Hi Lydia,

"q 14, i know that converting bicarbonate into carbon dioxide consumes bicarbonate and therefore also consumes H ions to increase pH, but intuitively im not getting it. If an increase in CO2 is associated with a decrease in pH, then how does it make sense that increasing CO2 results in a increase in pH?"

I think you are asking why the answer choice conversion of bicarbonate to carbon dioxide in the blood would increase pH. The wording is a bit weird, but if you think about what has to happen for bicarbonate to leave as CO2, the process would be as follows:

HCO3- + H+ --> H2CO3 --> H2O + CO2(g) , where CO2 (g) leaves the blood/bubbles off

The implication in this process is that you will "quench" one proton in the blood with bicarbonate acting as a base. Following this, the implication is that you are offgasing CO2 and losing it from the blood, not absorbing it, which is the reverse process and would result in a decreased pH.

I understand the wording can be unclear for chem passages, so I often found myself translating from chemical formulas to words or vice versa. Usually that can clear things up.

q 32, i understand the correct answer but having a hard time ruling out other aspects. does arterial blood refer to blood in the pulmonary arteries? because i know the pulmonary arteries carry oxygenated blood and pulmonary veins carry oxygenated blood towards the heart, its just that the answer said arterial blood as highly oxygenated so it was confusing.

Yeah, it can be tough sometimes when the MCAT tries to lead you astray - it's customary to say arteries will carry oxygenated blood because you only really have that exception with the pulmonary artery/vein system.

In a situation like that, try not to let the MCAT shake your confidence in your prior knowledge - any information you might have that helps supplement the passage can be a tool to use for the questions in the science sections.

In terms of how I might eliminate for this question:

1. portal vein seems reasonable because veins generally are not oxygen rich
2. arterial blood can be eliminated because it is definetely oxgyenated.
3. the snail host should contain both oxygenated and deoxygenated blood so doesn't seem like a great answer. Also I don't know why they say snail host when this is a question about humans. This is just an all round weird answer choice.
4. the pulmonary vein carries oxygenated blood because it is coming from the lungs to the heart after the gas exchange of CO2 for O2.

I hope this helps!

Katt