Scientist long believed that two nerve cluster in the human

Question

Scientists long believed that two nerve clusters in the human hypothalamus, called suprachiasmatic nuclei (SCNs), were what controlled our circadian rhythms. Those rhythms are the biological cycles that recur approximately every 24 hours in synchronization with the cycle of sunlight and darkness caused by Earth’s rotation. Studies have demonstrated that in some animals, the SCNs control daily fluctuations in blood pressure, body temperature, activity level, and alertness, as well as the nighttime release of the sleep-promoting agent melatonin. Furthermore, cells in the human retina dedicated to transmitting information about light level to the SCNs have recently been discovered.

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. 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. While scientists do not dispute the role of the SCNs in controlling core functions such as the regulation of body temperature and blood pressure, 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.   1 
 1. The primary purpose of the passage is to

(A) challenge recent findings that appear to contradict earlier findings
(B) present two sides of an ongoing scientific debate
(C) report answers to several questions that have long puzzled researchers
(D) discuss evidence that has caused a longstanding belief to be revised
(E) attempt to explain a commonly misunderstood biological phenomenon

2 
 2. The passage mentions each of the following as a function regulated by SCNs in same animals EXCEPT

(A) activity level
(B) blood pressure
(C) alertness
(D) vision
(E) temperature

3 
 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.

mikemcgarry · Accepted Answer

Dear JarvisR , I'm happy to respond. :-)

This of course is the 3rd RC passage in the OG2016, and the questions are RC #8-10. The primary purpose of the passage is to A) challenge recent findings that appear to contradict earlier findings B) present two sides of an ongoing scientific debate C) report answers to several questions that have long puzzled researchers D) discuss evidence that has caused a longstanding belief to be revise E) attempt to explain a commonly misunderstood biological phenomenon In Par 1, he talks about the role of the SCN in regulating circadian rhythms. In Par. 2, he cites new evidence that is not entirely compatible with the SCN running everything. The first paragraph really sets the stage of what the author wants to say. The second paragraph is really the author's main point, the juicy point he want to make--- the first paragraph just sets the stage so we have context for the second paragraph. The "SCN runs the whole thing" theory was called "long believed," so it is a longstanding theory that the new evidence calls into question, causing scientist to revise the longstanding theory. This is what (D) says. The passage mentions each of the following as a function regulated by SCNs in same animals EXCEPT A) activity level B) blood pressure C) alertness D) vision E) temperature The choices (A) , (B) , (C) , and (E) are all mentioned, in the second half of the first paragraph, as functions that the SCN controls. By contrast, vision is tricky. The SCN doesn't "control" vision. Instead, vision provides the crucial data, information about natural light, that allows the SCN to do its job. The SCN depends on vision, it doesn't control it. OA = (D) . 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. No, nonsense. The regulation of circadian rhythms occurs elsewhere in the body, but there is no SCN outside the hypothalamus. B) The SCNs play a critical but not exclusive role in regulating circadian rhythms. A good balanced assessment. The SCN is important, but is no longer believed to be "the only show in town." This is promising. C) The SCNs control clock genes in a number of tissues and organs throughout the body. There's zero evidence for this. The SCN is discussed, and then later, gene clocks with a similar role are discuss, but no connection is made back to the SCN. D) The SCNs are a less significant factor in regulating blood pressure than scientists once believed. The second paragraph says: " While scientist do not dispute the role of the SCNs in controlling core functions such as ... blood pressure ." This choice directly contradicts this quote. E) The SCNs are less strongly affected by changes in light levels than are by other external cues. No. Confuses different things. The SCNs respond to light. The gene clocks & circadian clocks in other parts of the body respond to other external cues. OA = (B) Here's a blog you may find useful: https://magoosh.com/gmat/2012/gmat-rc-el ... g-answers/ Does all this make sense? Please let me know if you have any further questions about any of these. Mike :-)

MagooshExpert · Answer

Hi rajatbanik , Carolyn from Magoosh here -- I can step in for Mike

This option is definitely tempting! Choice E) here states: E) attempt to explain a commonly misunderstood biological phenomenon Presumably, this "biological phenomenon" is the biological cycles, or circadian rhythms. Now, part of this fits, in a sense -- it seems reasonable to describe circadian rhythms as a "commonly misunderstood biological phenomenon". However, does the passage attempt to explain it ? Not really -- it mostly just describes the existing theory, and the problems with the theory. It doesn't present any alternative explanation, it just says that something other than SCNs must also contribute to the phenomenon of circadian rhythms. The passage mentions a few things like temperature changes, but it definitely doesn't focus on any particular alternative explanation. So, we can't say that attempting to explain this phenomenon is the primary purpose of this passage. Choice D fits better

Hope that helps!

