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Scientist long believed that two nerve cluster in the human hypothalam

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mSKR

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16 May 2021, 01:54

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vatsal323

Can someone help me with option D in the 3rd question please?

3. The author of the passage would probably agree with which of the following statement about the SCNs?

(A) The SCNs are found in other organs and tissues of the body besides the hypothalamus.
(B) The SCNs play a critical but not exclusive role in regulating circadian rhythms.
(C) The SCNs control clock genes in a number of tissues and organs throughout the body.
(D) The SCNs are a less significant factor in regulating blood pressure than scientists once believed.
(E) The SCNs are less strongly affected by changes in light levels than are by other external cues.

While I agree that the 2nd paragraph says - "While scientists do not dispute the role of the SCNs in controlling core functions such as the regulation of body temperature and blood pressure", it also says that there are other organs and tissues that are performing this role as well. So doesn't it imply that SCNs are a less significant factor in regulating blood pressure than they used to be?

You are very close. As you are clear that SCNs are not playing key role but there are other factors also , as observed in other species .

It is important to add : scientists once believed.
because this passage is based on hypothesis. There is no change in functionalities of SCNs from beginning. Only at some point , scientists discovered that SCN doesn't play key role.
If you don't mention about belief of scientists in D, it appears that there has been some change in process in body. But that's not what passage implies.

I hope it is clear.

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29 May 2021, 09:10

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vatsal323

Hi vatsal323, my two cents on this, the passage states in the end that in addition to SCN, other factors also play the role, but one key thing to note here is author didnt made any comparison between two, take for instance, we can have two metrics working to produce an output, not it could be the case that both are equally significant.

I hope this helps.

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30 Jul 2021, 19:38

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I am not able to bring my head around the question 3 " The author of the passage would probably agree with which of the following statement about the SCNs? " . As per the passage the author is explaining what the scientists have observed and its not mentioned as to whether the Author agrees or disagrees with it. So on what line of thinking is the option A correct ?

Please help explain

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31 Jul 2021, 05:32

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nivi2084

Hi nivi2084,

Please refer the detailed explanation for Question 3 here:
https://gmatclub.com/forum/scientist-long-believed-that-two-nerve-cluster-in-the-human-hypothalam-203724.html#p1562383

Let us know if you still have doubts.
Thanks.

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Updated on: 06 Jun 2022, 19:01

Originally posted by woohoo921 on 05 Oct 2021, 05:05.
Last edited by woohoo921 on 06 Jun 2022, 19:01, edited 1 time in total.

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26 Oct 2021, 03:28

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woohoo921
Let's understand the structure of passage to answer Q3, B
1)SCN controls the circadian cycles. SCN control daily fluctuations in blood pressure, body temperature etc
2)4 genes found everywhere control the circadian cycles apart from SCNs. The revised belief is that SCNs play a key role in controlling core functions but it will only respond to light levels while the other clock genes (described in 1st line of 2nd para) respond to external cues.

(B) The SCNs play a critical but not exclusive role in regulating circadian rhythms.
Meaning - SCNs play an important role in regulating circadian rhythms by controlling core functions but SCNs have some limitation for example, it doesn't respond to external cues. The SCNs are not the only one (not exclusive) regulating circadian rhythms. So the main point of introducing 2nd para was to introduce other genes that control circadian rhythms apart from SCNs.

I would suggest to avoid word match exercise (critical genes, critical role) in RC to avoid such traps.

Hope this helps!

woohoo921

mikemcgarry

ammuseeru

Hi Mike,

in above passage what does following sentence want to convey.

Four critical genes governing circadian cycles
have been found to be active in every tissue,
however, not just the SCNs, of flies, mice, and
humans.

Regards,
Ammu

I'm happy to respond.

So, the passage lets us know that the "suprachiasmatic nuclei (SCN)" is the place that runs the circadian cycles (that is, the 24-hour cycles of sleeping & waking). Naively, we would expect everything about circadian rhythms to be run from there. Then, this sentences surprises us.

Four critical genes governing circadian cycles have been found to be active in every tissue, however, not just the SCNs, of flies, mice, and humans.

Four of the genes that play crucial role in governing sleep/wake cycles are not just in the SCN, where we'd expect--instead, they're everywhere throughout the body!

My friend, if this sentence was a challenge to you, you need to practice reading. You need to read Scientific American every week for practice. See:
How to Improve Your GMAT Verbal Score

Does all this make sense?
Mike

Thank you for your helpful explanation!

My first question:
What confused me about the passage was the temperature part where it notes "the SCNs control daily fluctuations in blood pressure, BODY TEMPERATURE, activity level, and alertness..."

and then later mentions "scientists now believe that circadian clocks in other organs and tissues may respond to external cues other than light- including TEMPERATURE changes -that recur every 24 hours."

