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Help w/ Lab Assignment: How Things Get Into & Out Of Cell

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Help w/ Lab Assignment: How Things Get Into & Out Of Cell

Postby Funkfruit » Wed Oct 22, 2008 9:31 pm

Okay, so in the Lab Assignment that I'm currently working on in AP Biology, there is a question that says:
What results would you expect if a dialysis bag were filled with glucose and iodine and then placed into a beaker of starch and water?
Its a multiple choice question (which you think would make it easier but in all reality, it just confused me more.
The options were:
A.)There would be a movement of glucose into the bag, and the water outside of the bag would turn purple.
B.)There would be movement of glucose out of the bag, and the water outside of the bag would turn purple.
C.)There would be a movement of starch into the bag, and the inside of the bag would turn purple.
D.)There would be a movement of starch into the bag and the outside of the bag would turn purple.

First though was that water would move into the bag to an area of lower water potential but then I realized that there is no water in the bag to begin with and it isnt an option. I went over the lab several times and I can't seem to find the answer, the lab didn't come from my textbook so its not in there, and I dont know how to research it on the web because its not a definition or anything - Its lab results. I know that this isnt a place to come for straight answers on homework so I'm not asking for that. Just hoping maybe someone could shine a little light on this and point me in the right direction since at the moment, the information that I have (nothing) is getting me absolutely nowhere. Any help is highly appreciated. Thanks in advance.
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Re: Help w/ Lab Assignment: How Things Get Into & Out Of Cell

Postby MichaelXY » Wed Oct 22, 2008 10:22 pm

Actually the iodine by itself is not that soluble in water, but when mixed with potassium iodine the mixture become water soluble. So the KI solution does infact have water in it.

So considering that.

The dialysis bag will not allow starch molecules to penetrate.

The starch is a polysaccharide, and is thus highly concentrated chain of monosaccharides.

Thus the glucose side of the bag appears to be the lower solute concentrated side.

The aqueous KI solution would therfore leave the bag out into the beaker.

The KI will react with the amylose in the starch and the liquid in the beaker should turn purple.

Helpful link:
http://highered.mcgraw-hill.com/sites/0 ... works.html
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Re: Help w/ Lab Assignment: How Things Get Into & Out Of Cell

Postby MichaelXY » Wed Oct 22, 2008 11:17 pm

I actually think the wording of the answers is somewhat incorrect as neither glucose nor starch will penetrate the membrane. Well I am fairly certain that starch cannot penetrate as I looked this up. Not so sure about glucose. I would think the aqueous KI solution would leave the bag, but since that is not a choice, then the best answer seems to be.

B.)There would be movement of glucose out of the bag, and the water outside of the bag would turn purple.
---------------------------------------edit----------------------------------------
I was incorrect about glucose. It will pass through the bag, but in order for the outside to turn purple, the KI must pass too, which it would :)
http://en.wikipedia.org/wiki/Dialysis_tubing


Before you take this as correct, I would check back for possible corrections by the experts. :)
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Postby Funkfruit » Thu Oct 23, 2008 12:32 am

It's all good, man.
After combining my knowledge with that of which you shared of yours, I decided that the answer was in fact: B.) There would be a movement of glucose out of the bag, and the water outside of the bag would turn purple.

... I got it right. Thank you for your time and knowledge.
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Postby Elersong » Wed Oct 29, 2008 7:44 pm

Hmmm, well now I have a question: Where did the potassium come from? In the question, the bag was filled with glucose and iodine, and the beaker had water and starch- making no mention of potassium.

And why would the water become purple?
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Postby MichaelXY » Wed Oct 29, 2008 9:33 pm

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