The single-celled parasite known as Toxoplasma gondii infects more

Question

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.   1 
 1. According to the passage, all of the following are true of Toxoplasma gondii EXCEPT

(A) it can contaminate ground water
(B) it enters the human body through the food chain
(C) it can alter the usual behavior of human cells
(D) the human body is incapable of detecting it
(E) it must find a host cat in order to reproduce

2 
 2. It can be inferred from the passage that which of the following statements is true of dendritic cells in the human body?

(A) They are produced by the lymphatic system.
(B) They are more numerous in the digestive tract than in any other part of the human body.
(C) Most dendritic cells of persons infected with Toxoplasma carry the parasite.
(D) They are the only cells capable of being infected by Toxoplasma.
(E) They are able to penetrate the membranes surrounding the brain.

3 
 3. Which of the following is the most likely outcome for Toxoplasma cells that invade the human body?

(A) They will be destroyed by the immune system.
(B) They will collect in the lymphatic system.
(C) They will not reproduce.
(D) They will be detected after several weeks.
(E) They will be destroyed by other pathogens in the bloodstream.

4 
 4. The second paragraph performs which of the following functions in the passage?

(A) It describes a paradox that scientists were unable to resolve for some time.
(B) It explains the effectiveness of a lethal biological pathogen.
(C) It describes the mechanism by which a biological event occurs in humans.
(D) It demonstrates how the infectious agent reproduces itself.
(E) It introduces information that is essential to understanding the role of Toxoplasma in human development.

5 
 5. The author mentions “ pigs and chickens ” in the final paragraph in order to

(A) provide specific examples of animals that can carry Toxoplasma
(B) provide specific examples of animals that are often eaten by cats
(C) provide specific examples of other animals whose dendritic cells are exploited by Toxoplasma
(D) provide specific examples of animals in which Toxoplasma can breed
(E) provide specific examples of animals that are immune to Toxoplasma

Skywalker18 · Accepted Answer

Official Explanations:

1. According to the passage, all of the following are true of Toxoplasma gondii EXCEPT

(A) it can contaminate ground water
(B) it enters the human body through the food chain
(C) it can alter the usual behavior of human cells
(D) the human body is incapable of detecting it
(E) it must find a host cat in order to reproduce

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.

2. It can be inferred from the passage that which of the following statements is true of dendritic cells in the human body?

(A) They are produced by the lymphatic system.
(B) They are more numerous in the digestive tract than in any other part of the human body.
(C) Most dendritic cells of persons infected with Toxoplasma carry the parasite.
(D) They are the only cells capable of being infected by Toxoplasma.
(E) They are able to penetrate the membranes surrounding the brain.

The question asks us to infer something about dendritic cells from the information contained in the passage. The correct answer must be based only on the information contained in the passage. If any additional information is required to justify an answer choice, that choice cannot be the correct answer.

(A) The passage states only that dendritic cells are involved with the lymphatic system. No information is given as to the location of the cells' production.

(B) The passage states only that dendritic cells are common in the digestive tract. No information is given as to where the cells are most numerous.

(C) The passage states only that Toxoplasma infects dendritic cells. No information is given as to the proportion of the cells that are affected when a person is infected with Toxoplasma.

(D) The passage states only that dendritic cells are capable of being infected with Toxoplasma. No information is given regarding any other types of cell.

(E) CORRECT.  The passage states that Toxoplasma is capable of penetrating the barriers protecting the brain. The passage also states that Toxoplasma uses dendritic cells as transport around the human body. Thus, we can infer that the Toxoplasma uses the dendritic cells to penetrate the barriers around the brain.

3. Which of the following is the most likely outcome for Toxoplasma cells that invade the human body?

(A) They will be destroyed by the immune system.
(B) They will collect in the lymphatic system.
(C) They will not reproduce.
(D) They will be detected after several weeks.
(E) They will be destroyed by other pathogens in the bloodstream.

The question asks us to infer something about Toxoplasma from the information given in the passage. When answering questions of this type, remember that GMAT inferences are typically very close to the original text, although they never repeat information verbatim. Make sure to select an answer that is not stated explicitly but can be inferred without making any additional assumptions.

(A) The passage does not suggest that the immune system will destroy Toxoplasma cells.

(B) The passage does not suggest that Toxoplasma collects in the lymphatic system.

(C) CORRECT.  The passage states that Toxoplasma can reproduce only in a host cat. Therefore, any Toxoplasma cells that remain in the human body are not likely to reproduce.

