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Recently biologists have been interested in a [#permalink] New post 26 Jul 2012, 20:38
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Recently biologists have been interested in a tide-associated periodic behavior displayed by the diatom Hantzschia virgata, a 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 burrowed in the sand during high tide, and emerge on the sand surface during the daytime low tide. Just before the sand is inundated by the rising tide, the diatoms burrow 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 in pressure caused by tidal movement. However, when diatoms are observed under constant conditions in a laboratory, they still display periodic behavior, continuing to burrow on schedule for several weeks. This indicates that commuter diatoms, rather than relying on environmental cues to keep time, possess an internal pacemaker or biological clock that enables them to anticipate periodic changes in the environment. A commuter diatom has an unusually accurate biological clock, a consequence of the unrelenting 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 period of this biological clock is immutably fixed. Biologists have concluded that even though a diatom does not rely on the environment to keep time, environmental factors—including changes in the tide’s hydrostatic pressure, salinity, mechanical agitation, and temperature—can alter the period of its biological clock according to 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 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 exposed to the solar-day cycle as well as to the tidal cycle, and sometimes display both solar-day and tidal periods in a single behavior. Commuter diatoms, for example, emerge only during those low tides that occur during the day.
Q25: The passage suggests which of the following about the accuracy of the commuter diatom’s biological clock?
The accuracy of the commuter diatom’s biological clock varies according to changes in the tidal cycle.
The unusual accuracy that characterizes the commuter diatom’s biological clock is rare among intertidal species.
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.
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.
The accuracy of the commuter diatom’s biological clock tends to fluctuate when the diatom is observed under variable laboratory conditions.
[Reveal] Spoiler:
C


Q26: The author of the passage compares the relationship between an organism’s biological clock and its environment to the relation between a wristwatch and its owner most probably in order to
point out a fundamental difference between the function of biological clocks in organisms and the use of mechanical clocks by humans
illustrate the way in which the period of an organism’s biological clock can be altered by environmental factors
suggest that there are important similarities between the biological clock in organisms such as the commuter diatom and the biological clock in humans
support an argument regarding the methods used by certain organisms to counteract the influence of the environment on their biological clocks
question the accuracy of the biological clock in organisms such as the commuter diatom


Q27: According to the passage, the periodic behavior displayed by commuter diatoms under constant laboratory conditions is characterized by which of the following?
Greater unpredictability than the corresponding behavior under natural conditions
A consistent periodic schedule in the short term
No difference over the long term from the corresponding behavior under natural conditions
Initial variability caused by the constant conditions of the laboratory
Greater sensitivity to environmental factors than is the case under natural conditions
[Reveal] Spoiler:
B


28: The primary purpose of the passage is to
dispute the influence of environmental factors on the tide-associated behavioral rhythms displayed by the diatom Hantzschia virgata
describe how certain tide-associated behavioral rhythms displayed by the diatom Hantzschia virgata have changed over time
compare tide-associated behavioral rhythms to solar-day behavioral rhythms in the diatom Hantzschia virgata
examine how certain biological and environmental influences affect the tide-associated behavioral rhythms displayed by the diatom Hantzschia virgata
identify certain environmental factors that limit the effectiveness of the biological clock in the diatom Hantzschia virgata
[Reveal] Spoiler:
D


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Re: a good practice RC passage(RC99) [#permalink] New post 26 Jul 2012, 21:36
My Answers are as follows. What are the OAs

25. A
26. B
27. A
28. D
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Re: a good practice RC passage(RC99) [#permalink] New post 26 Jul 2012, 22:31
Expert's post
I'll go with CBCA here. I may chime in again with reasoning after others have had a chance
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Re: a good practice RC passage(RC99) [#permalink] New post 27 Jul 2012, 13:59
Expert's post
uledssul wrote:
Recently biologists have been interested in a tide-associated periodic behavior displayed by the diatom Hantzschia virgata, a 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 burrowed in the sand during high tide, and emerge on the sand surface during the daytime low tide. Just before the sand is inundated by the rising tide, the diatoms burrow 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 in pressure caused by tidal movement. However, when diatoms are observed under constant conditions in a laboratory, they still display periodic behavior, continuing to burrow on schedule for several weeks. This indicates that commuter diatoms, rather than relying on environmental cues to keep time, possess an internal pacemaker or biological clock that enables them to anticipate periodic changes in the environment. A commuter diatom has an unusually accurate biological clock, a consequence of the unrelenting 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 period of this biological clock is immutably fixed. Biologists have concluded that even though a diatom does not rely on the environment to keep time, environmental factors—including changes in the tide’s hydrostatic pressure, salinity, mechanical agitation, and temperature—can alter the period of its biological clock according to 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 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 exposed to the solar-day cycle as well as to the tidal cycle, and sometimes display both solar-day and tidal periods in a single behavior. Commuter diatoms, for example, emerge only during those low tides that occur during the day.


