Official DAT Destroyer Q&A Thread

[densaugeo]

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Hi guys, since I'm currently going through the DAT Destroyer and I'm sure many of you guys are as well I felt this thread would be helpful. I usually have various questions while going through Destroyer regarding why a certain answer choice is correct or other times I am in need of a more detailed explanation.

Instead of making multiple threads each time we have questions, I thought we could just post them here and anyone can chime in with an explanation or further clarification.

Please don't post entire questions as that would be a violation of copyright. You can ask specific questions regarding a particular problem in the Destroyers.

Hopefully others find this a useful thread. Thanks!

 

[tooth_hurty]

Destroyer 15 biology #563

What are the main differences between the early allantois in mammals vs birds and reptiles? Is it simply that the allantois in mammals transports waste products to the placenta while in birds/reptiles it stores nitrogenous waste?

 

[DAT Destroyer]

Destroyer 15 biology #563

What are the main differences between the early allantois in mammals vs birds and reptiles? Is it simply that the allantois in mammals transports waste products to the placenta while in birds/reptiles it stores nitrogenous waste?

Alantois in birds and reptiles stores Nitrogenous wastes but also functions in a process of supplying Oxygen to the embryo, it can adsorb oxygen from the egg shell.

In mammals, Alantois transports wastes and in later stages of development can become an axis for the development of the umbilical cord.

 

[Sigg]

2015 Destroyer Bio question #166.

I think there may be an error in the answer section to this question? The answer at the back discusses integrins and wound repair, but the question does not have anything to do with integrins.

In my book, question #166 in Bio involves asks which statement is false, some of the answers involve microtubules/cytoskeleton/smooth ER (nothing to do with integrins)

Is this an error? Or am I reading something wrong here...

 

[cacajuate]

Yea, I agree with sigg. That answer doesn't make sense for the question.

 

[DAT Destroyer]

2015 Destroyer Bio question #166.

I think there may be an error in the answer section to this question? The answer at the back discusses integrins and wound repair, but the question does not have anything to do with integrins.

In my book, question #166 in Bio involves asks which statement is false, some of the answers involve microtubules/cytoskeleton/smooth ER (nothing to do with integrins)

Is this an error? Or am I reading something wrong here...

The answer is correct, It says, which statement is false.
Choice C is talking about collagen. That is not correct. Collagen is not involve in molecules coming from cytoskeleton to the extracellular matrix. Integrins, however, are involved. That is their job. Wound healing is one of the examples.

 

[tyjacobs]

DAT destroyer biology question 530

Aren't there are ligand-gated Ca++ channels? When I saw this question, I immediately thought of the IP3/DAG pathway so I originally thought Ca ++ channels was the answer and then I saw acetylcholine receptors and knew that was a ligand-gated channel. But all of the above wasn't an answer choice.

the calcium channel in the IP3/DAG is a ligand-gated channel in reference to the paper http://www.ncbi.nlm.nih.gov/pubmed/17061256.


dat destroyer gen chem question 194

The answer says that [H+] will equal [N3-] at equilibrium. However, wouldn't the autoionization of water slightly increase the [H+] and thus make it larger than the [N3-] at equilibrium?

Wouldn't the ICE box look like this if we wanted to be most accurate (I understand you ignore the 1*10^-7 h3o+ concnetration in general calculations when the acid concentration is relatively high)?

 

[tooth_hurty]

Destroyer Gen Chem 2015 #36

How can we tell when a transition metal will form a complex ion? Does this only occur in certain cases or is it in any case where an acidic metal cation is added to a basic solution? When trying to do this problem quickly I saw silver which I thought was insoluble as Ag+...but forgot to consider that it forms a complex ion with NH3 making it more soluble.

 

[tyjacobs]

DAT destroyer biology question 235:

I got this question right, but I almost chose answer choice A. Doesn't capillaries have the greatest resistance to blood flow in circulation because they have the highest total surface area?

