Biology Forum Community General Discussion HoMeWoRk HeLp

last updated by HAiKUGiRL 16 years ago
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    • #9239
      HAiKUGiRL
      Participant

      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.

    • #82601
      MichaelXY
      Participant

      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.

    • #82623
      HAiKUGiRL
      Participant

      Thanks! and..

      Wll do, but I doubt I’ll be able to get them all, so help is still being kindly asked upon

    • #82637
      HAiKUGiRL
      Participant

      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

    • #82638
      MichaelXY
      Participant

      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.

    • #82641
      mith
      Participant

      3. Remember the subject is osmosis.
      6. http://en.wikipedia.org/wiki/Benedict’s_reagent

    • #82642
      HAiKUGiRL
      Participant

      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..

    • #82643
      HAiKUGiRL
      Participant

      that vocabulary hurts my head mith, ahhaha, ahh well.

    • #82644
      MichaelXY
      Participant

      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

    • #82645
      HAiKUGiRL
      Participant

      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 😆

      Appreciate it though!

    • #82646
      MichaelXY
      Participant
      quote HAiKUGiRL:

      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 😆

      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. 😐

    • #82651
      HAiKUGiRL
      Participant

      i can still pass if i fail this one thing so it’s alllll goood 😀

    • #82653
      MichaelXY
      Participant

      Ok, so here’s the thing. You still have a least one day (Assuming assingment is due on Monday) to work on your assignment. Suck it up, read what you need to, and you can still do well. Do not get into the habit of blowing off work, it only sets a pattern.
      Sure you will feel a moment of relief, but you will still have that nagging feeling in the back of your mind, I think they call it guilt.
      Do yourself a favor, forget about hanging with the friends, hit the books, and techno yucky stuff on the internet, and get yourself a good grade. You will feel good about yourself if you do. There is always time to hang out and chat with friends.
      If I still have failed to convince you, then I do not see you passing your bio course as it only gets more difficult if you do not understand basic concepts.

      Ok, I am finished being a nag. I think that is Canalons job 🙂

    • #82661
      HAiKUGiRL
      Participant

      which ones arent right and i might give them another go.

    • #82663
      mith
      Participant

      #3 is still wrong. Refer to my other post.

    • #82664
      HAiKUGiRL
      Participant

      i know but i don’t know what you’re trying to say

      the benedict reagent thing just determines the presence of glucose (which is in molasses) so i have no idea how thats useful

      And i realize there’s a concentration difference, being higher outside the cell causing a hypertonic solution ?? which means the molasses would attempt to move out of the tubing causing it to shrink?

    • #82670
      MichaelXY
      Participant

      Mith is right. Here is the deal. You have a bag with 5% solution placed in a beaker with 10% solution. That means the bag has a water concentration of 95% while the beakers water concentration is 90%. In osmosis water moves to equalize the concentrations, so in this case water from the bag will move out into the beaker in order balance the concentration.

      Does that make sense?

    • #82672
      HAiKUGiRL
      Participant

      so what i said above is true except for when i said molasses i should’ve said water?

      it makes sense, yes, but is a solution always with water? because i dont know where the ‘water’ came from :confused:

    • #82677
      mith
      Participant

      A solution is not always water, but we’re talking about sugar in solution, so it’s most probably water. Anyways, there should be water movement.

    • #82688
      MichaelXY
      Participant

      Be sure to let us know how you do in class.

      And Canalon, I was just joking about the nag part.

    • #82997
      HAiKUGiRL
      Participant

      Forgot about this i got a 47/50 .. w00t gotta love getting guesses right

    • #84176
      HAiKUGiRL
      Participant

      Canalon where in Canada do you reside?

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