PrepTest 131

Incorrect. While the stimulus does establish that the hemoglobin molecules become more effective as they pick up more oxygen molecules, there's no indication that one is likely to pick up that fourth molecule. Maybe they reach the target location where they're delivering the oxygen before they have time to pick up the fourth.

Incorrect. While the opening of the molecule is a factor in determining the affinity for more oxygen, there's no indication that it's the only factor. In fact, the number of molecules is also noted as being relevant, and it could be relevant for reasons other than each one opens up the hemoglobin molecule more.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Each oxygen molecule hemoglobin picks up makes it more effective at picking up the next one, up to 4.
Each oxygen molecule opens up the hemoglobin molecule.

Answer Anticipation:
We stripped a lot of the stimulus out and focused on two statements. These two statements are both strong, comparative statements that also feature some causality, all of which tend to lead to inferences in Must Be True questions. They could individually lead to an inference, but they could also be combined—something relating hemoglobin molecules being opened up more and more by each oxygen molecule, making it more likely to bind the next oxygen (up to 4).

Answer Explanation:
The stimulus establishes that each oxygen molecule makes the hemoglobin molecule more effective at picking up additional oxygen, up to 4. Therefore, a hemoglobin molecule with 3 oxygen molecules will be better at picking up oxygen molecules than one with only 1 oxygen molecule, as this answer states.

Key Takeaway:
Don't get lost in the science. Here, "hemoglobin" and "molecule" can easily knock you off your game, but focus on the logic—comparisons, causality, and strong statements.

Incorrect. Each oxygen molecule opens up the hemoglobin molecule, so, if anything, this answer is contradicted by the stimulus.

Incorrect. While hemoglobin is noted as picking up oxygen from the lungs and transporting it throughout the body, there's no indication that each molecule picks up at least one oxygen molecule. Maybe there are significantly more hemoglobin molecules than there are oxygen molecules so that there's a steady flow of oxygen to the rest of the body, while most of those hemoglobin molecules float around without oxygen just in case there's some spare oxygen to pick up. Think of a lazy river at a water park—there are a ton of extra floats just in case more people want to use them!