of Matacil, these results add weight to the argument that spraying where the pollinators are sensitive to the pesticide used decreases plant fecundity.
The question of whether the decrease in plant fecundity caused by the spraying of pesticides actually causes a decline in the overall population of flowering plant species still remains unanswered. Plant species dependent solely on seeds for survival or dispersal are obviously more vulnerable to any decrease in plant fecundity that occurs, whatever its cause. If, on the other hand, vegetative growth and dispersal (by means of shoots or runners) are available as alternative reproductive strategies for a species, then decreases in plant fecundity may be of little consequence.(Q2)The fecundity effects described here are likely to have the most profound impact on plant species with all four of the following characteristics:a short life span, a narrow geographic range, an incapacity for vegetative propagation, and a dependence on a small number of insect-pollinator species.(Q6)Perhaps we should give special attention to the conservation of such plant species since they lack key factors in their defenses against the environmental disruption caused by pesticide use.
1.Which of the following best summarizes the main point of the passage?
(A) Species interdependence is a point of weakness for some plants, but is generally beneficial to insects involved in pollination.
(B) Efforts to control the spruce budworm have had deleterious effects on the red-osier dogwood.
(C) The used of pesticides may be endangering certain plant species dependent on insects for pollination.
(D) The spraying of pesticides can reduce the fecundity of a plant species, but probably does not affect its overall population stability.（C）
(E) Plant species lacking key factors in their defenses against human environmental disruption will probably become extinct.
2.According to the author, a flowering plant species whose fecundity has declined due to pesticide spraying may not experience an overall population decline if the plant species can do which of the following?
(A) Reproduce itself by means of shoots and runners.
(B) Survive to the end of the growing season.
(C) Survive in harsh climates.
(D) Respond to the fecundity decline by producing more flowers.（A）
(E) Attract large insects as pollinators.
3.The passage suggests that the lack of an observed decline in the fecundity of the creeping dogwood strengthens the researchers conclusions regarding pesticide use because the
(A) creeping dogwood is a species that does not resemble other forest plants
(B) creeping dogwood is a species pollinated by a broader range of insect species than are most dogwood species
(C) creeping dogwood grows primarily in regions that were not sprayed with pesticide, and so served as a control for the experiment
(D) creeping dogwood is similar to the red-osier dogwood, but its insect pollinators are known to be insensitive to the pesticide used in the study（D）
(E) geographical range of the creeping dogwood is similar to that of the red-osier dogwood, but the latter species relies less on seeds for reproduction
4.The passage suggests that which of the following is true of the forest regions in New Brunswick sprayed with most anti-budworm pesticides other than Matacil?
(A) The fecundity of some flowering plants in those regions may have decreased to an even greater degree than in the regions where Matacil is used.
(B) Insect mortality in those regions occurs mostly among the larger species of insects, such as bumblebees.
(C) The number of seeds produced by common plant species in those regions is probably comparable to the number produced where Matacil is sprayed.
(D) Many more plant species have become extinct in those regions than in the regions where Matacil is used.（A）
(E) The spruce budworm is under better control in those regions than in the regions where Matacil is sprayed.
5.It can be inferred that which of the following is true of plant fecundity as it is defined in the passage?
(A) A plant’s fecundity decreases as the percentage of unpollinated flowers on the plant increases.
(B) A plant’s fecundity decreases as the number of flowers produced by the plant decreases.
(C) A plant’s fecundity increases as the number of flowers produced by the plant increases.
(D) A plant’s fecundity is usually low if the plant relies on a small number of insect species for pollination.（A）
(E) A plant’s fecundity is high if the plant can reproduce quickly by means of vegetative growth as well as by the production of seeds.
6.It can be inferred from the passage that which of the following plant species would be LEAST likely to experience a decrease in fecundity as a result of the spraying of a pesticide not directly toxic to plants?
(A) A flowering tree pollinated by only a few insect species
(B) A kind of insect-pollinated vine producing few flowers
(C) A wind-pollinated flowering tree that is short-lived
(D) A flowering shrub pollinated by a large number of insect species（C）
(E) A type of wildflower typically pollinated by larger insects
7.Which of the following assumptions most probably underlies the author’s tentative recommendation in lines 51-54?
(A) Human activities that result in environmental disruption should be abandoned.
(B) The use of pesticides is likely to continue into the future.
(C) It is economically beneficial to preserve endangered plant species.
(D) Preventing the endangerment of a species is less costly than trying to save an already endangered one.（B）
(E) Conservation efforts aimed at preserving a few well-chosen species are more cost-effective than are broader-based efforts to improve the environment.
第五问和第七问怎么也想不明白，在文中也找不到信息点，求助
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发表于 2012-3-4 19:53:43
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