A student asked us "According to answer "A" if fetal Hemoglobin is has higher affinity for oxygen than non-fetal hemoglobin, and 2,3-BPG is known to reduce Hemoglobin's affinity for oxygen, wouldn't it be a safe assumption to say that concentration of 2,3-BPG is higher in Maternal Blood?".
While it is true that fetal hemoglobin has a stronger affinity for oxygen compared to adult hemoglobin, it doesn't follow that any factors (e.g. 2,3-BPG, temperature, CO2 levels, pH etc....) that can affect the affinity of hemoglobin for oxygen would be the cause of that. The higher affinity of fetal hemoglobin is due to its structure and is also susceptible to all of the same factors that adult hemoglobin would be. It could be that the maternal bloodstream has higher levels of 2,3-BPG, but that is unknowable according to passage info and is not content students are expected to know walking into their MCAT.
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