Biology HESI A2 2024

Correct Answer: B

Rationale: The correct answer is B: Parasitism. In parasitism, one organism benefits (the pneumonia bacterium) at the expense of the other (the human). The bacterium causes harm to the human by causing pneumonia, which is detrimental. In mutualism (A), both organisms benefit; in commensalism (C), one benefits while the other is unaffected; in competition (D), both organisms are harmed by vying for the same resources. Hence, parasitism is the most fitting description of the relationship between the pneumonia bacterium and the human in this scenario.

Correct Answer: B

Rationale: The correct answer is B because it involves a controlled experiment with two distinct groups - one exposed to chocolate and the other not. This allows for comparison to determine the impact of chocolate consumption on acne. Option A lacks a control group for comparison. Option C only uses one participant, which is not enough to draw generalizable conclusions. Option D does not have a control group and the order of exposure is reversed, which may affect the results. In summary, choice B is the most appropriate as it includes a control group, clear exposure to the variable of interest, and enables comparison between the two groups.

Correct Answer: B

Rationale: The correct answer is B because meiosis creates cells with half the chromosomes of the parent cell through two rounds of cell division. This results in gametes with a haploid number of chromosomes. In contrast, mitosis produces identical diploid cells for growth and repair. Choices A, C, and D are incorrect because mitosis forms body cells, telophase occurs in both processes, and spermatogenesis and oogenesis specifically involve meiosis, respectively.

Correct Answer: C

Rationale: The correct answer is C because yeast carries out fermentation, producing ethanol and carbon dioxide. During fermentation, yeast breaks down sugars in the dough into ethanol and carbon dioxide gas. The carbon dioxide gas gets trapped in the dough, causing it to rise. Choice A is incorrect because yeast does not engage in photosynthesis. Choice B is incorrect because yeast does not carry out photosynthesis at all. Choice D is incorrect because yeast primarily produces carbon dioxide through fermentation, not aerobic respiration.

Correct Answer: C

Rationale: The correct answer is C: thymine. In DNA, adenine always pairs with thymine through two hydrogen bonds. This is a fundamental principle known as Chargaff's rule, where A pairs with T and C pairs with G. Thymine is a pyrimidine base, complementing adenine, which is a purine base. Therefore, thymine is the most suitable choice for adenine in a DNA strand. Choices A, B, and D are incorrect because adenine does not pair with cytosine (A), uracil (B), or guanine (D) in DNA.