Q25:
The passage suggests which of the following about the accuracy of the commuter diatom’s biological clock?

The accuracy of the commuter diatom’s biological clock varies according to changes in the tidal cycle. NOT ONLY
The unusual accuracy that characterizes the commuter diatom’s biological clock is rare among intertidal species. NOT MENTIONED
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.
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. NOT MENTIONED
The accuracy of the commuter diatom’s biological clock tends to fluctuate when the diatom is observed under variable laboratory conditions. FALSE IS STABLE


Q26:
The author of the passage compares the relationship between an organism’s biological clock and its environment to the relation between a wristwatch and its owner most probably in order to

point out a fundamental difference between the function of biological clocks in organisms and the use of mechanical clocks by humans OUT OF SCOPE
illustrate the way in which the period of an organism’s biological clock can be altered by environmental factors IS THE PHRASE JUST BEFORE IN SHORT,.....
suggest that there are important similarities between the biological clock in organisms such as the commuter diatom and the biological clock in humans NOT MENTIONED
support an argument regarding the methods used by certain organisms to counteract the influence of the environment on their biological clocks WE COUNTERACT .........NOTHING
question the accuracy of the biological clock in organisms such as the commuter diatom OUT OF SCOPE


Q27:
According to the passage, the periodic behavior displayed by commuter diatoms under constant laboratory conditions is characterized by which of the following?

Greater unpredictability than the corresponding behavior under natural conditions FALSE
A consistent periodic schedule in the short term FALSE (SEVERAL WEEKS)
No difference over the long term from the corresponding behavior under natural conditions
Initial variability caused by the constant conditions of the laboratory FALSE
Greater sensitivity to environmental factors than is the case under natural conditions NOT ONLY IS A SINERGY AND MORE


28:
The primary purpose of the passage is to

dispute the influence of environmental factors on the tide-associated behavioral rhythms displayed by the diatom Hantzschia virgata
describe how certain tide-associated behavioral rhythms displayed by the diatom Hantzschia virgata have changed over time OUT OF SCOPE
compare tide-associated behavioral rhythms to solar-day behavioral rhythms in the diatom Hantzschia virgata NOT ONLY
examine how certain biological and environmental influences affect the tide-associated behavioral rhythms displayed by the diatom Hantzschia virgata TO VAGUE
identify certain environmental factors that limit the effectiveness of the biological clock in the diatom Hantzschia virgata TO SPECIFIC

The OA is CBBD



CBCA
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Re: a good practice RC passage(RC99) [#permalink] New post 28 Jul 2012, 06:51
CBCA
interesting passage.OA Please?
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Re: a good practice RC passage(RC99) [#permalink] New post 30 Jul 2012, 17:03
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Re: a good practice RC passage(RC99) [#permalink] New post 31 Jul 2012, 03:04
My answers are C B B A

my 3rd answer was B because, I considered several weeks as short period as things changed after a while. I took the below
Quote:
This is not to suggest that the period of this biological clock is immutably fixed.


to believe that things changed after some time. I did not bother to go back. this might have made me choose C
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Re: Recently biologists have been interested in a [#permalink] New post 26 Nov 2012, 09:16
Can someone please explain why C in Q25?
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Re: Recently biologists have been interested in a [#permalink] New post 02 Dec 2013, 21:49
OA are C, n\a, B, D.
Just got it at GMAT Prep 4th Exam.
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Re: a good practice RC passage(RC99) [#permalink] New post 07 Feb 2014, 22:01
rjacobsMGMAT wrote:
I'll go with CBCA here. I may chime in again with reasoning after others have had a chance



Hi
Please explain.....

My take is "ABCB".
whts the OA and OE????

Rgds
Prasannajeet
Re: a good practice RC passage(RC99)   [#permalink] 07 Feb 2014, 22:01
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