11OG-43

nicolechan28

Passage 43

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 boy-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.

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 tolearte 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

(E) I, II, and III

 

263. It can be inferred from the passage that some mechanisms that regulate internal body

temperature, like sweating and panting, can lead to which of the following?

(A) A rise in the external body temperature

(B) A drop in the body’s internal fluid level

(C) A decrease in the osmotic pressure of the blood

(D) A decrease in the amount of renal water loss

(E) A decrease in the urine’s salt content

 

264. It can be inferred from the passage that the author characterizes the camel’s kidney as

“entirely unexceptional” (line 24) primarily to emphasize that it

(A) functions much as the kidney of a rat functions

(B) does not aid the camel in coping with the exceptional water loss resulting from the extreme

conditions of its environment

(C) does not enbale the camel to excrete as much salt as do the kidneys of marine vertebrates

(D) is similar in structure to the kidneys of most mammals living in water-deprived

environments

(E) requires the help of other organs in eliminating excess salt

三题都是选B，请nn帮忙解答，为什么我找不到文章里有讲CAMEL的部分呢？？