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Post your answer with explanation! Nearly a century ago,

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Post your answer with explanation! Nearly a century ago, [#permalink] New post 04 Aug 2008, 10:14
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Nearly a century ago, biologists found that if they separated an invertebrate animal embryo into two parts at an early stage of its life, it would survive and develop as two normal embryos. This led them to believe that the cells in the early embryo are undetermined in the sense that each cell has the potential to develop in a variety of different ways. Later biologists found that the situation was not so simple. It matters in which plane the embryo is cut. If it is cut in a plane different from the one used by the early investigators, it will not form two whole embryos.

A debate arose over what exactly was happening. Which embryo cells are determined, just when do they become irreversibly committed to their fates, and what are the “morphogenetic determinants” that tell a cell what to become? But the debate could not be resolved because no one was able to ask the crucial questions in a form in which they could be pursued productively. Recent discoveries in molecular biology, however, have opened up prospects for a resolution of the debate. Now investigators think they know at least some of the molecules that act as morphogenetic determinants in early development. They have been able o show that, in a sense, cell determination begins even before an egg is fertilized.
Studying sea urchins, biologist Paul Gross found that an unfertilized egg contains substances that function as morphogenetic determinants. They are located in the cytoplasm of the egg cell; i.e., in that part of the cell’s protoplasm that lies outside of the nucleus. In the unfertilized egg, the substances are inactive and are not distributed homogeneously. When the egg is fertilized, the substances become active and, presumably, govern the behavior of the genes they interact with. Since the substances are unevenly distributed in the egg, when the fertilized egg divides, the resulting cells are different from the start and so can be qualitatively different in their own gene activity. The substances that Gross studied are maternal
messenger RNA’s --products of certain of the maternal genes. He and other biologists studying a wide variety of organisms have found that these particular RNA’s direct, in large part, the synthesis of histones, a class of proteins that bind to DNA. Once synthesized, the histones move into the cell nucleus, where section of DNA wrap around them to form a structure that resembles beads, or knots, on a string. The beads are DNA segments wrapped around the histones; the string is the intervening DNA. And it is the structure of these beaded
DNA strings that guides the fate of the cells in which they are located.
1. It can be inferred from the passage that the initial production of histones after an egg is fertilized takes place
(A) in the cytoplasm
(B) in the maternal genes
(C) throughout the protoplasm
(D) in the beaded portions of the DNA strings
(E) in certain sections of the cell nucleus

2. According to the passage, the morphogenetic determinants present in the unfertilized egg cell are which of the
following?
(A) Proteins bound to the nucleus
(B) Histones
(C) Maternal messenger RNA’s
(D) Cytoplasm
(E) Nonbeaded intervening DNA


Last edited by lexis on 07 Aug 2008, 20:51, edited 1 time in total.
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Re: RC: Embryolic Research. [#permalink] New post 05 Aug 2008, 01:34
At the end of the nineteenth century, a rising interest
in Native American customs and an increasing desire to
understand Native American culture prompted ethnologists
to begin recording the life stories of Native Amer-
(5) ican. Ethnologists had a distinct reason for wanting to
hear the stories: they were after linguistic or anthropological
data that would supplement their own field
observations, and they believed that the personal
stories, even of a single individual, could increase their
(10) understanding of the cultures that they had been
observing from without. In addition many ethnologists
at the turn of the century believed that Native American
manners and customs were rapidly disappearing,
and that it was important to preserve for posterity as
(15) much information as could be adequately recorded
before the cultures disappeared forever.
There were, however, arguments against this method
as a way of acquiring accurate and complete information.
Franz Boas, for example, described autobiogra-
(20) phies as being “of limited value, and useful chiefly for
the study of the perversion of truth by memory,” while
232
Paul Radin contended that investigators rarely spent
enough time with the tribes they were observing, and
inevitably derived results too tinged by the investi-
(25) gator’s own emotional tone to be reliable.
Even more importantly, as these life stories moved
from the traditional oral mode to recorded written
form, much was inevitably lost. Editors often decided
what elements were significant to the field research on a
(30) given tribe. Native Americans recognized that the
essence of their lives could not be communicated in
English and that events that they thought significant
were often deemed unimportant by their interviewers.
Indeed, the very act of telling their stories could force
(35) Native American narrators to distort their cultures, as
taboos had to be broken to speak the names of dead
relatives crucial to their family stories.
Despite all of this, autobiography remains a useful
tool for ethnological research: such personal reminis-
(40) cences and impressions, incomplete as they may be, are
likely to throw more light on the working of the mind
and emotions than any amount of speculation from an
ethnologist or ethnological theorist from another
culture.


