OG-43-262

Baker

Homeostasis, an animal’s maintenance of certain internal variables within an acceptable range, particularly in extreme physical environments, has long interested biologists. The desert rat and the camel in the most water-deprived environments, and marine vertebrates in an all-water environment, encounter the same regulatory problem: maintaining adequate internal fluid balance.

For desert rats and camels, the problem is conservation of water in an environment where standing water is nonexistent, temperature is high, and humidity is low. Despite these handicaps, desert rats are able to maintain the osmotic pressure of their blood, as well as their total body-water content, at approximately the same levels as other rats. One countermeasure is behavioral: these rats stay in burrows during the hot part of the day, thus avoiding loss of fluid through panting or sweating, which are regulatory mechanisms for maintaining internal body temperature by evaporative cooling. Also, desert rats’ kidneys can excrete a urine having twice as high a salt content as sea water.

Camels, on the other hand, rely more on simple endurance. They cannot store water, and their reliance on an entirely unexceptional kidney results in a rate of water loss through renal function significantly higher than that of desert rats. As a result, camels must tolerate losses in body water of up to thirty percent of their body weight. Nevertheless, camels do rely on a special mechanism to keep water loss within a tolerable range: by seating and panting only when their body temperature exceeds that which would kill a human, they conserve internal water.

Marine vertebrates experience difficulty with their water balance because though there is no shortage of seawater to drink, they must drink a lot of it to maintain their internal fluid balance. But the excess salts from the seawater must be discharged somehow, and the kidneys of most marine vertebrates are unable to excrete a urine in which the salts are more concentrated than in seawater. Most of these animals have special salt-secreting organs outside the kidney that enable them to eliminate excess salt.

262. According to the passage, the camel maintains internal fluid balance in which of the following ways?

I. By behavioral avoidance of exposure to conditions that lead to fluid loss

II. By an ability to tolerate high body temperatures

III. By reliance on stored internal fluid supplies

(A) I only

(B) II only

(C) I and II only

(D) II and III only（B）

(E) I, II, and III

Internal water is not water? Since ETS indicats they conserve internal water,  
we can not eliminate III. So B is not complete answer. D is better.

Any comment is highly appreciated.

wangyu73cn

应该是储存store和节省conserve不是同一概念吧。

Baker

Hi wangyu,

Thank you!

swlfx

谢谢王牛牛。

snowjing

Camels, on the other hand, rely more on simple endurance. They cannot store water, and their reliance on an entirely unexceptional kidney results in a rate of water loss through renal function significantly higher than that of desert rats. As a result, camels must tolerate losses in body water of up to thirty percent of their body weight. Nevertheless, camels do rely on a special mechanism to keep water loss within a tolerable range: by seating and panting only when their body temperature exceeds that which would kill a human, they conserve internal water.

想问一下:

从文章得出:

1. Camel只有在温度很高的前提下, 才用sweating and panting来conserve internal water;--- special mechanism

2. sweating and panting又是降低interanl fluid level(internal water)的.

那么是否可以这么认为:

如果在极高温情况下, Camel不用sweating and panting, 就没办法来conserve interal water.

不知我的理解是否正确??

snowjing

Up!

fuyun

我的理解是：骆驼可以忍耐很高的温度，直到很高温度才panting & sweating,来降低体内温度的。panting or sweating, which are regulatory mechanisms for maintaining internal body temperature by evaporative cooling.从这里可以看出panting & sweating的作用。

所以panting & sweating是通过蒸发水分降温的，但是消耗体内水分，从而降低了internal fluid level，有可以推回来，骆驼的忍耐性很强，轻易不panting & sweating，为了conserve internal water.

[此贴子已经被作者于2005-9-21 0:07:37编辑过]

happysandy

我看答案的时候也觉得这句很绕，不能说明问题，后来发现是自己把句子成分看错了

by（sweating and panting only when their body temperature exceeds that which would kill a human）, they conserve internal water.

这里的when从句是修饰sweating and panting的，就是说，它们是通过（只有在体温极高的情况下才排汗和呼吸）来保持体内水分的，而不是说在体温极高的情况下，它们通过排汗和呼吸来保持体内水分。

希望能给和我犯了同样错误的人一点帮助。

baobaob

以下是引用happysandy在2005-9-29 4:19:00的发言：

我看答案的时候也觉得这句很绕，不能说明问题，后来发现是自己把句子成分看错了

by（sweating and panting only when their body temperature exceeds that which would kill a human）, they conserve internal water.

这里的when从句是修饰sweating and panting的，就是说，它们是通过（只有在体温极高的情况下才排汗和呼吸）来保持体内水分的，而不是说在体温极高的情况下，它们通过排汗和呼吸来保持体内水分。

希望能给和我犯了同样错误的人一点帮助。

谢谢mm，醒悟了

kevin5

12． Which of the following most accurately states the purpose of the passage?
(A)  To compare two different approaches to the study of homeostasis
(B)  To summarize the findings of several studies regarding organisms maintenance
of internal variables in extreme environments
(C)  To argue for a particular hypothesis regarding various organisms conservation of water in desert environments
(D)  To cite examples of how homeostasis is achieved by various organisms
(E)  To defend a new theory regarding the maintenance of adequate fluid balance

Main idea
To answer this question，look at the passage as a whole since the purpose is reflected
in the entire passage．The first paragraph defines homeostasis and names three animals
that must maintain internal fluid balance in difficult circumstances．
The topic of the second paragraph is how desert rats maintain fluid balance．
The third paragraph discusses how camels maintain fluid balance，
while the final paragraph describes maintenance of water balance in marine vertebrates。
Thus, the overall purpose is to give three examples of how homeostasis is achieved．

(A)Examples of homeostasis are given，but different approaches to studying it are not discussed．
(B)The passage describes examples but it does not summarize studies．
(C)While the passage does discuss two desert animals，it does not present any argument for a
particular hypothesis．
(D)Correct．The passage discusses the examples of desert rats，camels，and marine invertebrates to show how these organisms are able to achieve homeostasis．
(E) The passage describes how three organisms maintain water balance，but it presents no theory about it．

还不不明白B为什么不对，怎么样才算summarize studies。作题的时候就在B和D之间比较了半天，还是错了！！！