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  Dealing with Extreme Cold

  There are a number of environments in which organisms are exposed to temperatures below 0°C and thus the risk of freezing.In polar regions,terrestrial organisms are exposed to freezing temperatures for most of the year.In more temperate regions,they may have to tolerate several months of winter, when subzero temperatures persist for long periods of time.High mountains are another place where there is permanent snow and ice,even at the equator. Exposure to subzero temperatures may occur on a daily and/or seasonal basis.

  Endothermic animals(warm-blooded animals)can stop their bodies from freezing by generating their own heat.They retain heat because of the insulation provided by feathers or fur,and the layer of fat beneath the skin.Other heat conservation measures include huddling together, recovering heat from exhaled breath,and recovering heat from the extremities of the body.Endotherms can remain active in the cold if they can find enough food,or they can reduce their metabolism and lie dormant until warmer conditions return.Although air temperatures may be low,the temperature beneath an insulating layer of snow,under the ground,or at the bottom of a lake may remain above 0°C. Most organisms,however,can neither generate their own heat nor avoid the freezing temperatures,and for them,the choice is to survive ice formation within their bodies or to prevent their bodies from freezing.

  Organisms run the risk of freezing at temperatures that are below the melting point of their body and cell fluids.There are two main responses:either they can survive ice forming within them(they are freezing tolerant)or they have mechanisms that ensure that their flu ids remain liquid at temperatures that are below the freezing point of water and the melting point of their body fluids(they are freeze avoiding).The strategy that an organism uses depends on the freeze This may cause its body fluids to freeze by the ice traveling across the cell or body wall,or through body openings-a process known as inoculative freezing.Most organisms surviving low temperatures in such environments are thus likely to be freezing tolerant, since inoculative freezing will cause their bodies to freeze Some, however, may have a structure such as a cuticle,eggshell,cocoon,or sheath that allows them to prevent inoculative freezing by acting as a barrier to the spread of ice into their bodies This allows them to maintain their body or cell fluids as liquids, despite the fact that their surfaces are in contact with external ice,and enables them to avoid inoculative freezing.In a situation where the organism is likely to be exposed to subzero temperatures with little or no water in contact with its surface(many terrestrial insects, for example),it does not have the problem of inoculative freezing and it is perhaps easier for it to maintain its body fluids in a liquid state at low temperatures and thus survive by avoiding freezing.structure and physiology it has developed during its evolutionary history and on the particular demands of its environment. If the organism is living in a wet or damp environment,ice is likely to make contact with its surface when its surroundings

  The two strategies of cold survival are,however,not always mutually exclusive.There have been a few reports of insects that were apparently freezing tolerant switching to being freeze avoiding.The overwintering larvae of a beetle from northern Indiana,when studied in the winters of 1977-1979.froze at -8°C to -12°C but survived down to -28°C.When examined again in 1982,however,they froze and were killed at -26°C,apparently switching from a freezing-tolerant to a freeze-avoiding strategy during the intervening years.There are adaptations in common between freeze-avoiding and freezing-tolerant insects that may make it easy to switch between the two strategies.It must be said,however,there has been only one other report of an insect,another beetle,displaying a shift in strategy of this sort. One Antarctic nematode is freezing tolerant when immersed in water but,when free of surface water, there is,of course,no inoculative freezing and it can survive by avoiding freezing.The cold-tolerance strategy displayed thus depends on the particular characteristics of the animal's microenvironment.

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  1. The word "persist " in the passage is closest in meaning to

  A. continue

  B. return

  C. vary widely

  D. keep falling

  2. The word "conservation" in the passage is closest in meaning to

  A. contributing

  B. creating

  C. distributing

  D. saving

  3. According to paragraph 2, how does a layer of fat beneath the skin help an animal deal with subzero temperatures?

  A. It prevents blood from circulating to the animal's extremities

  B. helps the animal generate its own heat.

  C. It reduces the loss of body heat

  D. It helps the animal to adjust its metabolism

  4. Paragraph 2 supports which of the following statements about endothermic animals?

  A. Some avoid freezing by remaining under a layer of snow, under the ground, or near the bottom of a lake

  B. They are unable to rema in active when temperatures are below 0°C over long periods of time.

  C. They are sometimes able to survive ice formation within their bodies in addition to being able to avoid freezing

  D. The ones that lie dormant in freezing temperatures tend to have less effective insulation than those that remain active.

  5. According to paragraph 3, an organism is freezing tolerant if it

  A. can live in an environment in which temperatures are generally below freezing

  B. has body and cell fluids with a very low melting point

  C. has more than one effective response to freezing temperatures

  D. can survive having the fluids in its cells freeze

  6. According to paragraph 3, organisms that are freezing tolerant are likely to live in an environment that

  A. will not subject them to inoculative freezing

  B. is wet during periods of below freezing temperatures

  C. makes changing demands that allow the organisms to switch between different cold- adaptive strategies as needed10

  D. has no organisms that survive cold by using strategies that avoid freezing

  7. According to paragraph 3, having a cocoon or an eggshell may give an organism living in very low temperatures an advantage by

