Q. 32

[McatCrusher]

Hi,
In this question, there is an arrow to TSH which completely threw me off. I though it was a product or at least that is what the figure implies. How should i figure out what is product or not in this kind of question?

[admin]

Hello

There are a couple of ways that you could have properly interpreted Figure 1: (a) a true equilibrium has double arrows (arrows in both directions between reactants/products); notice that the answers follow this rule; or (b) notice that the arrow leading to the TSH is a broken arrow. That fact should have made you question the meaning of that arrow. Then, on reflection, you would remember that increases in thyroxine leads to decreased TSH due to a negative feedback loop (BIO 6.3.6 in The Gold Standard).

Keep at it !

[tjk447963]

I don't think that we should be required to have to interpret the meaning of a broken arrow. Just because it was broken isn't enough to imply that it inhibits the production of TSH. There should have been a key.

[mcat_premed3832]

Yes, there should be a key IF knowing that thyroxine inhibits TSH was not required knowledge for the MCAT. Because it is required knowledge, it is expected that no matter what the arrow looks like, you would instantly know that it is impossible for increasing thyroxine to lead to increasing TSH.