(D) The passage does not suggest that Toxoplasma will be detected after several weeks.

(E) The passage does not suggest that Toxoplasma will be destroyed by pathogens in the bloodstream.

4. The second paragraph performs which of the following functions in the passage?

(A) It describes a paradox that scientists were unable to resolve for some time.
(B) It explains the effectiveness of a lethal biological pathogen.
(C) It describes the mechanism by which a biological event occurs in humans.
(D) It demonstrates how the infectious agent reproduces itself.
(E) It introduces information that is essential to understanding the role of Toxoplasma in human development.

The second paragraph contains information describing the mechanism by which Toxoplasma is able to infiltrate the human body and remain undetected by the body's immune system. We need to find an answer choice that reflects this.

(A) The paragraph does not summarize research that remains to be done. Instead, it discusses what has already been discovered.

(B) The paragraph does not present any recommendations.

(C) CORRECT.  This matches our description of the paragraph.

(D) The paragraph does not introduce information about the role of Toxoplasma in human development. If anything, it introduces information about the role of humans in the development of Toxoplasma.

(E) The paragraph does not mention any outdated scientific models.

5. The author mentions “pigs and chickens” in the final paragraph in order to

(A) provide specific examples of animals that can carry Toxoplasma
(B) provide specific examples of animals that are often eaten by cats
(C) provide specific examples of other animals whose dendritic cells are exploited by Toxoplasma
(D) provide specific examples of animals in which Toxoplasma can breed
(E) provide specific examples of animals that are immune to Toxoplasma

The question asks us why the author mentions "pigs and chickens" in the final paragraph of the passage. The author mentions these animals in the context of explaining how Toxoplasma enters the human body. Specifically, Toxoplasma enters the human body when humans ingest the meat of infected animals, "such as pigs and chickens." So the author uses pigs and chickens as specific examples of animals that can carry the parasite.

(A) CORRECT.  This matches our assessment of the passage exactly.

(B) The author mentions only "small rodents" as examples of animals that are eaten by cats.

(C) The author does not mention the dendritic cells of any animals other than humans.

(D) The passage states that cats are Toxoplasma's "sole breeding ground." Thus, the author could not mention the pigs and chickens as examples of animals in which the parasite can breed.

(E) The author does not mention any animals at all that are immune to Toxoplasma.

ManasviHP · Answer

Q1- According to the passage, all of the following are true of Toxoplasma gondii EXCEPT
-it can contaminate ground water - Clearly given
-it enters the human body through the food chain - Clearly given
-it can alter the usual behavior of human cells - It does so for the dendritic cells. Hold this one.
-the human body is incapable of detecting it - Hold this
-it must find a host cat in order to reproduce - Clearly given
Between C and D, since option C applies to a specific type of cell,that can pass. Also D is strengthened as the para 1 says that no immune response is generated by the body and it's still a puzzle.
hence ans- Option D

Q2-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. - Nowhere given
-They are more numerous in the digestive tract than in any other part of the human body. - are they even present in other part, unsure. Cancel this out.
-Most dendritic cells of persons infected with Toxoplasma carry the parasite. - Nowhere particularly mentioned
-They are the only cells capable of being infected by Toxoplasma. - Where has this been 'explicitly' mentioned?
-They are able to penetrate the membranes surrounding the brain. ' 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.  '

Q3- 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. - the immune system cannot understand them, so no!
-They will collect in the lymphatic system. - where is this said? No!
-They will not reproduce. -  CORRECT. They can only reproduce inside a cat's body!  '.  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. ' 
-They will be detected after several weeks. - Cannot be infered
-They will be destroyed by other pathogens in the bloodstream.- NO. Nowhere mentioned

Q4- The second paragraph performs which of the following functions in the passage?
A) It describes a paradox that scientists were unable to resolve for some time. - Hold this
B) It explains the effectiveness of a lethal biological pathogen. - 'effectiveness?' - Nonsense
C) It describes the mechanism by which a biological event occurs in humans. -Hold this
D) It demonstrates how the infectious agent reproduces itself. - NO IT DOES NOT
E) It introduces information that is essential to understanding the role of Toxoplasma in human development. - Lol. toxoplasma and Human Development- Poles apart
Now between A and C.
Now although A seems tempting, there is no 'paradox' Paradox means contradiction. There's no contradiction here. It is just another topic that was unclear but latest research has shed some light on it. No opposing views. Hence, it is wrong. Correct answer hence is C.

donaldmcdonald · Answer

I have doubt on option B of question 2.

