Recently biologists have been interested in a tide-associated periodic

Good passage with fairly easy answers except for QUESTION 27 which is very iffy.

The answer can be B or C depending upon how the reader perceives period of time.

In evolutionary sense, several weeks are nothing more than a milliseconds because evolution takes place over hundreds of thousands of year. This behaviour of diatoms have evolved over thousands of years.

In real life sense for scientific studies, one can argue that several weeks is a considerable time, given that some experiments such as the generation of Higgs boson in a large particle collider last for one millionth of a second.

IN MY OPINION QUESTION 27 is a bit ambiguous. If the passage has mentioned some terms like evolution or hundred of years or something like that to give an idea about the time then B would have made more sense. But since the passage is talking about every day cycle , 24 hour cycle, low tides and high tides, diurnal cycles (day and night) etc etc, all of which are short term phenomenon's therefore going with option C makes more sense.

SO NOT HAPPY ABOUT QUESTION 27

The passage states that the diatoms continue to burrow on a periodic schedule for several weeks. This means that either the observation period only lasted a few weeks or the behavior changed after those few weeks. The latter seems more likely, otherwise the author should make it clear that the behavior persisted for the entire observation period. Similarly, if the diatoms all died off after those few weeks, the language used would be deceptive. In the end, what we know is that the behavior was not something that continued for a long time on the scientists' scale. This tells us that we have a short-term and not a long-term observation.

Another problem with C is its extreme nature. It says that there is "no difference" from the behavior that occurs under natural conditions. We have no idea about this. It seems quite plausible that the burrowing could be, for instance, shallower or less thorough. We'd have to know more to conclude that there is no difference in the long term. In any case, if there were never going to be a difference, then B would be correct, too! "Long term" is a higher standard to prove than "short term." There's no indication that there is an adjustment period, so if we have long term, we also have short term.

Taking this passage step by step

Question 1
A- be careful because the "accuracy" of the clock is not quite affected by changes in the tidal cycle- rather the time is "set" by the tidal waves. For example, tidal waves in California are what would set the alga's behavior to Western Shore time. False
B- Maybe. But the passage more explicitly supports another answer
C- The passage clearly states that the accuracy of the alga's biological is a result of environmental pressures. If we can negate that we can infer that low environmental pressure would lead to a less accurate clock because of the absence of a necessary precondition or even sufficient condition.
D- No because as in C the passage states a particular reason for by the alga's clock is so accurate
E- This contradicts the passage

Question 2
A The author is trying to explain how alga's clock can be controlled by some external factor- which is not what A states
B Yes
C The point of the analogy is not to draw a parallel between the biological clocks of alga and those of humans. The analogy is trying to explain that the clock is controlled by some external factor as is a clock; the external factor controlling a clock is the person setting it and the person setting it is analogous to the environemtn
D This is counterintuitive to the passage because the passage is saying that the biological clocks of alga are a defense mechanism that has developed as a natural result of environmental pressures; the clock is controlled by environmental factors which work to the alga's advantage
E The issue at point is not the accuracy of the clocks- the point of the analogy is to explain how the controlling mechanism of a clock and the biological clock of an alga are similar

Question 3
A contradicts passage
B correct
C contradicts passage
D contradicts passage
E contradicts passage

Question 4
A The passage is supporting the influence of environmental factors on alga's biological clock rather than disputing it
B Where does the passage say this? There's only sentence that explains the clock is an evolutionary feature but of course that's clearly too narrow
C This only mentioned briefly. Too narow
D Correct
E The passage doesn't even support this generalization

Question 5
A Correct through POE and because it is also simply unsupported
B Stated in passage
C Stated in passage
D Stated in passage
E Stated in passage

Question 6
A Passage doesn't state this
B No. On the contrary the solar-day cycle is responsible for a consistent pattern of behavior in alga
C The passage doesn't mention this
D Passage doesn't mentioned this
E Correct

Interesting passage. Took 11 mins , including 4 mins to read the passage . All correct .

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

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
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.
B: illustrate the way in which the period of an organism’s biological clock can be altered by environmental factors


Q27: According to the passage, the periodic behavior displayed by commuter diatoms under constant laboratory conditions is characterized by which of the following?
However, when diatoms are observed under constant conditions in a laboratory, they still display periodic behavior, continuing to burrow on schedule for several weeks.

A: Greater unpredictability than the corresponding behavior under natural conditions -- Incorrect
B: A consistent periodic schedule in the short term -- Correct
C: No difference over the long term from the corresponding behavior under natural conditions -- Not sure -- May or may not be true-- but we are told only about several weeks
D: Initial variability caused by the constant conditions of the laboratory -- Incorrect
E: Greater sensitivity to environmental factors than is the case under natural conditions -- Incorrect


28: The primary purpose of the passage is to

D: examine how certain biological and environmental influences affect the tide-associated behavioral rhythms displayed by the diatom Hantzschia virgata -- Correct


According to the passage, each of the following is characteristic of the tide-associated periodic behavior of commuter diatoms EXCEPT:

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.

