2015年1月11日托福阅读真题P2+题目+答案：The Role of Diapause

2015年1月11日托福阅读真题P2+题目+答案：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!

15. According to paragraph 1, why do some organisms have a resting stage during their life cycle?

A.To recover from injuries suffered during harsh conditions

B.To devote all of their energy to a period of growth and reproduction

C.To wait for local conditions to become favorable for important life events

D.To prepare to move to a different environment if conditions become harsh

16. Why does the author mention “seeds of the arctic lupine”?

A.To argue that members of the pea family are extremely resistant to cold temperature

B.To provide information about what ancient lemmings ate during their long resting periods

C.To provide an example of an organism with a resting stage that has many different levels of suppression of physiological activities

D.To support that some resting stages last an extremely long time.

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?

17. According to paragraph 2, why do many seeds require a period of stratification?

A.To slowly build up a tolerance for lower and lower temperatures

B.To guarantee that the seeds grow after and not before unfavorable weather

C.To make sure that the seeds can deal with unpredictable conditions

D.To give the seeds enough time to germinate before winter

18. The word “severity” in the passage is closet in meaning to

A.length

B.harshness

C.unexpectedness

D.completeness

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).

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