 

[DAT Destroyer]

Destroyer Gen Chem 2015 #36

How can we tell when a transition metal will form a complex ion? Does this only occur in certain cases or is it in any case where an acidic metal cation is added to a basic solution? When trying to do this problem quickly I saw silver which I thought was insoluble as Ag+...but forgot to consider that it forms a complex ion with NH3 making it more soluble.

A property of metal ions is their ability to act as Lewis acids....and accept electrons. Most all transition metals can form Complex ions.....Ag, Cd, Cr, Au, Mo,Ni, Fe,Co, and Ag. D orbitals love to share !!!!! Some common ligands include H2O, NH3, CN-, and Cl-. Ag is not very soluble in water...but in Ammonia it is VERY soluble. We form a stable Complex ion......Hopefully this question allows you to see that ion solubility is greatly affected by the solvent !!!!

Hope this helps.

Dr. Romano

 

[cacajuate]

DAT destroyer biology question 235:

I got this question right, but I almost chose answer choice A. Doesn't capillaries have the greatest resistance to blood flow in circulation because they have the highest total surface area?

Arterioles only allow very few RBC to pass through at a time. Causes huge resistence.

 

[GBP12]

DAT Destroyer QR #56

In the solution it says 26 black cards left/51 total cards=26/51

But based on the question, how do you know there are 26 black cards left? Couldn't the heart that is drawn be a black heart?

 

[StudentDoc1234]

DAT Destroyer QR #56

In the solution it says 26 black cards left/51 total cards=26/51

But based on the question, how do you know there are 26 black cards left? Couldn't the heart that is drawn be a black heart?

In a deck of cards hearts are always red, never black.

 

[GBP12]

In a deck of cards hearts are always red, never black.

Damn, I've never even realized that... thanks. Time to go study a deck of cards b/c I need to know it to become a dentist!

 

[DAT Destroyer]

Damn, I've never even realized that... thanks. Time to go study a deck of cards b/c I need to know it to become a dentist!

Very funny GBP12!

 

[super frank]

I will be taking the DAT next summer and am looking into study materials for the exam. When will the 2016 Destroyer be released? Or is it okay to purchase the 2015 edition?

 

[DAT Destroyer]

I will be taking the DAT next summer and am looking into study materials for the exam. When will the 2016 Destroyer be released? Or is it okay to purchase the 2015 edition?

I would wait, never know what the ADA is up to...They have been talking change change change for several years..We are still waiting..and we will adjust accordingly when necessary..

Nancy

 

[GBP12]

DAT Destroyer QR #88

When you say between 10 and 90 does that include 10 and 90 or only the numbers between?

I mean obviously you mean it does include them based on the answer, but how can that be inferred from between 10-90?

 

[DAT Destroyer]

DAT Destroyer QR #88

When you say between 10 and 90 does that include 10 and 90 or only the numbers between?

I mean obviously you mean it does include them based on the answer, but how can that be inferred from between 10-90?

Unless the question states otherwise you should always assume that the lower and the higher number are inclusive.

Hope this helps!

 

[Sigg]

DAT destroyer 2015 bio question #299

This statement is true: "RNA viruses are called retroviruses"

I get that all retroviruses are RNA viruses...but i didn't think the opposite was true - that ALL RNA viruses are called "retroviruses"...So is it not exactly accurate to say "RNA viruses are called retroviruses" because there could be some RNA viruses that aren't retroviruses?

I found a similar thread on this, and it apparently was the consensus:
http://forums.studentdoctor.net/threads/dat-destroyer-bio-133.787535/

 

[Sigg]

DAT destroyer biology question 235:

I got this question right, but I almost chose answer choice A. Doesn't capillaries have the greatest resistance to blood flow in circulation because they have the highest total surface area?

Hey, not sure if you still need clarifying on this, but I had the exact same issue and found this thread helpful:

http://forums.studentdoctor.net/threads/why-are-arterioles-resistance-vessels.982497/

The part that helped me was a post that said:
" arterioles have the greatest wall thickness to vessel diameter ratio"

 

[Sigg]

Sorry for all the posts, but I have another question!

