AAMC BS Self-Assessment Official Q&A

[gettheleadout]

This thread shall serve as the site for discussion of questions from the AAMC Self-Assessment in MCAT Biological Sciences.

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[texan2414]

Biology #59: http://puu.sh/cg05J.png

Can someone explain why Hb is involved to regulate oxygen perfusion?

 

[sps27]

Biology #59: http://puu.sh/cg05J.png

Can someone explain why Hb is involved to regulate oxygen perfusion?

More Hb means more O2 can bind. Fully oxygenated blood is HbO8. Btw,,,,I got that acholinesterace blocker question wrong too and my ans was same as yours.

 

[texan2414]

More Hb means more O2 can bind. Fully oxygenated blood is HbO8. Btw,,,,I got that acholinesterace blocker question wrong too and my ans was same as yours.

Ahh so I guess in this question, Hb refers to the perfusion aspect. Didn't occur to me at the time.

Yeah the AChase question boiled down to the word "repeated transmission" - which could have narrowed answer choice to C.

 

[young_gohard]

View attachment 184901 View attachment 184902 View attachment 184903 someone please explain why it is B? it says NaOH will make a salt COO- group but it says the IR has no peak at 1700. unless it's because the carbonyl oxygen in COOH is more around 1720? that would be very specific though considering there's a range or IR measurements for ketones and COOH
http://www.chem.ucla.edu/~webspectra/irtable.html

I'm also curious about Oh-Gee's question (# 56 in the organic chemistry self-assessment). How can compound C be the result of NaOH hydrolysis of an ester when that would yield a carboxylate ion, which has a C=O bond and DOES have a peak around 1700, even though figure 1 indicates there was no peak found at 1700.

 

[young_gohard]

I'm also curious about Oh-Gee's question (# 56 in the organic chemistry self-assessment). How can compound C be the result of NaOH hydrolysis of an ester when that would yield a carboxylate ion, which has a C=O bond and DOES have a peak around 1700, even though figure 1 indicates there was no peak found at 1700.
View attachment 186680

After looking into this a bit more, it seems carboxylate salts have peaks closer to 1600, like sodium formate (below). But I guess the real takeaway might be to not think about that when picking an answer since I don't think carboxylate peaks are required knowledge.

 

[ahisma]

Biology #45:

Does acceptance of the mechanism of self-tolerance described in Hypothesis 1 rule out acceptance of the mechanism described in Hypothesis 2?

C. No; suppressor T cell formation can only occur after clonal deletion has occurred
D. No; clones of self-reactive lymphocytes not destroyed by clonal deletion may e controlled by suppressor T cells

Why is C correct and not D?

Looks like this was never answered but I'm wondering the same thing. Anyone have any ideas on this?

Here's the relevant passage info:

Hypothesis 1
Most of the body's self-tolerance is generated within a few months of birth, when the body is processing T and Blymphocytes. Identical groups (clones) of circulating lymphocytes remain inactive until they encounter their specific antigens, after which they proliferate. During this time, the process of clonal deletion destroys any newly formed groups of lymphocytes that might attack the body's own tissues. If clonal deletion of such lymphocytes does not occur or is hindered, these lymphocytes will incorrectly recognize a specific body tissue as foreign or non-self, and begin to destroy it.

Hypothesis 2
In addition to effector lymphocytes (such as helper T cells and cytotoxic T cells) that selectively attack and destroy antigens, the body contains other lymphocytes (suppressor T cells) that prevent this destruction by selectively limiting the action of the effector cells. Normally, a regulatory balance is maintained between effector and suppressor T cells. However, when this balance is disturbed (for example, by loss or inactivation of suppressor-cell clones), an autoimmune disease may result.

 

[neuro_nerd14]

Looks like this was never answered but I'm wondering the same thing. Anyone have any ideas on this?

Here's the relevant passage info:



Hypothesis 2
In addition to effector lymphocytes (such as helper T cells and cytotoxic T cells) that selectively attack and destroy antigens, the body contains other lymphocytes (suppressor T cells) that prevent this destruction by selectively limiting the action of the effector cells. Normally, a regulatory balance is maintained between effector and suppressor T cells. However, when this balance is disturbed (for example, by loss or inactivation of suppressor-cell clones), an autoimmune disease may result.

thanks for replying to me on the jan 10th thread

as for #45 I think the answer is C because "Normally, a regulatory balance is maintained between effector and suppressor T cells. However, when this balance is disturbed (for example, by loss or inactivation of suppressor-cell clones), an autoimmune disease may result"

which tells that suppressor T cells forms only when ( clonal deletion has occured) ... which matches hypotheses 1 because " During this time, the process of clonal deletion destroys any newly formed groups of lymphocytes that might attack the body's own tissues. If clonal deletion of such lymphocytes does not occur or is hindered, these lymphocytes will incorrectly recognize a specific body tissue as foreign or non-self, and begin to destroy it."