A. It is triggered when the diatoms are inundated by the tide -- Correct
B.It is correlated with the rise and fall of the tide -- Incorrect
C. It adjusts to changes in the tidal cycle -- Incorrect
D.It is influenced by the solar-day cycle -- 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.
E.It is regulated by an innate time-keeping mechanism -- 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.

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?

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.

A The solar-day cycle makes this behavior less advantageous to the commuter diatoms at certain times of the year.
B The solar-day cycle makes this behavior somewhat more erratic.
C The solar-day cycle makes this behavior less important to the survival of the commuter diatoms.
D 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.
E Because of the solar-day cycle, this behavior is not expressed at certain times during the 24-hour day. - Correct

Answer choice A of question 25 is incorrect because it is not the “accuracy of the biological clock” that varies according to the change in the tidal cycle. The biological clock just adapts itself to the new tidal cycle. The ability to adapt to new tidal cycle and to maintain that new cycle is again accurately managed by the biologic clock.

Hope this helps

Hi GMATNinja,

I was wondering could you please go over Q6? Though I answered this question correctly, I was only able to reach the correct answer by poe. If you could please run through each of the options, I would greatly appreciate it!

Hello GMAT experts GMATNinja Sir, VeritasKarishma ma'am,

Could you please help me with Q1 ( The passage suggests which of the following about the accuracy of the commuter diatom's biological clock)
I chose option A, but looking carefully I see why it is wrong.

Can you please help me with my reasoning ( is it correct or not):
Is option A wrong because it says the accuracy VARIES but as per the option it is the time or mechanism of the BIOLOGICAL CLOCK that varies and accuracy remains same?

Regards,
Rishav

Question 1:

(C) 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.

We can infer (C) from the last sentence of paragraph 1: "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."

So we can say that commuter diatom's clock is likely to be more accurate than that of another species that is not subject to such intense environment.
Answer (C)


(A) is not correct.

(A) The accuracy of the commuter diatom’s biological clock varies according to changes in the tidal cycle.

"environmental factors -...- can alter the period of its biological clock according to changes in the tidal cycle"

According to changes in tidal cycle, the period of the clock varies, not its accuracy.

The thing to note about Q1 is that throughout the passage we are taught that the commuter diatom's biological clock is more accurate due to external factors that influence its above/below sand appearance, so C must be correct.

I noticed a lot of people chose A, but A is completely false.

The accuracy doesn't vary. The biological clock varies. The biological clock MUST BE 100% accurate otherwise the creature dies. We are told this.

I got the 'primary purpose of the passage' question wrong. As per OA, the correct answer is D: "examine how certain biological and environmental influences affect the tide-associated behavioral rhythms displayed by the diatom Hantzschia virgata". While I understand that passage does say that environmental factors do have some effect on the tide-associated rhythms, the passage does not explain how. In other words, there is no explanation of the mechanism or the process to explain how the environmental factors are playing the role.

Hence, I selected A: "dispute the influence of environmental factors on the tide-associated behavioral rhythms displayed by the diatom Hantzschia virgata". The first para says that these factors directly control the rhythms but the second para disputes it. The second para indicates that the environmental factors play a cursory role.

Can someone please clarify? Thanks.

GMATNinja can you please explain:
. According to the passage, each of the following is characteristic of the tide-associated periodic behavior of commuter diatoms EXCEPT:

(A) It is triggered when the diatoms are inundated by the tide
(B) It is correlated with the rise and fall of the tide
(C) It adjusts to changes in the tidal cycle
(D) It is influenced by the solar-day cycle
(E) It is regulated by an innate time-keeping mechanism

Question 4

You're right that, in the first paragraph, the author dismisses the idea that the environment is the primary influence on diatom behaviors, but the second paragraph tells us that the environment plays more than a "cursory" role. In fact, environmental factors play a key role in altering a diatom's internal clock.

So, we can't say that the author's primary purpose is to "dispute" the role of environmental factors. The author doesn't dispute that these factors play a role -- he/she merely tells us that there is another mechanism that also plays a role. (A) is out for question 4.

Take another look at (D):

The author does, to some extent, explain how environmental influences affect the behavior of diatoms. In the first paragraph, he/she rules out the possibility that the creatures sense low tide such as a change in pressure/temperature. In the second paragraph, the author explains that certain environmental factors do impact the animal by "altering the period" of its internal clock.

Does the passage go into super satisfying detail about how these factors impact diatoms? Perhaps not. However, we definitely get a sense of how biological and environmental factors influence the behavior of diatoms.