To confirm that my understanding is correct, SCNs control fluctuations in temperature but do not respond to temperature changes in the external environment itself? In other words, SCNs only control temperature when they are exposed to light?

My second question:
For number 463, the use of "critical" in choice B. seemed strong to me at first given that you see the word "critical" in the passage when referring to the "four critical genes".

Are the SCNs critical because they control "core functions" whereas the passage does not describe ways how the other four genes control "core functions"? Is that where the inference is made... between "critical" and "core"?

So in all, to clarify, is B mainly correct because the passage does NOT say that these other four genes control "core functions", rather, that they just play a ROLE?

Thank you in advance

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[3]

Updated on: 03 Apr 2022, 02:40

Originally posted by ag153 on 31 Mar 2022, 21:02.
Last edited by ag153 on 03 Apr 2022, 02:40, edited 1 time in total.

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Question1:

Choice D says the PP is to discuss evidence that has caused the long standing belief to be revised.
Evidence: 1) 4 genes have also been found and 2) The peak activity in rats..... Longstanding belief: SCNs controlled the circadian rythm

What I don't understand is how is this longstanding belief revised. The final conclusion is the last line which says that while scientists don't dispute role of SCNs, they now believe that clocks in organs may respond to external cues other than light. The long standing belief talk about SCNs being used and the last line talks about what the clocks are affected by so how is this a revision? They are talking about two separate things.

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Updated on: 02 Apr 2022, 22:51

Originally posted by Hoozan on 02 Apr 2022, 00:51.
Last edited by Hoozan on 02 Apr 2022, 22:51, edited 1 time in total.

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KarishmaB GMATNinja Vinit800HBS

For Q3 we have choice (A) The SCNs are found in other organs and tissues of the body besides the hypothalamus.
The passage states the following:

"Four critical genes governing circadian cycles have been found to be active in every tissue, however, not just the SCNs, of flies, mice, and humans."

If we dissect the sentence structure we get: "Four critical genes ~~governing circadian cycles~~ have been found to be active in every tissue, however, not just the SCNs, of flies, mice, and humans."

Doesn't it seem as if the sentence is saying "not just SCNs but four critical genes have been found to be active in every tissue of flies, mice, and humans?"

So based on the sentence structure and based in the meaning we get (if I am correct) how do we reject (B)

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02 Apr 2022, 22:40

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Hoozan

KarishmaB GMATNinja Vinit800HBS

For Q3 we have choice (B) The SCNs play a critical but not exclusive role in regulating circadian rhythms.

The passage states the following:

"Four critical genes governing circadian cycles have been found to be active in every tissue, however, not just the SCNs, of flies, mice, and humans."

If we dissect the sentence structure we get: "Four critical genes ~~governing circadian cycles~~ have been found to be active in every tissue, however, not just the SCNs, of flies, mice, and humans."

Doesn't it seem as if the sentence is saying "not just SCNs but four critical genes have been found to be active in every tissue of flies, mice, and humans?"

So based on the sentence structure and based in the meaning we get (if I am correct) how do we reject (B)

Hoozan - Why would we reject (B)? It is indeed the answer.
The passage does suggest that SCNs play a critical role (light cycles) but not an exclusive role (other genes responsible for judging temp etc) in regulating circadian rhythm.

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02 Apr 2022, 22:52

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KarishmaB

Hoozan

I am sorry. I meant choice (A) The SCNs are found in other organs and tissues of the body besides the hypothalamus. I have edited my doubt accordingly.

I agree that (B) is the answer but based on the SC mentioned above, how to we eliminate (A)?

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04 Apr 2022, 01:51

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Hoozan

KarishmaB

Hoozan

Given:

Scientist long believed that two nerve cluster in the human hypothalamus, called suprachiasmatic nuclei (SCNs), were what controlled our circadian rhythms.

SCNs are nerve clusters found in hypothalamus.

Four critical genes governing circadian cycles have been found to be active in every tissue, however, not just the SCNs,

means

Four critical genes governing circadian cycles have been found to be active in every tissue, however, not just in the SCNs... i.e. the genes governing circadian cycles have been found to be active in every tissue, not just active in the SCNs

Note:
In addition, when laboratory rats that usually ate at will were fed only once a day, peak activity of a clock gene in their livers shifted by 12 hours, whereas the same clock gene in the SCNs remained synchronized with light cycles.

The clock gene has been found in the liver which shifted .. the same clock gene is in the SCNs too but that remained synchronised with light cycles. So it seems that these genes are found in other tissues too and they play a role in circadian cycles too.

The SCN is found in hypothalamus only. The genes governing circadian cycles are found in other places too.

Hence (A) is incorrect.

