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 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,
Paragraph 1: 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.
1. The word “Consequently” in the passage is closest in meaning to
○Therefore
○Additionally
○Nevertheless
○Moreover
2. In paragraph 1, the experiment on the fungus Neurospora is mentioned to illustrate
○the existence of weekly periods of activity as well as daily ones
○the finding of evidence that organisms have internal clocks
○the effect of space on the internal clocks of organisms
○the isolation of one part of an organism's cycle for study
3. According to paragraph 1, all the following are generally assumed to be true EXCEPT:
○It is important for animals' daily activities to be coordinated with recurring events in their environment.
○Eukaryotes have internal clocks.
○The relationship between biological function and environmental cycles is a topic of intense research.
○Animals' daily rhythms are more dependent on external cues than on internal clocks.
Paragraph 2: 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.
4. The word “persistent” in the passage is closest in meaning to
○adjusted
○strong
○enduring
○predicted
5. Which of the sentences below best expresses the essential information in the highlighted sentencein the passage? Incorrect choices change the meaning in important ways or leave out essential information.
○Stability, a feature of the biological clock's period, depends on changeable factors such as temperature.
○A major feature of the biological clock is that its period does not change despite significant changes in the environment.
○A factor such as temperature is an important feature in the establishment of the biological clock's period.
○Biological activity is not strongly affected by changes in temperature.
6. According to paragraph 2, which of the following is true about the circadian periods of animals deprived of environmental cues?
○They have the same length as the daily activity cycles of animals that are not deprived of such cues.
○They can vary significantly from day to day.
○They are not the same for all members of a single species.
○They become longer over time.
7. According to paragraph 2, what will an animal experience when its internal rhythms no longer correspond with the daily cycle of the environment?
○Disorientation
○Change in period of the internal rhythms
○Reversal of day and night activities increased
○Sensitivity to environmental factors
8. In paragraph 2, the author provides evidence for the role of biological clocks by
○listing the daily activities of an animal's cycle: sleeping, feeding, moving, reproducing, metabolizing, and producing enzymes and hormones
○describing the process of establishing the period of a biological clock
○presenting cases in which an animal's daily schedule remained stable despite lack of environmental cues
○contrasting animals whose daily schedules fluctuate with those of animals whose schedules are constant
9. The word duration in the passage is closest in meaning to
○length
○feature
○process
○repetition
10. In paragraph 2, why does the author mention that the period for different horseshoe crabs ranges from 22.2 to 25.5 hours?
○To illustrate that an animal's internal clock seldom has a 24-hour cycle
○To argue that different horseshoe crabs will shift from daytime to nighttime vision at different times
○To illustrate the approximate range of the circadian rhythm of all animals
○To support the idea that external cues are the only factors affecting an animal's periodic behavior
Paragraph 3: 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.
11. The word “it” in the passage refers to
○ an external cue such as sunrise
○ the daily rhythm of an animal
○ the local solar day
○ a cycle whose period is precisely 24 hours
12. The word “sustained” in the passage is closest in meaning to
○ intense
○ uninterrupted
○ natural
○ periodic
Paragraph 3: 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.
13. Look at the four squares [■] that indicate where the following sentence could be added to the passage.
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.
Where would the sentence best fit?
14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting 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.
The activity of animals is usually coordinated with periodically recurring events in the environment.
●
●
●
Answer Choices
○Most animals survive and reproduce successfully without coordinating their activities to external environmental rhythms.
○The circadian period of an animal's internal clock is genetically determined and basically unchangeable.
○Environmental cues such as a change in temperature are enough to reset an animal's clock.
○Animals have internal clocks that influence their activities even when environmental cues are absent.
○Animals are less affected by large differences between their internal rhythms and the local solar day than are humans.
○ internal clock does not operate on a 24-hour cycle, environmental stimuli are needed to keep the biological day aligned with the solar day.
