OG－5－25

xealot

^_^，我觉得“这种特定embryo的个别性”确实存在，但我有点不同意见，我认为：问题中 the morphogenetic determinants present in the early embryo 是不受这种个别性所影响的，E选项所述内容是完全准确地正确的。

Sigh... 还是不明白，为什么不受这种个别性影响呢~~？

wangyu73cn

我理解，你所说的个别性，是有的切割后的单体胚胎能够存活，有的单体胚胎不能存活。我所说不受影响，是说，只要切割得当，那胚胎完全是可以存活的。也就是说，只要切割得当，其形态基因决定物质是可以供多个胚胎正常存活的，因此，是能够满足一个以上的胚胎需要的。可能有误解之处，再探讨。
形象上，这有点像单胞胎和双胞胎，甚至多胞胎的形成机制。每个单胞胎蕴涵着发展成为双胞胎的可能。

[此贴子已经被作者于2005-3-11 13:23:33编辑过]

xealot

我所说不受影响，是说，只要切割得当，那胚胎是可以存活的。

其实从常识上，偶十分赞成你的说法；偶觉得不爽的原因是原文中不太看的出这种合理的推断，或者说暗示，而这种推断/暗示是GMAT考试强调的...

偶觉得我们的理解差异存在于对推断/暗示的深度的看法上...是一个more or less的问题，而不是一个yes or no的问题...

wangyu73cn

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.
这句说，无脊椎动物胚胎可以分成两个正常胚胎。

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.
这使他们相信胚胎中的每个细胞都有潜力以多种方式生长。

Later biologists found that the situation was not so simple. It matters in which plane the embryo is cut.
是否可以分成两个正常胚胎在于分割面。

If it is cut in a plane different from the one used by the early investigators, it will not form two whole embryos.
如果不以原先分割面进行切割，则不能形成两个完整的胚胎。

从上述来看，科学家们质疑第一句内容的焦点在于切割面，即是否能分成两个正常胚胎与分割面有关。而如果排除这种切割面的因素，象原来那样切割得当，就不能否定第一句中的命题了。当然，我同意楼上的观点，这是一个程度上的问题，而不是一个是与非的问题。E是最好的选项。

bigmouse

请问这篇文章的30题为什么答案D为什么不对？正确答案是C

30. 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

wangyu73cn

Studying sea urchins, biologist Paul Gross found

that an unfertilized egg contains substances that func-

tion as morphogenetic determinants. They are located

in the cytoplasm of the egg cell; i.e., in that part of the

(30) cell’s protoplasm that lies outside of the nucleus.

由上可知，morphogenetic determinants存在于cytoplasm之中，而不是cytoplasm(细胞质)

skidals

  30题中OG的解释 C is the best answer. Lines 26-28 in from us that in his study of sea urchins, Gross “found that an unfertilized egg contains substances that function as morphogetic determinants.” Lines 39-40 assert that the “substances that Gross studied are maternal messenger RNA’s,” and in lines 41-42 we learn that these maternal messenger RNA’s can be found in “ a wide variety of organisms.” B is incorrect. Although after becoming active these messenger RNA’s are said to direct the synthesis of histones, the synthesis of the histones is said to occur after, not before, the egg has been fertilized. 标绿色的对解题有什么作用，我觉得没有这句话也能作出这道题目亚？

wangyu73cn

C is the best answer.

Lines 26-28 in from us that in his study of sea urchins, Gross “found that an unfertilized egg contains substances that function as morphogetic determinants.”
只说明了sea urchins的特殊情况。

Lines 39-40 assert that the “substances that Gross studied are maternal messenger RNA’s,” and in lines 41-42 we learn that these maternal messenger RNA’s can be found in “ a wide variety of organisms.”
这里将这种物质扩大到多种生命有机体中。也就是递进了一下。更加对应问题的题目。

注：我在上一个帖子中强调的是D选项的错误。

swlfx

楼上不愧是大牛，顶。

swlfx

谢王牛牛.