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04 Apr 2022, 01:59

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ag153

Circadian rhythms are the biological cycles that recur approximately every 24 hours. Every 24 hrs, there are light patterns, temperature changes etc that recur. As per those, our biological cycles are synchronised (we will get sleepy in the night - no light, lower temperature etc)

Long standing belief:
Scientist long believed that two nerve cluster in the human hypothalamus, called suprachiasmatic nuclei (SCNs), were what controlled our circadian rhythms.

SCNs control our circadian rhythms.

Revision:
scientists now believe that circadian clocks in other organs and tissues may respond to external cues other than light—including temperature changes—that recur regularly 24 hours.

Initially, scientists believed that SCNs controlled our circadian rhythms. Now they believe that circadian genes in other organs and tissues also have a role to play in our circadian rhythms. These genes in other organs respond to temperature changes etc that recur regularly every 24 hrs (day is hot, night is cold) etc.
So SCNs still respond to light cycles but other factors such as temp changes over 24 hours could be taken into account by other tissues/organs.

ag153

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04 Apr 2022, 08:45

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KarishmaB

ag153

Thanks for taking the time to reply KarishmaB. I still do not get why the revised belief cited by you a revision of the longstanding belief. In other words, how is "scientists now believe that circadian clocks in other organs and tissues may respond to external cues other than light—including temperature changes—that recur regularly 24 hours" a revision of "Scientist long believed that two nerve cluster in the human hypothalamus, called suprachiasmatic nuclei (SCNs), were what controlled our circadian rhythms"? They are 2 completely different pieces. Long standing belief is talking sth that influences rythms and the revised argument talks about other factors, that also influence rythms, being affected by factors other than light.

Also are both these the evidences being referred to or one of them? 1) 4 genes have also been found and 2) The peak activity in rats..... Longstanding belief: SCNs controlled the circadian rythm

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04 Apr 2022, 10:36

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ag153

Great question! I have the same doubt. Please experts, do respond to this one.

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04 Apr 2022, 22:23

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ag153

KarishmaB

ag153

ag153
sanjayparihar16

Long standing belief was that SCNs exclusively controlled circadian rhythms.
Now they have revised it to 'SCNs play an important role but other organs also play a role in controlling circadian rhythms'.

Both are talking about biological changes in us in 24 hr intervals (which is called our circadian rhythm).

The passage tells us that SCNs are synced to light changes every 24 hrs but other genes in other organs are synced to temperature changes in 24 hrs, to say food cycle every 24 hrs, to variation in magnetic field every 24 hrs etc.
With this understanding, read the passage again.

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05 Apr 2022, 03:21

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A. As per the passage and as per your previous message, isn’t the revised belief the part after “scientists now believe......” , which is the fact that genes in other organs are affected by external cues AND NOT REALLY that rythms are affected by other organs as well? Given the structure of the pssage and how it’s written, it seems the last sentence is the revised belief and not the first sentence of the second para. Pls clarify

In your previous message, you have mentioned 2 different revised beliefs: light's affect in SCN vs genes of other organs as one revision and SCNs only vs SCNs being one of the factors affecting light as the other revision. Looking at the structure I am not clear which one is supposed to be revision

And how does the rat thing serve as an evidence for the revision if the revision is that "genes in other organs also affect rythms". I mean this was already concluded before the evidence was given so I am not sure how the evidence had any role to play.

B. On a separate note: when it says 4 genes are present in every tissue, other than SCNs - I’m confused in the interpretation because of parallelism- is it implying :
1) “4 genes are present in every tissue other than IN SCNs” thereby implying same genes are present in SCNs and in other organs too but they are affected by external cues in the other organs?
Or
2) does it imply “besides SCNs , there are also 4 genes, which are present in every tissue and that effect the rythms”?

C) Also are both of these the evidence or only the rat sentence? Evidence: 1) 4 genes have also been found and 2) The peak activity in rats.....

KarishmaB

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JarvisR

Scientist long believed that two nerve cluster in the human hypothalamus

This portion needs to be changed to "Scientists long believed that two nerve clusters in the human hypothalamus".

Sajjad1994

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06 Jun 2022, 20:57

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JarvisR

Scientist long believed that two nerve cluster in the human hypothalamus

This portion needs to be changed to "Scientists long believed that two nerve clusters in the human hypothalamus".

Sajjad1994

Edited accordingly.

Thank you!

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29 Jun 2022, 10:17

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3. The author of the passage would probably agree with which of the following statement about the SCNs?

(A) The SCNs are found in other organs and tissues of the body besides the hypothalamus.
(B) The SCNs play a critical but not exclusive role in regulating circadian rhythms.
(C) The SCNs control clock genes in a number of tissues and organs throughout the body.
(D) The SCNs are a less significant factor in regulating blood pressure than scientists once believed.
(E) The SCNs are less strongly affected by changes in light levels than are by other external cues.

I generally commit mistake in these type of question where it is asked that author probably agree/disagree in the passage? Is there any way to improve on it please?