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HoMeWoRk HeLp

Debate and discussion of any biological questions not pertaining to a particular topic.

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HoMeWoRk HeLp

Postby HAiKUGiRL » Sat Mar 08, 2008 4:31 am

LoL, well, since my teacher is the devil he is making us do some experiment and answer questions about it.. I was sick the day we went to the lab, so now I have to buy all the materials used because I'm obligated to hand-in the work.. problem is there is nowhere out here where I can buy a iodine solution.

If anyone has a clue as to what could've happened let me know (if this requires money reward then let me know)

Experiment Was About Diffusion and Osmosis:

Steps Were


A. Osmosis

Procedure

1. Obtain a 10 cm piece of 2.5-cm dialysis tubing that has been soaking in water. Twist one end of the tubing and fold it over, then tie off that end with string to form a bag. To open the other end of the bag, rub the end between your thumb and forefinger until the sides separate.
2. Pour molasses solution into the tube until it is about 5 cm from the top.
3. Twist the top of the tube and tie securely. Be sure to leave a gap of about 2 cm between the top of the liquid and the thread.
4. Rinse the outside of the tube with water to remove any molasses which may have contaminated it.
5. Place about 300 mL of water in a 500 mL beaker and place the tube inside. Label the beaker 'A.'
6. Let stand overnight and record observations in the morning.



B. Diffusion

Procedure

1. Prepare another tube as in procedure A but pour starch solution in the tube.
2. Tie and rinse the tube.
3. Place the tube in a beaker of water and label it 'B.'
4. Add iodine solution to the water slowly until the water is a faint yellow color.
5. Let stand 20 min and record observations.
6. Prepare a similar setup except put glucose solution in the tube and do not add iodine solution. Be sure to rinse the tube before putting it in the beaker of water. Label this beaker 'C.' Let stand 20 min.
7. Pour about 5 mL of water from beaker 'C' into a test tube and add half of a Clinitest tablet. Do not shake the test tube. Record the color about 15 s after the tablet stops bubbling.
8. Let beaker 'B' stand overnight and then record any changes.

Questions Were:

1. Explain your observations.
2. Is the membrane 100% selective? Explain. (I already know this one)
3. Suppose that a tube filled with a 5% molasses solution was placed in a beaker filled with a 10% molasses solution. What would happen? Why?
4. Describe and account for any changes that occurred in beaker 'A.'
5. Describe and account for any changes that occurred in beaker 'B.'
6. Describe and account for any changes that occurred in beaker 'C.'
7. What happened to the tube in beaker 'B' after it was allowed to stand overnight? What does this suggest?
8. For each of the following questions, explain your answers.
a) Which molecules pass through the membrane with ease?
b) What molecules pass through the membrane slowly?
c) What molecules were unable to pass through the membrane?

I know it nearly defeats the purpose if you just tell me the answers and you'll assume I'll learn nothing, but I honestly just don't know what else to do.
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Postby MichaelXY » Sat Mar 08, 2008 4:58 am

With a little research into dialysis tubing, Clinitest, Osmosis and diffusion, you should be able to predict the correct answers. Oh, and maybe lookup Lugol's reagent.
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Postby HAiKUGiRL » Sat Mar 08, 2008 4:32 pm

Thanks! and..

Wll do, but I doubt I'll be able to get them all, so help is still being kindly asked upon
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Re: HoMeWoRk HeLp

Postby HAiKUGiRL » Sat Mar 08, 2008 10:39 pm

Alright, I did some reasearch and here are my guesses. Will someone correct any wrong ones?

1. Explain your observations. This will be answered by the other questions, will it not?
2. Is the membrane 100% selective? Explain. No, It is selectively-permeable meaning some substances can enter and exit, while others cannot.
3. Suppose that a tube filled with a 5% molasses solution was placed in a beaker filled with a 10% molasses solution. What would happen? Why?c Nothing because molasses would not be able to diffuse across the tubing.
4. Describe and account for any changes that occurred in beaker 'A.' The water diffused into the tubing until it reached equilibrium, while the molasses remained unchanged due to it being unable to diffuse across the tubing (or would the water diffusion through it affect it?)
5. Describe and account for any changes that occurred in beaker 'B.' The iodine and water diffused through the tubing and when the iodine came in contact with the starch it turned to a blueish color
6. Describe and account for any changes that occurred in beaker 'C.' The glucose diffused into the dialysis tubing and turned a reddish color until equilibrium was reached.
7. What happened to the tube in beaker 'B' after it was allowed to stand overnight? What does this suggest? More iodine diffused through the tubing and made the starch a darker color of bluish black. This suggests (don't know yet)
8. For each of the following questions, explain your answers.
a) Which molecules pass through the membrane with ease? Water, Iodine
b) What molecules pass through the membrane slowly? Glucose
c) What molecules were unable to pass through the membrane? Starch, molasses
Last edited by HAiKUGiRL on Sun Mar 09, 2008 3:23 pm, edited 1 time in total.
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Re: HoMeWoRk HeLp

Postby MichaelXY » Sun Mar 09, 2008 1:06 am

Looks like your getting the right idea but, when you say:

2. Is the membrane 100% selective? Explain. No, It is selectively-permeable meaning some substances can enter and exit, while others cannot. This is due to the proteins because they control the movement of molecules into the membrane.

I think you mention protein as they apply to cellular membranes, but in this case the tubing is a cellulose membrane, and permeability is not a function of proteins.
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Postby mith » Sun Mar 09, 2008 2:39 am

3. Remember the subject is osmosis.
6. http://en.wikipedia.org/wiki/Benedict's_reagent
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Re: HoMeWoRk HeLp

Postby HAiKUGiRL » Sun Mar 09, 2008 2:39 am

You told me to research Clintiest or something, but I do not know which it applies too .. help?

And I'll research dialysis tubing more to find the answer..
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Postby HAiKUGiRL » Sun Mar 09, 2008 2:43 am

that vocabulary hurts my head mith, ahhaha, ahh well.
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Postby MichaelXY » Sun Mar 09, 2008 2:57 am

Clinitest is like Benedict's solution. They both test for reducing sugars.
http://en.wikipedia.org/wiki/Reducing_sugar

Here is another link that you may find useful.

http://pirate.shu.edu/~rawncarr/osmolab/PermLab.htm
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Re: HoMeWoRk HeLp

Postby HAiKUGiRL » Sun Mar 09, 2008 4:57 am

lol i appreciate the help but I'm fed up with reading paragraphs and paragraphs of scientific vocabulary filled knowledge, so im just gonna take the easy way out on this one and copy a classmates :lol:

Appreciate it though!
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Re: HoMeWoRk HeLp

Postby MichaelXY » Sun Mar 09, 2008 5:26 am

HAiKUGiRL wrote:lol i appreciate the help but I'm fed up with reading paragraphs and paragraphs of scientific vocabulary filled knowledge, so im just gonna take the easy way out on this one and copy a classmates :lol:

Appreciate it though!


Well, what appears to be the easy way now is really going to make the rest of your class much harder. The concepts in the lab your are doing are essential to biology. A weak foundation here is like not understanding factoring in algebra.
If you do not enjoy reading these sort of topics, then perhaps you should ask why you are studying biology. Maybe you are just fulfilling a prereq or something, I dunno, but good luck in your class.

Just keep in mind, the easy path, usually turns out to be a difficult one. :|
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Re: HoMeWoRk HeLp

Postby HAiKUGiRL » Sun Mar 09, 2008 7:33 am

i can still pass if i fail this one thing so it's alllll goood :D
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