Questions Qpack 1 and 2 AAMC: THank you!

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lotus0618
Posts: 164
Joined: Sun Dec 29, 2019 5:47 pm

Questions Qpack 1 and 2 AAMC: THank you!

Post by lotus0618 » Sun Jun 21, 2020 6:58 pm

Qpack 1 Biology:
#110:
I chose C because I thought the build-up of salts in the distal tubules means that the salt is being absorbed in the medulla. Thus high salt concentration will draw more water back into the medulla, vasa recta, which leads to reduced urinary output.

Can you please explain to me why C is wrong and why is A the correct answer?

Qpack II Biology:
#104: Can you please explain options B and C to me?
#112: Why Isn’t the answer B? I understand why there would be more CO2. However, based on the reaction CO2+ H20 <-> H2CO3- <-> HCO3- + H
-> of course, if the question were to ask for the compensated pH, then I would choose C since more CO2 causes the reaction to shift right, which decreases pH. But here the question asks specifically for the pH at a high amount of CO2, so I chose B.
Can you please point out my flaw and explain it to me?
NS_Tutor_Yuqi
Posts: 40
Joined: Fri May 29, 2020 11:43 pm

Re: Questions Qpack 1 and 2 AAMC: THank you!

Post by NS_Tutor_Yuqi » Sun Jun 21, 2020 10:47 pm

110: In the distal tubules, salts are actively transported out through the sodium potassium pumps, which are regulated by aldosterone. Therefore, dehydration would not necessarily lead to a build up of salts in the distal tubule since salt movement is controlled through hormones. In contrast, answer A directly relates to the effects of dehydration through addressing the inadequate blood volume. Even if there were to be excess water absorbed into the medulla, leading to decreased urinary output, the root cause would still be the low volume of fluids caused by the dehydration. I hope that makes sense!

104: B is correct because it directly answers why a test for mutagens is also used to test for carcinogens. Especially since Salmonella lacks a mechanism for DNA repair, the effects of the mutagens can be seen if the Salmonella mutates and is able to survive in the harmful environment. As most carcinogens are mutagens of some sort, the Ames test can therefore be used as a test for carcinogens. C states that Salmonella contains oncogenes, which are genes that can potentially cause cancer. Even though this may be true, it doesn't answer the question of why the Ames test is effective for carcinogens.

112: There is usually an inverse relationship between O2 and CO2. As one increases in blood, the other decreases. For example, aortic blood is oxygen rich and delivers oxygen across the body. At the same time, it also removes CO2 from the blood. Therefore, the later in the cycle, the higher the amount of CO2 and the lower the amount of O2 that is in the blood. Blood in the pulmonary artery is passing through the lungs in order to become reoxygenated and is essentially equivalent to systemic venous blood in its levels of CO2 and O2. Therefore, pulmonary arterial blood has less O2 and more CO2 than aortic blood.
As for pH, you're right in thinking of the bicarbonate buffer system. However, this buffer system doesn't constantly stay on the left side just because there's a high concentration of CO2. As the buffer system is always in equilibrium, higher amounts of CO2 will automatically shift the equation to the right, thereby generating more H+ ions and lowering the pH.
lotus0618
Posts: 164
Joined: Sun Dec 29, 2019 5:47 pm

Re: Questions Qpack 1 and 2 AAMC: THank you!

Post by lotus0618 » Thu Jul 02, 2020 10:18 pm

110: Ohhh, so the 2 keys here are 1) interpret the question correctly - here it asks Severe dehydration causes what that leads to kidney failure, so we need to choose the answer that is caused by kidney failure, 2) yes, severe dehydration triggers the retention of water in the medulla, but it DOES not DIRECTLY trigger the build-up of salts; dehydration triggers hormones that control the absorption of salts, which INDIRECTLY affects the amount of water being retained.
Therefore, A is the best answer.
NS_Tutor_Yuqi
Posts: 40
Joined: Fri May 29, 2020 11:43 pm

Re: Questions Qpack 1 and 2 AAMC: THank you!

Post by NS_Tutor_Yuqi » Sat Jul 04, 2020 11:56 am

Just a note that we are not looking for the answer that is caused by kidney failure, but rather the one that would lead directly to kidney failure. But other than that, I agree with your reasoning!
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