  A. making it freezing tolerant

  B. lowering the melting point of its body fluids

  C. protecting its outer surface from contact with ice

  D. preventing ice from getting inside its body

  8. 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

  [ Paragraph 3]Organisms run the risk of freezing at temperatures that are below the melting point of their body and cell fluids. There are two main responses: either they can survive ice forming within them (they are freezing tolerant) or they have mechanisms that ensure that their flu ids remain liquid at temperatures that are below the freezing point of water and the melting point of their body fluids (they are freeze avoiding). The strategy that an organism uses depends on the structure and physiology it has developed during its evolutionary history and on the particular demands of its environment. If the organism is living in a wet or damp environment,ice is likely to make contact with its surface when its surroundings freeze. This may cause its body flu ids to freeze by the ice traveling across the cell or body wall, or through body openings-a process known as inoculative freezing. Most organisms surviving low temperatures in such environments are thus likely to be freezing tolerant,since inoculative freezing will cause their bodies to freeze. Some, however, may have a structure such as a cuticle, eggshell, cocoon, or sheath that allows them to prevent inoculative freezing by acting as a barrier to the spread of ice into their bodies. This allows them to maintain their body or cell fluids as liquids, despite the fact that their surfaces are in contact with external ice, and enables them to avoid inoculative freezing. In a situation where the organism is likely to be exposed to subzero temperatures with little or no water in contact with its surface (many terrestrial insects,for example), it does not have the problem of inoculative freezing and it is perhaps easier for it to maintain its body fluids in a liquid state at low temperatures and thus survive by avoiding freezing.

  A. Organisms that find it easy to maintain their body fluids in a liquid state at low temperatures may be able to avoid the problem of inoculative freezing when exposed to water.

  B. Organisms that are unlikely to be in contact with water can avoid the problem of inoculative freezing at subzero temperatures by maintaining their body fluids in a liquid state

  C. it is easier for an organism to tolerate being frozen than to keep its body fluids liquid at subzero temperatures, inoculative freezing may not be a problem.

  D. Organisms that are not in contact with water during periods of subzero temperature may find it easier to survive the cold by using a strategy that keeps their body fluids from freezing

  9. The information about the "overwintering larvae of a beetle from northern Indiana"is presented to show

  A. that the particular cold-survival strategy an organism adopts is not necessarily a permanent characteristic of the species

  B. how long it takes an organism lo switch from one cold-surviving strategy to the other

  C. what types of adaptation make it possible for an organism to switch between the two cold-surviving strategies

  D. why adopting a freeze-avoiding strategy for cold survival rather than a freezing-tolerant strategy might be advantageous

  10. The phrase "intervening years" in the passage is closest in meaning to

  A. remaining years

  B. colder years

  C. years in between

  D. years studied

  11. The word "immersed" in the passage is closest in meaning to

  A. caught

  B. floating

  C. hiding

  D. covered

  12. At the end of paragraph 4, the author discusses an Antarctic nematode because

  A. it illustrates the kind of adaptations that freeze-avoiding and freezing-tolerant organisms have in common

  B. it shows that it is possible for organisms to switch between the two cold-survival strategies more than once

  C. it explains why it is easy for beetles to switch between the two cold-survival strategies

  D. the cold-survival strategy it displays is determined by the particular circumstances in which it finds itself

  13. Look at the four squares [ ] that indicate where the following sentence could be added to the passage

  Thus there are usually places available where an inactive organism can wait out the cold without expending much energy to keep itself from freezing.

  Where would the sentence best fit? Click on a square [ ] to add the sentence to the passage.

  [ Paragraph 2]Endothermic animals (warm-blooded animals) can stop their bodies from freezing by generating their own heat. They retain heat because of the insulation provided by feathers or fur, and t he layer of fat beneath the skin. [ A ] Other heat conservation measures include huddling together, recovering heat from exhaled breath, and recovering heat from the extremities of the body. [ B] Endotherms can remain active in the cold if they can find enough food, or they can reduce their metabolism and lie dormant until warmer conditions return. [ C] Although air temperatures may be low, the temperature beneath an insulating layer of snow, under the ground, or at the bottom of a lake may remain above 0°C.[ D] Most organisms,however, can neither generate their own heat nor avoid the freezing temperatures,and for them, the choice is to survive ice formation within their bodies or to prevent their bodies from freezing.

  14. In many diverse environments, organisms must deal with the danger of freezing.

  A. Even in environments in which air temperatures are below freezing for long periods,there are generally some protected places in which temperatures remain safely above freezing.

  B. Organisms in wet environments that cannot avoid inoculative freezing can survive extreme cold only by being able to tolerate having their body fluids freeze.

  C. Freezing-tolerant beetles have been found to survive temperatures as low as -28°C,whereas beetles of the same species that are freeze avoiding could not survive temperatures below -26°C

  D. Most endothermic animals must hibernate below an insulating layer of snow to avoid freezing because fur and feathers alone do not provide enough insulation.

  E. Freeze-avoiding organisms have body fluids that remain liquid below 0°C, and they either live in dry environments or are protected from inoculative freezing by their outer covering

  F. Certain adaptations are shared by freezing -tolerant and freeze-avoiding organisms,and in rare cases this allows organisms to switch between the two cold-survival strategies.

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