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"Urodeles," a class of vertebrates that includes newts and salamanders

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"Urodeles," a class of vertebrates that includes newts and salamanders  [#permalink]

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New post Updated on: 03 Oct 2019, 01:20
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"Urodeles," a class of vertebrates that includes newts and salamanders, have the enviable ability to regenerate arms, legs, tails, heart muscle, jaws, spinal cords, and other organs. "Planaria," simple worms, can be sliced and diced in hundreds of pieces, with each piece giving rise to a completely new animal. However, while both "urodeles" and "planaria" have the capacity to regenerate, they use different means to accomplish this feat.

In effect, a "urodeles" specimen turns back the biological clock. First, the animal heals the wound at the site of the missing limb. Then various specialized cells at the site, such as bone, skin, and blood cells, lose their identity and revert to cells as unspecialized as those in the embryonic limb bud. This process is called dedifferentiation, and the resulting blastema, a mass of unspecialized cells, proliferates rapidly to form a limb bud. Ultimately, when the new limb takes shape, the cells take on the specialized roles they had previously cast off.

In contrast, "planaria" regenerate using cells called neoblasts. Scattered within the planarian body, these neoblasts remain in an unspecialized, stem-cell state, which enables them at need to differentiate into any cell type. Whenever "planari"a are cut, the neoblasts migrate to the site and form a blastema by themselves. It is interesting to note that this mechanism is similar to that following reproductive fission in these animals, and that species incapable of this form of asexual reproduction have poorly developed regenerative capacities.

1. The primary purpose of the passage is to:

A describe the roles of blastemas in regenerating "urodeles" and "planaria."
B describe how "urodeles" use the process of dedifferentiation to regenerate.
C contrast the mechanisms by which "urodeles" and "planaria" accomplish regeneration.
D show how methods of cellular regeneration have evolved in different animal species.
E explain the link between reproductive fission and regeneration in simple worms.


2. All of the following are true of dedifferentiation in regenerating "urodeles" EXCEPT:

A the cells recover their specialized roles after the limb bud takes shape.
B it involves a regression by cells to an earlier stage of development.
C specialized cells migrate to the site of the blastema and proliferate rapidly.
D the healing of the wound at the site of the injury is the first step of the process.
E dedifferentiation is characterized by a loss, and then recovery, of cellular identity.



Source: Master GMAT
Difficulty Level: 600

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Originally posted by SajjadAhmad on 14 Jan 2017, 00:51.
Last edited by SajjadAhmad on 03 Oct 2019, 01:20, edited 5 times in total.
Updated - Complete topic (778).
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Re: "Urodeles," a class of vertebrates that includes newts and salamanders  [#permalink]

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New post 14 Jan 2017, 08:30
First paragraph discusses about regenerative capacity of Urodeles and Planaria.
Second paragraph discusses about the mechanism of regeneration in Urodeles.
Third paragraph discusses about the mechanism of regeneration in Planaria.

1. The primary purpose of the passage is to:

A describe the roles of blastemas in regenerating "urodeles" and "planaria." - Incorrect. Partial scope.
B describe how "urodeles" use the process of dedifferentiation to regenerate. - Incorrect. Partial scope.
C contrast the mechanisms by which "urodeles" and "planaria" accomplish regeneration. - Correct.
D show how methods of cellular regeneration have evolved in different animal species. - Incorrect. Out of scope. Evolution of cellular regeneration is not discussed in the passage.
E explain the link between reproductive fission and regeneration in simple worms. - Incorrect. Reproductive fission is discussed only in the last paragraph. Also the link between fission and regeneration is nowhere discussed in the passage.

Answer: C

2. All of the following are true of dedifferentiation in regenerating "urodeles" EXCEPT:

A the cells recover their specialized roles after the limb bud takes shape. - Incorrect. True.
B it involves a regression by cells to an earlier stage of development. - Incorrect. True.
C specialized cells migrate to the site of the blastema and proliferate rapidly. - Correct. False. It must be unspecialized cells and not specialized.
D the healing of the wound at the site of the injury is the first step of the process. - Incorrect. True.
E dedifferentiation is characterized by a loss, and then recovery, of cellular identity. - Incorrect. True.

Answer: C
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Re: "Urodeles," a class of vertebrates that includes newts and salamanders  [#permalink]

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New post 15 Jun 2018, 03:49
1. The primary purpose of the passage is to:

A describe the roles of blastemas in regenerating "urodeles" and "planaria." - True, but it is not the primary purpose.
B describe how "urodeles" use the process of dedifferentiation to regenerate. - True, but it is not the primary purpose.
C contrast the mechanisms by which "urodeles" and "planaria" accomplish regeneration. - This the primary purpose.
D show how methods of cellular regeneration have evolved in different animal species. - False, there is no talk about evolution in the passage.
E explain the link between reproductive fission and regeneration in simple worms. - It does speak about it at the end of the passage but this is not the primary purpose.