 

[neuro_nerd14]

and my question is about Bio self assessment question 26 and 27 >.< anyone help me with that please?

 

[ahisma]

and my question is about Bio self assessment question 26 and 27 >.< anyone help me with that please?

What does your question 26 and 27 say? I have the paper version that seems to have different questions than some of the posts here.

 

[ahisma]

thanks for replying to me on the jan 10th thread

as for #45 I think the answer is C because "Normally, a regulatory balance is maintained between effector and suppressor T cells. However, when this balance is disturbed (for example, by loss or inactivation of suppressor-cell clones), an autoimmune disease may result"

which tells that suppressor T cells forms only when ( clonal deletion has occured) ... which matches hypotheses 1 because " During this time, the process of clonal deletion destroys any newly formed groups of lymphocytes that might attack the body's own tissues. If clonal deletion of such lymphocytes does not occur or is hindered, these lymphocytes will incorrectly recognize a specific body tissue as foreign or non-self, and begin to destroy it."

Thanks for your reply. I see what you are saying, it seems pretty straight forward. But I'm still wondering why can't suppressor T cells act as a check on clonal deletion, regulating those self-reactive clones that should have been destroyed but somehow "slipped through"?

 

[neuro_nerd14]

Thanks for your reply. I see what you are saying, it seems pretty straight forward. But I'm still wondering why can't suppressor T cells act as a check on clonal deletion, regulating those self-reactive clones that should have been destroyed but somehow "slipped through"?

the answer is actually D not C I'm sorry for the confusion this is the explanation hope this helps !

 

[ahisma]

Well I guess the key I have to the paper version is wrong then, thanks!

Did you ever figure out #26 and #27? If not let me know if your #26 and #27 are the same as mine:

I got them right so can explain if needed.

 

[neuro_nerd14]

Well I guess the key I have to the paper version is wrong then, thanks!

Did you ever figure out #26 and #27? If not let me know if your #26 and #27 are the same as mine:
View attachment 187940

I got them right so can explain if needed.

No problem ... I got 26 but 27 still do not get it ... it is the same questions u have

 

[ahisma]

Last paragraph of the passage states, "Dietary restriction [aka fasting]... increases the maximum life span of rats from 125 to 185 weeks." So the fasting group should have the longer survivorship curve with a maximum point around 185 weeks. C is the only plot that reflects this info given in the passage.

 

[magictouch]

Anyone understand 41?

I get how B is plausible (its what I originally thought) but the passage doesn't indicate that, and I didn't know how to rule out D either so I went conservative and picked A.

 

[neuro_nerd14]

Last paragraph of the passage states, "Dietary restriction [aka fasting]... increases the maximum life span of rats from 125 to 185 weeks." So the fasting group should have the longer survivorship curve with a maximum point around 185 weeks. C is the only plot that reflects this info given in the passage.
View attachment 187942

thank you so much that really helped! i get it now

 

[erythrocyte666]

Anyone understand 41?

I get how B is plausible (its what I originally thought) but the passage doesn't indicate that, and I didn't know how to rule out D either so I went conservative and picked A.

View attachment 187952

A assumes that w/o carcinogen, the bacterium is there but not visible; however, the passage specifically says that the "test strains do not survive" in His- medium (also ignore wild-type part since Ames test uses test strains according to passage). hence a is false
B is true because before/after carcinogen, medium is still same but bacterial growth increases - hence a previous disability is corrected

 

[ahisma]

Anyone understand 41?

I get how B is plausible (its what I originally thought) but the passage doesn't indicate that, and I didn't know how to rule out D either so I went conservative and picked A.

View attachment 187952

The passage states the test strain needs histidine in the culture medium to survive. So when the test strain is placed on a histidine-deficient culture they should not grow. If they do grow it means they have mutated, likely due to mutagen exposure. This is basically how the Ames test works. See this article for more.

 

[magictouch]

A assumes that w/o carcinogen, the bacterium is there but not visible; however, the passage specifically says that the "test strains do not survive" in His- medium (also ignore wild-type part since Ames test uses test strains according to passage). hence a is false
B is true because before/after carcinogen, medium is still same but bacterial growth increases - hence a previous disability is corrected

The passage states the test strain needs histidine in the culture medium to survive. So when the test strain is placed on a histidine-deficient culture they should not grow. If they do grow it means they have mutated, likely due to mutagen exposure. This is basically how the Ames test works. See this article for more.

Thanks guys! I think I finally see how they eliminated D. Looking back I see how lacking histidine is much less likely given that would require mutations to every protein that contains it, while the ability to synthesize it is probably one enzyme. Is that how you guys eliminated D?

 

[ahisma]

Never thought about it that in depth. I simply recalled from the passage that if they lacked histidine then they wouldn't be able to grow. The question states they can grow so they must have mutated to produce histidine, the factor previously limiting their growth.

Don't overanalyze and make it more complicated than it needs to be! That gets me in trouble all the time. Keep it simple, do POE, and go go go.