Osmosis Investigation

????

* Gather all the equipment needed. A measuring cylinder, a set of weighing scales, 12 test tubes, a scalpel, a potato, the different solution strengths, a timer and a borer.

* Get the potato and boar out around 6 or 7 pieces of potato. Then choose a standard size for each piece of potato, e.g. 3 cm. Then cut 12 potato pieces into the specified size using the scalpel to cut and the ruler to measure. Be careful because the scalpels are sharp and could easily injure someone.

* Then weigh all the potatoes and record their weight. Also take the diameter of the borer, also record this.

* Place your potato pieces in separate test tubes and mark the test tubes with numbers which correlate with the strengths of solution that you are going to place in them, 1 for water to 6 for the strongest, do this with the other 6 test tubes as well.

* Then place 5mm? of each solution in the correlating test tube, do this by using your measuring cylinder and pouring the solution into that and then into your test tube.

* Leave the test tubes for thirty minutes; make sure you time this period using the timer.

* After thirty minutes take all the potatoes out of the solutions. Make sure all excess water is gotten rid of because it could cause anomalous results if left on the potatoes.

* When all the excess water is gotten rid of, weigh and measure the potatoes. Take the diameter of the potato as well.

* Record the results in a table, and take an average mass increase for each potato. You can do this by using the following formula ?r? ? length. Work out the radius by dividing the diameter by 2.

* Repeat this process, as many times as possible, it will give a wider range of results that will be more accurate.

* When everything is done and recorded plot a graph using the averages.

Diagram of set up

??????????????????????????????????????????????????????????

??????????????????????????

????????????????????????????????????????????????????????????????????????????????????Sugar solution

???????????potatoe chip

?

Prediction

I predict that the potatoes in the solutions with the highest glucose content will shrink and lose weight and that the potatoes in the weakest solutions will gain weight and increase in size. The ones in the solution where the sugar and water content is the same as the potatoes sugar and water content will not increase or decrease in size and will not increase or decrease in weight. I think this is because of a process that takes in the potato place called osmosis. This is when water molecules diffuse from a dilute solution into a concentrate solution through a semi permeable membrane. So if you put a potato chip in a solution which has a concentration of X. If you put a potato in a solution, which was less than x the potato would grow because there will movement in the water from the weak outside into the potato, this will give the appearance of growth. However if you put a potato in a solution 3 times stronger than x the water will move out of the cell to the surrounding solution to try and dilute it. This will make the potato shrink. If you put a potato in a solution with strength of x there would be no movement because the strength inside the cells is the same as outside the cells.

Osmosis Diagram

Sugar molecules Water molecules Partially permeable membrane

Results

2

3

4

5

6

Mass Before

0.1800

0.1800

0.1800

0.1800

0.1800

0.1800

Mass After

.3086

0.9331

0.5010

0.2333

0.1006

0.0100

Difference

.1296

0.7531

0.3210

0.0533

- 0.0794

- 0.1700

% Change

6.27 %

4.18%

.78 %

0.30 %

-0.44 %

-1.00 %

Length Before

2.00 cm.

2.00 cm.

2.00 cm.

2.00 cm.

2.00 cm.

2.00 cm.

Length After

2.4 cm.

2.2 cm.

2.1 cm.

2.0 cm.

.8 cm.

.6 cm.

Change in length

0.4 cm.

0.2 cm.

0.1 cm

0 cm

-0.2 cm

-0.4 cm

% Change

0.2 %

0.1 %

0.05 %

0 %

-0.1 %

-0.2 %

I used the average mass for each solutions results. I used the averages because they will be more accurate and give a result that incorporates all my results for each solution.

See graph attached for the percentage change in mass and length.

Conclusion

In my original prediction I predicted that the potatoes in the solutions with the highest glucose content would shrink and lose weight and that the potatoes in the weakest solutions will gain weight and increase in size. The ones in the solution where the sugar and water content is the same as the potatoes sugar and water content will not increase or decrease in size and will not increase or decrease in weight. As you can see for my results and graph where 1 is water to 6 which is the solution with the highest glucose content, my prediction was proved right. I predicted this because I knew that Osmosis would take place, osmosis is when water molecules diffuse from a dilute solution into a concentrate solution through a semi permeable membrane. So with solution 1 the water from outside the potato, diffused through the PPM to dilute the high concentration of sugar in the cells of the potato. This gave the appearance that the potato chip had grown and increased in weight, this is because of the excess water in the cells. Where as in solution 6 the potato lost weight and decreased in size. This is because the water from inside the cells diffused out through the PPM into the high concentrate sugar solution to try and dilute it and make it equal to the cells sugar concentration.

I think that my experiment was conducted in a fair way, this is because I used the same variety of potato, I used the same measuring equipment, conducted it in the same environment where the light intensity and temperature were constant. Also I left the potatoes in the solutions for the same length of time and made sure that all excess water was gotten rid of. Also I think it was a safe experiment because I was safe when using the sharp cutting equipment and I also made sure that all my equipment was in safe places where it couldn't do anyone any harm if anything happened.

The results show that osmosis takes place in the potato and that the rules of osmosis are true, those rules being when water molecules diffuse from a dilute solution into a concentrate solution through a semi permeable membrane. Also I found out that differing strengths of glucose solution do have differing effects on potato chips.

Evaluation

As you can see form my graph there are some anomalous results that don't follow the pattern, this could be because of a number of things. These things could include:

* Inaccurate equipment, which could have lead to inaccurate measuring of weight, size or volume of solution.

* Inaccurate measuring of time.

* Using different potato types, which have different genetics.

However my results were accurate enough to draw a firm conclusion.

We did this experiment to see how differing strengths of glucose solution effect a potato chip of a specified size and length. We did this to observe the changes in mass and size and to see if osmosis takes place.

If I were to do the experiment again I would make some changes. I would use more accurate measuring equipment. I would use calipers to measure the size of the potato; this would make it accurate to millimeters depending on the accuracy of them. This more accurate measuring equipment would make a more accurate mass calculation so then the percentage change would be more accurate, meaning the results would be more accurate. I would also perform the experiment in a temperature and light intensity controlled room, this would prevent changes in both of these. The changes could cause the cell work rate to rise or drop also it could cause the water and sugar molecules to speed up movement which could effect osmosis. I would also leave the chips in the solutions for a longer period time, as 1/2 and hour isn't long enough to see big changes, the recommended minimum time is a hour. I would also use a wider strength of solutions; this would then give a wider range of results, which in turn will make the experiment more accurate.

If I were going to change the experiment I would see how different light intensities and how different temperatures effected the rate of osmosis in a potato chip.