PSAT Reading Question 508: Answer and Explanation

Question: 508

The processing or lack thereof of which chemical intermediate shown in Figure 2 does the author argue is particularly distinctive for Methanosphaera stadtmanae relative to other methanogens?

• A. H₂ oxaloacetate
• B. CO₂
• C. succinate
• D. CO

Correct Answer: C

Explanation:

(C) In the second paragraph, the author explains how Methanosphaera stadtmanae is different from other methanogens. These other methanogens can reduce CO2 to methane, but M. stadtmanae lacks the enzyme to initiate this pathway. Thus, M. stadtmanae can reduce methanol only to methane. Therefore, the inability to process CO2 sets the species apart from other methanogens. Choice (A) is incorrect because all of the methanogens the author references use H2 in reduction. Choices (B) and (D) aren't mentioned in the passage.