20 February 2024

Daily practice questions for CLAT - (20 February 2024)



Contrary to infectious-disease dogma, the mutations that enable bacteria to resist antibiotics do not always result in weaker strains, according to a study published in the June 30 issue of the journal Science. This is bad news for public-health efforts, especially because the germ in question is the tuberculosis-causing Mycobacterium tuberculosis, once the leading cause of death in the United States. Classic laboratory experiments once suggested that bacteria pay a price for antibiotic resistance that resistant bacteria are weaker than their susceptible counterparts and should not spread through the human population when forced to compete with hardier strains. But the new study, headed by scientists at Stanford University, has undermined this comforting conventional wisdom. It shows that in real human patients, tuberculosis bacteria can evolve resistance to antibiotics and still be just as aggressive as their susceptible ancestors. “It’s generally bad news for the world that some tuberculosis strains can get something for nothing,” said Sebastien Gagneux, one of the lead authors of the study and a research associate at the Institute of Systems Biology. “Even though many drug-resistant strains are less hardy than susceptible strains, others evolve over the course of treatment and remain virulent.” The investigators looked at the evolution of resistance to the drug rifampin, one of the preferred first-line treatments for the disease. Rifampin binds to the molecule that makes, or polymerizes, bacterial RNA. The drug disables the so-called polymerase molecule and prevents the crucial flow of information from DNA to RNA. Without RNA, bacteria can’t make the proteins they need to survive. But simple mutations in the gene that encodes RNA polymerase can change its structure. The different shape decreases the drug’s ability to bind and allows M. tuberculosis to persist in the face of the antibiotic onslaught. Classic studies suggested that such a change would carry some cost, such as decreased efficiency of the polymerase molecule. Such a penalty would cause the mutants to grow more slowly than unmodified strains, thereby retarding the spread of the antibiotic-resistant mutation in the population. Not so, according to the new study, which found that some resistant bugs are every bit as robust as unmodified strains. The Stanford group collected tuberculosis bacteria from the sputum of patients, first at the beginning of their infections, and a second time after some of those patients developed rifampin-resistant infections. The investigators then pitted the resistant strains against their susceptible counterparts in antibiotic-free competition assays. These tests force the two strains to compete for limited resources in a common culture flask, so the harder bug should take over as the weaker one gets crowded out. Contrary to expectations, five of the ten resistant strains held their own in these tests, and one actually dominated its antibiotic-susceptible ancestor.

Question1:- What is the primary purpose of the passage?
  • A. Support the findings of classic laboratory experimentation.
  • B. Assert that controversial findings should cause alarm.
  • C. Present concerns raised by the results of a study.
  • D. Criticize the methodology of an existing study.
Answer is C is correct. This question asks about the primary purpose of the passage. The passage describes the results of a Stanford University study that showed that antibiotic-resistant strains of tuberculosis evolve over the course of treatment and remain virulent. The passage goes on to discuss the concerns raised by the study. The passage concludes by stating that drug-resistant bacteria are here to stay. Find an answer that matches this prediction. Choice (A) can be eliminated because, while the passage does mention classic laboratory studies, it does not support those findings. Choice (B) can be eliminated because it is the opposite of what the passage says. The passage does review the Stanford University study and discusses the concerns raised by the study. Keep (C). Eliminate (D) because the passage does not criticize the methodology of any study. The correct answer is (C).
Question2:- What did the scientists in the Stanford University study discover about tuberculosis bacteria that “undermined this comforting conventional wisdom” (third paragraph)?
  • A. Bacteria have shown the ability to resist antibiotics through mutation without losing strength.
  • B. Mycobacterium tuberculosis has become the leading cause of death in the United States.
  • C. RNA and DNA interchangeability in tuberculosis have led to stronger antibiotics.
  • D. Rifampin can no longer be used to treat disease due to the proliferation of polymerase molecules.
Answer is A is correct. This question asks what the scientists in the Stanford University study discovered about tuberculosis bacteria that “undermined this comforting conventional wisdom.” Notice that this is a question with best evidence answers that cover a large part of the text. Look at the answer choices for the “best evidence” of the question first. The lines in the last paragraph state that five of the ten resistant strains held their own in these tests and one actually dominated its antibiotic-susceptible ancestor. This supports the idea in option (A) that bacteria can resist antibiotics without losing strength. The correct answer is option (A).
Question3:- As used in the line from the fourth paragraph, “hardy” most nearly means
  • A. Difficult
  • B. Strong
  • C. Terrible
  • D. Thick
Answer is B is correct. This question asks what the word hardy most nearly means, as used in line as highlighted in the fourth paragraph of the passage. Read the window, cross out the word hardy and replace it with another word or phrase that makes sense based on the context of the passage. Then, eliminate anything that does not match the prediction. In the passage, the word hardy is used in connection with drug-resistant strains that remain virulent. In other words, these are potent strains that keep their strength. Look for a word that means “strong” or “tough.” The only answer choice that matches is (B). While (C) may be tempting since a virulent strain would be terrible; no such value judgment about the drug-resistant strains is made in the passage. The correct answer is (B).
Question4:- Which statement about rifampin can be most reasonably inferred from the passage?
  • A. It stopped tuberculosis from being the leading cause of death in the United States.
  • B. It has successfully inhibited protein production in bacteria.
  • C. It makes RNA for tuberculosis bacteria compatible with other DNA.
  • D. It is the most effective known treatment for tuberculosis.
Answer is B is correct. This question asks what statement about rifampin can be most reasonably inferred from the passage. Use the lead word rifampin and chronology to find the window. The answer to the question was in the sentence “Even though many drug-resistant strains are less hardy than susceptible strains, others evolve over the course of treatment and remain virulent.” Therefore, start looking for rifampin after this sentence. The first mention of rifampin is in the first part of the fifth paragraph. According to the passage, rifampin…disables the so-called polymerase molecule and prevents the crucial flow of information from DNA to RNA. Without RNA, bacteria can’t make the proteins they need to survive. Find an answer that matches this prediction. Choice (A) may be tempting at first because the passage states that rifampin is one of the preferred first-line treatments for the disease. However, the passage does not say that this drug stopped tuberculosis from being the leading cause of death in the U.S. Eliminate (A). Choice (B) is a good paraphrase of the prediction, so keep it. Choice (C) can be eliminated because there is no suggestion in the passage that rifampin makes RNA compatible with DNA. Choice (D) can be eliminated because there is no mention in the passage as to whether rifampin is more effective than other drugs. The correct answer is (B).
Question5:- As presented in the passage, the Stanford University study relied on which type of evidence?
  • A. Anecdotal opinion
  • B. Second-Hand observation
  • C. Animal studies
  • D. Clinical testing
Answer is D is correct. This question asks which type of evidence the Stanford University study relied on. Use Stanford as the lead word to find the window to read. The answer to the question is in the part of the fifth paragraph, so the answer to this question should come somewhere after the lines from the mid-part of the same paragraph. Lines from the last paragraph also contain the word, Stanford. According to the passage, the Stanford group collected tuberculosis bacteria from the sputum of patients, first at the beginning of their infections, and a second time after some of those patients developed rifampin-resistant infections. Look for an answer that matches this prediction. Given that the Stanford group did research using patients, the only answer that matches is (D) clinical testing. The correct answer is (D).

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