Find out if different concentrations of sucrose solution cause a selectively permeable membrane, in this case a potato chip, to become larger or smaller.
Osmossis experiment
PLAN
Investigation.
I intend to find out if different concentrations of sucrose solution cause a selectively permeable membrane, in this case a potato chip, to become larger or smaller.
I plan to use six different concentrations of sucrose solution and for each concentration I will take three results. I will then find the percentage change for each result. Finally I will find the average weight change and the average percentage change.
Prediction.
I predict that the lower concentrations of sucrose solution will cause the chip to become larger and the higher concentrations will cause the chip to become smaller.
Fair test.
To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed. We have chosen to vary the concentration of the sucrose solution.
For the purpose of my experiment I am going to carry out all the experiments at the same time so the temperature is kept almost the same throughout.
The mass of the potato is a dependent variable. This means that it will be measured throughout the experiment. I will measure the mass in grams. The potato chip will be measured before it is put in the solution, and after. This will allow us to see whether osmosis has taken place, and to what extent. The volume of the solution that the potato chips are kept in must be the same. The potato chip must be totally covered in the solution, and the amount of solution will be kept the same because
all the potato chips will be the same size. I am also going to use the same balance to weigh my potato chips. This is because the measurements may slightly vary between different sets of scales.
Apparatus.
· 6 petri dishes (with lids)
· 150ml beaker
· Ruler
· Scalpel
· Small cutting board · Core borer
· Sticky labels
· Sucrose solution
· Measuring cylinder (100cm3)
Diagram.
Conversion table.
Concentration
Water (cm3)
Sucrose (cm3)
0.0
30
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all the potato chips will be the same size. I am also going to use the same balance to weigh my potato chips. This is because the measurements may slightly vary between different sets of scales.
Apparatus.
· 6 petri dishes (with lids)
· 150ml beaker
· Ruler
· Scalpel
· Small cutting board · Core borer
· Sticky labels
· Sucrose solution
· Measuring cylinder (100cm3)
Diagram.
Conversion table.
Concentration
Water (cm3)
Sucrose (cm3)
0.0
30
0
0.2
24
6
0.4
8
2
0.6
2
8
0.8
6
24
.0
0
30
Method.
· Stick labels on each of the petri dish lids and label them 0.0, 0.2, 0.4, 0.6, 0.8, 1.0.
· Using the measuring cylinder, carefully measure out, using the conversion table, the correct amounts of sucrose and water for each concentration and place them into the appropriate petri dishes.Next, using the core borer, bore approximately 20 pieces of potato from your own potato. Using the ruler, cutting board and scalpel, measure out 18 pieces of potato, each 2cm each and cut to size with the scalpel.
· Weigh each piece of potato and make sure each weighs 0.5g. This will make the test fair as we are looking for changes in weight.
· Put three pieces of potato into each petri dish and put on the lids. Make sure you record the time, as the potatoes must only be in the solutions for up to 48 hours.
· Leave the potatoes for 48 hours, as this will give enough time for osmosis to take place.
· After 48 hours, take out each potato chip and put them onto a piece of paper towel to dry. Once they have dried, weigh each of them, making sure you note which concentration each was in. · Draw up a table of results and enter in your results.
· Find the weight for each concentration and then find the percentage increase/decrease for each and find the average for this too.
Results.
Concentration
Mass before (g)
Mass after (g)
% Change
0.0
0.5
0.6
20%
0.0
0.5
0.7
40%
0.0
0.5
0.6
20%
0.2
0.5
0.5
0%
0.2
0.5
0.6
20%
0.2
0.5
0.6
20%
0.4
0.5
0.5
0%
0.4
0.5
0.4
-20%
0.4.
0.5
0.5
0%
0.6
0.5
0.4
-20%
0.6
0.5
0.4
-20%
0.6
0.5
0.4
-20%
0.8
0.5
0.4
-20%
0.8
0.5
0.3
-40%
0.8
0.5
0.4
-20%
.0
0.5
0.3
-40%
.0
0.5
0.3
20%
.0
0.5
0.2
-40%
Concentration
Average weight change
Average % change
0.0
0.1
20%
0.2
0.0
0%
0.4
-0.1
-20%
0.6
-0.1
-20%
0.8
-0.2
-40%
.0
-0.3
-60%
The graph above shows the line of best fit for the average weights of potato chips before and after Osmosis in different concentrations of sucrose solution. It clearly shows that in low concentrations of sucrose solution, the potato chips get larger and in higher concentrations of sucrose solution, the potato chips get smaller. This graph shows that the average weight after Osmosis and the concentration of sucrose solution are not directly proportional. There is, however, a pattern in my graph, showing that the average weight after Osmosis and the concentration of sucrose are inversely proportional. As the concentration of sucrose rises, the average weight after Osmosis decreases. This graph shows that my first predictions were correct. It shows that the potato cells increase in mass in solutions with a high water concentration and decrease in mass in solutions with a lower water concentration
Analysis.
From these experiments, I have found out that my predictions were correct. In lower concentrations of sucrose, Osmosis takes place and the potato chips become turgid. In higher concentrations of sucrose, Osmosis takes place but the potato chips become plasmolysed.
Evaluation.
In my opinion the experiment was very successful. I obtained a large quantity of quite accurate results. I was able, from these results, to draw up a somewhat informative graph. I think I took enough results for the amounts of concentrations I was using. I also think that I gave the experiment ample time for Osmosis to occur. Maybe if I were to repeat the experiments again I would probably try using a wider range of concentrations as to find a wider range of more varied results.
The most difficult part of this experiment, in my opinion, was the accurate cutting of the potatoes. It was very difficult to accurately cut the potatoes to the same length and to get them all to the same weight. To get more accurate results I could have used a scale to measure, instead of 0.0g, 0.00g.
In my opinion, there were not many of my results, which were out of the ordinary. Slight differences may have been the result of human hands drying each, some more thoroughly than others. This could mean that some would have had more excess water than others, resulting in an increased mass. However, I think that my experiment was successful and am quite pleased with my results.