EK 1001 Biology answer error?

[evoviiigsr]

pg 75 #412
The question is completely based on a table that gives the properties of FXC-5 cells:

resting membrane potential: -90mv
depolarization ion: Na
duration of action potential: 5 ms
type of think filament: actin G
action potential spread: t-tubules


"Which of the following must be true regarding the experimental muscle cell FXC-5?"
A. FXC-5 is a smooth muscle cell that is controlled by the autonomic nervous system
B. FXC-5 is hyperpolarized at -110mV
C. FXC-5 is a voluntary controlled cell
D. FXC-5 is identical to the muscle that makes up the wall of the heart

The answer in the book is B. I think the best answer is C. The table says that the AP lasts for 5ms, which is true for skeletal muscle cells, but NOT cardiac cells since their APs last like 500ms or so in order to prevent tetany. This leaves skeletal and smooth muscle only. The table says the cells have t-tubules, which rules out smooth muscle, so the FXC-5 cells must be skeletal muscles, and hence voluntary.

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[CATallergy]

if resting potential is -90mV, doesn't -110mV necessarily have to represent hyperpolarization? Skeletal=voluntary always seemed more like a general guideline than a rule, but I don't offhand know any exceptions. Based on your info, B is definitely the best answer, regardless of whether you are right in your reasoning for C.

Also, the question is about an experimental cell - is your info about cardiac action potential duration from the passage, or your own?

 

[bioteach]

Choice B is the most immediate and obvious choice. Hyperpolarization would be considered anything < -90 mV. The word "must" in the question suggests this has to be the answer.

 

[evoviiigsr]

if resting potential is -90mV, doesn't -110mV necessarily have to represent hyperpolarization? Skeletal=voluntary always seemed more like a general guideline than a rule, but I don't offhand know any exceptions. Based on your info, B is definitely the best answer, regardless of whether you are right in your reasoning for C.

Also, the question is about an experimental cell - is your info about cardiac action potential duration from the passage, or your own?

The knowledge of the cardiac AP is my own, not from the passage

 

[CATallergy]

my general approach to bio passages is that you should start out by assuming that you don't know anything. thereafter, only bring in your own knowledge when you think "Aha - this definitely requires outside knowledge". Actual MCAT physio passages (vs. those in review companies) seem overly concerned with seeing if you can read tables and graphs, but definitely do require you to have enough background to put the data into context.

In all sections, I would generally start off each passage by assuming that using their presented information correctly is the primary ability being tested by the question, before rushing to find a way to apply your background knowledge.

 

[Dr. Gangrene]

The knowledge of the cardiac AP is my own, not from the passage

That is where they get you. Just go off info in the passage. It is hard to tell yourself to choose the best answer from info IN THE PASSAGE when your personal knowledge gives you some extra insight. But for the MCAT, you gotta roll that way.

 

[Blondnuttyboy]

Yeah - go with your gut on that...B HAS to be true.

Be careful with Examcrackers Bio - there are alot of mistakes.

For example - Question 18, passage 103 answer claims that cholesterol is water insoluble.

 

[CATallergy]

Yeah - go with your gut on that...B HAS to be true.

Be careful with Examcrackers Bio - there are alot of mistakes.

For example - Question 18, passage 103 answer claims that cholesterol is water insoluble.

I also thought it was pretty much water insoluble. Isn't that the why it needs lipoproteins for transport?

 

[akinf]

Ummm...i thought cholesterol was water-insoluble too.

 

[EMTB2MD]

This might answer your question,

http://www.cholesterol-and-health.com/cholesterol_structure.html

Ken

 

[sehnsucht]

Yeah - go with your gut on that...B HAS to be true.

Be careful with Examcrackers Bio - there are alot of mistakes.

For example - Question 18, passage 103 answer claims that cholesterol is water insoluble.

i thought that cholesterol, because it is a lipid, is insoluble in water.

 

[evoviiigsr]

Wait if its soluble then why are there carrier proteins for lipid hormones? With peptides dissolving in the blood.

 

[phospho]

its amphipathic... i probably spelled that wrong...

 

[sehnsucht]

Wait if its soluble then why are there carrier proteins for lipid hormones? With peptides dissolving in the blood.

i would say that because it has that lone OH on one end of its structure, it can dissolve to an extent but not very much which is why the thing needs carrier proteins to get around in the blood.

 

[CATallergy]

i would say that because it has that lone OH on one end of its structure, it can dissolve to an extent but not very much which is why the thing needs carrier proteins to get around in the blood.

yeah, and other than that one hydroxyl group, the rest of the molecule looks pretty nonpolar. Id guess that while amphipathic, it leans toward nonpolar.