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The single-celled parasite known as Toxoplasma gondii

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The single-celled parasite known as Toxoplasma gondii [#permalink] New post 08 Sep 2009, 03:49
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The single-celled parasite known as Toxoplasma gondii infects more than half of the world's human population without creating any noticeable symptoms. Once inside the human body, Toxoplasma rapidly spreads to the heart and other organs. It can even penetrate the tight barrier that normally protects the brain from most pathogens. Yet, the blood of infected persons carries very few free-floating Toxoplasma cells. Scientists have long been puzzled by this ability of Toxoplasma to parasitize the human body without triggering an immune response and without an appreciable presence in the bloodstream. Recent research, however, has shed light on the ways in which Toxoplasma achieves its remarkable infiltration of the human body.

Though there are few individual Toxoplasma cells coursing freely in the blood of an infected person, scientists have discovered that the parasite is quite common in certain cells, known as dendritic cells, involved in the human immune system. Dendritic cells are found in the digestive tract and frequently come into contact with the various pathogens that enter the human body through food and water. When the dendritic cells encounter pathogens, they travel to lymph nodes and relay this information to other immune cells that then take action against the reported pathogen. Scientists have found, however, that Toxoplasma is capable of hijacking dendritic cells, forcing them from their usual activity and using them as a form of transportation to infect the human body quickly. Without this transport mechanism, Toxoplasma could not reach the better-protected areas of the body.

Toxoplasma invades the human body through consumption of the undercooked meat of infected animals, primarily pigs and chickens. Other animals, such as cats, can become infected as well. In fact, cats are a necessary component in the reproductive cycle of Toxoplasma, since the animal's intestines are the parasite's sole breeding ground. Toxoplasma creates egg-like cysts, known as oocysts, in the cats' intestines. These oocysts are shed in the cats' droppings and contaminate ground water and soil, eventually finding their way into the food chain. Because Toxoplasma must somehow find its way into a new host cat in order to reproduce, it cannot kill its current host. Instead, it waits for the host, usually a small rodent, to be eaten by a cat, thus providing Toxoplasma the opportunity to reproduce.
According to the passage, all of the following are true of Toxoplasma gondii EXCEPT
-it can contaminate ground water
-it enters the human body through the food chain
-it can alter the usual behavior of human cells
-the human body is incapable of detecting it
-it must find a host cat in order to reproduce
[Reveal] Spoiler:
D


It can be inferred from the passage that which of the following statements is true of dendritic cells in the human body?
-They are produced by the lymphatic system.
-They are more numerous in the digestive tract than in any other part of the human body.
-Most dendritic cells of persons infected with Toxoplasma carry the parasite.
-They are the only cells capable of being infected by Toxoplasma.
-They are able to penetrate the membranes surrounding the brain.
[Reveal] Spoiler:
E


Which of the following is the most likely outcome for Toxoplasma cells that invade the human body?
-They will be destroyed by the immune system.
-They will collect in the lymphatic system.
-They will not reproduce.
-They will be detected after several weeks.
-They will be destroyed by other pathogens in the bloodstream.
[Reveal] Spoiler:
C

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Re: Toxoplasma [#permalink] New post 08 Sep 2009, 13:22
1 - X( :( )
2 - C
3 - D

Could you please post OA / expln for 1st.
I guess 2nd and 3rd are comparitively easier.
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Re: Toxoplasma [#permalink] New post 08 Sep 2009, 22:33
anyone else ???
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Re: Toxoplasma [#permalink] New post 09 Sep 2009, 07:08
Good RC!
1. E ( must is too extreme even in the passage it has been mentioned that
Quote:
In fact, cats are a necessary component in the reproductive cycle of Toxoplasma
, it is necessary not a must condition)

2.E
(In first paragraph
Quote:
It can even penetrate the tight barrier that normally protects the brain from most pathogens

Please see the last line of the second paragraph
Quote:
Without this transport mechanism, Toxoplasma could not reach the better-protected areas of the body.
hence we can conclude that d-cells are able to penetrate protected areas such as brain)

3.D
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Re: Toxoplasma [#permalink] New post 09 Sep 2009, 07:15
OA
D
E
C
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Re: Toxoplasma [#permalink] New post 09 Sep 2009, 23:47
that was brutal....got all wrong????
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Re: Toxoplasma [#permalink] New post 10 Sep 2009, 12:31
I got C E C

Got first one wrong.
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Re: Toxoplasma [#permalink] New post 15 Sep 2009, 11:46
1. C -- Incorrect (D)
2. E
3. C
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Re: Toxoplasma [#permalink] New post 07 Dec 2012, 05:57
nikhilpoddar wrote:
anyone else ???