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14. The circadian period…
Animals have internal…
Because an animal's…
生物鐘
通常動(dòng)物的繁衍生息需要?jiǎng)游锏幕顒?dòng)與周?chē)深A(yù)測(cè)活動(dòng)同步。因此，生物功能的時(shí)間與節(jié)律也就理所應(yīng)當(dāng)必須與晝夜交替、潮漲潮落、月圓月缺和四季更迭這樣的周期性事件保持大體一致。動(dòng)物的活動(dòng)與這些周期之間的關(guān)系，特別是與晝夜交替之間的關(guān)系，引起人們濃厚的興趣，而且因?yàn)榇罅康墓ぷ鞫际窃谄浠A(chǔ)之上完成的而意義重大，從而也延伸出了一個(gè)特別的研究領(lǐng)域：生物鐘學(xué)。通常意義上講，動(dòng)物活動(dòng)的經(jīng)常性轉(zhuǎn)變——例如，睡覺(jué)、喂食、活動(dòng)、繁殖、新陳代謝以及產(chǎn)生酶和荷爾蒙，都與環(huán)境的節(jié)律同步。但是關(guān)鍵問(wèn)題在于，動(dòng)物的作息時(shí)間是否受制于外界環(huán)境，比如日出日落，又或者是依賴于他們自身獨(dú)立的生物節(jié)律。生物學(xué)家普遍認(rèn)為，所有真核生物（包括除病毒和某些藻類之外的所有生物）都有內(nèi)部的生物鐘。通過(guò)將生物與外界的周期性現(xiàn)象完全隔離，生物學(xué)家們發(fā)現(xiàn)生物的確有生物鐘。例如，一種叫脈孢菌的細(xì)菌在航天飛機(jī)中與一切地球時(shí)間線索隔離的情況下，所有生物日�；顒�(dòng)周期可以持續(xù)一個(gè)禮拜左右。在沒(méi)有外界信號(hào)的時(shí)候生物也能延續(xù)生物節(jié)律，這說(shuō)明生物是具有生物鐘的。
將小龍蝦置于黑暗環(huán)境中，即使持續(xù)四五個(gè)月，它們的復(fù)眼也仍然繼續(xù)按晝夜交替時(shí)間來(lái)調(diào)節(jié)視野。人們發(fā)現(xiàn)，馬蹄蟹可以在黑暗中連續(xù)待一年依然能保持連續(xù)的大腦周期活動(dòng)，這與他們的眼睛適應(yīng)日常交替的強(qiáng)光光與弱光的周期一致。如同大多數(shù)失去外界線索的日循環(huán)動(dòng)物一樣，馬蹄蟹在這種無(wú)光的情況下時(shí)長(zhǎng)也不一定是準(zhǔn)確的24小時(shí)。這種和一天的循環(huán)周期很接近但不完全同步的循環(huán)叫做生理節(jié)奏。不同的馬蹄蟹生理節(jié)奏也不一樣，在22.2小時(shí)到25.5小時(shí)之間浮動(dòng)。有的動(dòng)物可以將其特有的準(zhǔn)確循環(huán)時(shí)間維持很多天。的確，穩(wěn)定性是生物鐘最重要的特性之一，即使生物所處環(huán)境的諸多要素發(fā)生顯著變化，例如溫度可能會(huì)對(duì)生物活性產(chǎn)生很大影響。通常外部循環(huán)發(fā)生突變以后，生物鐘持續(xù)性就會(huì)出現(xiàn)進(jìn)一步的證據(jù)，如科研或者橫跨東西快速的長(zhǎng)途旅行通常，動(dòng)物日常的周期循環(huán)活動(dòng)仍然會(huì)繼續(xù)并不會(huì)發(fā)生什么改變。但與此同時(shí)，生物活動(dòng)又因?yàn)樾颅h(huán)境的外部循環(huán)而產(chǎn)生變化。外界時(shí)間信號(hào)與內(nèi)部固有的時(shí)間表不同步時(shí)出現(xiàn)的迷亂的癥狀，比如飛行時(shí)差綜合癥，我們會(huì)因此持續(xù)幾天活數(shù)周,直到某些信號(hào)改變之后，比如日照和黑暗循環(huán)需要重新設(shè)定生物鐘并同步到新環(huán)境的日常節(jié)律之。
動(dòng)物需要日出等自然界的周期信號(hào)來(lái)保持24小時(shí)的循環(huán)周期。這樣的外部信號(hào)不僅可以通過(guò)當(dāng)?shù)匕讜兊奶匦哉{(diào)節(jié)動(dòng)物的日常節(jié)律，而且還保證生物鐘循環(huán)周期接近地球自轉(zhuǎn)周期——因?yàn)檫@些活動(dòng)日復(fù)一日。但是盡管與生物鐘周期同步，動(dòng)物的時(shí)鐘仍然延續(xù)著它遺傳上區(qū)別于外部的循環(huán)周期，接近24小時(shí)但不完全一致。在沒(méi)有外部信號(hào)時(shí)，不同的收集方式和這種內(nèi)在的調(diào)節(jié)機(jī)制作用下的生物活動(dòng)保持著繼續(xù)，比如潮汐，就與太陽(yáng)日有關(guān)系。這一趨勢(shì)在許多動(dòng)物和生物活動(dòng)中被廣泛研究，從孵化的果蠅卵到松鼠的滾輪跑都有涉及。光在調(diào)節(jié)生物鐘里占主導(dǎo)位置。甚至在持續(xù)黑暗環(huán)境下僅15分鐘的強(qiáng)光照射也會(huì)改變動(dòng)物的生理節(jié)律。通常來(lái)講，內(nèi)部節(jié)律會(huì)緊隨環(huán)境循環(huán)的步伐。舉個(gè)例子，如果一個(gè)家鴿以太陽(yáng)作為其導(dǎo)航飛行，那么它的生物鐘就必須嚴(yán)格遵守日出日落的循環(huán)周期。
真核生物：由真核細(xì)胞構(gòu)成的生物。具有細(xì)胞核和其他細(xì)胞器。所有的真核生物都是由一個(gè)類似于細(xì)胞核的細(xì)胞（胚、孢子等）發(fā)育出來(lái)，包括除病毒和原核生物之外的所有生物。
脈孢菌屬(NeurosPora) 因子囊孢子表面有縱形花紋，猶如葉脈而得名，又稱鏈孢霉。