3. It can be inferred from the passage that a characteristic of the ethnological research on Native Americans conducted during the nineteenth century was the use of which of the following?
(A) Investigators familiar with the culture under study
(B) A language other than the informant’s for recording life stories
(C) Life stories as the ethnologist’s primary source of information
(D) Complete transcriptions of informants’ descriptions of tribal beliefs
(E) Stringent guidelines for the preservation of cultural data
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Re: RC: Embryolic Research. [#permalink] New post 07 Aug 2008, 17:02
1st paragraph:
1. A . The passage says "Once synthesized, the
histones move into the cell nucleus", implying that the initial production is in the cytoplasm

2. C
"The substances that Gross studied are maternal messenger RNA’s --products of certain of the maternal
genes."
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Re: RC: Embryolic Research. [#permalink] New post 07 Aug 2008, 17:13
2nd passage:
I think B. In the second paragrahp, the author notes some limitations of the method of research: "these life stories moved
from the traditional oral mode to recorded written form", and "Native Americans recognized that the essence of their lives could not be communicated in English", which is the interviewers' language. So B is inferred.
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Re: RC: Embryolic Research. [#permalink] New post 07 Aug 2008, 20:58
chan_nhu78 wrote:
1st paragraph:
1. A . The passage says "Once synthesized, the
histones move into the cell nucleus", implying that the initial production is in the cytoplasm
"


Why not E? In "in certain sections of the cell nucleus"


OA:
Pas1:
2.C
Pas2.
3.B
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Re: RC: Tough (Various sources) [#permalink] New post 07 Aug 2008, 20:59
Pas.3

Historians who study European women of the Renaissance try to measure independence,” “options,” and other indicators of the degree to which the expression of women’s individuality was either permitted or suppressed. Influenced by Western individualism, these historians define a peculiar form of personhood: an innately bounded unit, autonomous and standing apart from both nature and society. An anthropologist, however, would contend that a person can be conceived in ways other than as an “individual.” In many societies a person’s identity is not intrinsically unique and self-contained but instead is defined within a complex web of social relationships.
In her study of the fifteenth-century Florentine widow Alessandra Strozzi, a historian who specializes in European women of the Renaissance attributes individual intention and authorship of actions to her subject. This historian assumes that Alessandra had goals and interests different from those of her sons, yet much of the historian’s own research reveals that Alessandra acted primarily as a champion of her sons’ interests, taking their goals as her own. Thus Alessandra conforms more closely to the anthropologist’s notion that personal motivation is embedded in a social context. Indeed, one could argue that Alessandra did not distinguish her personhood from that of her sons. In Renaissance Europe the boundaries of the conceptual self were not always firm and closed and did not necessarily coincide with the boundaries of the bodily self.

4. It can be inferred that the author of the passage believes which of the following about the study of Alessandra Strozzi done by the historian mentioned in the second paragraph?
A. Alessandra was atypical of her time and was therefore an inappropriate choice for the subject of the historian’s research.
B. In order to bolster her thesis, the historian adopted the anthropological perspective on personhood.
C. The historian argues that the boundaries of the conceptual self were not always firm and closed in Renaissance Europe.
D. In her study, the historian reverts to a traditional approach that is out of step with the work of other historians of Renaissance Europe.
E. The interpretation of Alessandra’s actions that the historian puts forward is not supported by much of the historian’s research
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Re: RC: Tough (Various sources) [#permalink] New post 07 Aug 2008, 23:30
4.C
I inferred from the statement.

In many societies a person’s identity is not intrinsically unique and self-contained but instead is defined within a complex web of social relationships.


I am not good at the inference question. Please post your comments
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Re: RC: Tough (Various sources) [#permalink] New post 12 Aug 2008, 09:05
amkumar2 wrote:
4.C
I inferred from the statement.

