Find out if different concentrations of sucrose solution cause a selectively permeable membrane, in this case a potato chip, to become larger or smaller.

Introduction

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.

Equipment
150ml beaker
Ruler
Scalpel
Small cutting board.
Core borer
Sticky labels

Sucrose solution

Measuring cylinder (100cm3)
Stop clock
Test tube
Test tube holder
Mass machine

Safety

In our experiment we used a variety of equipment. Some of which were quite dangerous. For example we used the razors to cut the potato cells into shape so we had to be extra careful not to cut ourselves. We were in the presence of glass and ceramic so we had to be careful not to break anything.

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.

Prediction

I predict that when we put the potato piece in the balanced solution, in theory, the size will remain the same. When we put it in the more surcease solution, the potato will decrease in size. And in the more watery solution where the sucrose is diluted or not present it will increase in size.

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Prediction

This will happen because in each of the cells in the ovate piece we used is surrounded by a cell membrane. This cell membrane is only partially permeable so it only permits small molecules to pass through. This process in osmosis, the definition of osmosis is the movement of water from an area of low concentration to an area of high water concentration through the partially permeable membrane. So the water molecules concealed within the potato moved to the area of higher concentration (the sucrose in the solution)

So if I put another piece of potato cell in a more diluted sucrose solution, (for example 75% water and 25% sucrose), it is very likely that the potato will increase in mass because the water molecules in the potato cell will diffuse into the cell making it grow. And if we put it in a more concentrated sucrose solution (for example 25% water and 75% sucrose) it is likely that it will reduce in size and decrease in length because the water molecules in the potato cell will diffuse into the concentrated solution.

I can justify my prediction because when we placed the potato cell in 100% water for 10 minutes, the mass increased. When we put the same pieces into diluted sucrose and water, equally balanced in the experiment, the mass remained the same. However when I put the potato piece in concentrated sucrose its mass decreased.

my graph 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

Method

Create a table in which I shall record the results in
Label the five test tubes with the amounts of solution to be put in them
Measure using the measuring cylinder out the different solutions and concentrations according to my plan.
Using the potato borer to cut 8 extra potato strip out of the potato.
Use razor to cut to a suitable length of size equally similar to each other.
Give each test tube a potato piece
Weigh the potato pieces, and note them down in the table I created
Set up the clock watch ready and drop them all in their test tube at the same time.
Wait 15mins before removing them using hands and automatically proceed to weigh them
Note down the new mass in the table.
Work out the mass difference and write them down in the table.
Safely put away all equipment

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 I am quite pleased with my results.