Background/Introduction: Diffusion is the flow of energy or matter from a higher concentration to a lower concentration, resulting in an even distribution. If one end of a rod is heated or electrically charged, the heat or electricity will diffuse from the hot or charged portion to the cool or uncharged portion. If the bar is made of metal, this diffusion will be rapid for heat and almost instantaneous for electricity. Diffusion of matter is general even slower. Even diffusion of one solid into another is possible.
Osmosis is the flow of one constituent of a solution through a semi-membrane while the other constituents are blocked and unable to pass through the membrane. Experimentation is necessary to determine which membranes permit selective flow, or osmosis, because not all membranes act in this way. Many membranes allow all or none of the constituents of a solution to pass through; only a few allow a selective flow.
Osmosis is the process of water molecules passing through a very thin solid membrane whereas Diffusion is the movement of molecules from a higher concentration to a lower concentration resulting in an even distribution.
Osmosis is a special case of diffusion. Outside the cell, there is a low concentration of solute molecules and a high concentration of water molecules. Inside the cell, there is a high concentration of solute molecules and a low concentration of water molecules. The solute molecules can't diffuse out because the plasma membrane won't let them through. The water molecules however can diffuse in - this is osmosis. Osmosis can be defined as the passage of water molecules through a partially permeable membrane, from a region where they are in higher concentration to a region where they are in a lower concentration.
Fat-soluble molecules, such as glycerol, can diffuse through the membrane easily. They dissolve in the phospholipid bilayer and pass through it in the direction of the concentration gradient, from a high concentration to a low concentration.
Water, oxygen and carbon dioxide can also diffuse through the bilayer, passing easily through the temporary small spaces between the 'tails' of the .
Some molecules such as those that are soluble in water cannot pass through the phospholipids in the bilayer. They are transported across the membrane by carrier proteins. A carrier protein will have a specific binding site for the substance it transports. Solute molecules moving about on either side of the membrane will randomly come into contact with their specific binding site. Once they bind, the protein changes shape and the molecules come off the binding site on the other side of the membrane.
Bibliography: Microsoft Encarta, (search), (search), (search), .
Independent Variable: The independent variable in these experiments is the sugar
concentration of the solution. The range of values for this variable is 0.1ml, 0.3ml, 0.5ml and 0.7ml.
Dependant Variable: The dependant variable in these experiments is the mass of the potatoes. The dependant variable will by observed by weighing the potato before inserting it into the solution and then weighing the potato after it has stayed in the solution for 48 hours.
Fixed Variable: The other variables that I think are important in this investigation that will have to be controlled to make the tests fair are;
Reliability and Accuracy: To make sure that my results are reliable I will repeat the experiment 3 times then I will come up with an average. If there is an anomalous result I will just disregard it and make an average with the remaining two results.
Equipment: The equipment that will be used for the experiments are;
- Potato
- Scale
- Water
- Sugar
- Timer
- Beaker x4
- Cork borer
- Measuring Cylinder
- May need paper towels
Preliminary Work: First we gathered the equipment ready to start the experiment; we then used the cork borer to cut out 4 pieces of long cylindrical potato pieces. Then we weighed the potato pieces and recorded them in a table like this;
After that we poured 100ml of sucrose solution of 0.1, .0.3, 0.5 and 0.7 molars into four beakers, to make the solution look at the table below;
And placed one potato in each beaker and left them in the beakers for 48 hours.
When we returned we took out the potatoes put them onto paper towels and weighed them these are the results that we obtained;
As the results show the molar range that we should use for the final method is between 0.1mol and 0.3mol as 0.1mol is a gain of weight and 0.3mol is a loss of weight so obviously the right molar would be somewhere in between those two molars. But for one reason or another we decided to use the range of molar between 0.3mol and 0.5mol, the range we decided was, 0.3, 0.35, 0.4, 0.45, and 0.5mol. I now see that this was a foolish mistake and could have been avoided. We had been accidentally misadvised on what range to do. This affected our final method because in our final method we used the wrong range and we were never going to find the same concentration as they were both higher than the concentration of the potato. If we had used the right molar range we would have done the following molars; 0.1, 0.15, 0.2, 0.25 and 0.3.
Method:
- Make the sugar solution by adding a certain amount of sucrose to 100ml of water, as shown below,
- Cut out 4 pieces of potato, roughly the same size using the cork borer.
- Weigh all the pieces and record them in the table.
- Place one potato in each beaker and leave for 24/48 hours.
- After 24/48 hours take the potatoes out and weigh them and record the results in the table.
- Work out the difference between the before and after results if the potato gained weight then the solution had a lower concentration of sugar and if the potato loses weight then the solution had a higher concentration of sugar, if the weight remains the same then the concentrations of both the solution and potato are the same.
Safety: Safety is an important aspect in every experiment, even if the experiment seems to be very harmless. And that is why we take this into consideration, no matter what.
We will be using a very sharp corer, which could injure someone. And we will also be careful that the solutions don’t get into our bodies internally, just in case, because we are not fully aware of the damage it could do to us. But other than that, there weren’t any bigger matters to be cautious of. But there is the obvious one like don’t run in the lab and tuck in the stools and don’t leave bags on the floor.
Results: Preliminary results;
Investigation results;
Analysis: Obviously my results are incorrect; we were never going to get the correct results. They are all a too high concentration and so all have a loss in mass of the potato. I can safely say that there is a trend that the higher the concentration is the more there is in the loss of mass.
Conclusion: My conclusion is that the sucrose concentration is between 0.1 and 0.3 molar. The exact molar I cannot say due to my odd results, but according to my background information and my hypothesis I said that the 0.3 molar solutions of sucrose was similar to the 0.1 molar solution of sucrose and compared to the potato, both substances have very close concentration gradients and that is why I am predicting that the weight of the potato in this experiment should be decreased by only a fraction, but my results show that 0.1 molar solution increase the weight and 0.3 decreases the weight and there is a lot of difference between the two molars.
Evaluation: The first problem we encountered even before we had started the experiments was who was working with us, there was a lot of confusion at this time but we finally worked everything out. And the obvious problem we encountered was which range to choose and because of some misadvise chose the wrong range and so none of our results were anywhere near the actual one; they were all below the correct molar. Even though we did this we did encounter two anomalies;
Here you can see that these two results do not follow the pattern of the increase in weight loss and I think that these two potatoes were done incorrectly.
Next time we will check twice on all our decisions and we will do a lot more repetition to double or even triple check the results that we get.