In many societies a person’s identity is not intrinsically unique and self-contained but instead is defined within a complex web of social relationships.


I am not good at the inference question. Please post your comments


Sorry! C is not correct answer.
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Re: RC: Tough (Various sources) [#permalink] New post 16 Aug 2008, 12:41
IMO E) The interpretation of Alessandra’s actions that the historian puts forward is not supported by much of the historian’s research
"This historian assumes that Alessandra had goals and interests different from those of her sons, yet much of the historian’s own research reveals that Alessandra acted primarily as a champion of her sons’ interests, taking their goals as her own."

Historians assumed that Alessandra's goals are different from her sons BUT research revealed something different that she acted promarily as sons' interest. Therefore interpretation is different from research. E states the same.
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Re: RC: Embryolic Research. [#permalink] New post 16 Aug 2008, 23:04
lexis wrote:
chan_nhu78 wrote:
1st paragraph:
1. A . The passage says "Once synthesized, the
histones move into the cell nucleus", implying that the initial production is in the cytoplasm
"


Why not E? In "in certain sections of the cell nucleus"


OA:
Pas1:
2.C
Pas2.
3.B

Histones are produced in cytoplasm and cytoplasm is the portion of cell
outside the nucleus.
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Re: Post your answer with explanation! Nearly a century ago, [#permalink] New post 17 Nov 2013, 15:19
lexis wrote:
Nearly a century ago, biologists found that if they separated an invertebrate animal embryo into two parts at an early stage of its life, it would survive and develop as two normal embryos. This led them to believe that the cells in the early embryo are undetermined in the sense that each cell has the potential to develop in a variety of different ways. Later biologists found that the situation was not so simple. It matters in which plane the embryo is cut. If it is cut in a plane different from the one used by the early investigators, it will not form two whole embryos.

A debate arose over what exactly was happening. Which embryo cells are determined, just when do they become irreversibly committed to their fates, and what are the “morphogenetic determinants” that tell a cell what to become? But the debate could not be resolved because no one was able to ask the crucial questions in a form in which they could be pursued productively. Recent discoveries in molecular biology, however, have opened up prospects for a resolution of the debate. Now investigators think they know at least some of the molecules that act as morphogenetic determinants in early development. They have been able o show that, in a sense, cell determination begins even before an egg is fertilized.
Studying sea urchins, biologist Paul Gross found that an unfertilized egg contains substances that function as morphogenetic determinants. They are located in the cytoplasm of the egg cell; i.e., in that part of the cell’s protoplasm that lies outside of the nucleus. In the unfertilized egg, the substances are inactive and are not distributed homogeneously. When the egg is fertilized, the substances become active and, presumably, govern the behavior of the genes they interact with. Since the substances are unevenly distributed in the egg, when the fertilized egg divides, the resulting cells are different from the start and so can be qualitatively different in their own gene activity. The substances that Gross studied are maternal
messenger RNA’s --products of certain of the maternal genes. He and other biologists studying a wide variety of organisms have found that these particular RNA’s direct, in large part, the synthesis of histones, a class of proteins that bind to DNA. Once synthesized, the histones move into the cell nucleus, where section of DNA wrap around them to form a structure that resembles beads, or knots, on a string. The beads are DNA segments wrapped around the histones; the string is the intervening DNA. And it is the structure of these beaded
DNA strings that guides the fate of the cells in which they are located.
1. It can be inferred from the passage that the initial production of histones after an egg is fertilized takes place
(A) in the cytoplasm
(B) in the maternal genes
(C) throughout the protoplasm
(D) in the beaded portions of the DNA strings
(E) in certain sections of the cell nucleus

2. According to the passage, the morphogenetic determinants present in the unfertilized egg cell are which of the
following?
(A) Proteins bound to the nucleus
(B) Histones
(C) Maternal messenger RNA’s
(D) Cytoplasm
(E) Nonbeaded intervening DNA



I'll go with A and C on this one.

Cheers
J :)
Re: Post your answer with explanation! Nearly a century ago,   [#permalink] 17 Nov 2013, 15:19
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