[求助]GWD18-Q23-Q26

Q23 to 26:

      Recently biologists have been

       interested in a tide-associated

       periodic behavior displayed by

Line       the diatom Hantzschia virgata, a

  (5)       microscopic golden-brown alga that

inhabits that portion of a shoreline

washed by tides (the intertidal zone).

Diatoms of this species, sometimes

called “commuter” diatoms, remain

(10)      burrowed in the sand during high

tide, and emerge on the sand sur-

face during the daytime low tide.

Just before the sand is inundated by

the rising tide, the diatoms burrow

(15)      again.  Some scientists hypothesize

that commuter diatoms know that it

is low tide because they sense an

environmental change, such as an

alteration in temperature or a change

(20)      in pressure caused by tidal move-

       ment.  However, when diatoms are

       observed under constant conditions

in a laboratory, they still display

periodic behavior, continuing to bur-

(25)      row on schedule for several weeks.

This indicates that commuter diatoms,

rather than relying on environmental

cues to keep time, possess an inter-

nal pacemaker or biological clock

(30)      that enables them to anticipate peri-

odic changes in the environment.

A commuter diatom has an unusu-

       ally accurate biological clock, a

consequence of the unrelenting

(35)     environmental pressures to which

it is subjected; any diatoms that do

not burrow before the tide arrives

are washed away.

      This is not to suggest that the

(40)     period of this biological clock is

immutably fixed.  Biologists have

concluded that even though a

diatom does not rely on the envi-

ronment to keep time, environmental

(45)      factors—including changes in the

tide’s hydrostatic pressure, salin-

ity, mechanical agitation, and

temperature—can alter the period

of its biological clock according to

(50)      changes in the tidal cycle.  In short,

the relation between an organism’s

biological clock and its environment

is similar to that between a wristwatch

and its owner:  the owner cannot

(55)      make the watch run faster or slower,

but can reset the hands.  However,

this relation is complicated in intertidal

dwellers such as commuter diatoms

by the fact that these organisms are

(60)      exposed to the solar-day cycle as

well as to the tidal cycle, and some-

times display both solar-day and

tidal periods in a single behavior.

Commuter diatoms, for example,

(65)      emerge only during those low tides

that occur during the day.

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Q23:      

Which of the following can be inferred from the passage about the effect of the solar-day cycle on the tide-associated periodic behavior displayed by commuter diatoms?

well as to the tidal cycle, and some-

times display both solar-day and

tidal periods in a single behavior.

Commuter diatoms, for example,

(65)      emerge only during those low tides

that occur during the day.

同时受两种的影响, 没说谁让谁就不重要了

24的E是FLUCTUATE, 即使在实验情况下, 也是先保持了几周之后才根据周围环境有了变化,但是这些应该不是FLUCTUATE, 这词应该是波动起伏吧

23题：

(65)   emerge only during those low tides

any diatoms that do

not burrow before the tide arrives

are washed away.

看看这里，C一定不对！这个behavior对diatoms来说是性命攸关的，怎么可能不重要？solar只是与tides同时作用，而不是不重要！

24题请楼主仔细看那个case和line 50-56,文章说diatoms的cycle会改变，但是accuracy是永远不会改变的！！！

Q23:      

Which of the following can be inferred from the passage about the effect of the solar-day cycle on the tide-associated periodic behavior displayed by commuter diatoms?

1. The solar-day cycle makes this behavior less advantageous to the commuter diatoms at certain times of the year.
   
   
2. The solar-day cycle makes this behavior somewhat more erratic.
   
   
3. The solar-day cycle makes this behavior less important to the survival of the commuter diatoms.
   
   
4. Because of the solar-day cycle, this behavior is forced to proceed at a more rapid pace at certain times during the 24-hour day.
   
   
5. Because of the solar-day cycle, this behavior is not expressed at certain times during the 24-hour day.

Answer:

楼主要建立一个概念，任何细节题都能在文中找到出处，而不是从细节引申出来自己的推断，这也是我以前经常犯的错误，不要去想得更深，文中说到哪就想哪，别推断。C中的less important文中是没有，所以你会选原因是你去比较了solar-day cycle与tidal cycle两者对影响生物钟的重要性，但是文中没有这个比较只是并列了两者而已。

Q24:

The passage suggests which of the following about the accuracy of the commuter diatom’s biological clock?

1. The accuracy of the commuter diatom’s biological clock varies according to changes in the tidal cycle.
   
   
2. The unusual accuracy that characterizes the commuter diatom’s biological clock is rare among intertidal species.
   
   
3. The commuter diatom’s biological clock is likely to be more accurate than the biological clock of a species that is subject to less intense environmental pressures.
   
   
4. The commuter diatom’s biological clock tends to be more accurate than the biological clocks of most other species because of the consistency of the tidal cycle.
   
   
5. The accuracy of the commuter diatom’s biological clock tends to fluctuate when the diatom is observed under variable laboratory conditions.

Answer:

我也选了E，但是后来又想通了，E中的错误就在 fluctuate上，波动表示了一个比较快速的上下起伏的意思，但是diatom在实验室中的表现是一个时期的保持原生物钟的状态，所以用fluctuate就不正确了，应该说生物钟的改变是挺缓慢的，所以无法上下起伏的波动。