【OG24-537题】It can be inferred from the passage that while inside its polyhedrin protein crystals, the nuclear polyhedrosis virus_mofa留学圈mofaGRE在线题库系统_GRE在线搜题_GRE题库解析_GRE真题机经_GRE课程_GRE培训机构

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A small number of the forest species of lepidoptera (moths and butterflies, which exist as caterpillars during most of their life cycle) exhibit regularly recurring patterns of population growth and decline—such fluctuations in population are known as population cycles. Although many different variables influence population levels, a regular pattern such as a population cycle seems to imply a dominant, driving force. Identification of that driving force, however, has proved surprisingly elusive despite considerable research. The common approach of studying causes of population cycles by measuring the mortality caused by different agents, such as predatory birds or parasites, has been unproductive in the case of lepidoptera. Moreover, population ecologists’ attempts to alter cycles by changing the caterpillars’ habitat and by reducing caterpillar populations have not succeeded. In short, the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites.

Recent work suggests that this agent may be a virus. For many years, viral disease had been reported in declining populations of caterpillars, but population ecologists had usually considered viral disease to have contributed to the decline once it was underway rather than to have initiated it. The recent work has been made possible by new techniques of molecular biology that allow viral DNA to be detected at low concentrations in the environment. Nuclear polyhedrosis viruses are hypothesized to be the driving force behind population cycles in lepidoptera in part because the viruses themselves follow an infectious cycle in which, if protected from direct sunlight, they may remain virulent for many years in the environment, embedded in durable crystals of polyhedrin protein. Once ingested by a caterpillar, the crystals dissolve, releasing the virus to infect the insect’s cells. Late in the course of the infection, millions of new virus particles are formed and enclosed in polyhedrin crystals. These crystals reenter the environment after the insect dies and decomposes, thus becoming available to infect other caterpillars.

One of the attractions of this hypothesis is its broad applicability. Remarkably, despite significant differences in habitat and behavior, many species of lepidoptera have population cycles of similar length, between eight and 11 years. Nuclear polyhedrosis viral infection is one factor these disparate species share.

It can be inferred from the passage that while inside its polyhedrin protein crystals, the nuclear polyhedrosis virus

is exposed to direct sunlight is attractive to predators cannot infect caterpillars’ cells cannot be ingested by caterpillars cannot be detected by new techniques of molecular biology

正确答案： C

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文章大意逻辑
文章开篇指出森林中少数鳞翅目（飞蛾和蝴蝶）物种存在定期重复的种群增长和下降模式，即种群周期。虽然影响种群水平的变量众多，但这种规律模式似乎暗示存在主导驱动力，然而确定该驱动力却很困难。接着说明通过测量捕食性鸟类或寄生虫等不同因素导致的死亡率来研究种群周期原因的常见方法在鳞翅目方面没有成效，改变栖息地和减少种群数量的尝试也未成功。随后提出近期研究表明这种驱动力可能是病毒，过去种群生态学家认为病毒疾病是在种群数量下降过程中起作用而非引发下降，而新技术使检测低浓度病毒DNA成为可能，核型多角体病毒被假设为鳞翅目种群周期背后的驱动力，因为其自身有感染周期，在晶体中受保护时可长期保持毒性，被毛毛虫摄入后能感染细胞。 文章类型及逻辑简图
文章类型：新旧观点对比 逻辑简图： Old view: Many variables influence lepidoptera population levels, common study approaches unproductive, population ecologists' view on viral disease New view: A virus (nuclear polyhedrosis virus) may be the driving force behind population cycles in lepidoptera 做题方法及问题类型
这是一道推断题，通过定位到文中关于核型多角体病毒在多角体蛋白晶体中时相关描述来进行推断。 选项分析
A选项：文中明确提到病毒在晶体中可免受直射阳光影响，所以该项错误。 B选项：文中未提及在晶体中的病毒对捕食者有吸引力，属于无中生有，该项错误。 C选项：根据文中“一旦被毛毛虫摄入，晶体就会溶解，释放出病毒来感染昆虫细胞”可推断出在晶体中时病毒不能感染毛毛虫细胞，该项正确。 D选项：文中说病毒被毛毛虫摄入后晶体溶解释放病毒，说明是可以被摄入的，该项错误。 E选项：文中提到新技术能检测低浓度病毒DNA，未表明在晶体中不能被检测，该项错误。

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