Nearly a century ago, biologists found that if they separated an inver

Question 2

Let's start by considering some key points from the third paragraph:

• Morphogenetic determinants are found in the cytoplasm of the unfertilized egg cell (outside the nucleus).
• The morphogenetic determinants are inactive, but become active when the egg is fertilized
• The morphogenetic determinants are not distributed homogeneously (not distributed evenly).

Let's now consider the answer choices:


Since the morphogenetic determinants are located outside the nucleus, (A) is out.


Since the morphogenetic determinants are NOT distributed homogeneously (i.e. NOT distributed evenly), we can eliminate (B).


According to paragraph 3, the morphogenetic determinants become active when the egg is fertilized. Since the embryo develops AFTER the egg is fertilized, the morphogenetic determinants in the early embryo must already be active. Because (C) claims that the morphogenetic determinants in the early embryo are inactive, it's wrong. Eliminate (C).


The morphogenetic determinants in the unfertilized egg are inactive, while the morphogenetic determinants in the early embryo are active. So the morphogenetic determinants in the unfertilized egg can't be identical to those in the early embryo, and (D) is out.


In the first paragraph, we learn that if an embryo is separated into two parts "at an early stage of its life," it develops into two normal embryos. Since one early embryo can develop into two embryos when cut in half, there must have been enough morphogenetic determinants in the early embryo for both of them (i.e. more than was needed for a single individual). So (E) is correct.

Hello, any expert can explain Q6? Why is E wrong? Thanks in advance.

Question 6

Here's question 6:

Fertilization of an egg is discussed in the second and third paragraphs. In the second paragraph we learn that certain substances are already present in an unfertilized egg, but those substances are inactive until the egg is fertilized. The third paragraph gives us more detail on what happens once the egg is fertilized.

Here's (E):

The issue with (E) is the word "generation." The fertilization of an egg doesn't generate the morphogenetic determinants -- those things are already present in the unfertilized egg. Fertilization makes those substances become active, but does not actually generate the substances in the first place.

(E) is out for question 6.

Here's (B):

In paragraph 3, the author tells us that after fertilization, the RNA's become active and synthesize histones.

(B) is the correct answer to question 6.

I hope that helps!

For question 2, I still think that choice A can be correct.

In paragraph 2, the passage says "what are the “morphogenetic determinants” ", implying that the determinants could be more than one thing. It is true that maternal messenger RNA's, as mentioned explicitly, is one of the morphogenetic determinants. But from the last sentence that the beaded DNA strings guide the fate of the cell, aligning with the definition of the morphogenetic determinants in the paragraph 2 that they tell a cell what to do, these beaded DNA strings can be another morphogenetic determinant. And these strings are located in the nucleus of embryo cells, so I think answer choice A can be correct.

Could experts please suggest what's wrong with my reasoning? Thank you!

Question 2

As you point out, the passage tells us that certain "morphogenetic determinants" are located outside the nucleus ("maternal messenger RNA's"). We also learn that these substances "direct the synthesis of histones," which move into the cell nucleus. So do these histones count as morphogenetic determinants?

Well, the passage defines a morphogenetic determinant as something that "tells a cell what to become." Based on the description of "maternal messenger RNA's," it's clear they fit this bill -- since they start the process of determining a cell's development, they "tell a cell what to become." Considering this analysis, it sounds like the histones themselves aren't "telling the cell what to become" exactly. They're merely doing what the "maternal messenger RNA's" told them to do. So from that angle, they aren't "morphogenetic determinants."

From another angle: let's pretend for a moment that histones actually could be considered "morphogenetic determinants." And let's say we justify this idea because histones are carrying out the steps started by the maternal messenger RNA. By that logic, DNA itself would also have to be a morphogenetic determinant, since it's also part of this process. And what about the next step in the process -- would that also involve "morphogenetic determinants?" And what about all of the steps that come after that?

Notice this chain of reasoning leads to a problematic conclusion: anything involved along the way in this causal chain is a "morphogenetic determinant." By contrast, the idea that the first step in the chain is the "morphogenetic determinant" aligns better with the intention of the passage.

For that reason, we can conclude that histones are not "morphogenetic determinants," and (A) is incorrect.

I hope that helps!

Can someone please explain Q4 please, I don't understand the part "as far as the fate of the two parts was concerned"
Thank you so much.

Question 4

Question 4 asks us about the mistakes made by biologists who "believed that the cells in the early embryo were undetermined."

These biologists are the ones discussed at the beginning of the first paragraph. Nearly a century ago, they sliced some embryos in two and discovered that BOTH of the pieces became full embryos. This led them to believe that the embryos were "undetermined," or, in other words, that they were not fated to become any particular thing. The bits of the half-embryos could adapt and become whatever they needed to be.

Later, some different biologists found that it wasn't that simple: they "cut [the embryos] in a plane different from the one used by the early investigators," and suddenly the two pieces did NOT become full embryos. Just by slicing the embryos differently, they didn't get the same result as the earlier biologists. The "fates" of the embryos were more determined than previously believed.

So, what mistake did the earlier biologists make? They sliced the embryos in one particular way and drew a conclusion without confirming that the WAY that they made the slice would impact the results. That's precisely what (E) says:

Separating the embryos in one way made it seem like the fates of the embryos were "undetermined." Separating them in another way showed the opposite.

(E) is the correct answer to question 4.

I hope that helps!­
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2. It can be inferred from the passage that the morphogenetic determinants present in the early embryo are

(A) located in the nucleus of the embryo cells
(B) evenly distributed unless the embryo is not developing normally
(C) inactive until the embryo cells become irreversibly committed to their final function
(D) identical to those that were already present in the unfertilized egg
(E) present in larger quantities than is necessary for the development of a single individual

I was unable to zero in on E as the answer. However, later analysis revealed that is is indeed easy to eliminate the other choices.
I have found that eliminating the wrong answers is also a very valid strategy.

can anyone give detailed explanation for ques 2,5 and 6?

 

­Question 2 is explained here:

­Question 5 is explained here:

­Question 6 is explained here:

 Please review these posts and feel free to ask for any specifics if anything remains unclear