The second paragraph performs which of the following functions in the passage?
It describes a paradox that scientists were unable to resolve for some time.
It explains the effectiveness of a lethal biological pathogen.
It describes the mechanism by which a biological event occurs in humans.
It demonstrates how an infectious agent enters the human body.
It introduces information that is essential to understanding the role of Toxoplasma in human development.
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Re: The single-celled parasite known as Toxoplasma gondii [#permalink] New post 09 Dec 2012, 20:05
passage is not hard but question is hard. The hardness of answering questions come from the problem that we can not find the place to yield the answer. all questions do not show the relevant places. on real gmat we do not get this situation. only a few question do not show the relevant places.

I get all 3 wrong.
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Re: Toxoplasma [#permalink] New post 16 Dec 2012, 02:40
nikhilpoddar wrote:
OA
D
E
C


What is source of these passage?
How 'E' can be answer for second question no where its stated that dendritic cell can penetrate brain membrane
its Taxoplasma(mentioned in passage 1)
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Re: The single-celled parasite known as Toxoplasma gondii [#permalink] New post 10 Apr 2014, 04:00
Hi can anyone explain the second question? Thanks!
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Re: The single-celled parasite known as Toxoplasma gondii [#permalink] New post 03 May 2014, 17:11
can some one please elaborate on the Ans.

1- D (how is it possible, Para 1 says it can can pass through human immune system and is detected much later due to the symptoms caused..)
Why is A wrong -- passage says the water is contaminated by cat droppings containing mould -- via soil and water(but the pathogen itself dosent goto soil to contaminate it)

2- E ( 2nd para never says that they are produced by lump nodes --they only travel towards lymp nodes when encountered by pathogens)
* B is clearly given in passage why not B? :-p

Any one can shed some light please.
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Re: Toxoplasma [#permalink] New post 06 May 2014, 05:22
Aristocrat wrote:
nikhilpoddar wrote:
OA
D
E
C


What is source of these passage?
How 'E' can be answer for second question no where its stated that dendritic cell can penetrate brain membrane
its Taxoplasma(mentioned in passage 1)



HEY,
first of all, this is inference question.....the answer choice will not be stated as it is in the passage , rather it will be distorted. For the E can be inferred
from the passage. Taxoplasma can penetrate human brain ( mentioned in the first paragraph)..but Taxoplasma can move to the body only by using Dendritic cell
( mentioned in the last line of 2nd paragraph).
SO dendritic cell can penetrate brain membrane.
hope it helps!!!!
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Re: The single-celled parasite known as Toxoplasma gondii [#permalink] New post 23 Jun 2014, 14:12
Can someone please explain the first question.
"Scientists have long been puzzled by this ability of Toxoplasma to parasitize the human body without triggering an immune response and without an appreciable presence in the bloodstream."
So how can D be the correct answer?
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Re: The single-celled parasite known as Toxoplasma gondii [#permalink] New post 18 Aug 2014, 00:42
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ronr34 wrote:
Can someone please explain the first question.
"Scientists have long been puzzled by this ability of Toxoplasma to parasitize the human body without triggering an immune response and without an appreciable presence in the bloodstream."
So how can D be the correct answer?


We are asked to determine which one of the five choices is NOT true of Toxoplasma, according to the passage. In other words, four of the five choices are stated in the passage and one choice is not. The choice that is not stated is the correct answer.

(A) The passage explicitly states that Toxoplasma can contaminate soil and water.

(B) The passage explicitly states that Toxoplasma enters the human body through contaminated food.

(C) The passage explicitly states that Toxoplasma alters the behavior of human dendritic cells.

(D) CORRECT. The word "incapable" in this answer choice is too strong; the passage does not state that the human body cannot detect Toxoplasma. Rather, it merely indicates that Toxoplasma does not trigger the body's immune system in the same way as other parasites. We have no information about the human body's ability to detect free-floating Toxoplasma cells.

(E) The passage explicitly states that Toxoplasma can breed in a host cat only.
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The single-celled parasite known as Toxoplasma gondii [#permalink] New post 18 Sep 2014, 04:19
Its fair to consider D as one of the option due to its strong tone "incapable". However, Option C states that " it affects the usual behavior of human cells".
Going by the same yardstick, i think the option should be specific: human dendritic cells. But since it does not, why is this statement (C) loosely accepted and not "Incapable" one (D)

Also there are million types of cells in human body so the statement should be SPecific.
The single-celled parasite known as Toxoplasma gondii   [#permalink] 18 Sep 2014, 04:19
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