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[机经题库答案] 托福阅读生物类真题The Role of Diapause原文+题目汇总

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发表于 2017-5-15 14:56 |显示全部楼层
类别:生物类
真题150111CN-P2
Title:The Role of Diapause
If conditions within an organism’s  environment occasionally or regularly become  harsh, it may be advantageous for an organism  to have a resistant stage built into the  life cycle. In such a life history strategy, the organism suspends any growth, reproduction, or other  activities for a period of time so that they may occur at a later, more hospitable time. This  genetically determined resting stage, characterized by the cessation of development and protein synthesis and  suppression of the metabolic rate,  is called diapause. Many other  kinds of resting stages, with different levels of suppression of physiological activities, are known. Some  of these resistant stages can be extremely long-lived. In one case, seeds of the arctic lupine,  a member of the pea family recovered from ancient lemming burrows in the Arctic,  germinated in three days even though they were  carbon-dated at more than 10,000 years old!
Unfavorable conditions that are  relatively predictable probably pose a simpler  problem for organisms than do unpredictable conditions. Adaptations to the regular change of seasons in the temperate and polar regions may be relatively simple. For  example, many seeds require a period of stratification,  exposure to low temperatures for  some minimum period, before they will germinate. This is a simple adaptation to ensure that germination occurs  following the winter conditions rather than  immediately prior to their onset. In contrast, unfavorable conditions that occur unpredictably pose  considerable problems for organisms. In fact, unpredictability is probably a greater  problem than is the severity of the unfavorable period. How can organisms cope with the  unpredictable onset of good or poor conditions?
Many adaptations to this general problem are based  on a resting stage that  awaits favorable conditions. We will  consider two examples from the vertebrates. The first is the red kangaroo. This marsupial inhabits the deserts of central Australia where the onset of rains and  the resulting sudden  growth of vegetation are extremely  unpredictable. Obviously, it is advantageous for a kangaroo female to produce young at a time when  plant productivity is sufficient to support her offspring. For such a relatively large mammal, however,  gestation (the period of development during  pregnancy) is so long that if a female waited  to mate and carry the young until after  the rains came, the favorable period might be past. The kangaroo’s life history adaptation to this problem involves the use of embryonic diapause during gestation (development in the uterus).
After a 31-day gestation period, the  female gives birth to a tiny helpless young  typical of marsupials. The newborn crawls  into the mother’s pouch and attaches to a teat where it continues to grow and develop. After  235 days it leaves the  pouch but remains with the mother  and obtains milk from her. Two days after giving  birth, the female mates  again. The fertilized egg enters a 204-day period of embryonic diapause during which it remains in the  uterus but does not attach. It then implants, and 31 days later, birth of the second  young occurs. Note that the first young leaves the pouch at just this time. Again, the female  mates, fertilization occurs, and another diapause  follows. The eventual result is that  at any one time, the female has three young  at various stages of development: one in diapause, one in the pouch,  and one outside the pouch. Among  other benefits, this allows her to freeze the development of an embryo during times of drought  and food shortage until the offspring in the pouch is able to  leave.
A similar strategy—accelerated  development combined with a resting stage—has also allowed amphibians to inhabit deserts. The spadefoot  toads, such as Couch’s spadefoot toad, inhabit some of the most severe  deserts in North America. Adults  of this species burrow deeply into the substrate where it is cooler  and perhaps more moist. Here they  enter into a resting state in which they are covered with a protective layer of dead skin. When it  rains, the adults emerge and congregate to mate at temporary ponds. Development is greatly accelerated: the  eggs hatch within 48 hours, and the  tadpoles change into toads at 16-18 days. Consequently, they can complete the life cycle during the brief window  of favorable conditions, then return to the  resistant resting stage to await the next rainfall. Resting stages  thus comprise a series of  adaptations that allow the species to avoid the most difficult conditions for life.
Paragraph  1  
If conditions within an organism’s  environment occasionally or regularly become  harsh, it may be advantageous for an organism  to have a resistant stage built into the  life cycle. In such a life history strategy, the organism suspends any growth, reproduction, or other  activities for a period of time so that they may occur at a later, more hospitable time. This  genetically determined resting stage, characterized by the cessation of development and protein synthesis and  suppression of the metabolic rate,  is called diapause. Many other  kinds of resting stages, with different levels of suppression of physiological activities, are known. Some  of these resistant stages can be extremely long-lived. In one case, seeds of the arctic  lupine, a member  of the pea family recovered from ancient lemming burrows in the Arctic,  germinated in three days even though they were  carbon-dated at more than 10,000 years old!
  