DAT destroyer Biology Q #331

It says an egg cell will contain 23 chromosomes and 23 chromatids.

However, I thought the answer was 23 chromosomes and 46 chromatids.

To my knowledge, an egg is arrested at the beginning of meiosis II (I've read somewhere that it's metaphse of meiosis II). It doesn't complete meiosis II until after fertilized, at which point it's no longer an "egg". So if it's at the beginning of meiosis II, there should be 23 chromosomes (due to meiosis I), BUT each chromosome would contain 2 sister chromatids, wouldn't it? This would allow it to complete meiosis I, which is similar to mitosis, where each sister chromatid can be pulled to opposite poles. So shouldn't there would be 23 chromosomes, with 46 chromatids?

I found another thread on this, where someone had the same issue.

http://forums.studentdoctor.net/threads/bio-question-an-egg-cell-contain.454176/

Thanks!

 

[Sigg]

...and yet another question, haha sorry...

DAT Destroyer 2015 bio 334.
This is a Hardy Weinberg equilibrium question. It said the frequency for the allele for cystic fibrosis is 1/2500, so I let q=0.0004, but the answers made q^2=0.0004. From my knowledge, I thought that p and q designated the alleles, and q^2 and p^2 were the frequency of the recessive and dominant genotypes

I think the wording "frequency for the allele for cystic fibrosis..." is a little misleading, no? Or were we expected to have recognized that this question was indicating for q^2 = 0.0004, instead of q=0.0004 (which is what I thought)

And again, here's a similar thread
http://forums.studentdoctor.net/threads/destroyer-bio-q.842269/

 

[DAT Destroyer]

Sorry for all the posts, but I have another question!

DAT destroyer Biology Q #331

It says an egg cell will contain 23 chromosomes and 23 chromatids.

However, I thought the answer was 23 chromosomes and 46 chromatids.

To my knowledge, an egg is arrested at the beginning of meiosis II (I've read somewhere that it's metaphse of meiosis II). It doesn't complete meiosis II until after fertilized, at which point it's no longer an "egg". So if it's at the beginning of meiosis II, there should be 23 chromosomes (due to meiosis I), BUT each chromosome would contain 2 sister chromatids, wouldn't it? This would allow it to complete meiosis I, which is similar to mitosis, where each sister chromatid can be pulled to opposite poles. So shouldn't there would be 23 chromosomes, with 46 chromatids?

I found another thread on this, where someone had the same issue.

http://forums.studentdoctor.net/threads/bio-question-an-egg-cell-contain.454176/

Thanks!

No, it is correct, because egg and sperm are haploid cells.

 

[Jackthesparrow]

Biology # 183

I am having hard time understanding the concept of this problem.
Let restate or... reword what you what you said on solution

Increase in degree of unsaturation, will increase fatty acids, fluidity, and decrease in MP
Decrease in degree of unsaturation, will decrease fatty acids, fluidity, and increase in MP

Increase in saturated fatty acid, will decrease fatty acids, fluidity, and increase in MP
Decrease in saturated fatty acid, will increases fatty acids, fluidity, and decrease in MP

perheps... what I need to understand is the relationship between degree of unsaturation and saturated fatty acid?

 

[DAT Destroyer]

Biology # 183

I am having hard time understanding the concept of this problem.
Let restate or... reword what you what you said on solution

Increase in degree of unsaturation, will increase fatty acids, fluidity, and decrease in MP
Decrease in degree of unsaturation, will decrease fatty acids, fluidity, and increase in MP

Increase in saturated fatty acid, will decrease fatty acids, fluidity, and increase in MP
Decrease in saturated fatty acid, will increases fatty acids, fluidity, and decrease in MP

perheps... what I need to understand is the relationship between degree of unsaturation and saturated fatty acid?

