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OG Scientists long believed that two nerve clusters

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OG Scientists long believed that two nerve clusters

Post Thu Jul 27, 2017 7:43 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    Scientist long believed that two nerve cluster 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.

    412) 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

    413) 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

    414) 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.

    Q412: D
    Q413: D
    Q414: B

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    Post Fri Jul 28, 2017 12:47 pm
    Paragraph Tone, and Quick Summary (Ladder):
    1 = SCN role; input/output
    2 =/+ Circadian rhythm not limited to SCNs (other organs)

    Analysis:
    This passage is a surprisingly complex biology Passage given it’s placement in the OG, which is generally sorted by order of difficulty. Our ladder really helps us to distinguish the roles of the 2 paragraphs. The first paragraph is neutral in that it describes the role of SCNs, including what influences them, and how they influence the body’s sleep cycle. Paragraph 2 is where the author really establishes the agenda of the passage. Here the author really appears to be going out of the way to highlight the idea that circadian rhythm is not limited to SCNs; specifically that other organs play a role.

    412) 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

    Type: Passage Purpose
    Analysis: Paragraph one just sets the stage, and it's really paragraph 2 in which the author gets to the primary purpose of the passage. The author is going out of the way to build awareness that circadian clocks and other organs play a role, and that SCNs don't tell the whole story.

    A This option has the right tone, but it just gets it backwards. It’s not that the author is challenging recent findings that appear to contradict earlier findings. It’s that the prior findings appear to be contradicted by newer findings. Gone.
    B This option plays it too neutral. The author isn't merely acting as a mediator between two sides. In the 2nd paragraph, the author is clearly trying to inform readers that the other organs play a role in that the prior, and that circadian cycles are not just dictated by SCNs. The author is placing far too great a stand in challenging the older understanding to label the purpose of the passage as a presentation of two sides of an ongoing debate.
    C This option goes too far. Reporting answers is a very different concept than updating a view. Just because the author announces the new evidence appears to contradict the prior understanding in no way reaches the level of providing absolute answers to questions that have long puzzled researchers. Think about that. Have scientists actually answered a question? I mean, definitively solved the mystery? No. For all we know the author could be intrigued by the new findings but in no way is comfortable making any firm conclusions at this point. This option is to extreme in that regard, and is absolutely there for wrong.
    D Yes, here we go. The second paragraph concludes that scientists now believe that circadian clocks and other organs and tissues May respond to external cues other than light. Therefore the primary purpose of this passage is to discuss the evidence that has caused a long-standing belief to be revised.
    E This option warps the perspective of the passage. It's not that the issue is commonly misunderstood, but rather that new evidence required an update to the overall understanding. We can't actually conclude from this passage that at this point in time the concept is even commonly misunderstood. Perhaps the scientific community has actually reached a consensus.

    D

    413) 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

    Type: Detail EXCEPT
    Analysis: Four options will entail things that are specifically mentioned as a function regulated by SCNs, and one option will not be specifically mentioned as a function regulated by SCNs. That will be the correct option. Since we know the details except questions tend to draw from a list in the passage, we could have seen this question coming a mile away when we got to this part of the passage:
    “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”

    Let’s start attacking the options. Cross out any option that's included in the list.

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

    A, B, C, and E were all specifically mentioned. Only D was not, so it’s the correct option.
    D

    414) 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 they are by other external cues.

    Type: Author Agree Inference
    Analysis: We need to select the option that we can conclude with absolute certainty is something the author would have to agree with.

    A) The passage is just saying that SCNs work and play a role in the Circadian rhythm it, not that SCNs are actually found in other organs.
    B) Here we go. This option absolutely nails it. The author is saying that, yes, SCNs play a role but SCNs are not the exclusive factor in regulating circadian rhythm.
    C) This option is directly contradicted by the sentence in paragraph 2 that mentions “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”. That means we can’t say that the author would attribute control of clock genes specifically to SCNs. Chuck it.
    D) The author is not discounting the role that SCNs play, but rather revising the understanding that there is a bigger range of inputs on circadian rhythm than just SCNs alone. Although this is a tempting option, the passage does not enable us to conclude that the author would agree that SCNs are any less significant. It could very well be that the SCNs are highly significant, and that the author is just pointing out that other factors might play some additional, and supporting role for all we know.
    E) This option brutally warps the passage. The passage acknowledges that SCNs are impacted by light, but the revision is that there are other factors besides SCNs that play a role in Circadian rhythm.
    B

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