1.       According to paragraph 1, why do some organisms have a resting  stage during their life  cycle?  
¡  To recover from injuries suffered during harsh conditions  
¡  To devote all of their energy to a period of  growth and reproduction  
¡  To wait for local conditions to become favorable  for important life events  
¡  To prepare to move to a different environment if  conditions become harsh  
  
2.       Why does the author mention “seeds of the arctic lupine”?  
¡  To argue that members of the  pea family are extremely resistant to cold  temperature  
¡  To provide information about  what ancient lemmings ate during their long  resting periods  
¡  To provide an example of an  organism with a resting stage that has  many different levels of suppression  of physiological activities  
¡   To support  that some resting stages last an extremely long time.  
  
Paragraph 2  
Unfavorable conditions that are  relatively predictable probably pose a simpler  problem for organisms than do unpredictable conditions. Adaptations to the regular change of seasons in the temperate and polar regions may be relatively simple. For  example, many seeds require a period of stratification,  exposure to low temperatures for  some minimum period, before they will germinate. This is a simple adaptation to ensure that germination occurs  following the winter conditions rather than  immediately prior to their onset. In contrast, unfavorable conditions that occur  unpredictably pose considerable problems for organisms. In fact, unpredictability is probably a greater  problem than is the severity of the unfavorable period.  How can organisms cope with  the unpredictable onset of good or poor conditions?  
  
3.      According  to paragraph 2, why do many seeds require a period of stratification?  
¡  To slowly build up a tolerance for lower and  lower temperatures  
¡  To guarantee that the seeds grow after and not  before unfavorable weather  
¡  To make sure that the seeds can deal with  unpredictable conditions  
¡  To give the seeds enough time to germinate  before winter /  
  
4.       The word “severity”  in the passage is closet in meaning to  
¡   length  
¡   harshness  
¡   unexpectedness  
¡   completeness  
  
Paragraph 3  
Many adaptations to this general problem are based  on a resting stage that  awaits favorable conditions. We will  consider two examples from the vertebrates. The first is the red kangaroo. This marsupial inhabits the deserts of central Australia where the onset of rains and  the resulting sudden  growth of vegetation are extremely  unpredictable. Obviously, it is advantageous for a kangaroo female to produce young at a time when  plant productivity is sufficient to support her offspring. For such a relatively large mammal, however,  gestation (the period of development during  pregnancy) is so long that if a female waited  to mate and carry the young until after  the rains came, the favorable period might be past. The kangaroo’s life history adaptation to this problem involves the use of embryonic diapause during gestation (development in the uterus).  
  
5.       According to paragraph 4,  all of the following statements are true about the young offspring of the red kangaroo EXCEPT:  
¡  After birth,  a newborn crawls into the mother’s pouch where it grows and develops.  
¡   After a young kangaroo leaves its mother’s  pouch, it still needs its mother’s milk.  
¡   A mother usually gives birth to three baby  kangaroos at the same time.  
  
Paragraph 4  
After a 31-day gestation period, the  female gives birth to a tiny helpless young  typical of marsupials. The newborn crawls  into the mother’s pouch and attaches to a teat where it continues to grow and develop. After  235 days it leaves the  pouch but remains with the mother  and obtains milk from her. Two days after giving  birth, the female mates  again. The fertilized egg enters a 204-day period of embryonic diapause during which it remains in the  uterus but does not attach. It then implants, and 31 days later, birth of the second  young occurs. Note that the first young leaves the pouch at just  this time. Again,  the female mates,  fertilization occurs, and another diapause follows. The  eventual result is that at any one time, the female has three young  at various stages of development: one in diapause, one in the pouch,  and one outside the pouch. Among  other benefits, this allows her to freeze the development of an embryo during times of drought  and food shortage until the offspring in the pouch is able to  leave.  
  
6.       Paragraph 4 supports all  of the following statements about the red kangaroo of central Australia EXCEPT:  
¡   A female kangaroo mates again shortly after  her newborn enters her pouch.  
¡  During diapause, a young kangaroo stays in the female’s pouch and growth of a second fertilized egg inside the uterus  is delayed.  
¡  To put different young  kangaroos at various stages of development  is advantageous for the female kangaroo to handle them at the same time.  
¡  The  pause of the development of an embryo has more benefits for preparing it to avoid the harsh times than for  competing with its siblings.  
  
