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Germs make us sick. It's an elementarytruth that we teach to our children. It's whywe wash our hands before eating. It's why wepasteurize our milk, and refrigerate our food.05When they do make us sick, our ability tosafely exterminate them is nothing short of amodern miracle. Beginning with penicillin in1928, antibiotics forever transformed the waywe both treat and prevent infectious disease.10Today, moreover, one can stroll down anycleaning supply aisle at a supermarket, anddiscover a bevy of products boasting of theirbroad-spectrum antimicrobial activity.For better or for worse, our culture of15"germophobia" was hard-won by its proponents.From the time it was first proposed inthe 16th century, the germ theory of diseasefaced three hundred years' worth of influentialnaysayers, and it was not until the20late 1800's that the theory began to gain thepervasive public vindication it enjoys today.However, an emerging body of research indicatesthat we have been perhaps overzealousin our crusade to eradicate the germs that25live within us.The "human microbiome" refers collectivelyto the microscopic organisms thatnaturally colonize the human body, and theapplication of dynamic ecological theories30to this biome represents a rapidly expandingfield of study. Comprised of fungi, viruses,archaea, and perhaps 1,000 species of bacteria,the population of this microbiome isthought to outnumber our own cells by as35much as ten to one. What's more, much likeour own cells, a significant portion of theseorganisms play crucial roles in our metabolicand immunological processes.For example, Oxalobacter formigenes,40which colonizes the colon, is a primarysource of the enzyme oxalyl-CoA decarboxylase,which allows us to safely eliminatedietary oxalate. Without this enzyme, calciumoxalate salts tend to accumulate in the45kidney tubules, and eventually precipitate asrenal stones. Other colonic bacteria catalyzethe reduction of bilirubin into urobilinogen:a reaction critical to our digestion offats, and absorption of fat-soluble vitamins.50Interestingly, many bacteria within ourgastrointestinal tracts also directly synthesizeseveral vitamins in excess of their own metabolicneeds, and, as a result, represent animportant source of both vitamin B12, which55is necessary for the production of new redblood cells, and vitamin K, which is a cofactorin the synthesis of several blood clottingfactors.The benefits we gain from a balanced,60thriving microbiome are diverse, and we areonly just beginning to appreciate their truecomplexity, though perhaps no single functionit serves is more significant than its rolein regulating our immune systems. There are65numerous mechanisms by which the microbiomehelps protect us from disease. Somespecies, for instance, secrete special proteins,known as "bacteriocins," that are directlytoxic to pathogenic bacteria, but harmless70to our own cells. One particularly impressivemember of the microbiome, Lactobacillus,produces a powerful bacteriocin calledreuterin, as well as lactic acid and hydrogenperoxide, which inhibit the growth of disease-75causing organisms by lowering local pHand damaging lipid membranes respectively.Of no less importance, there are a numberof more indirect, ecologically-oriented waysin which the microbiome confers protection80to its host. Abundant colonization ofour bodies by benign microorganisms, forexample, inhibits the overgrowth of moredangerous ones through the sheer depletionof microbial nutrients. This notion of ecological85balance has been of particular interestto scientists studying the microbiome, as ithinges upon both the variable diversity ofspecies that colonize an individual, as well asfactors that affect the dynamism of a microbiotic90population. Age, geography, diet, andstress have all been implicated in influencingboth the composition and balance of themicrobiome. None, however, has been shownto have so drastic an effect as the use of antibiotics,95which, unlike bacteriocins, tend to bejust as deadly to disease-causing bacteria asthey are to those that colonize us naturally.Admittedly, antibiotics save lives. Yetour decision to use them must be weighed100carefully, as artificially upsetting the ecologicalbalance of our bodies can have direconsequences. There is perhaps no greaterexample of this than Clostridium difficile, acolonic bacterium that is both highly resistant105to antibiotics, and an increasing causeof hospital-acquired disease. When properlycounterbalanced by its neighboring species,C. difficile is harmless to humans. However,following the administration of antibiotics,110and the elimination of its ecologicalcompetitors, C. diff proliferation proceedsunchecked, resulting in a frequently fatalinfection for which very few effective treatmentsexist.
The table illustrates variations in microbiota for individuals following either vegetarian or omnivorous diets across three geographical demographics.
Diversity of Human Microbiomes
1. The general structure of the passage is best described as
2. As used in line 1, the word "elementary" most closely means
3. The paragraph in lines 14-25 most directly serves to
4. What is the overall purpose of the paragraph in lines 39-58?
5. Which of the following does the passage explicitly state illustrates the potential danger in overusing antibiotics?
6. Which option gives the best evidence for the answer to the previous question?
7. As used in line 87, the word "hinges" most closely means
8. The information in the table would be most helpful to the study of which of the following concepts mentioned in the passage?
9. Which option gives the best evidence for the answer to the previous question?
10. Based on the information in the table, analysis of the variations of which two microorganisms would be most helpful in roughly determining the country of residence of a randomly selected human test subject?
11. Based on the information in the table, knowing the percentage of each of the following microorganisms would be useful in determining whether someone had a vegetarian or omnivorous diet, no matter his or her geographical location, EXCEPT:
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