Help with NBME 3 question. - crazy4step1

[ArchivalUser]

Hi friends!!
It would be super if you kindly help me with this question.
There's a graphic in the question 4, block 1, of NBME 3, about an RBC in a saline solution.
Among the options, there are 2 possible answers that show an hypotonic solution, but the answer that I have as correct is A (75mM)
Someone can explain me why?

Thanks an advance!
Good luck!

[ArchivalUser]

* Re:NBME#3 block 1 Q1----------------------Q50
#2355226
maryam2009 - 03/15/11 23:54

4.A
drona99 - 03/15/11 23:44

To answer these kind of qs we shud know some of the following osmoles and their corresponding concentration .


OSMOLES -------------------------------CONCENTRATION OF ALL PARTICLES

1-100 m M/L of Nacl -----------------------------------200 mosm/L

2-100m M/L of glucose ---------------------------------100 mosm/L

3- 100m M/L of CaCL2------------------------ ------------3mosm/L

4-100mM/LNacl +100mM/L urea -----------------------------300mosm/L



mosm = milliosmolar or mosm/L = is aindex of concentration of particle per liter of solution

mM =millimolar or mM/L =an index of concentration of molecules dssolved per liter of solution.

Isotonic solution =300mosm=150 mM [becoz one molecule of NACL yields two particles in solution]

1-Now when u add hypotonic solution of ECF - then effective osmolslity decreases that leads to movement of water in to the cell-- cell will swell

2- when we add hypertonic sol to ECF - then effective osmolality increases that leads to movement of water out of the cell -- cell will shrink


coming back to q
After adding NACL solution cell volume has increased from 1 to 2 that means we must has added hypotonic solution that correlates with option A ie 75 mM ==150 mosm

option B 150 mM= 300 mosm = isotonic no movement of water

option c 300mM=600mosm;500mM=1000mosm,1500mM=3000osm all hypertonic cell will shrink and decrease in volume .

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[ArchivalUser]

Thank you so much mili99!!!
You are the best!

[ArchivalUser]

For mili99 or some other friend...

With the help of Mily I got an awesome resource for nbme 3 (anwers and explanations).
There's a post (bacterial genetic's question) that give like answer D

"D) TRANSFORMATION.

in this case when two strains of bacteria grow together in one medium, they exchange antibiotic resistance by means TRANSFORMATION and become both resistant to both antibiotics (gentamicin and ampicillin)...
if two strains were cultured in the medium containing DNAse, transformation can't occur, b/c DNAse cleaves DNA fragments outside the cells, so both strain remain susceptible to another antibiotic, and both strain can't grow in medium containing both antibiotics..

they discribe two experiments... in first two bacterial strains X and Y were grown in mixed culture in medium without antibiotics, without DNAse....

in the second experiment they added DNAse...

in first experiment (without DNAse) transformation occured and bacterial strains obtained cross resistance to antibiotic to which they were before susceptible...

in the second experiment (with DNAse) no transformation occure and both strains were susceptible in medium containing both antibiotics."

But, I understood that in transposition there's also exposition of DNA in the enviroment...So why D is not a possibility?

Thank you for your patience.

Regards!

[ArchivalUser]

Please friends, maybe is very easy, but really I would like to understand it fully.
Thanks in advance