(D) is the correct answer to question 4.

I hope that helps!

Question 5

One key element to answering "EXCEPT" questions is to be crystal clear about what you're looking for as you go through the answer choices. Here, we want to cross out options that ARE characteristics of the behavior of diatoms. The remaining answer choice is something that is NOT a characteristic of the diatoms.

With that in mind, go through process of elimination:

This is how the passage describes the diatoms' behavior in the first paragraph: the 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."

Everything described above happens BEFORE the sand is inundated by the rising tide. So, it's not accurate to say that the behavior is triggered WHEN the diatoms are inundated by the tide. That would be too late for the little diatoms!

(A) is NOT a characteristic of diatom behavior, so keep (A) for now.


(B) is much broader than (A) -- instead of specifying exactly when the behavior is triggered, it just says that the behavior is correlated with the rise and fall of the tide.

This is a good description of the diatoms' behavior -- the animals do certain things at low tide, and different things when the tide rises.

(B) IS a characteristic of diatom behavior, so eliminate (B).


This is discussed near the beginning of the second paragraph: "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."

This sentence tells us that diatom behavior changes as the tidal cycle changes.

Because (C) is a characteristic os diatom behavior, eliminate (C).


The solar-day cycle is discussed as the end of the second paragraph. The author tells us that diatoms "sometimes display both solar-day and tidal periods in a single behavior." For example, diatoms only come out in low tides during the day.

From this, we know that diatom behavior is influenced by the solar-day cycle. (D) is out.


The author clearly states this fact in the first paragraph: "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. "

(E) is a characteristic of diatom behavior, so eliminate (E).

(A) is the only option left standing, and (A) is the correct answer to question 5.

I hope that helps!

Just to chime in here on Q25, I am stuck between A and C, frustrated for a bit but realise what has gone wrong:
(A) The accuracy of the commuter diatom’s biological clock varies according to changes in the tidal cycle.
(C) 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.

Re A, after reading through all the options, if you skim through too quickly, you might think that this is the best out of all bad options. It is categoric in the passage that biological period can be shifted by external factors, but nothing is mentioned about accuracy, one might mistakenly think that the diatom is a living thing, not a mechanical watch, so there may still be some degree of variation hence affect the accuracy. Fair, but if you look at C, it is actually a better choice if you read carefully. A is a definitive statement, while C merely said "it is likely to be..." - which is not a wrong statement.

C will be wrong if it did not say "likely", because the passage merely commented on the commuter diatom itself (...a consequence of the unrelenting environmental pressures to which it is subjected...), it has no mentioning of the other species, and we cannot assume that.

Dear Experts,

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

(A) The accuracy of the commuter diatom???s biological clock varies according to changes in the tidal cycle.
(B) The unusual accuracy that characterizes the commuter diatom???s biological clock is rare among intertidal species.
(C) 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.
(D) 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.
(E) The accuracy of the commuter diatom???s biological clock tends to fluctuate when the diatom is observed under variable laboratory conditions.

I read all comments. All said the key word is the last sentence in 1st Paragraph

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.

How can we infer that 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 ?

My understanding is that any diatoms (commuter diatom) that don't burrow before the tide arrives are washed away -> Then, this is the reason why a commuter diatom has an unusually accurate biological clock. How can we inter that this sentence mean the commuter diatom's biological clock is more accurate than that of other species?

Question 1

Question 1 asks us what the passage suggests -- in other words, we're not necessarily hunting for something that is explicitly stated in the passage. It is enough to say that the correct answer choice is implied by the information in the passage.

As you've mentioned, the stakes are really high for commuter diatoms to have an accurate internal clock. If they don't burrow on time, they get washed out to sea! So, there is a lot of "environmental pressure" for commuter diatoms to tell the time accurately. The author argues that this pressure causes commuter diatoms to have an unusually accurate internal clock.

What if there wasn't so much pressure? Well, then the species would not be as motivated to have an accurate internal clock. This would apply to any species -- commuter diatom or other. Because the author links environmental pressure to an accurate internal clock, the passage suggests that a LACK of environmental pressure would lead to a comparatively LESS accurate clock.

That's why (C) is the correct answer to question 1.

I hope that helps!

ThatDudeKnows

IN question 3, I was torn between B and C. I finally chose C as the passage says " they still display periodic behavior, continuing to burrow on schedule for several weeks". The word several made me go for C. I now think C is incorrect because of the extreme language such as " no change" and "long periods". We would have to assume a lot of stuff if we consider the "no change" situation. Is my understanding correct?

Furthermore, I want to ask how can we analyze the phrase "several weeks"? There is little context to precisely place this period of time in a "short term" or "long term" category. Or is this analysis not needed at all?