Extract:
Microbes and Health
There are 10 times more microbes than human cells in the human body. Scientists have long known that the human body is host to a staggering number of microorganisms, but recent information is shedding light on just how pivotal a role these bacteria play in the development of the human immune system.
The human body plays host to a wide array of microorganisms that are specially adapted to survive in particular portions of the human body. There is such a great amount of variation in these microorganisms that few people will share the same strains of bacteria in the same quantities. This process begins at birth: a newborn infant emerges from the womb, a germ-free environment, and is immediately coated with germs from its mother’s birth canal. These germs immediately begin to breed and colonize the human body that will now be its new host.
The most intriguing discovery is not that the body’s immune system tolerates these millions of harmless organisms, but that it may rely upon their presence to function properly. Scientists recently found that with laboratory mice that could not produce a particular inflammation-reducing molecule, upon being injected with a particular strain of bacteria that was then allowed to breed, their immune system quickly developed the ability to synthesize that molecule. Simply put, the mice needed the bacteria for their immune systems to function properly.
This same basic concept is also being used with humans. A relatively experimental process known as fecal bacteriotherapy is now being used to reintroduce healthy bacteria into a colon that lacks the capability to defend itself against pathogenic agents. Scientists are just beginning to understand the important role that these microorganisms play in the body of a healthy human being, but early tests have yielded remarkable discoveries.
What is the main idea of the passage?
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A
Recent discoveries are revealing just how critical microorganisms are to maintaining a properly functioning immune system.
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B
The human body is host to a wide array of microorganisms.
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C
Bacteriotherapy is being used to reintroduce healthy bacteria into a colon that lacks the capability to defend itself against pathogenic agents.
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D
Early tests have shown remarkable potential for the possibilities of bacteriotherapy.
The main idea of the passage is that recent discoveries are revealing just how critical microorganisms are to maintaining a properly functioning immune system.
A) Recent discoveries are revealing just how critical microorganisms are to maintaining a properly functioning immune system.
This option captures the passage's central thesis developed across all paragraphs: the opening establishes microbes' numerical dominance and hints at immune importance; paragraph two describes colonization beginning at birth; paragraph three presents the pivotal mouse study showing immune systems requiring bacteria to synthesize inflammation-reducing molecules; and paragraph four extends this concept to human applications like fecal bacteriotherapy. The unifying thread is microbes' essential, not merely tolerated, role in immune function.
B) The human body is host to a wide array of microorganisms.
This represents only introductory context establishing microbial presence, not the passage's developmental focus on their functional necessity. While factually accurate, it's too narrow to encompass the immune system dependency revealed through research examples.
C) Bacteriotherapy is being used to reintroduce healthy bacteria into a colon that lacks the capability to defend itself against pathogenic agents.
This describes a single supporting detail from the final paragraph, a human application of the broader principle. It functions as evidence for the main idea rather than the central thesis itself.
D) Early tests have shown remarkable potential for the possibilities of bacteriotherapy.
This overemphasizes one application while underrepresenting the foundational discovery about immune-microbe interdependence that makes bacteriotherapy theoretically possible. The passage presents bacteriotherapy as consequence, not focus.
Conclusion
Main ideas must encompass a passage's comprehensive developmental arc, not isolated details or applications. Option A successfully integrates the quantitative microbial dominance with the qualitative functional dependency demonstrated through animal research and human therapeutic applications, establishing microbes as essential immune partners rather than passive residents.