That is correct. Unsaturation means double bonds between 2 carbons. The more of them there are, the higher degree of unsaturation. High unsaturation means higher membrane fluidity due to the lack of tight packing of those lipids. Unsaturation also reduces boiling points.

 

[510586]

For number 26 on the GC part of 2015 Dat destroyer, is it supposed to be nMV1=n2M2V2 of the H's and OH's or is it just simply moles acid= moles base for neutralization?

 

[cacajuate]

M is Molarity, and N is the normality.

so Ba(OH)2 would have a normality of 2.

 

[510586]

You are given an acid that has an EXTREMELY low concentration.......thus one must consider the hydrolysis of water ! Water will contribute 1x10 exp-7.......thus pH will be close to 7. Lets say that you forget to do this.....the negative log of 1x10exp-12 would have given you a pH of 12....yes ? How can an HCl solution be 12 ? That would be the tell-tale sign that this is a trick problem !

Hope this helps.

Dr. Jim Romano

When do we know if it is extremely low in concentration? Would 1*10^-8 be extremely low?

 

[510586]

M is Molarity, and N is the normality.

so Ba(OH)2 would have a normality of 2.

That's odd I guess they just didn't put that in there. It just says mol acid mol base not normalities or anything. Just making sure.
So if it's 1 M BaOH2 diluted with 100 mL of 1 M HCl, it would be 50 mL BaOH2 correct? (2*1*x)=(1*1*100)

 

[510586]

That's odd I guess they just didn't put that in there. It just says mol acid mol base not normalities or anything. Just making sure

 

[cacajuate]

That's odd I guess they just didn't put that in there. It just says mol acid mol base not normalities or anything. Just making sure.
So if it's 1 M BaOH2 diluted with 100 mL of 1 M HCl, it would be 50 mL BaOH2 correct? (2*1*x)=(1*1*100)

I didn't look at the actual question sorry. I just assumed it was about that based on the formula you gave.

On that one you have to convert the HCl to moles. Since HCl is a strong acid, and NaOH is a strong base, the solution will neutralize when they are in a 1:1 ratio. So once you have HCl in moles, that is how many moles of NaOH you have.

About the BaOH2 one. Yes that is correct.

 

[510586]

I didn't look at the actual question sorry. I just assumed it was about that based on the formula you gave.

On that one you have to convert the HCl to moles. Since HCl is a strong acid, and NaOH is a strong base, the solution will neutralize when they are in a 1:1 ratio. So once you have HCl in moles, that is how many moles of NaOH you have.

About the BaOH2 one. Yes that is correct.

Alright so it's always taking into account normality on neutralizations got it. THanks!

 

[510586]

The oxygens in number 4 of gc destroyer would be considered electron withdrawing groups, correct?

 

[510586]

What's the difference between poikilotherms and cold blooded animals? I believe in cliff and ferali notes, they are somewhat synonymous. But number 55 on destroyer 2015 said that poikilotherms was the best answer.

 

[DAT Destroyer]

The oxygens in number 4 of gc destroyer would be considered electron withdrawing groups, correct?

I am unclear of what you are referring to......Please re-state the question ?

 

[510586]

I am unclear of what you are referring to......Please re-state the question ?

Would these be considered ewg is that the reasoning?

 

[510586]

Would these be considered ewg

 

[DAT Destroyer]

Would these be considered ewg is that the reasoning?

Oh, you stated gc not ochem....The question had the " tone " of organic chemistry🙂

Indeed so,,,,,,these groups will withdraw electron density AWAY from the Nitrogen........more electron withdrawal.....the less basic will the compound become.

Hope this helps.

Dr. Romano

 

[510586]

Oh, you stated gc not ochem....The question had the " tone " of organic chemistry🙂

Indeed so,,,,,,these groups will withdraw electron density AWAY from the Nitrogen........more electron withdrawal.....the less basic will the compound become.

Hope this helps.

Dr. Romano

Oh sorry about that. Alright got it thanks! Wouldn't resonance be an even greater factor since the added carbonyl group can resonate with the nitrogen?