-Carolyn

rajatbanik · Answer

Hi Mike,

I am having confusion in Q1. in both option D and E. I chose E due to the fact that it was long standing belief on SCNs,however in the last sentence the scientist agreed the role of SCNs and provided an new piece of information for cardiac system.

So why D is correct.

AliciaSierra · Answer

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

mikemcgarry · Answer

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

Gmatprep550 · Answer

I felt that A also could be answer as

"Par. 2, he cites new evidence that is not entirely compatible with the SCN running everything"  Which can be also inferred as "recent findings that appear to contradict earlier findings"

Not sure if I making any mistake in understanding it.

XyLan · Answer

In RC, The correct answer should be correct on  ALL  grounds, i.e.,  100% in line with the passage.

Excerpt from the passage: 
 
 While scientists do not dispute the role of the SCNs in controlling core functions such as the regulation of body temperature and blood pressure, 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.

The gist of the above lines:
 
Scientists (now believe): Apart from SCNs, Clocks MAY respond to external cues other than light.

The author  agrees  with the above-mentioned stance of the scientists. ( the recent findings ).

To answer your query  :

True, the recent findings MAY appear contradicting to earlier findings.
However, 
Reading entire Q in conjunction with Option A:  challenge recent findings that appear to contradict earlier findings . 
 
 The primary purpose of the passage is to  challenge  recent findings that appear to contradict earlier findings

No where in the passage the author  challenges  the recent findings.
 The author is not in disagreement with the recent findings.

Moreover, he   emphasizes to add   the recent findings to the earlier findings, suggesting longstanding belief to be revised.

homersimpsons · Answer

OE 
Q1. The primary purpose of the passage is to
A. challenge recent findings that appear to contradict earlier findings
B. present two sides of an ongoing scientific debate
C. report answers to several questions that have long puzzled researchers
D. discuss evidence that has caused a long-standing belief to be revised
E. attempt to explain a commonly misunderstood biological phenomenon
 Main idea 
This question depends on understanding the passage as a whole. The passage begins by describing a longheld belief regarding humans’ circadian rhythms: that the SCNs control them. It then goes on to explain that new findings have led scientists to believe that other organs and tissues may be involved in regulating the body’s circadian rhythms as well.
A. The passage does not challenge the more-recent findings. Furthermore, the recent findings that the passage recounts do not contradict earlier findings; rather, when placed alongside those earlier findings, they have led scientists to reach additional conclusions.
B. The passage does not discuss a two-sided debate; no findings or conclusions are disputed by any figures in the passages.
C. There is only one question at issue in the passage: whether the SCN alone control human circadian rhythms. Furthermore, nothing in the passage suggests that researchers have been puzzled for a long time about this.
D.  Correct . The new evidence regarding circadian rhythm–related gene activity in all the body’s tissue has led scientists to revise their long-standing belief that the SCN alone control circadian rhythms.
E. The biological phenomenon of circadian rhythms is not, at least as far as the passage is concerned, misunderstood. Its causes are being investigated and refined.
 The correct answer is D.

Q2. The passage mentions each of the following as a function regulated by the SCNs in some animals EXCEPT
A. activity level
B. blood pressure
C. alertness
D. vision
E. temperature
 Supporting idea 
This question asks about what is NOT specifically mentioned in the passage with regard to functions regulated by the SCN. Those functions, as identified in the passage, are blood pressure, body temperature, activity level, alertness, and the release of melatonin.
A. The passage includes activity level in its list of functions regulated by the SCN.
B. The passage includes blood pressure in its list of functions regulated by the SCN.
C. The passage includes alertness in its list of functions regulated by the SCN.
D.  Correct . While the passage does say that cells in the human retina transmit information to the SCN, there is no suggestion that the SCN reciprocally control vision.
E. The passage includes temperature in its list of functions regulated by the SCN.
 The correct answer is D.

Q3. The author of the passage would probably agree with which of the following statements 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 they are by other external cues.
 Main idea 
The author of the passage discusses the SCN in the passage in order to explain that they are most likely not, as long believed, solely responsible for the control of our circadian rhythms.
A. The author states that the SCN are nerve clusters in the hypothalamus, and nothing in the passage contradicts or undermines the supposition that they are only in the hypothalamus.
B.  Correct . The author points out in the second paragraph that the SCN control core circadian function, but that circadian clocks found elsewhere in the body have an effect as well.
C. The evidence offered in the second paragraph about the activity of the clock gene in rat livers suggests that these clock genes are not under the SCN’s control. The passage does not suggest that the SCN control any of the non-SCN controllers of circadian rhythms.
D. The author states in the second paragraph that scientists do not dispute the idea that the SCN regulate blood pressure.
E. The first paragraph indicates that the SCN respond to light levels; clock genes in other tissues are the ones that may respond to other external cues.
 The correct answer is B.

ag153 · Answer

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.

egmat   ScottTargetTestPrep   GMATNinja   ManhattanPrep 
 mikemcgarry   MagooshExpert   KarishmaB

Hoozan · Answer

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)

KarishmaB · Answer

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.

