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.
Choose the best summary of the passage.
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A
Scientists have used experiments on mice to prove the body’s need for certain microorganisms. Instead of damaging the immune system, it turns out that bacteria of certain types may in fact support immunity, at least in lower organisms.
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B
Bacteriotherapy was originally tried on mice, and the results were positive enough that it now is being used in human trials as well. The essential theory states that introducing bacteria into a damaged colon can help with reconstruction and immune response.
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C
Although scientists have known for years that the body tolerates certain microorganisms, experiments now show that some bacteria may be required for a healthily functioning immune system. For example, introducing harmless bacteria seems to help the colon defend itself against pathogens.
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D
Humans are born germ-free, but it does not take long for pathogens to find their way into the body, often destroying an otherwise healthy immune system. Replacing these harmful bacteria with harmless ones is a new and exciting process known as bacteriotherapy.
The best summary acknowledges that while scientists long knew the body tolerates microbes, new research shows certain bacteria may be required for proper immune function, with bacteriotherapy applications helping colons defend against pathogens.
A) Scientists have used experiments on mice to prove the body's need for certain microorganisms. Instead of damaging the immune system, it turns out that bacteria of certain types may in fact support immunity, at least in lower organisms.
Introduces unsupported limitation "at least in lower organisms", the passage explicitly extends the concept to humans through bacteriotherapy, contradicting this restrictive framing.
B) Bacteriotherapy was originally tried on mice, and the results were positive enough that it now is being used in human trials as well. The essential theory states that introducing bacteria into a damaged colon can help with reconstruction and immune response.
Factual error: bacteriotherapy wasn't "originally tried on mice", the mouse study demonstrated immune dependency generally; bacteriotherapy is a separate human application. This conflates two distinct research threads.
C) Although scientists have known for years that the body tolerates certain microorganisms, experiments now show that some bacteria may be required for a healthily functioning immune system. For example, introducing harmless bacteria seems to help the colon defend itself against pathogens.
Accurately synthesizes the passage structure: opening with historical knowledge of microbial tolerance, pivoting to new research showing functional necessity (mouse study), then illustrating human application (bacteriotherapy for colon defense), all with appropriately cautious language ("may be required") matching the passage's scientific tone.
D) Humans are born germ-free, but it does not take long for pathogens to find their way into the body, often destroying an otherwise healthy immune system. Replacing these harmful bacteria with harmless ones is a new and exciting process known as bacteriotherapy.
Multiple errors: microbes colonizing newborns aren't described as "pathogens" (they're beneficial); colonization doesn't "destroy" immune systems (it enables them); and bacteriotherapy isn't about replacing "harmful" with "harmless" bacteria but reintroducing missing beneficial strains.
Conclusion
Effective summaries must balance accuracy with conciseness, capturing historical context, pivotal discovery, and practical application without factual errors or unsupported limitations. Option C achieves this balance while other options introduce significant misrepresentations of microbial roles or research chronology.