 

[DAT Destroyer]

Oh sorry about that. Alright got it thanks! Wouldn't resonance be an even greater factor since the added carbonyl group can resonate with the nitrogen?

Resonance is another reason that 2 carbonyl groups withdraw significant electron density from the nitrogen. Good call, resonance and induction are both operating together making this nitrogen non- basic.

Hope this help!

Dr. Romano🙂

 

[510586]

Resonance is another reason that 2 carbonyl groups withdraw significant electron density from the nitrogen. Good call, resonance and induction are both operating together making this nitrogen non- basic.

Hope this help!

Dr. Romano🙂

Yes it does! Would they ever ask why one is more acidic than the other? Or do they ask CARDIO base ranking by just comparing molecules?

 

[DAT Destroyer]

Yes it does! Would they ever ask why one is more acidic than the other? Or do they ask CARDIO base ranking by just comparing molecules?

It is important to understand the concept. Anything is fair game. Many Destroyer problems will test your knowledge of acid-base chemistry. If you understand them you are set to go.

Hope this helps

Dr. Romano

 

[Jackthesparrow]

Gchem question # 66
on the solution, you said x = kilo = 10^3
I was wondering if x was correct, instead of k

 

[cacajuate]

Gchem question # 66
on the solution, you said x = kilo = 10^3
I was wondering if x was correct, instead of k

yes, it is supposed to be k

 

[510586]

Can someone explain number 60 on the OC part of 2015 dat destroyer? Why doesn't cyclobutane with 3 methyl groups count as a constitutional isomer? Also, why are the isomers with wedges turned to dashes considered the same? Like a wedge at c1 and dash at c2 then a dash at c1 and wedge at c2? Counting one way or the other gets it the same name doesn't it?

 

[Drenalin]

I really don't understand (2015) Bio #260 how come it is not 2N?

 

[DAT Destroyer]

yes, it is supposed to be k

Thank you! slight typo(mine), it will be fixed Good catch guys, eagle eyes...

 

[DAT Destroyer]

I really don't understand (2015) Bio #260 how come it is not 2N?

Because at Anaphase you only separated chromosomes into sister chtomatids, which become individual chromosomes.

So, instead of 46 (2n), you have 92 (4n).

At Anaphase, you do not break up the cell, so all chromosomes still remain in the cell. Only after Telophase cell is 2n.

Hope this helps

 

[DAT Destroyer]

Can someone explain number 60 on the OC part of 2015 dat destroyer? Why doesn't cyclobutane with 3 methyl groups count as a constitutional isomer? Also, why are the isomers with wedges turned to dashes considered the same? Like a wedge at c1 and dash at c2 then a dash at c1 and wedge at c2? Counting one way or the other gets it the same name doesn't it?

Let me clarify this problem.

I want isomers containing the cyclopentane skeleton.....and methyl groups. Sorry for the confusion.

The dashes and wedges will differentiate cis/trans isomers,,,,,,Just be careful of meso compounds.

For example....the 1,3-dimethyl isomer in the cis form is meso.....thus would not have an enantiomer.....However.....trans does. To be sure.....Do the R/S configuration to assure yourself as a check.

Hope this helps.

Dr. Romano

 

[510586]

So they aren't considered the same? They're in the same position but the wedges and dashes swapped. When naming and counting it, couldn't you just count in the counterclockwise direction and come out with the same molecule? I cant tell why they arent equivalent.

Let me clarify this problem.

I want isomers containing the cyclopentane skeleton.....and methyl groups. Sorry for the confusion.

The dashes and wedges will differentiate cis/trans isomers,,,,,,Just be careful of meso compounds.

For example....the 1,3-dimethyl isomer in the cis form is meso.....thus would not have an enantiomer.....However.....trans does. To be sure.....Do the R/S configuration to assure yourself as a check.

Hope this helps.

Dr. Romano

Like 1-bromo-2-chlorobenzene can be drawn with be to the left of cl or vice versa and be the same molecule. Thanks for the help