7.       What is the main purpose of paragraph 4 in  the passage?  
¡   To give  the details of an adaptation mentioned in paragraph 3  
¡   To describe  an adaptation different from the one explained in paragraph 3  
¡   To introduce  an adaptation that is described in detail in paragraph 5  
¡   To discuss  an adaptation that is set as successful as the one mentioned before.  
  
Paragraph 5  
A similar strategy—accelerated  development combined with a resting stage—has also allowed amphibians to inhabit deserts. The spadefoot  toads, such as Couch’s spadefoot toad, inhabit some of the most severe  deserts in North America. Adults  of this species burrow deeply into the substrate where it is cooler  and perhaps more moist. Here they  enter into a resting state in which they are covered with a protective layer of dead skin. When it  rains, the adults emerge and congregate to  mate at temporary ponds.  Development is greatly accelerated: the eggs hatch within 48 hours, and the tadpoles change into  toads at 16-18 days. Consequently, they can complete the life cycle during the brief window of favorable  conditions, then return to the resistant  resting stage to await the next rainfall. Resting stages thus comprise a series of adaptations that allow the species to avoid the most  difficult conditions for life.  
  
8.       The word “congregate”  in the passage is closet in meaning to  
¡   begin  
¡   gather  
¡   hurry  
¡   expect  
  
9.       The word “comprise”  in the passage is closet in meaning to  
¡   consist of
¡   bring about  
¡   are similar  to  
¡   take the place of  
  
10.   According to paragraph 5,  how do amphibians such as spadefoot toads survive the severe heat conditions in the North American deserts?  
¡   They dig down into the ground and go into a  resistant resting state.  
¡   They remain in the ponds that develop after  it has rained.  
¡   They lose their outer layer of skin.  
¡   Their eggs live dormant until the desert air  becomes cooler and more moist.   
  
11.   According to paragraph 5, which of the following occurs during the life cycle of  the spadefoot toad?  
¡   The female’s eggs hatch under the surface of  the desert.  
¡  The  adults mate during the dry period.  
¡  The  newborn grows into an adult before unfavorable conditions return.  
¡  The  newborn enters a resting stage before it becomes an adult.  
  
Paragraph  2  
Unfavorable conditions that are  relatively predictable probably pose a simpler  problem for organisms than do unpredictable conditions. Adaptations to the regular change of seasons in the temperate and polar regions may be relatively simple. For  example, many seeds require a period of stratification,  exposure to low temperatures for  some minimum period, before they will germinate. ■This is a simple adaptation to ensure that germination occurs  following the winter conditions rather than  immediately prior to their onset. ■In contrast, unfavorable conditions that occur unpredictably pose considerable  problems for organisms. ■In fact, unpredictability is probably a greater  problem than is the severity  of the unfavorable period. ■How can  organisms cope with the unpredictable onset of good or poor conditions?  
  
12.   Look at the four  squares [■] that indicate where  the following sentence can be added to the passage.  
Such adaptations to  predictable conditions can also be made by  animals, such as by hibernating during the coldest months.  
Where would  the sentence best  fit? Click on a square  [■] to add the sentence to the passage.
  
13.  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 answer choices 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.  
Drag your choices to the spaces where they belong. To review the passage, click on View  Text.
   
            
Some organisms adapt to periodic harsh conditions by building a resistant stage, or diapause,      into their life cycle.     
   
   
  

   Answer choices  

¡   The diapause stage evolved  very early and is most common in  species that first appeared more  than 10,000 years ago.  
¡   Unpredictable conditions  are more problematic for organisms  than are fairly predictable  changes such as the seasons.
¡   Some seeds may germinate in  three days even if they have been  exposed to very low temperatures  for a long time.  
¡   Some marsupials can care  for three newborns in their pouch at  the same time, allowing the young to leave  the pouch only when conditions are  favorable for their growth.  
¡   The female red kangaroo  adapts to unfavorable conditions by  delaying the development of the  embryo in the uterus.  
¡   Some amphibians adapt to arid environments by completing accelerated development with resting  stages deep underground.  
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