Correct choice: C
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Re: "Urodeles," a class of vertebrates that includes newts and salamanders  [#permalink]

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New post 15 Jun 2018, 03:54
2. All of the following are true of dedifferentiation in regenerating "urodeles" EXCEPT:

A the cells recover their specialized roles after the limb bud takes shape. - True, clearly stated in the passage.
B it involves a regression by cells to an earlier stage of development. - True, the passage tells that specialized cells to lose their identity and become unspecialized.
C specialized cells migrate to the site of the blastema and proliferate rapidly. - False, the passage does not speak about this migration at all.
D the healing of the wound at the site of the injury is the first step of the process. - True, clearly stated in the passage.
E dedifferentiation is characterized by a loss, and then recovery, of cellular identity. - True, as it can be inferred that loss refers to specialized cells turning into unspecialized and recovery refers to them turning back into specialized.

Correct choice: C
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Re: "Urodeles," a class of vertebrates that includes newts and salamanders  [#permalink]

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New post 16 Jan 2019, 06:33
SajjadAhmad wrote:
Source: http://www.petersons.com

"Urodeles," a class of vertebrates that includes newts and salamanders, have the enviable ability to regenerate arms, legs, tails, heart muscle, jaws, spinal cords, and other organs. "Planaria," simple worms, can be sliced and diced in hundreds of pieces, with each piece giving rise to a completely new animal. However, while both "urodeles" and "planaria" have the capacity to regenerate, they use different means to accomplish this feat.

In effect, a "urodeles" specimen turns back the biological clock. First, the animal heals the wound at the site of the missing limb. Then various specialized cells at the site, such as bone, skin, and blood cells, lose their identity and revert to cells as unspecialized as those in the embryonic limb bud. This process is called dedifferentiation, and the resulting blastema, a mass of unspecialized cells, proliferates rapidly to form a limb bud. Ultimately, when the new limb takes shape, the cells take on the specialized roles they had previously cast off.

In contrast, "planaria" regenerate using cells called neoblasts. Scattered within the planarian body, these neoblasts remain in an unspecialized, stem-cell state, which enables them at need to differentiate into any cell type. Whenever "planari"a are cut, the neoblasts migrate to the site and form a blastema by themselves. It is interesting to note that this mechanism is similar to that following reproductive fission in these animals, and that species incapable of this form of asexual reproduction have poorly developed regenerative capacities.
1. The primary purpose of the passage is to:

A describe the roles of blastemas in regenerating "urodeles" and "planaria."
B describe how "urodeles" use the process of dedifferentiation to regenerate.
C contrast the mechanisms by which "urodeles" and "planaria" accomplish regeneration.
D show how methods of cellular regeneration have evolved in different animal species.
E explain the link between reproductive fission and regeneration in simple worms.


2. All of the following are true of dedifferentiation in regenerating "urodeles" EXCEPT:

A the cells recover their specialized roles after the limb bud takes shape.
B it involves a regression by cells to an earlier stage of development.
C specialized cells migrate to the site of the blastema and proliferate rapidly.
D the healing of the wound at the site of the injury is the first step of the process.
E dedifferentiation is characterized by a loss, and then recovery, of cellular identity.




Hello SajjadAhmad,

Could you please provide explanation of question-2. I am not getting why is answer-C. In 2nd paragraph it is specially mentioned that "This process is called dedifferentiation, and the resulting blastema, a mass of unspecialized cells, proliferates rapidly to form a limb bud."

Thanks,
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Re: "Urodeles," a class of vertebrates that includes newts and salamanders  [#permalink]

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New post 11 May 2019, 11:41
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ammuseeru

The statement says “unspecialised cells” grow to form a limb bud.
The option states “specialised cells” which is not correct.

Hope it’s clear now

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Re: "Urodeles," a class of vertebrates that includes newts and salamanders  [#permalink]

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New post 11 May 2019, 22:49
took a whopping 13mins for this. I need to improve timings.

p1)U- regenerative 1,2,3,4,5,6 and etc
Pl-minced gives new births

p2) U-1)clock 2) wounds heals 3) bones, skin, and blood cells lose identity become ELB "dediff" -> blast...

p3)1) neoblasts = unspecialised and stem state
2)neoplasm move and form B
3) reproductive fission <- asexual
reproduction species-poor fission
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Re: "Urodeles," a class of vertebrates that includes newts and salamanders   [#permalink] 11 May 2019, 22:49
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