In the second paragraph the passage states that:
" Dendritic cells are found in the digestive tract "

I think, the chances of whether " ARE FOUND " part of this sentence gives us " CAN BE FOUND " or " ONLY FOUND " is  50%-50% . This sentence alone neither  EXPLICITLY  or  IMPLICITLY  tells us which one.

I simply cannot  100%  infer that " ARE FOUND "  =  " CAN BE FOUND " ( in other words  " they can be in other parts of the body ")

Though I am also aware that we cannot  100%  infer that " ARE FOUND "  =  " ONLY FOUND "

Please, help me understand this.

svasan05 · Answer

Hi

You are absolutely correct. The passage tells us that "Dendritic cells are found in the digestive tract...". We cannot infer anything more than that these cells are found (or can be found) in the digestive tract. We cannot infer that they are only found in the digestive tract - in fact the passage suggests quite the opposite since the parasite uses these cells to reach other parts of the body. Therefore, surely dendritic cells can also be found in other parts of the body.

Option (B), on the other hand, is much more specific:  They are  more numerous  in the digestive tract  than in any other part  of the human body.

There is absolutely nothing in the passage that tells us where dendritic cells are found  in larger quantities . Therefore, we cannot infer this option from the passage.

Hope this helps.

GMATCoachBen · Answer

You're correct that "Dendritic cells ARE FOUND in the digestive tract" does NOT necessarily mean ONLY FOUND. You're correct that the passage does not specify. That's why we can  eliminate B.  In the passage, no comparison is being made, but choice B says: "They are MORE numerous in the digestive tract than in ANY OTHER part of the human body."

Note that these "Wrong Comparison Traps" are very common, throughout verbal. When we see "Comparison Markers" (more X than Y, as X as Y, etc.) in an answer choice, we must always be careful to check that it's fully supported.

Saha23 · Answer

The answer to question 4 should be choice B because in choice C the phrase ' biological event occurs in humans' seem to be vague.

DmitryFarberMPrep · Answer

Saha23

Actually, we often find that vagueness is a  good  trait in an RC answer. The less the answer says, the easier it is for it to be true. For instance, if C said "tells us some things," how could it be wrong? Surely the purpose is to tell us some things, even if that's not very specific! Now, as soon as we add detail, that detail can be wrong. For instance, of C said "tell us some things about dendritic cells," it would now fail. Of course, it does indeed tell us things about dendritic cells, but providing that information is not the sole point, since the passage is only telling us about these cells to explain how Toxoplasma does its work in the body. In a similar vein, B fails because it adds a single unsupported word: "lethal."

In short, one wrong detail can sink an RC answer, so the less an answer says, the safer it is.

ananya88888888888 · Answer

I have a doubt in question 2 especially part C, and how is E an answer for the same. The paragraph which talks about dendritic cells is two, but this line was in para 1. Can someone please explain

guddo · Answer

2. It can be inferred from the passage that which of the following statements is true of dendritic cells in the human body?

The passage says dendritic cells are part of the immune system, are found in the digestive tract, encounter pathogens there, and then travel to lymph nodes to relay information. It also says Toxoplasma can hijack them and use them as transport to reach protected areas.

(A) They are produced by the lymphatic system.

Not stated. The passage only says they travel to lymph nodes.

(B) They are more numerous in the digestive tract than in any other part of the human body.

Not stated. We only know they are found there.

(C) Most dendritic cells of persons infected with Toxoplasma carry the parasite.

Too strong. The passage says Toxoplasma is “quite common” in dendritic cells, not that most dendritic cells carry it.

(D) They are the only cells capable of being infected by Toxoplasma.

Not stated. The first paragraph says Toxoplasma spreads to the heart and other organs, so it infects more than dendritic cells.

(E) They are able to penetrate the membranes surrounding the brain.

This follows best. The passage says Toxoplasma can cross the brain barrier, and that  without  hijacking dendritic cells it could not reach better-protected areas. That implies dendritic cells can access those protected areas and serve as the transport route.  So (E) is the supported inference.

Answer: (E)

Official explanation of question 2 is given in  THIS POST . Question 2 is also addressed  HERE  and  HERE .

The single-celled parasite known as Toxoplasma gondii infects more

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GMAT Reading Comprehension (RC) Questions

The single-celled parasite known as Toxoplasma gondii infects more

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