Osmosis Lab Report

Introduction

Cells have to interact with their environment, chemicals and water and in order to do so they must be able to move across the cell membrane and the cell. The movements within a cell are called Diffusion. When molecules move across a cell membrane it is known as Osmosis. Diffusion is the process by which molecules of a substance move from areas of higher concentration of that substance to areas of lower concentration. Diffusion can be the transfer of anything anywhere. However, that is not true for osmosis. Osmosis is diffusion, but a specific type of diffusion. Osmosis is only the diffusion of water molecules through a selectively permeable membrane and a concentration gradient. Only certain molecules can cross the membrane
to either go in our out of the cell.

If outside the cell there is a lower concentration of molecules than inside the cell, it is called hypotonic and water will move from outside the cell into the cell.
If the solution outside the cell has a larger concentration of dissolved materials the solution is hypertonic, so the water would move from the cell into the solution.

Aim
The aim of this experiment was to verify the concept of Osmosis and Diffusion with a semi-permeable membrane (dialysis tubing), it will be exposed to different environments and concentration gradients.
Hypothesis
I thought that that dialysis tubing would end up weighing more as there would be less water and more molecules within the tubing so water would move through the semi-permeable using a concentration gradient into the cell.
Variables
Independent Variable – Solution
Dependent Variable - Weight of the dialysis tubing
Controlled Variable - Length of dialysis tubing - Amount of substance in each of the tubes - Amount of water in the beakers
` - Measuring in the same measurement - Time between each weighing session
Unable to control Variables - Temperature in room and beaker
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Materials

• 4 - 4" pieces of dialysis tubing and string
• 4 - 250 mL beakers
• Distilled water
• Egg white
• 10% salt solution
• 20% sucrose solution
• 10% starch Solution
• String
• Balance
• Paper towels

Procedure

Method

To start off with, 6" of dialysis tubing was cut and soaked in water and then tied at the bottom of the tube with a piece of string.
You then add 2" of 10% Salt solution into the tube, and close the top end of the tube, fold it and tie a string over the top so it is fully sealed. Once done we cleaned the outside of a tube by rinsing it and then using paper towels to dry it. These steps were repeated for the egg white, sucrose and starch solutions. Then immediately weigh the tubes on an electronic scale (make sure it is set to 0) using grams and mark down the readings. Then place each tube in a 250ml beaker with enough distilled water to cover all of the tube. Mark each beaker so that they do not get confused. Then after every ten minutes for one hour you take the tube out, dry it off and weigh it whilst writing down what the scale was
reading.

Results
The weight of each tube every 10mins:
Time 10% Starch 10% Sucrose 10% salt Egg White
Before putting in beaker 9.93g 7.69g 12.46g 10.24g
10mins 11.09g 9.09g 14.42g 11.35g
20mins 10.23g 9.08g 14.75g 10.60g
30mins 10.28g 9.26g 15.21g 10.80g
40mins 10.27g 9.64g 15.44g 10.79g
50mins 10.28g 9.80g 15.51g 10.77g
60mins 10.39g 9.83g 15.62g 10.73g

A graph of the following data:

Discussion and Conclusion

With my data, it is almost certain to say that the end results weighs more than the start results, yet with each substance there is random fluctuation where the weight goes up and down, this could be due to the concentration differing therefore water was moving in and out to go to the low concentration. Yet this data supports my hypothesis due to tubes weighing more than started because the distilled water had gone through the semi-permeable membrane. Yet with the data going up and down randomly, I am not sure what that could be, but with more research I can find the conclusion.

Evaluation

I knew exactly what I was supposed to be doing going into this experiment, but the place where I felt a little worried about was the amount of substances I was putting into the dialysis tubing, next time I would you a measuring cylinder to be more precise. For my data to be more accurate I feel like I should have done the experiment with more detail, I also had a feeling that the string at the bottom of one of the dialysis tubing might have been a bit loose which would have seriously affected our results. For future experiments I think overall I would need to look more carefully into the experiment and make sure I cover all the small details as they add up to be important in the results of your experiment.