Official13托福阅读Passage2Biological Clocks文本+题目原文+答案解析【雷哥托福】2019-01-27 10:07:57 发布 来源：雷哥托福
Survival and successful reproduction usually require the activities of animals to be coordinated with predictable events around them. Consequently, the timing and rhythms of biological functions must closely match periodic events like the solar day, the tides, the lunar cycle, and the seasons. The relations between animal activity and these periods, particularly for the daily rhythms, have been of such interest and importance that a huge amount of work has been done on them and the special research field of chronobiology has emerged. Normally, the constantly changing levels of an animal's activity—sleeping, feeding, moving, reproducing, metabolizing, and producing enzymes and hormones, for example—are well coordinated with environmental rhythms, but the key question is whether the animal's schedule is driven by external cues, such as sunrise or sunset, or is instead dependent somehow on internal timers that themselves generate the observed biological rhythms. Almost universally, biologists accept the idea that all eukaryotes (a category that includes most organisms except bacteria and certain algae) have internal clocks. By isolating organisms completely from external periodic cues, biologists learned that organisms have internal clocks. For instance, apparently normal daily periods of biological activity were maintained for about a week by the fungus Neurospora when it was intentionally isolated from all geophysical timing cues while orbiting in a space shuttle. The continuation of biological rhythms in an organism without external cues attests to its having an internal clock.
When crayfish are kept continuously in the dark, even for four to five months, their compound eyes continue to adjust on a daily schedule for daytime and nighttime vision. Horseshoe crabs kept in the dark continuously for a year were found to maintain a persistent rhythm of brain activity that similarly adapts their eyes on a daily schedule for bright or for weak light. Like almost all daily cycles of animals deprived of environmental cues, those measured for the horseshoe crabs in these conditions were not exactly 24 hours. Such a rhythm whose period is approximately—but not exactly—a day is called circadian. For different individual horseshoe crabs, the circadian period ranged from 22.2 to 25.5 hours. A particular animal typically maintains its own characteristic cycle duration with great precision for many days. Indeed, stability of the biological clock's period is one of its major features, even when the organism's environment is subjected to considerable changes in factors, such as temperature, that would be expected to affect biological activity strongly. Further evidence for persistent internal rhythms appears when the usual external cycles are shifted—either experimentally or by rapid east-west travel over great distances. Typically, the animal's daily internally generated cycle of activity continues without change. As a result, its activities are shifted relative to the external cycle of the new environment. The disorienting effects of this mismatch between external time cues and internal schedules may persist, like our jet lag, for several days or weeks until certain cues such as the daylight/darkness cycle reset the organism's clock to synchronize with the daily rhythm of the new environment.
Animals need natural periodic signals like sunrise to maintain a cycle whose period is precisely 24 hours. ■Such an external cue not only coordinates an animal's daily rhythms with particular features of the local solar day but also—because it normally does so day after day-seems to keep the internal clock's period close to that of Earth's rotation. ■Yet despite this synchronization of the period of the internal cycle, the animal's timer itself continues to have its own genetically built-in period close to, but different from, 24 hours. ■Without the external cue, the difference accumulates and so the internally regulated activities of the biological day drift continuously, like the tides, in relation to the solar day. ■This drift has been studied extensively in many animals and in biological activities ranging from the hatching of fruit fly eggs to wheel running by squirrels. Light has a predominating influence in setting the clock. Even a fifteen-minute burst of light in otherwise sustained darkness can reset an animal's circadian rhythm. Normally, internal rhythms are kept in step by regular environmental cycles. For instance, if a homing pigeon is to navigate with its Sun compass, its clock must be properly set by cues provided by the daylight/darkness cycle.
TPO13 托福阅读Passage2 Biological Clocks 题目
Question 1 of 14: Paragraph 1：The word "Consequently" in the passage is closest in meaning to
Question 2 of 14: In paragraph 1, the experiment on the fungus Neurospora is mentioned to illustrate
A. the existence of weekly periods of activity as well as daily ones
B. the finding of evidence that organisms have internal clocks
C. the effect of space on the internal clocks of organisms
D. the isolation of one part of an organism's cycle for study
Question 3 of 14: According to paragraph 1, all the following are generally assumed to be true EXCEPT:
A. It is important for animals' daily activities to be coordinated with recurring events in their environment.
B. Eukaryotes have internal clocks.
C. The relationship between biological function and environmental cycles is a topic of intense research.
D. Animals' daily rhythms are more dependent on external cues than on internal clocks.
Question 4 of 14: Paragraph 2：The word "persistent" in the passage is closest in meaning to
Question 5 of 14: 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. Stability, a feature of the biological clock's period, depends on changeable factors such as temperature.
B. A major feature of the biological clock is that its period does not change despite significant changes in the environment.
C. A factor such as temperature is an important feature in the establishment of the biological clock's period.
D. Biological activity is not strongly affected by changes in temperature.
Question 6 of 14: According to paragraph 2, which of the following is true about the circadian periods of animals deprived of environmental cues?
A. They have the same length as the daily activity cycles of animals that are not deprived of such cues.
B. They can vary significantly from day to day.
C. They are not the same for all members of a single species.
D. They become longer over time.
Question 7 of 14: According to paragraph 2, what will an animal experience when its internal rhythms no longer correspond with the daily cycle of the environment?
B. Change in period of the internal rhythms
C. Reversal of day and night activities Increased
D. Sensitivity to environmental factors
Question 8 of 14: In paragraph 2, the author provides evidence for the role of biological clocks by
A. listing the daily activities of an animal's cycle: sleeping, feeding, moving, reproducing, metabolizing, and producing enzymes and hormones
B. describing the process of establishing the period of a biological clock
C. presenting cases in which an animal's daily schedule remained stable despite lack of environmental cues
D. contrasting animals whose daily schedules fluctuate with those of animals whose schedules are constant
Question 9 of 14: The word "duration" in the passage is closest in meaning to
Question 10 of 14: In paragraph 2, why does the author mention that the period for different horseshoe crabs ranges from 22.2 to 25.5 hours?
