#3 - Hemoglobin, a substance in human blood, transports

[Adam Tyson]

The problem with answer B, Chica, is the word "only". We have no information in the stimulus to support the claim that an open shape is the only thing that matters. Perhaps overall size plays a part? Maybe the health of the molecule matters? Maybe blood type also has an impact, or the phase of the moon, or the price of tea in China? We know that open shape matters, but we don't know that nothing else matters. Beware of such strong language, and be sure it's supported if you are going to select it!

[nutcracker]

Hello,

I see answer choice (C) as relying on two assumptions that aren't necessarily true, that each hemoglobin starts out being equally effective at picking up oxygen molecules and that their effectiveness at picking up additional oxygen molecules increase by the same amount with each additional oxygen molecule. This looks similar to saying "the more one exercises, the fitter he or she becomes", and inferring from this information that someone who exercises three hours per day is fitter than someone who only exercises an hour per day. A lot of factors can influence how fit someone is, and I don't think this logic of using a general rule to make comparisons across individual entities should work in the LSAT.

I would like to know what specifically makes (C) a correct answer choice in this case. I thought we can only go as far as saying that "A hemoglobin molecule that has picked up three oxygen molecules is more effective at picking up another oxygen molecule than when it has picked up only one oxygen molecule", limiting the scope to that same hemoglobin. I crossed out (C) almost immediately and chose (A), since in my opinion "probably" qualifies the statement to allow for the possibility that there are not a fourth oxygen molecule available at times. I am really confused and quite frustrated to have gotten the third question wrong in a LR section... I would really appreciate some help!

[Adam Tyson]

Interesting point, nutcracker! Yes indeed, answer C does require assuming that every hemoglobin molecule is just about the same as every other hemoglobin molecule in both of those respects. If this was a pure Must Be True question, C would not be a very good answer at all.

However, this is a Most Strongly Supported question, the weak little brother to Must Be True, and in these questions we want to focus on what is most likely to be true, which one follow the stimulus the most and seems to be the most reasonable inference to draw, even if it isn't absolutely necessary. Is it reasonable to believe that hemoglobin molecules are all the same as each other in those two respects? Maybe. Given that they open up each time they pick up an oxygen molecule, and there has to some upper limit on how much they can open up, it seems reasonable to believe that any given one that has picked up three is probably more open than another that has picked up only one. Not certain, mind you, but reasonable. Maybe that's why they didn't compare one to two or two to three?

Is it reasonable to assume that once a hemoglobin molecule has picked up three oxygen molecules that it will pick up a fourth? Maybe, but that will also require at least one key assumption, and that's that there are more oxygen molecules around to pick up! What if there are none? Is it reasonable to assume that there are always more available to be picked up? I'm not sure about that.

You've raised a point that might be worth further debate with the authors of the test! You're not wrong, in my view, but I think you might be slightly over-thinking this one, and maybe allowing your dislike of one answer to lower your defenses to the flaws in another. Don't get too hung up on this one question, as I don't think you are likely to find many more where the answer is as open to debate as this one might be.

Finally, review this one again, and ask yourself, of the two answers under contention, why is A better than C? What makes you feel so sure about that probability in A? Picking the best answer is what this is all about, which means sometimes the credited response is lousy. That's okay, as long as it is better than the others. C needs less help here, in my opinion, and the assumptions you have to make seem more reasonable under the circumstances in than the ones required by A.

Keep up the good work and deep analysis! That will do you a lot of good on this test, usually.

[nutcracker]

I knew I was overthinking this one when I spent about two minutes on question #3 in a LR section... A and C looked about equally unsatisfactory but both seemed better than the others. I'll let go of this one and hope nothing like this appears on my actual test. Thanks for your explanation!