A group of scientists studying calcium metabolism in laboratory rats discovered that removing the rats' parathyroid g...

Irina on August 5, 2019

@Marissa,

The argument tells us that removing the rats' parathyroid glands resulted in substantially lower levels of calcium. This finding resulted in a hypothesis that the parathyroid gland regulates the level of calcium by raising it when it falls below the normal range. Removing both the parathyroid gland and the adrenal gland resulted in the level of calcium decreasing less sharply.

How do we resolve this paradox consistent with the hypothesis?

The question essentially asks us to determine the role for the adrenal gland assuming that the parathyroid gland raises the level of calcium when it falls below the normal range:

P A C
up ? down

Let's think about all the options for A:

P A C
up up down

If both glands raise the level of calcium or A raises the level of calcium when P is removed, then removing both would result in an even sharper decrease rather than less sharp decrease per the argument, hence we can eliminate (B) & (C).

P A C
up no effect down

If A has no impact on the level of calcium, then both experiments would produce identical results, hence we can eliminate (D).

P A C
up down down

If A lowers the level of calcium then removing both would result in a less sharp decline in the level of calcium then removing P alone and A continuing to lower the level of calcium without P to counterbalance it. Thus, (A) helps to explain the results of the second experiment assuming that the hypothesis is true and P acts to raise the level of calcium.

Does this make sense?

Let me know if you have any further questions.