Digital PSAT Reading and Writing Practice Question 214: Answer and Explanation

Question: 214

Much like our own cells, a significant portion of bacteria play crucial roles in our metabolic and immunological processes. Oxalobacter formigenes, which colonizes the colon, is a primary source of the enzyme oxalyl-CoA decarboxylase, which allows us to safely eliminate dietary oxalate. Without this enzyme, calcium oxalate salts tend to accumulate in the kidney tubules, and eventually precipitate as renal stones. Other colonic bacteria catalyze the reduction of bilirubin into urobilinogen: a reaction critical to our digestion of fats, and absorption of fat-soluble vitamins. Interestingly, many bacteria within our gastrointestinal tracts also directly synthesize several vitamins in excess of their own metabolic needs, and, as a result, represent an important source of both vitamin B12, which is necessary for the production of new red blood cells, and vitamin K, which is a cofactor in the synthesis of several blood clotting factors.

What is the primary purpose of the text as a whole?

• A. To recommend specific bacteriological treatments to common gastrointestinal illnesses
• B. To provide concrete examples of the utility of some bacteria to our metabolic and immunological processes
• C. To address the objections of those who are inherently skeptical towards the existence of bacteria
• D. To explain the metabolic processes whereby bacteria lead to the creation of vitamins B12 and K

Correct Answer: B

Explanation:

(B) The text furnishes a direct example of the general statement made in the first sentence, pointing out the metabolic and immunological advantages of some natural bacteria. Hence, (B) is correct. (A) and (D) misunderstand details of the text. (C) is appealing because it is true that this example could be used to address an objection toward all germ theory, but this text is more interested in giving that illustrative example rather than responding to objections.