Hoozan · Answer

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)?

KarishmaB · Answer

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.

KarishmaB · Answer

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

ag153 · Answer

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

KarishmaB · Answer

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.

mohitwadhwa28 · Answer

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?

armaankumar · Answer

Scientists long believed that two nerve clusters in the human hypothalamus, called suprachiasmatic nuclei (SCNs), were what controlled our circadian rhythms. Those rhythms are the biological cycles that recur approximately every 24 hours in synchronization with the cycle of sunlight and darkness caused by Earth’s rotation. Studies have demonstrated that in some animals, the SCNs control daily fluctuations in blood pressure, body temperature, activity level, and alertness, as well as the nighttime release of the sleep-promoting agent melatonin. Furthermore, cells in the human retina dedicated to transmitting information about light level to the SCNs have recently been discovered.

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. 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. While scientists do not dispute the role of the SCNs in controlling core functions such as the regulation of body temperature and blood pressure, 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.

1. The primary purpose of the passage is to

(A) challenge recent findings that appear to contradict earlier findings 
There is not a challenge rather an acceptance.

(B) present two sides of an ongoing scientific debate 
There is no conflict of opinion throughout the passage

(C) report answers to several questions that have long puzzled researchers 
The passage suggests that researchers were already clear about the functioning of SCNs. Further information has expanded their understanding.

(D) discuss evidence that has caused a longstanding belief to be revised 
The revision is that factors other than light affect the SCNs.

(E) attempt to explain a commonly misunderstood biological phenomenon 
The passage does not suggest anywhere that the functioning of SCNs is misunderstood

2. The passage mentions each of the following as a function regulated by SCNs in same animals EXCEPT

(A) activity level 
 (B) blood pressure 
 (C) alertness 
 (D) vision 
 (E) temperature

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. 
Cells sending information to SCNs are present in other body parts but not SCNs themselves.

(B) The SCNs play a critical but not exclusive role in regulating circadian rhythms. 
The first line of the passage says the SCNs are what controls the circadian rhythms, but the last passage suggests that other external clues also play a role.

(C) The SCNs control clock genes in a number of tissues and organs throughout the body. 
This is not mentioned anywhere in the passage.

(D) The SCNs are a less significant factor in regulating blood pressure than scientists once believed. 
The passage doesn't undermine the role of SCNs in regulating blood pressure.

(E) The SCNs are less strongly affected by changes in light levels than are by other external cues. 
The passage suggests external cues also affecting SCNs but doesn't undermine the role of light levels.

GMATNinja · Answer

Question 3 
 
To accurately answer questions like this (and RC questions in general), start by thinking through  why  the author wrote the passage. What is he/she trying to accomplish?

In the first paragraph, the author tells us about something that was "long believed": that SCNs control our circadian rhythms. In the second paragraph, the author gives us some updated information: while SCNs play a role, circadian clocks in other organs and tissues ALSO impact circadian rhythms.

So overall, why did the author write this passage? To introduce and support an updated belief about circadian rhythms.

The next thing to consider is the exact language of the question, which asks which answer choice the author would " probably  agree with" regarding SCNs. The word "probably" means that the author might not outright state what he/she thinks -- we may have to make an inference based on the evidence in the passage.

Finally, go through process of elimination:
 
The author wouldn't agree with this, because he/she tells us that SCNs are located in the hypothalamus, while  different  "critical genes" exist in other tissues and also control circadian rhythms.

Eliminate (A).

This is right in line with the information in the second paragraph! Now, the author doesn't explicitly say that he/she agrees with this hypothesis, but the information is presented and not critiqued in any way. So, we have enough to say that the author would  probably  agree with (B).

The info in the passage says that BOTH the SCNs and the other "critical genes" control circadian rhythms. There's no implication at all that the SCNs control the "critical genes." We can't say that the author would agree with (C), so get rid of it.

The new scientists  agree  with the old scientists about the SCNs' role "in controlling core functions such as the regulation of body temperature and  blood pressure ." The author never undermines this fact at all. So, the author wouldn't agree with (D).

In the second paragraph, we learn that the "SCNs remained synchronized with light cycles" while the clocks in other organs shift based on feeding patterns. So, the author wouldn't agree that SCNs are LESS affected by changes in light than by other external cues -- if anything, the author would support the opposite claim.

(E) is out, and (B) is the correct answer.

I hope that helps!

Scientist long believed that two nerve cluster in the human

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Scientist long believed that two nerve cluster in the human

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