A. To illustrate that an animal's internal clock seldom has a 24-hour cycle
B. To argue that different horseshoe crabs will shift from daytime to nighttime vision at different times
C. To illustrate the approximate range of the circadian rhythm of all animals
D. To support the idea that external cues are the only factors affecting an animal's periodic behavior
Question 11 of 14: Paragraph 3：The word "it" in the passage refers to
A. an external cue such as sunrise
B. the daily rhythm of an animal
C. the local solar day
D. a cycle whose period is precisely 24 hours
Question 12 of 14: The word "sustained" in the passage is closest in meaning to
Question 13 of 14: Paragraph 3：Look at the four squares [■] that indicate where the following sentence could be added to the passage. Where would the sentence best fit?
Because the internal signals that regulate waking and going to sleep tend to align themselves with these external cues, the external clock appears to dominate the internal clock.
A. Such an external cue not only coordinates an animal's daily rhythms with particular features of the local solar day but also—because it normally does so day after day-seems to keep the internal clock's period close to that of Earth's rotation.
B. Yet despite this synchronization of the period of the internal cycle, the animal's timer itself continues to have its own genetically built-in period close to, but different from, 24 hours.
C. Without the external cue, the difference accumulates and so the internally regulated activities of the biological day drift continuously, like the tides, in relation to the solar day.
D. This drift has been studied extensively in many animals and in biological activities ranging from the hatching of fruit fly eggs to wheel running by squirrels.
Question 14 of 14: The activity of animals is usually coordinated with periodically recurring events in the environment.
A. Most animals survive and reproduce successfully without coordinating their activities to external environmental rhythms.
B. The circadian period of an animal's internal clock is genetically determined and basically unchangeable.
C. Environmental cues such as a change in temperature are enough to reset an animal's clock.
D. Animals have internal clocks that influence their activities even when environmental cues are absent.
E. Animals are less affected by large differences between their internal rhythms and the local solar day than are humans
F. Because an animal's internal clock does not operate on a 24-hour cycle, environmental stimuli are needed to keep the biological day aligned with the solar day.
Question 1 of 14
Question 2 of 14
解析：根据Neurospora定位原文段落的“For instance, apparently normal…”所以这个for instance是对前一句话论点的例证，前一句说到“By isolating organisms completely … have internal clocks.” 通过把生物同外部周期性诱因完全隔绝之后生物学家就可以发现生物的内部节律，所以答案是B。
Question 3 of 14
Question 4 of 14
解析： persistent“持续的”，所以C的“enduring”正确。本句说养在黑暗中一年的Horseshoe crabs会有什么样的节律能够去适应光线较弱的环境，一年当然是比较久的，所以“持续的”正确，而且前文都一直在说continuous怎么样，所以答案是C。
Question 5 of 14
解析：将原句进行简化，stability of the biological clock's period is one of its major features, even when the organism's environment is subjected to considerable changes in factors，such as 后面是举例，全句引导一个让步逻辑关系，所以只有B选项符合高亮句表述，意思是生物钟的一个重要特征是无论外界环境发生什么样重大的变化，它的周期是不会发生变化的。
Question 6 of 14
解析：题干的关键信息“the circadian periods of animals deprived of environmental cues”，从原文段落第三句开始看“Like almost all daily cycles of animals…”提到如果没有environmental cue，那么horseshoe crabs的period就不是24小时，这个24小时就叫circadian，接着文章又说可能是22.2 to 25.5小时。因为前文特别强调没有外部环境因素的时候circadian不是24小时，所以same length一定不是正确的，注意排除A干扰项。
Question 7 of 14
解析：以cycle of the environment做关键词定位至倒数第二句，这句之前说通常生物的内部日常的节律不变，接着说但是生物的日常活动不得不因为新环境而发生改变，然后就出现了The disorienting effects of this mismatch，后句中的disorientation就是正确答案。
Question 8 of 14
解析：题目问的是作者通过什么样的方式证明了biological clocks的作用的论据的。第二段的整体结构是先给出了crayfish和Horseshoe crabs 的例子，然后说生物钟的一个重要特征是无论外界环境发生什么样重大的变化，它的周期是不会发生变化的。然后探讨了有无外界诱因的情况，所以从段落整体结构来看，C选项是最贴切的。
Question 9 of 14
Question 10 of 14
Question 11 of 14
解析：定位it所在的句子，Such an external cue not only coordinates an animal's daily rhythms with particular features of the local solar day but also—because it normally does so day after day-seems to keep the internal clock's period close to that of Earth's rotation. It所在的小分句其实是句子中的一个插入语，并不是主句成分；所以在插入语中的it引导这个部分是前半句的一个解释说明，not only 和but also是并列结构，所以共用一个主语，particular features of the local solar day 作为一个整体出现，所以只可能指代的是前半句的主语 an external cue。
Question 12 of 14
Question 13 of 14
解析：代词these说明正确插入点之前必须有后面的名词external cues，所以B和D有可能是答案；A前面没提到内部生物钟，所以与插入句的the internal signals 不相符；C前文没有 external cues出现，错误；但D之后的this drift与前文的drift衔接紧密，插入句说external clock appear to dominate the internal clock是属于转折前意群的，所以答案是B。而且待插入句说internal dominate external，紧接着B之后说this synchronization，这种同步与待插入句对应，也说明B正确。
Question 14 of 14
解析： the circadian选项对应原文第二段和第三段内容，正确；animals have选项对应原文第一段，正确；because选项对应原文第三段，正确。